Upcoming Talks and Events:

Rudolf Haindl

Affiliation: Max Planck Institute for Multidisciplinary Sciences and Georg August University of Göttingen (Germany)

Research Interests: Physics, Electron Microscopy

Title: Coulomb-correlated few-electron states in a transmission electron microscope beam

Abstract: Correlations between electrons are at the core of numerous phenomena in atomic, molecular, and solid-state systems. However, harnessing free-particle correlations remains challenging, with the recent implementation of nanoscale single-electron sources [1] and observation of anti-bunching in electron beams [2, 3, 4]. A powerful approach to induce strong inter-electron interactions is femtosecond-triggered photoemission from nanotips [5,6] with high spatial and temporal confinement. However, ensemble-averaged detection typically conceals few-body effects. In this work, we characterize Coulomb correlations in laser-triggered electron number states generated at a Schottky field emitter in an ultrafast transmission electron microscope [7]. Based on an event-based detection scheme, we separate the state-averaged spectrum into the n-state components with a characteristic n-peak spectral shape. Furthermore, we identify a characteristic pair-correlation energy of around 2 eV. The strong inter-particle energy exchange is caused by acceleration-enhanced inter-particle Coulomb interaction, as confirmed by trajectory simulations. State-sorted beam caustics reveal a discrete increase in virtual source size, a longitudinal source shift, and a pronounced angular distribution of the few-electron states compared to single-electron pulses. The high fidelity of few-electron pulses in conjunction with single-particle detection enables the application of various experimental schemes typically employed in quantum optics. Specifically, we propose a scheme to generate an electron beam with sub- and super-Poissonian two-electron statistics. Applications of such beams include heralded single-electron sources and may foster new developments in free-electron quantum optics and quantum-enhanced electron microscopy.

John H. Gaida

Affiliation: Max Planck Institute for Multidisciplinary Sciences and Georg August University of Göttingen (Germany)

Research interests: Physics

Title: Attosecond electron microscopy using Lorentz PINEM and free-electron homodyne detection

Abstract:  Transmission electron microscopy (TEM) offers high spatial resolution and is widely used to characterize optical ex citations and near fields by electron energy loss spectroscopy (EELS). This method probes self – induced electric fields in the nanostructure, using spontaneous inelastic scattering of electrons. Importantly, it is difficult to experimentally access near – fie ld phase information. Using external laser excitation, strong optical near fields can induce stimulated inelastic electron – light scattering, as employed in photon – induced near – field electron microscopy (PINEM). In this case, optical modes populated at the laser frequency are excited, providing enhanced spectral resolution and polarization sensitivity. Importantly, in this process, the induced near field is phase – locked to the exciting laser, which translates to a coherent phase modulation of the electron wa ve function. In this talk , we present two phase contrast techniques for imaging optical near fields at nanostructures. Specifically, we implement Lorentz – mode PINEM and free – electron homodyne detection (FREHD). Using these techniques, we image optical fields with subwave length (10 nm) spatial and sub – cycle temporal resolutions. Lorentz microscopy is an in – line holography technique, employing Fresnel diffraction at a small defocus. The electron wave function is locally mixed, and contrast arises near phase gradients. Sensitivity to the light field is obtained by energy filtering T EM (EFTEM) of PINEM – induced sidebands in the electron spectrum. We obtain complementary information about the phase profile by exploiting the conjugate symmetry of the energy gain and loss sidebands. From two complementary measurements, we reconstruct the light – imprinted phase using an iterative reconstruction algorithm. In the newly developed FREHD technique, on the other hand, we measure the phase profile by means of a phase – controlled reference interaction. The near field at a sample modulates the phase of the electron wavefunction. This wavefunction modulation is amplified or attenuated for in – phase and anti – phase reference interactions, respectively, which allows for a coherent read – out of a position – dependent phase. Overall, FREHD transfers concepts from homodyne detection in optics and amplitude (AM) and frequency modulation (FM) in radio techno logy to the realm of electron microscopy. Combining free electrons with phase – locked laser excitation offers fascinating new possibilities to image local attosecond and phase – resolved responses on the nanometer scale.

Giorgio Sangiovanni

Affiliation: Julius-Maximilians-Universität Würzburg
Research Interests: condensed matter theory
Title: Real-space Obstruction in Quantum Spin Hall Insulators
Abstract: In the hunt for room-temperature quantum spin Hall insulators, bismuthene [1] has demonstrated the impressive advantage of a local spin-orbit coupling experienced by the in-plane p-orbitals. This alternative to pi-bond graphene can be pushed to a conceptually even more essential level upon halving the honeycomb lattice, i.e. considering chiral p-orbitals on a triangular lattice [2]. Here, we theoretically conceive and experimentally realize for the first time a triangular QSHI, indenene, an indium monolayer exhibiting non-trivial valley physics and a large gap. We identify an interference mechanism of the Bloch functions and the emergence of a hidden honeycomb pattern in the charge localization, which makes the topological classification accessible to bulk experiments, without the necessity of quantum edge transport.

