Postdoc
Piotr Kot
During his time as a PhD student, Piotr helped develop a state of the art ESR-STM capable of probing energies three times of what was demonstrated beforehand. With this STM he studied the effect of microwave radiation on the tunneling processes between two superconductors. Furthermore, he used ESR-STM to investigate the coupling between the electric field in the STM junction and the molecular spins probed in the experiment. His findings demonstrate a new way of controlling atomic spins and he hopes to use these findings to develop an atomic scale quantum computer at QNS. Aside from his research focus, Piotr is interested in spintronics and quantum information processing, and searches for applications where these two are combined.
- Education
- Work Experience
- Selected Publiations
| 2022 | PhD in Physics, University of Stuttgart, Stuttgart, Germany |
| 2017 | MS in Physics, University of Stuttgart, Stuttgart, Germany |
| 2015 | BS in Physics, University of British Columbia, Vancouver, Canada |
| 2022 – Current | Postdoctoral Researcher at Center for Quantum Nanoscience (QNS), Institute for Basic Science (IBS), Ewha Womans University, Seoul, Korea |
2023
Kot P; Ismail M; Drost R; Siebrecht J; Huang H; Ast C R
Electric control of spin transitions at the atomic scale Journal Article
In: Nature Communications, vol. 14, no. 1, pp. 6612, 2023, ISSN: 2041-1723.
@article{kot_electric_2023,
title = {Electric control of spin transitions at the atomic scale},
author = {Piotr Kot and Maneesha Ismail and Robert Drost and Janis Siebrecht and Haonan Huang and Christian R. Ast},
url = {https://www.nature.com/articles/s41467-023-42287-2},
doi = {10.1038/s41467-023-42287-2},
issn = {2041-1723},
year = {2023},
date = {2023-10-01},
urldate = {2024-11-16},
journal = {Nature Communications},
volume = {14},
number = {1},
pages = {6612},
abstract = {Abstract
Electric control of spins has been a longstanding goal in the field of solid state physics due to the potential for increased efficiency in information processing. This efficiency can be optimized by transferring spintronics to the atomic scale. We present electric control of spin resonance transitions in single TiH molecules by employing electron spin resonance scanning tunneling microscopy (ESR-STM). We find strong bias voltage dependent shifts in the ESR signal of about ten times its line width. We attribute this to the electric field in the tunnel junction, which induces a displacement of the spin system changing the
g
-factor and the effective magnetic field of the tip. We demonstrate direct electric control of the spin transitions in coupled TiH dimers. Our findings open up new avenues for fast coherent control of coupled spin systems and expands on the understanding of spin electric coupling.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract
Electric control of spins has been a longstanding goal in the field of solid state physics due to the potential for increased efficiency in information processing. This efficiency can be optimized by transferring spintronics to the atomic scale. We present electric control of spin resonance transitions in single TiH molecules by employing electron spin resonance scanning tunneling microscopy (ESR-STM). We find strong bias voltage dependent shifts in the ESR signal of about ten times its line width. We attribute this to the electric field in the tunnel junction, which induces a displacement of the spin system changing the
g
-factor and the effective magnetic field of the tip. We demonstrate direct electric control of the spin transitions in coupled TiH dimers. Our findings open up new avenues for fast coherent control of coupled spin systems and expands on the understanding of spin electric coupling.
Electric control of spins has been a longstanding goal in the field of solid state physics due to the potential for increased efficiency in information processing. This efficiency can be optimized by transferring spintronics to the atomic scale. We present electric control of spin resonance transitions in single TiH molecules by employing electron spin resonance scanning tunneling microscopy (ESR-STM). We find strong bias voltage dependent shifts in the ESR signal of about ten times its line width. We attribute this to the electric field in the tunnel junction, which induces a displacement of the spin system changing the
g
-factor and the effective magnetic field of the tip. We demonstrate direct electric control of the spin transitions in coupled TiH dimers. Our findings open up new avenues for fast coherent control of coupled spin systems and expands on the understanding of spin electric coupling.
