Mesoscale And Nanoscale Physics
Current-driven Rashba Field in a Magnetic Quantum Well (1907.07116v1)
Abdulkarim Hariri, Meshal Alawein, Aurelien Manchon
2019-07-16
In materials lacking inversion symmetry, the spin-orbit coupling enables the direct connection between the electron's spin and its linear momentum, a phenomenon called inverse spin galvanic effect. In magnetic materials, this effect promotes current-driven torques that can be used to control the magnetization direction electrically. In this work, we investigate the current-driven inverse spin galvanic effect in a quantum well consisting in a magnetic material embedded between dissimilar insulators. Assuming the presence of Rashba spin-orbit coupling at the interfaces, we investigate the nature of the non-equilibrium spin density and the influence of the quantum well parameters. We find that the torque is governed by the interplay between the number of states participating to the transport and their spin chirality, the penetration of the wave function into the tunnel barriers, and the strength of the Rashba term.
Spectroscopy of classical environmental noise with a qubit subjected to projective measurements (1907.01784v2)
Fattah Sakuldee, Łukasz Cywiński
2019-07-03
We show theoretically how a correlation of multiple measurements on a qubit undergoing pure dephasing can be expressed as environmental noise filtering. Measurement of such correlations can be used for environmental noise spectroscopy, and the family of noise filters achievable in such a setting is broader than the one achievable with a standard approach, in which dynamical decoupling sequences are used. We illustrate the advantages of this approach by considering a case of noise spectrum with sharp features at very low frequencies. We also show how appropriately chosen correlations of a few measurements can detect the non-Gaussian character of certain environmental noises, particularly the noise affecting the qubit at the so-called optimal working point.
Quantum skyrmions in frustrated ferromagnets (1901.03343v2)
Vivek Lohani, Ciarán Hickey, Jan Masell, Achim Rosch
2019-01-10
We develop a quantum theory of magnetic skyrmions and antiskyrmions in a spin-1/2 Heisenberg magnet with frustrating next-nearest neighbor interactions. Using exact diagonalization we show numerically that a quantum skyrmion exists as a stable many-magnon bound state and investigate its quantum numbers. We then derive a phenomenological Schr"odinger equation for the quantum skyrmion and its internal degrees of freedom. We find that quantum skyrmions have highly unusual properties. Their bandwidth is exponentially small and arises from tunneling processes between skyrmion and antiskyrmion. The bandstructure changes both qualitatively and quantitatively when a single spin is added or removed from the quantum skyrmion, reflecting a locking of angular momentum and spin quantum numbers characteristic for skyrmions. Additionally, while for weak forces the quantum skyrmion is accelerated parallel to the force, it moves in a perpendicular direction for stronger fields.
Topological phase diagram of a three-terminal Josephson junction: From the conventional to the Majorana regime (1904.10472v3)
Lucila Peralta Gavensky, Gonzalo Usaj, Carlos A. Balseiro
2019-04-23
We study the evolution of averaged transconductances in three-terminal Josephson junctions when the superconducting leads are led throughout a topological phase transition from an
-wave to a
-wave (Majorana) phase by an in-plane magnetic field
. We provide a complete description of this transition as a function of
threading the junction. For that we use a spinful model within a formalism that allows to treat on equal footing the contribution to the transconductance from both the Andreev subgap levels and the continuum spectrum. We unveil a fractionalization in the quantization of the transconductance due to the presence of Majorana quasiparticles, reflecting the effective pumping of half a Cooper pair charge in the
Zeeman effect induced 0-
transitions in ballistic Dirac semimetal Josephson junctions (1807.07725v2)
Chuan Li, Bob de Ronde, Jorrit de Boer, Joost Ridderbos, Floris Zwanenburg, Yingkai Huang, Alexander Golubov, Alexander Brinkman
2018-07-20
One of the consequences of Cooper pairs having a finite momentum in the interlayer of a Josephson junction, is
-junction behavior. The finite momentum can either be due to an exchange field in ferromagnetic Josephson junctions, or due to the Zeeman effect. Here, we report the observation of Zeeman effect induced 0-
Sb
, 3D Dirac semimetal-based Josephson junctions. The large g-factor of the Zeeman effect from a magnetic field applied in the plane of the junction allows tuning of the Josephson junctions from 0- to
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