Alessandro Toschi

Affiliation: Institute of Solid State Physics (Technische Universität Wien)
Research Interests: Theoretical Physics, Electronic Correlations, Superconductivity, Quantum Criticality
Title: Local Moment Formation and Kondo screening from the Charge-Sector Perspective: How Perturbation Theory breaks down
Abstract: In this talk, I will discuss how the correct physical description of the formation of local moments and of their Kondo screening gets reflected in the charge-scattering sector. In particular, by a systematic analysis of the on-site charge and spin fluctuations on Hubbard atom, Anderson Impurity Model and Hubbard model solved by means of dynamical mean-field theory, I will demonstrate [1] how the strong intertwining between the different (spin and charge) sectors, which is crucial for a coherent description of correlated metallic and Mott insulating phases, necessarily drives the breakdown of the self-consistent perturbation expansion [1,2].
The improved understanding of the frequency structures of the two-particle correlation functions has also allowed us [2] to identify the typical fingerprints of the Kondo physics in the charge sector and, on an even more quantitative level, to introduce a new, quite accurate criterion for estimating the Kondo temperature. Interestingly, the same scattering processes responsible for the on-site charge localization may result in an effective electronic attraction [3,4], triggering the phase-separation instabilities emerging in the proximity of Mott-Hubbard or Hund’s-Mott metal-insulator transitions.

Pascal Ruffieux

Affiliation: Swiss Federal Laboratories for Materials Science and Technology

Research Interests: nanographene, graphene nanoribbon, surface science
Title: On-surface synthesis of magnetic nanographenes
Abstract: Recent progress in the on-surface synthesis of nanographenes has given access to an extremely rich materials class where physical properties can be tuned in a wide range. The most prominent nanographenes include armchair graphene nanoribbons (GNRs) with width-dependent electronic band gaps [1], zigzag GNRs with spin-polarized edge states [2] and width-modulated GNRs hosting tunable topological bands [3]. Most recently, the successful synthesis of a series of open-shell nanographenes with magnetically nontrivial ground states has catapulted carbon-based magnetism to a new level. The basic concept followed here is realization of sublattice-imbalanced or topologically frustrated nanographenes hosting unpaired electrons. A deterministic realization of such nanographenes is achieved through a combined solution on and on-surface synthesis approach. Here, I will report recent advances in the on-surfaces synthesis of nanographenes with chemically tuned magnetic interaction strength between unpaired electrons in diradical nanographenes [4]. The controlled combination of different magnetic nanographenes allows formation of both, antiferromagnetically and ferromagnetically coupled dimers and trimers based on spin-½ and spin-1 molecular building blocks as well as extended spin chains [5]. Here, we investigate the length and site-dependent spin excitations with inelastic scanning tunneling spectroscopy and compare them theoretical predictions on spin-1 chains and confirm Haldane gap and fractional edge excitations for open chains. As an extension of the on-surface synthesis approach, we recently achieved successful formation of open-shell nanographenes using scanning tunneling microscopy tip-based activation of hydrogen-protected precursors [6,7]. This has the advantage that magnetic nanographenes can be prepared and characterized on a larger range of substrates since no specific catalytic substrate properties are needed here.

Andreas Osterwalder

Affiliation: Ecole Polytechnique Federale de Lausanne (EPFL)

Research Interests: Physics

Title: From cold gas-phase stereodynamics to kinetics at water-water interfaces

Abstract: I will briefly introduce the two primary research directions covered in our group:
A first part will be on experiments to study sub-Kelvin stereodynamics in merged beams. We investigate prototypical energy transfer reactions in the gas phase, namely between metastable Ne(3P2) and other rare gas atoms or small molecules. Such reactions can proceed along two pathways according to       NeX+ + e ̄← Ne(3P2) + X → Ne(1S) +X+ + e ̄       called Penning ionization (producing X+) and associative ionization (producing NeX+), respectively. At high energies the branching ratio between these channels can be controlled through the orientation of the Ne(3P2) atom, but this ability is lost at low energies due to a reorientation of the reactants. In the second part I will be describing our efforts towards studies of gas — liquid water scattering dynamics, for which we cross a molecular beam with a liquid water flat-jet. Liquid flat-jets can be produced by impinging two cylindrical microjets at controlled angles and flow-rates. Such an arrangement produces a series of drop-shaped leaves that provide a flat surface from which gas-phase molecules can be scattered. But, as will be shown, the first leaf in this chain can also serve as a tool to prepare a controlled interface between two liquids, possible miscible, an arrangement that is ideally suited for the study of chemical kinetics at liquid-liquid interfaces.

Claudiu Genes

Academic Affiliation: Max Planck Institute for the Science of Light

Research Interests: Quantum optics, Molecular quantum technologies, Quantum information, Quantum sensing, Organic opto-electronics, Cooperative quantum phenomena, Quantum metrology, Quantum optomechanics, Energy and charge transport

Title: Quantum optics with molecules

Abstract: Theoretical tools of quantum optics, such as the master equation and the quantum Langevin equations approaches, are ideally suited to treat the dynamics of complex open quantum systems. A reduction to basic ingredients has seen such methods successfully applied to ensembles of two level quantum emitters, where the electronic degree of freedom is interfaced with single or multimode quantum light. Standard aspects tackled within this formalism include free space cooperative effects such as super – and subradiance (radiative emission rates larger or smaller than that of an isolated individual system) and cavity quantum electrodynamics effects such as strong coupling, polariton physics or Purcell enhancement of spontaneous emission rates.

