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Nicolaj Betz Academic Affiliation: University of Stuttgart, Institute for Functional Matter and Quantum Technologies Date and Time of the Talk: Sept 14th, 2021;
Academic Affiliation: University of Stuttgart, Institute for Functional Matter and Quantum Technologies
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New insights into spin dynamics – Stochastic resonance as a tool
Stochastic scattering between magnetic atoms and electrons of a metal shortens excitation lifetimes and accelerates decoherence. However, this scattering also creates characteristic time scales, that carry information about dynamics of the system. Modulating the scattering close to a threshold leads to frequency-dependent synchronization of the spin of the magnetic atoms and the modulation . This
effect, known as Stochastic Resonance, amplifies the dynamic response to the modulation and can be used to investigate quantum fluctuations of the system . Here we introduce a measurement technique which uses the synchronization effect that underlies Stochastic Resonance to control and measure characteristic time scales of magnetic atoms with a scanning tunneling microscope. This enables the investigation of spin dynamics in a bandwidth ranging from milliseconds to picoseconds. In some spin structures this reveals multiple switching paths between higher excited states, thus providing insight into new, previously inaccessible dynamics.
 Hänze et al., Sci. Adv. 2021, 7 (2021).
 R. Löfstedt, S. N. Coppersmith, Phys Rev. Lett. 72, 1947 (1994)
(Tuesday) 5:00 pm - 7:00 pm KST
Arzhang Ardavan Affiliation: Professor of Physics at the Clarendon Laboratory, University of Oxford Date: August 17, 2021; Electric field control of spins in piezoelectrics, ferroelectrics, and molecules Magnetic fields are challenging to localise
Affiliation: Professor of Physics at the Clarendon Laboratory, University of Oxford
Date: August 17, 2021;
Electric field control of spins in piezoelectrics, ferroelectrics, and molecules
Magnetic fields are challenging to localise to short length scales because their sources are electrical currents. Conversely, electric fields can be applied using electrostatic gates on scales limited only by lithography. This has important consequences for the design of spin-based information technologies: while the Zeeman interaction with a magnetic field provides a convenient tool for manipulating spins, it is difficult to achieve local control of individual spins on the length scale anticipated for useful quantum technologies. This motivates the study of electric field control of spin Hamiltonians .
Mn2+ defects in ZnO exhibit extremely long spin coherence times and a small axial zero-field splitting. Their environment is inversion-symmetry-broken, and the zero-field splitting shows a linear dependence on an externally applied electric field. This control over the spin Hamiltonian offers a route to controlling the phase of superpositions of spin states using d.c. electric field pulses, and to driving spin transitions using microwave electric fields . An analogous sensitivity to external electric fields is exhibited by Fe3+ defect spins in the archetypal ferroelectric PbTiO3. The Fe spin anisotropy axis is set by the ferroelectric order, so the spin Hamiltonian is controllable by manipulating the ferroelectric polarization direction .
Electric fields may couple to spins in molecular magnets by a range of mechanisms , including via intramolecular exchange interactions or hyperfine interactions, as well as through anisotropy terms. Through chemical design it is possible to optimise the conditions for molecular spin-electric coupling, yielding systems showing strong effects .
 W. Mims, The linear electric field effect in paramagnetic resonance (Oxford University Press, 1976)
 R.E. George et al., Phys. Rev. Lett. 110, 027601 (2013)
 J. Liu et al., Sci. Adv. 7, eabf8103 (2021)
 J. Liu et al., Phys. Rev. Lett. 122, 037202 (2019)
 J. Liu et al., arXiv:2005.01029, to appear in Nat. Phys.
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