Geometrische Dissipation in nicht-Abel'schen Quantenspinsystemen und darüber hinaus
Zusammenfassung der Projektergebnisse
The conceptual ambition of the present project was to combine the physics of geometric phases with the dynamics of quantum dissipative systems and to look for concrete scenario where geometric effects and dissipation are not antagonistic. Specifically we have focused on the dynamics of ferromagnetic nano-particles coupled to external dissipative reservoirs and driven far from equilibrium. The results show that geometric effects control not only the deterministic dynamics, but also the kinetics of the distribution functions as well as noise. Not surprisingly, some of our results (see e.g. item (v) below) go way beyond the promise of the work packages. We note that the very recent results emerging from our project are in the stage of the refereeing process or are being written up. Importantly, many of our predictions are susceptible to experimental test. While not following the mainstream of work in spintronics (we mostly consider dephasing/equilibration dictated by the dissipative environment rather than by processes within our magnetic particles), the results highlight the conceptually important links among dissipation - geometric effects - quantum phase transitions. Our main results are as follows: (i) We have adjusted the Ambegaokar-Eckern-Schön formalism developed for the U(1) charge dynamics to the case of the magnetic SU(2) dynamics. We have demonstrated the strong difference of this approach to the more common Caldeira-Leggett approach in the quantum regime (at low temperatures). (i) We studied the dynamics of magnetization driven by a spin-torque current as well as by a thermal bias. We have demonstrated the crucial role played by the non-equilibrium distribution function adjusting itself self-consistently to the magnetization trajectory. This effect can produce a 100% change in the behavior of the magnetization and in the charge and thermal transport characteristics of the system. (iii) We have shown that ferromagnetic resonance (FMR) can be detected via the noise of the charge current even if the leads are non-magnetic and no signal appears in the average current. (iv) We have shown how a spin impurity at the edge of a two-dimensional time reversal invariant topological insulator may give rise to backscattering and shot noise. The dissipative spin dynamics plays here a decisive role. (v) We have predicted a novel dissipative quantum phase transition, involving a continuous symmetry (an SU(2) symmetry of a quantum dot in the mesoscopic Stoner regime coupled to metallic leads). We have found that at a critical coupling strength the Curie part of the susceptibility vanishes in a fashion characteristic of a second order phase transition. This is a manifestation of the suppression of the Coleman-Weinberg mechanism by dissipation.
Projektbezogene Publikationen (Auswahl)
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U(1) and SU(2) quantum dissipative systems: the Caldeira–Leggett Versus Ambegaokar– Eckern–Schön approaches, Journal of Experimental and Theoretical Physics 122, 576–586 (2016)
A. Shnirman, A. Saha, I. S. Burmistrov, M. N. Kiselev, A. Altland & Y. Gefen
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Emulating Majorana fermions and their braiding by Ising spin chains, Phys. Rev. B 96, 195402 (2017)
Stefan Backens, Alexander Shnirman, Yuriy Makhlin, Yuval Gefen, Johan E. Mooij, and Gerd Schön
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Strong nonequilibrium effects in spin-torque systems, Phys. Rev. B 95, 075425 (2017)
Tim Ludwig, Igor S. Burmistrov, Yuval Gefen, and Alexander Shnirman
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Dynamics of a Magnetic Needle Magnetometer: Sensitivity to Landau-Lifshitz-Gilbert Damping, Phys. Rev. Lett. 121, 160801 (2018)
Yehuda B. Band, Yishai Avishai, Alexander Shnirman
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Fingerprints of single nuclear spin energy levels using STM – ENDOR, Journal of Magnetic Resonance 289, 107 (2018)
Yishay Manassen, Michael Averbukh, Moamen Jbara, Bernhard Siebenhofer, Alexander Shnirman, Baruch Horovitz
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Thermally driven spin transfer torque system far from equilibrium: Enhancement of thermoelectric current via pumping current, Phys. Rev. B 99, 045429 (2019)
Tim Ludwig, Igor S. Burmistrov, Yuval Gefen, and Alexander Shnirman
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Unrestricted electron bunching at the helical edge, Phys. Rev. Lett. 123, 056803 (2019)
Pavel D. Kurilovich, Vladislav D. Kurilovich, Igor S. Burmistrov, Yuval Gefen, Moshe Goldstein
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Current noise geometrically generated by a driven magnet, PRL
Tim Ludwig, Igor S. Burmistrov, Yuval Gefen, Alexander Shnirman
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Mesoscopic Stoner instability in open quantum dots: suppression of Coleman-Weinberg mechanism by electron tunneling, PRL
Igor S. Burmistrov, Yuval Gefen, Dmitri S. Shapiro, Alexander Shnirman