Duck-Ho Kim

Affiliation: Korea Institute of Science and Technology (KIST)

Research interests: Spintronics

Title: Spin Transport and Dynamics in Ferrimagnetic Materials

Abstract: The dynamic phenomena of topological spin objects in magnetic materials have been actively studied not only for their academic interest but also for their potential applications in next – generation memory devices [1 – 4]. Representative topological spin objec ts include chiral magnetic domain walls [1, 2] and magnetic skyrmions [3, 4]. It is possible to manipulate topological spin objects using electric current, and the underlying mechanism involves the conservation of angular momentum arising from the interact ion between the electron’s spin and the spin of the phase spin structure as the electron traverses the magnetic material [5, 6]. This interaction is known as spin torque and can be divided into spin – transfer torque and spin – orbit torque depending on the tr ansmitting materials . Recently, ultrafast motion of topological spin objects has been predicted in antiferromagnetic materials (total magnetization = 0) through theoretical studies [7]. Unfortunately, antiferromagnetic materials are difficult to measure (t otal magnetization = 0) and challenging to control (due to strong coupling energy), making it difficult to experimentally verify the theory. However, in the case of ferrimagnetic materials, which have a finite magnetization at the angular momentum compensa tion point where the angular momentum is zero, it has been possible to investigate the spin dynamics of antiferromagnetic materials. With this possibility, ultrafast motion has been observed at the angular momentum compensation point when topological spin objects are driven by a magnetic field [8]. In this presentation, we will discuss the spin transfer torque phenomenon [9] and the phenomenon of skyrmion hall effect [10] at the angular momentum compensation point when topological spin structures is driven by electric current in ferrimagnetic materials

Woo-Joong Kim

Affiliation: Professor of Physics, Seattle University

Research interests: Precision force measurements, Casimir and van der Waals forces, surface patch effect, quantum conductance in nanowire
Title: An optically-driven macroscopic cantilever
Abstract: I will report an interferometric experiment to detect optically-driven resonance on a macroscopic object. Utilizing dynamic force microscopy, the resonant motion of a cm-sized cantilever driven by an amplitude-modulated laser is directly observed. I will also discuss other experimental techniques underway in our research lab and their potential applications to precision measurements such as tests of short-range gravity.

Sungkyun Choi

Affiliation: Center for Integrated Nanostructure Physics IBS, SungKyunKwan University

Research interests: Quantum Spin Liquids, Multiferroics, Topology in Magnetism, Quantum Phase Transitions
Title: Spectroscopy on Quantum Magnetism
Abstract: In this seminar, we will introduce how spectroscopy can be utilized in understanding contemporary research topics in condensed matter physics, in which quantum magnetism plays an important role. To this end, our primary experimental technique is neutron spectroscopy, complemented by X – ray and Raman spectroscopy. Case examples such as quantum spin liquids, multiferroics, and insulator – metal transitions will be discussed.

Pierre Josse

Affiliation: University of Angers, Yonsei University

Research interests: Organic Chemistry, Dye Chemistry, Organic Electronics
Title: Tailoring π-conjugated molecular and macromolecular systems for addressing specific needs and requirements: from organic photovoltaics to theranostics
Abstract: Active materials for organic electronic applications such as solar cells or light emitting diodes usually requires strong absorbers and/or emitters in the visible/NIR range. Over the last 30 years, researchers around the world have been developing new materials, optimizing devices and rationalizing structures/properties relationships to demonstrate the interest of these technologies and potentially bring them on the market. The rapid growth of organic electronics was then closely related to the capacity of synthetic chemists to generate new and original molecular and macromolecular structures . With the only limitation being basically the imagination, organic synthesis indeed offers countless reactivities, tools and possibilities to afford functional compounds with specific properties. As a chemist specialized in π-conjugated systems, I’ll thus cover, through this presentation, projects and strategies developed to address specific needs and requirements for practical applications ranging from organic photovoltaics to light emitting devices and even photosensitizers for theranostic applications.

Vasily Kravtsov

Affiliation: ITMO University

Research interests: Two-dimensional quantum materials, ultrafast spectroscopy, nonlinear nano-optics
Title: Near-field spectroscopy and control of excitons in 2D van der Waals heterostructures.
Abstract: Atomically thin transition metal dichalcogenides (TMDs) are direct band gap semiconductors that host excitons with large binding energies and sizeable exciton – exciton interaction strength. When stacked into heterostructures, these materials acquire many unique optical properties associated with the interlayer coupling and formation of new excitonic and polaritonic states. Near – field spectroscopy provides an indispensable tool for studying such states, as well as their coupling, dynamics, and control. I w ill present results of our recent investigation of excitonic effects in van der Waals heterostructures via different near – field spectroscopy implementations including tip – enhanced spectroscopy and spectroscopy in the Fourier plane via evanescent wave coupling through a solid immersion lens. First, I will discuss the possibility of controlling the intralayer and interlayer excitons within a nanoscopic volume of TMD heterobilayers. Second, I will discuss experiments on probing and controlling exciton – polarito ns in all van-der-Waals heterostacks in the strong light-matter coupling regime.

Paul Weiss

Academic Affiliation: University of California, Los Angeles (UCLA)

Research interests: Nanoscience, Chemistry, Physics, Nanotechnology, Biotechnology

Title: Understanding and Controlling Charge, Heat, and Spin at Atomically Precise Interfaces

Abstract: One of the key advances in nanoscience and nanotechnology has been our increasing ability to reach the limits of atomically precise structures. By having developed the “eyes” to see, to record spectra, and to measure function at the nanoscale, we have been able to fabricate structures with precision as well as to understand the important and intrinsic heterogeneity of function found in these assemblies. The physical, electronic, mechanical, and chemical connections that materials make to one another and to the outside world are critical. Just as the properties and applications of conventional semiconductor devices
depend on these contacts, so do nanomaterials, many nanoscale measurements, and devices of the future. We explore the important roles that these contacts can play in preserving key transport and other properties. Initial nanoscale connections and measurements guide the path to future opportunities and challenges ahead. Band alignment, minimally disruptive connections, and control of spin and heat are all targets and can be characterized in both experiment and theory. I discuss our initial forays into this area in a number of materials systems.