2022
Drost R; Uhl M; Kot P; Siebrecht J; Schmid A; Merkt J; Wรผnsch S; Siegel M; Kieler O; Kleiner R; Ast C R
Combining electron spin resonance spectroscopy with scanning tunneling microscopy at high magnetic fields Journal Article
In: vol. 93, no. 4, 2022, ISSN: 1089-7623.
@article{Drost2022,
title = {Combining electron spin resonance spectroscopy with scanning tunneling microscopy at high magnetic fields},
author = {Robert Drost and Maximilian Uhl and Piotr Kot and Janis Siebrecht and Alexander Schmid and Jonas Merkt and Stefan Wรผnsch and Michael Siegel and Oliver Kieler and Reinhold Kleiner and Christian R. Ast},
doi = {10.1063/5.0078137},
issn = {1089-7623},
year = {2022},
date = {2022-04-01},
urldate = {2022-04-01},
volume = {93},
number = {4},
publisher = {AIP Publishing},
abstract = {<jats:p>The continuous increase in storage densities and the desire for quantum memories and computers push the limits of magnetic characterization techniques. Ultimately, a tool that is capable of coherently manipulating and detecting individual quantum spins is needed. Scanning tunneling microscopy (STM) is the only technique that unites the prerequisites of high spatial and energy resolution, low temperature, and high magnetic fields to achieve this goal. Limitations in the available frequency range for electron spin resonance STM (ESR-STM) mean that many instruments operate in the thermal noise regime. We resolve challenges in signal delivery to extend the operational frequency range of ESR-STM by more than a factor of two and up to 100 GHz, making the Zeeman energy the dominant energy scale at achievable cryogenic temperatures of a few hundred millikelvin. We present a general method for augmenting existing instruments into ESR-STM to investigate spin dynamics in the high-field limit. We demonstrate the performance of the instrument by analyzing inelastic tunneling in a junction driven by a microwave signal and provide proof of principle measurements for ESR-STM.</jats:p>},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
<jats:p>The continuous increase in storage densities and the desire for quantum memories and computers push the limits of magnetic characterization techniques. Ultimately, a tool that is capable of coherently manipulating and detecting individual quantum spins is needed. Scanning tunneling microscopy (STM) is the only technique that unites the prerequisites of high spatial and energy resolution, low temperature, and high magnetic fields to achieve this goal. Limitations in the available frequency range for electron spin resonance STM (ESR-STM) mean that many instruments operate in the thermal noise regime. We resolve challenges in signal delivery to extend the operational frequency range of ESR-STM by more than a factor of two and up to 100 GHz, making the Zeeman energy the dominant energy scale at achievable cryogenic temperatures of a few hundred millikelvin. We present a general method for augmenting existing instruments into ESR-STM to investigate spin dynamics in the high-field limit. We demonstrate the performance of the instrument by analyzing inelastic tunneling in a junction driven by a microwave signal and provide proof of principle measurements for ESR-STM.</jats:p>
2020
Kot P; Parnell J; Habibian S; Straรer C; Ostrovsky P M; Ast C R
Band dispersion of graphene with structural defects Journal Article
In: Phys. Rev. B, vol. 101, no. 23, 2020, ISSN: 2469-9969.