Ruslan Temirov

Academic Affiliation: Peter Grunberg Institute, Forschungszentrum Jülich

Research interests: Scanning Probe Microscopy, Cryogenics

Kyoung-Duck Park

Academic Affiliation: Pohang University of Science and Technology (POSTECH)
Research interests: Physics
Title: Tip-enhanced cavity-spectroscopy

Maria Spethmann

Affiliation: University of Basel

Title: High-fidelity two-qubit gates of hybrid superconducting-semiconducting singlet-triplet qubits

Abstract:

Hybrid systems comprising superconducting and semiconducting materials are promising architectures for quantum computing. Superconductors induce interactions between the spin degrees of freedom of semiconducting quantum dots, based on crossed Andreev processes. In the talk I will present our theory where we show that these interactions are widely anisotropic when the semiconductor material has strong spin-orbit interactions. This anisotropy is tunable and enables fast and high-fidelity two-qubit gates between singlet-triplet spin qubits. The reason is that the design is immune to leakage into non-computational states and removes always-on  interactions between the qubits (crosstalk). We estimate two-qubit gate fidelities exceeding 99.9% without fine-tuning of parameters.

Daniel Kyungdeock Park

Academic Affiliation: Yonsei University

Title: Quantum machine learning: opportunities and challenges

Abstract:

Quantum computing has the potential to outperform any foreseeable classical computers for solving certain computational problems. With the growing demand for advanced computing power and methods in big data and artificial intelligence, quantum machine learning (QML) has emerged as one of the most exciting applications of quantum computing. In its early developments, QML gathered much attention mainly due to the quantum algorithm that solves the system of linear equations exponentially faster than its classical counterpart. However, this algorithm requires a fault-tolerant quantum computer and a quantum random access memory, which remain long-term prospect. Thus an important and challenging question is how noisy intermediate-scale quantum (NISQ) computers that are within reach can be utilized for QML. In this talk, I will first briefly introduce quantum machine learning. Then I will present several QML approaches that aim to utilize NISQ to the full extent and attain quantum advantages in the near future.

Joseph A Stroscio

Title: Unraveling Quantum Geometry and Orbital Magnetism Contributions to Landau Levels in Moiré Superlattices

Abstract:

Flat and narrow band physics in moiré quantum matter (MQM) has proven to be extremely rich with new emergent quantum phases which can be tuned with applied electric and magnetic fields. The topological properties of the eigenstates of the moiré Hamiltonian are critical for establishing the quantum phase of the system. While the emergence of non-trivial Chern numbers has been observed, it is important to characterize the quantum geometry in detail including the Berry curvature and the less known quantum metric effects which give rise to orbital magnetism in these systems. For almost a century, magnetic oscillations have been a powerful “quantum ruler” for measuring Fermi surface topology. In this presentation, I show the use of a quantum ruler of Landau levels via scanning tunneling spectroscopy to probe quantum geometry and topology in twisted double bilayer graphene (TDBG) [1]. The high-resolution Landau level spectra reveal tunable electron- and hole-like pockets that deviate significantly in their magnetic response from the semiclassical Onsager relation. A quantitative analysis of the Landau levels demonstrates the significance of quantum geometry contributions to the magnetic energy levels, highlighting the effect of the tunable Berry curvature and local orbital magnetism. The deviation from semiclassical behavior is due to the higher order magnetic field response of TDBG, which in turn is related to the quantum geometry of the electronic structure. The first-order correction in magnetic field, interpreted as an orbital magnetic moment, manifests as a valley splitting of the Landau levels. The second-order correction—orbital magnetic suscepti

Clément Cabanetos

Academic Affiliation: University of Angers

Title: “Sooner or later, everything old is new again”: Functionalization and use of a forgotten dye

Abstract:

Abstract: Since the advent of organic electronics, various classes of π-conjugated molecular and macromolecular semiconductors have been reported. Among them, imide-containing rylenes have attracted considerable research attention due to their redox, electron-withdrawing and charge-carrier transport properties, as well as their excellent chemical, thermal, and photochemical stabilities. Naphthalene diimide (NDI) and perylene diimide (PDI) can be unequivocally recognized as the most studied imide based building blocks for the preparation of high-performance electron transporting optoelectronic materials. Within these wide-ranging studies, considerable effort has been undertaken to functionalize both the bay positions and the nitrogen atom constituting the imide group (N-positions) to bring solubility, tune the molecular (opto)electronic characteristics, and build extended π-conjugated architectures. Despite interesting fluorescent properties, the N-(alkyl)benzothioxanthene-3,4-dicarboximide (BTI), a sulfur containing rylene-imide dye, has not yet triggered such interest. Exclusively functionalized on the N-position for imaging and staining applications, we recently focused our attention in functionalizing the p-conjugated core of this forgotten dye for the preparation of new and original materials for organic electronics, but not only… 

Clément Cabanetos: clement.cabanetos@cnrs.fr

 After graduation in 2008, Clément Cabanetos undertook a PhD at the CEISAM laboratory (Nantes, France) on the synthesis of new crosslinkable polymers for nonlinear optical applications. Shortly after his thesis defense, he joined the group of Jean Fréchet (KAUST, (Saudi Arabia) as a postdoctoral fellow to prepare efficient π-conjugated macromolecular materials for organic photovoltaics. In 2013, he was recruited as a permanent CNRS researcher and joined the MOLTECH-Anjou laboratory in Angers to develop new and original concepts for organic electronics. He then defended his habilitation in 2018 (associate professorship) and received in 2019 the CNRS bronze medal that awards young and promising researchers. Recently (august 2021) he moved to Seoul in a joint French (CNRS)-Korean International laboratory (2BFUEL) hosted by the Yonsei University where he was promoted director in September 2022.

Pavel Jelinek

Academic Affiliation: Institute of Physics of the Czech Academy of Sciences (FZU)

Title: Quinone-based 1D molecular chains on surfaces: magnetism and nuclear quantum effects

Abstract:

Low dimensional materials offer very interesting material and physical properties due to reduced dimensionality. At present, 2D materials are the focus of attention. However, 1D systems often show far more exotic behavior due to reduced dimensionality enhancing substantially quasiparticle interactions. However, synthesis of purely 1D molecular systems still remains elusive. In this talk, we will explore on-surface chemistry using 2,5-diamino-1,4-benzoquinonediimines (2HQDI) precursor [1], which offers interesting playground for growing molecular chains of distinct chemical character.

In first part of the talk, we will present formation of hydrogen-bonded 2HQDI molecular chains on Au(111) surface. We will discuss a significant influence of nuclear quantum effects on structural, mechanical and electronic properties of these 2HQDI molecular chains. Namely, we demonstrate that the presence of concerted proton motion not only enhances significantly the cohesive energy of intermolecular hydrogen bonds but it also causes emergence of new electronic states located at the edges [2].

In the second part, we introduce on-surface synthesis of 1D coordination p-d conjugated polymers, achieved by co-deposition of 2HQDI molecular precursor and various transition metals (Fe, Co, Ni, Cr, Cu) atoms on metal surfaces under UHV conditions [3]. This route results in formation of flexible coordination polymers with length up to hundreds of nanometers. We characterize physical and chemical properties by means of low temperature UHV scanning probe microscopy supported by theoretical simulations. We will discuss distinct coordination of transition metal and corresponding atomic, electronic and magnetic structure [4]

Finally, we will demonstrate fully reversible multiconfigurational light-driven spin crossover switches in a single p-d organometallic Co-QDI chain suspended between two electrodes.  The external light enables us to realize reversible spin cross over between low and high-spin states of individual cobalt centers within the chain.

[1] O. Siri, et al  J. Am. Chem. Soc. 125, 13793 (2003).

[2] A. Cahlik et al ACS Nano 15, 10357 (2021).

[3] V.M. Santhini et al, Angew. Chem. Int. Ed. 60, 439 (2021).

[4] Ch. Wackerlin et al, ACS Nano (2022) DOI: 10.1021/acsnano.2c05609

Wolf-Dieter Schneider

Academic Affiliation: Ecole Polytechnique Fédérale de Lausanne (EPFL)

Title: A short history of spectroscopic manifestations of the Kondo effect

Han-woong Yeom

Academic Affiliation: CALDES, IBS & POSTECH

Title: Nano-tsunami along atomic chains and domain walls for robust informatics

Abstract:

Storing and manipulating information in robust and dissipationless ways is of prime interest in various fields of science and technology. Using topologically protected local excitations, form examples, skyrmions and Majorana fermions, such robust informatics may be realized. This talk reviews our own approach to this issue, which deals with new types of solitons in electronic systems. We will first discuss atomic chains formed on silicon surfaces in charge-density-wave ground states and their solitons. We recently identified individual electronic solitons in indium atomic chains on a Si(111) surface and, more recently, in silicon chains on stepped silicon surfaces . Due to their unique structures, they represent unprecedented topological systems of Z₄ [1] and Z₃ [2], respectively, with three and two distinct solitons. These solitons can store, deliver, and operate multi-level information bits, which are protected topologically [3]. We further demonstrate solitons with higher multiplicity can be formed as a form of mobile kinks [4] along the charge-density-wave domain walls on a 2D material of 1T-TaS₂ [5]. Thus, the possibility of multi-level and topologically protected information processing with solitons, or solitonics, is well demonstrated. Further studies on soliton-defect, soliton-soliton, and soliton-excitation interactions are exciting for soliton applications.

References:

[1] S. M. Cheon, S. H. Lee, T. H. Kim, and H. W. Yeom, Science 350, 182 (2015).

[2] J. W. Park, E. Do, J. S. Shin, S. K. Song, O. P. Jelinek, and H. W. Yeom, Nature Nanotechnology 17, 244 (2022).

[3] S. M. Cheon, T. H. Kim, and H. W. Yeom, Nature Physics 13, 444 (2017).

[4] J. W. Lee, J. W. Park, and H. W. Yeom, PRL, under review (2022).

[5] D. Cho, G. Gye, J. Lee, S. H. Lee, L. Wnag, S-W. Cheong, and H. W. Yeom, Nature Commun. 8, 392 (2017)

Han Woong Yeom^1,2

¹Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang 37673, Korea.