@article{Kot2020,
title = {Band dispersion of graphene with structural defects},
author = {Piotr Kot and Jonathan Parnell and Sina Habibian and Carola Straรer and Pavel M. Ostrovsky and Christian R. Ast},
doi = {10.1103/physrevb.101.235116},
issn = {2469-9969},
year = {2020},
date = {2020-06-03},
journal = {Phys. Rev. B},
volume = {101},
number = {23},
publisher = {American Physical Society (APS)},
abstract = {We study the band dispersion of graphene with randomly distributed structural defects using two complementary methods, exact diagonalization of the tight-binding Hamiltonian and implementing a self-consistent ๐ matrix approximation. We identify three distinct types of impurities resulting in qualitatively different spectra in the vicinity of the Dirac point. First, resonant impurities, such as vacancies or 585 defects, lead to stretching of the spectrum at the Dirac point with a finite density of localized states. This type of spectrum has been observed in epitaxial graphene by photoemission spectroscopy and discussed extensively in the literature. Second, nonresonant (weak) impurities, such as paired vacancies or Stone-Wales defects, do not stretch the spectrum but provide a line broadening that increases with energy. Finally, disorder that breaks sublattice symmetry, such as vacancies placed in only one sublattice, open a gap around the Dirac point and create an impurity band in the middle of this gap. We find good agreement between the results of the two methods and also with the experimentally measured spectra.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We study the band dispersion of graphene with randomly distributed structural defects using two complementary methods, exact diagonalization of the tight-binding Hamiltonian and implementing a self-consistent ๐ matrix approximation. We identify three distinct types of impurities resulting in qualitatively different spectra in the vicinity of the Dirac point. First, resonant impurities, such as vacancies or 585 defects, lead to stretching of the spectrum at the Dirac point with a finite density of localized states. This type of spectrum has been observed in epitaxial graphene by photoemission spectroscopy and discussed extensively in the literature. Second, nonresonant (weak) impurities, such as paired vacancies or Stone-Wales defects, do not stretch the spectrum but provide a line broadening that increases with energy. Finally, disorder that breaks sublattice symmetry, such as vacancies placed in only one sublattice, open a gap around the Dirac point and create an impurity band in the middle of this gap. We find good agreement between the results of the two methods and also with the experimentally measured spectra.
Kot P; Drost R; Uhl M; Ankerhold J; Cuevas J C; Ast C R
Microwave-assisted tunneling and interference effects in superconducting junctions under fast driving signals Journal Article
In: Phys. Rev. B, vol. 101, no. 13, 2020, ISSN: 2469-9969.
@article{Kot2020b,
title = {Microwave-assisted tunneling and interference effects in superconducting junctions under fast driving signals},
author = {Piotr Kot and Robert Drost and Maximilian Uhl and Joachim Ankerhold and Juan Carlos Cuevas and Christian R. Ast},
doi = {10.1103/physrevb.101.134507},
issn = {2469-9969},
year = {2020},
date = {2020-04-16},
journal = {Phys. Rev. B},
volume = {101},
number = {13},
publisher = {American Physical Society (APS)},
abstract = {As scanning tunneling microscopy is pushed towards fast local dynamics, a quantitative understanding of tunnel junctions under the influence of a fast ac driving signal is required, especially at the ultralow temperatures relevant to spin dynamics and correlated electron states. We subject a superconductor-insulator-superconductor junction to a microwave signal from an antenna mounted in situ and examine the dc response of the contact to this driving signal. Quasiparticle tunneling and the Josephson effect can be interpreted in the framework of Tien-Gordon theory. The situation is more complex when it comes to higher-order effects such as multiple Andreev reflections. Microwave-assisted tunneling unravels these complex processes, providing deeper insights into tunneling than are available in a pure dc measurement.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
As scanning tunneling microscopy is pushed towards fast local dynamics, a quantitative understanding of tunnel junctions under the influence of a fast ac driving signal is required, especially at the ultralow temperatures relevant to spin dynamics and correlated electron states. We subject a superconductor-insulator-superconductor junction to a microwave signal from an antenna mounted in situ and examine the dc response of the contact to this driving signal. Quasiparticle tunneling and the Josephson effect can be interpreted in the framework of Tien-Gordon theory. The situation is more complex when it comes to higher-order effects such as multiple Andreev reflections. Microwave-assisted tunneling unravels these complex processes, providing deeper insights into tunneling than are available in a pure dc measurement.