²Department of Physics, POSTECH, Pohang 37673, Korea.

Harald Brune

Academic Affiliation: Ecole Polytechnique Fédérale de Lausanne (EPFL)

Title: The role of External Shells in the Magnetic Stability of Single Rare-Earth Adatoms, new SAMs,  and Graphene Transfer under UHV

Abstract:

An important and often neglected fact in the magnetic stability of single rare-earth adatoms is the spin-polarization of their outer shells. It stems from charge transfer to the surface [1] and gives rise to an additional magnetic moment that is strongly coupled to the large and well-screened moment of the 4f electrons [2]. We present experimental evidence for Dy/g/Ir(111) that the total angular momentum resulting from these coupled 4f 5d6s moments is in fact the good quantum number that decides which states are stable and which mechanisms for reversal exist in a given crystal field [3]. Recent theoretical works have pointed out the importance of valence 5d6s shells for single atom and single ion molecular magnets [4], however, direct experimental evidence for the importance of these shells in the spin dynamics was so far lacking.

We discuss the most recent single atom magnets (SAMs) with focus on two cases where the easy axis is lying in-plane. The first is Dy on the TiO2(100)-terminated Dy/SrTiO3(100) surface [5] and the second Dy on MgO bridge sites [6]. In the first case, we present XMCD results and in the second preliminary SP-STM results studying the two-state switching as function of tunnel bias that we discuss in the context of published XMCD data [7]. In order to cap, respectively, seal samples that are sensitive to oxidation and other chemical reactions in ambient, we have transferred graphene under ultra-high vacuum. Since this is potentially relevant also for single atom magnets, we present our results that show clean graphene transfer under UHV onto Cu(100) and Ir(111) target samples using a wafer bonding approach.

[1] M. Pivetta et al. PRB 98, 115417 (2018).
[2] M. Pivetta et al. PRX 10, 031054 (2020).
[3] A. Curcella et al. to be published (2022).
[4] V. Dubrovin et al. Chem. Communic. 55, 13963 (2019) & Inorg. Chem. Front. 8, 2373 (2021).
[5] V. Bellini et al. ACS Nano 16, 11182 (2021).
[6] C. Soulard et al. in preparation (2022).
[7] F. Donati et al. Nano Lett. 21, 8266 (2021).
[8] D. Merk et al. submitted (2022).

Jingcheng Li

Academic Affiliation: Sun Yat-sen University

Title: Inducing magnetic properties in graphene nanostructures

Abstract:

Spin in carbon-based materials shows long coherence time, tunable coupling strength, and can be incorporated into scalable carbon platform, which makes it promising for quantum computing and spintronics applications.  Predictions state that graphene structures with specific edge topology can spontaneously develop magnetism, but the difficulty in their synthesis and magnetism characterization hinders the experimental verification. Here in this talk, I will show you our latest results on the observation and manipulation of magnetic moments in such graphene open-shell nanostructures. The graphene open-shell nanostructures with different edge topology, size and doping are created on a gold surface through on-surface synthesis route with atomic precision. Using scanning tunneling spectroscopy, we can detect the presence of electron spins and map their localization. With the experimental results and theoretical simulations, I will demonstrate that how the electronic correlations, πbond frustration or topological band engineering can be used to induce spin states in graphene nanostructures.

Yousoo Kim

Academic Affiliation: University of Tokyo

Title: Single-molecule spectroscopy using localized-surface plasmon

Abstract:

Irradiation of light to the metallic nanostructure causes collective vibration of free electrons (plasmon), followed by the creation of an electromagnetic field, i.e., localized surface plasmon (LSP). The LSP has a characteristic interaction with matter, especially a single molecule. The scanning tunneling microscope (STM) is a versatile and powerful tool for investigating and controlling the chemistry of individual molecules on solid surfaces. We have developed an optical STM technology that combines the STM with light irradiation and detection technologies for our own purpose [1], which allows us to apply the LSP to exploring novel chemical reactions and spectroscopy based on the interaction between the LSP and electronic/vibrational quantum states of a single molecule at the STM junction. We have developed single molecule emission and absorption (Fig. 1(a)) spectroscopy [1] using the interaction between the LSP and a molecule, in which the LSP participates in the exciton formation in a target molecule [2,3]. Combining the emission and absorption spectroscopies, we visualized fluorescence resonance energy transfer between two different molecules [4]. We have also explored the detailed mechanism of single-molecule chemical dynamics induced by the LSP (Fig. 1(b)) [5]. We also applied the LSP to measure tip-enhanced resonance Raman spectra of a single molecule (Fig. 1(c)) [6]. Furthermore, we achieved an ultrahigh-energy resolution photoluminescence measurement of a single molecule using a tunable excitation laser (Fig. 1(d)) [7]. These optical setups enable a real-space measurement of photocurrent pathways at a single molecule (Fig. 1(e)) [8]. In this talk, I will discuss recent issues focusing on single-molecule spectroscopy based on the molecular excitation by localized surface plasmon at the STM junction, which has been applied to exploring the quantum states of a phthalocyanine and its derivatives.

REFERENCES
[1] H. Imada et al., Physical Review Letters, 119 (2017) 013901
[2] K. Miwa et al., Nano Letters, 19 (2019) 2803
[3] K. Kimura et al., Nature, 570 (2019) 210
[4] H. Imada et al., Nature, 538 (2016) 364
[5] E. Kazuma et al., Science, 360 (2018) 521
[6] R.B. Jaculbia et al., Nature Nanotechnology, 15 (2020) 105
[7] H. Imada et al., Science, 373 (2021) 95
[8] M. Imai-Imada et al., Nature 603 (2022) 829

Youngchan Kim

Academic Affiliation: University of Surrey

Title: Quantum biology in fluorescent protein: a new model system to study quantum effects in biology

Abstract:

Quantum effects are usually thought to be too delicate to manifest in biology since random molecular interactions were thought to be instantaneously obliterated quantum coherent molecular interactions occurring in wet biological environments. However, recent biological, chemical, and physical breakthroughs have revealed that subtle quantum effects may shape biological processes and functions, as exemplified by photosynthesis, enzyme catalysed reactions, and magnetic field effects on spin-dependent reactions in biology, to name a few. Studying coherent dipole-dipole coupling between biomolecular systems is challenging but holds many fascinating, fundamental questions that will inspire new ways to better understand and enhance health and medicine. A recent study suggests that the yellow fluorescent proteins, Venus_A206, exhibit room-temperature exciton coupling when they form a dimer. Because cryogenic temperature is not required to observe such quantum effects, genetically engineered fluorescent protein assemblies could inspire a new way towards developing biological quantum technologies, such as quantum-enhanced biosensors. In this talk, I will present the recent progress in studying quantum biology using fluorescent proteins.

Jens Wiebe

Academic Affiliation: University of Hamburg

This lecture is intended for Master and PhD students as well as young Postdocs. After a short historical review of the discoveries of materials which are conventional and unconventional superconductors, I will give an introduction to Cooper pairing and the Bardeen–Cooper–Schrieffer (BCS) theory, the microscopic theory for the description of conventional superconductivity. Then, I will describe the quasiparticle excitation spectrum of such a superconductor and explain how it can be experimentally measured using scanning tunnel spectroscopy, both with normal-metal and superconducting tips. Subsequently, I will talk about the effects of magnetic fields and single magnetic impurities on a superconducting substrate, where the latter leads to the so-called Yu-ShibaRusinov bound states. Finally, I will explain different strategies to tailor a topological superconductor, including the spin chain platform where bands formed by the hybridization of Yu-Shiba-Rusinov states in chains of magnetic atoms in contact to a superconducting surface can host Majorana bound states.

Literature

C. Enss and S. Hunklinger, Low Temperature Physics (Springer 2005)
R. Gross and A. Marx, Festkörperphysik (De Gruyter 2014): unfortunately only in german so far…
Several original publications

Jens Wiebe

Academic Affiliation: University of Hamburg

Title: Search for Large Topological Gaps and Isolated Majorana Bound States in Atom-by-Atom Fabricated Shiba Chains

Abstract:

Paul Weiss

Academic Affiliation: California NanoSystems Institute and Departments of Chemistry & Biochemistry, Bioengineering, and Materials Science & Engineering, UCLA, Los Angeles

Title: Atomically Precise Chemical, Physical, Electronic, and Spin Contacts and Interfaces

Abstract:

One of the key advances in nanoscience and nanotechnology has been our increasing ability to reach the limits of atomically precise structures. By having developed the “eyes” to see, to record spectra, and to measure function at the nanoscale, we have been able to fabricate structures with precision as well as to understand the important and intrinsic heterogeneity of function found in these assemblies. The physical, electronic, mechanical, and chemical connections that materials make to one another and to the outside world are critical. Just as the properties and applications of conventional semiconductor devices depend on these contacts, so do nanomaterials, many nanoscale measurements, and devices of the future. We discuss the important roles that these contacts can play in preserving key transport and other properties. Initial nanoscale connections and measurements guide the path to future opportunities and challenges ahead. Band alignment and minimally disruptive connections are both targets and can be characterized in both experiment and theory. I discuss our initial forays into this area in a number of materials systems.

Daniel Loss

Academic Affiliation: University of Basel

Title: Hole spin qubits for quantum computing in Si and Ge quantum dots

Abstract: 

Hole spin qubits are frontrunner platforms for scalable quantum computers in Si and Ge semiconductors because of their large spin-orbit interaction which enables ultrafast all-electric qubit control at low power. The fastest spin qubits to date are defined in long quantum dots with two tight confinement directions, when the driving field is aligned to the smooth direction [1]. However, in these systems the lifetime of the qubit is strongly limited by charge noise, a major issue in hole qubits. I will give an overview of recent theoretical and experimental results [1-5] that have led to a series of testable predictions such as sweet spots for devices in Si and Ge semiconductors currently implemented in the Swiss National Center on Spin Qubits led by the University of Basel and IBM Zurich.

References

[1] Ultrafast Hole Spin Qubit with Gate-Tunable Spin-Orbit Switch. F. N. M. Froning, L. C. Camenzind, O. A. H. van der Molen, A. Li, E. P. A. M. Bakkers, D. M. Zumbühl, F. R. Braakman; Nature Nanotechnology 16 (2021).

[2] Fully tunable hyperfine interactions of hole spin qubits in Si and Ge quantum dots.
S. Bosco and D.Loss, Phys. Rev. Lett. 127, 190501 (2021).

[3] Hole spin qubits in Si FinFETs with fully tunable spin-orbit coupling and sweet spots for charge noise. S. Bosco, B. Hetényi, and D.Loss; PRX Quantum 2, 010348 (2021).

[4] The germanium quantum information route. G. Scappucci, C. Kloeffel, F. A. Zwanenburg, D. Loss, M. Myronov, J.-J. Zhang, S. De Franceschi, G. Katsaros, and M. Veldhorst; Nat Rev Mater (2020).

[5] A hole spin qubit in a fin field-effect transistor above 4 Kelvin. L. C. Camenzind, S. Geyer, A. Fuhrer, R. J. Warburton, D. M. Zumbühl, A. V. Kuhlmann; Nature Electronics 2022.

Valeria Sheina

Academic Affiliation: C2N, Université Paris – S aclay

Talk title: The development of Quantum Technologies

Abstract:

Quantum spin states constitute a resource for the development of quantum technologies. They have been considered for the realization of quantum computers, quantum simulators and quantum sensors. These long-term goals demand for the identification of appropriate hosts for quantum spin states with long coherence time and compatible with microfabrication technologies. Because of their two-dimensional character that enables an easier localization of the dopants in the material, monoatomic layer of Van-der-Waals materials is of intense interest. My Ph.D. describes experimental works that address two issues in this field. First, the identification of point-defects with interesting spin properties in Van-der-Waals materials; second, the Electrical Detection of Magnetic Resonance (EDMR) in those Van-der-Waals materials.

My work addresses two layered materials possessing spin and valley degrees of freedom: the Br-doped  2H-MoTe2 semiconductor belonging to the transition metal dichalcogenide (TMD) family and graphene. In 2H-MoTe2, we found that the electronic levels of the Br-dopants electronic levels are hybridized to the valleys in the conduction band. This produces spin-valley states where the spin and valley quantum numbers are locked. Moreover, by spin resonance methods, we find that the Br dopant carries an unpaired spin with coherence lifetime reaching 50 ns at the lowest temperature of 4.2 K. This is of practical interest as such states can be manipulated conveniently by electric fields. In graphene, encapsulated in hBN. we show that the spin resonance can be detected by transport measurements and propose a simple model relating the spin-resonant signal to the time average of the perpendicular magnetization component <Mz>.

Mario Ruben

Academic Affiliation: INT, IQMT, Karlsruhe Institute of Technology (KIT) & ISIS, CESQ, University of Strasbourg

Talk title: Quantum Computing with Molecules

Abstract:

Metal complexes will be proposed to acting as active quantum units for Quantum Computing (QC). We report on the implementation of metal complexes into nanometre-sized (single-)molecular spintronic devices by a combination of isotopologue chemistry, bottom-up self-assembly and top-down lithography techniques. The control of the Hilbert space of the molecular quantum magnets on conducting surfaces/electrodes will be shown and persistence of magnetic properties under confinement in Supramolecular Quantum Devices (SMQD) will be proven. The quantum behaviour (e.g.. superposition) of the metal complexes will be addressed at the single molecule level^1-13 to finally implement a quantum algorithm on a TbPc₂-Qudit performing quantum computing  operations.¹⁰ Moreover, we will show that that the components of SMQDs as the Quantum Magnet¹⁴ and the graphene sheets¹⁵ can be made from CO₂ guaranteeing a negative Carbon footprint and sustainability of the molecular approach towards QC.

Franz Josef Giessibl

Academic Affiliation: University of Regensburg

Title: The character of chemical bonds to natural and artificial atoms revealed by atomic force microscopy

Abstract: Atomic force microscopy with CO terminated tips has demonstrated outstanding spatial resolution on organic molecules [1], metallic clusters [2] and many other samples. Experimental evidence and calculations show that the CO tip is chemically inert and probes organic molecules mainly by Paulirepulsion [3]. Thus, images of organic molecules, graphene, etc. observed with a CO tip can be interpreted as a map of the absolute charge density of the sample. The total charge density of a single adatom is approximately given by a Gaussian peak. While single silicon adatoms appear similar to a Gaussian peak when imaged by AFM with a CO terminated tip, copper and iron adatoms adsorbed on Cu(111) and Cu(110) appear as tori [2,4]. Experiments and DFT calculations show that the total charge density of Cu and Fe adatoms is approximately Gaussian–in contrast to a hypothesis that proposes 4spz hybridization of Cu and Fe adatoms on a Cu surface[4]. The bonding strength between the AFM tip and the atoms of the sample depends not only on the chemical identity but also on the coordination-corner atoms in clusters are more reactive than center atoms [5]. Progress in force resolution [6] opens up the fN-regime, enabling to study engineered surface structures such as quantum corrals [7] that can be viewed as artificial atoms. Surprisingly, these artificial atoms interact in a similar way with AFM tips as natural atoms, yet with a force of only 1/1000of what is experienced in natural atoms [8].

References:

[1] L. Gross et al.,Science325, 1110 (2009).

[2] M. Emmrich et al.,Science348, 308 (2015).

[3] N. Moll et al.,New Journal of Physics12, 125020 (2010).

[4] F. Huber et al.,Science366, 235 (2019).

[5] J. Berwanger et al.,Phys.Rev. Lett.124, 096001 (2020).

[6] A. Liebig et al.,New Journal of Physics22, 063040 (2020).

[7]M.F. Crommie, C.P. Lutz, D.M. Eigler,Science262, 218(1993).

[8] F. Stilp, et al.,Science372, 1196 (2021).

Date: June 17, 11:00 (KST)

Location: B1 Jupiter, Center for Quantum Nanoscience