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Register a new userInterference effects induced by a precessing easy-plane magnet coupled to a helical edge state
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The interaction of a magnetic insulator with the helical electronic edge of a two-dimensional topological insulator has been shown to lead to many interesting phenomena. One of these is that for a suitable orientation of the magnetic anisotropy axis, the exchange coupling to an easy-plane magnet has no effect on DC electrical transport through a helical edge, despite the fact that it opens a gap in the spectrum of the helical edge [Meng {em et al.}, Phys. Rev. B {bf 90}, 205403 (2014)]. Here, we theoretically consider such a magnet embedded in an interferometer, consisting of a pair of helical edge states connected by two tunneling contacts, at which electrons can tunnel between the two edges. Using a scattering matrix approach, we show that the presence of the magnet in one of the interferometer arms gives rise to AC currents in response to an applied DC voltage. On the other hand, the DC Aharonov-Bohm effect is absent at zero temperature and small DC voltages, and only appears if the applied voltage or the temperature exceeds the magnet-induced excitation gap.
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In this work, it is considered a nanostructure composed by a quantum dot coupled to two ferromagnets and a superconductor. The transport properties of this system are studied within a generalized mean-field approximation taking into account proximity effects and spin-flip correlations within the quantum dot. It is shown that the zero-bias transmittance for the co-tunneling between the ferromagnetic leads presents a dip whose height depends on the relative orientation of the magnetizations. When the superconductor is coupled to the system, electron-hole correlations between different spin states leads to a resonance in the place of the dip appearing in the transmittance. Such an effect is accompanied by two anti-resonances explained by a leakage of conduction channels from the co-tunneling to the Andreev transport. In the non-equilibrium regime, correlations within the quantum dot introduce a dependence of the resonance condition on the finite bias applied to the ferromagnetic leads. However, it is still possible to observe signatures of the same interference effect in the electrical current.
We calculate the frequency-dependent shot noise in the edge states of a two-dimensional topological insulator coupled to a magnetic impurity with spin $S=1/2$ of arbitrary anisotropy. If the anisotropy is absent, the noise is purely thermal at low frequencies, but tends to the Poissonian noise of the full current $I$ at high frequencies. If the interaction only flips the impurity spin but conserves those of electrons, the noise at high voltages $eVgg T$ is frequency-independent. Both the noise and the backscattering current $I_{bs}$ saturate at voltage-independent values. Finally, if the Hamiltonian contains all types of non-spin-conserving scattering, the noise at high voltages becomes frequency-dependent again. At low frequencies, its ratio to $2eI_{bs}$ is larger than 1 and may reach 2 in the limit $I_{bs}to 0$. At high frequencies it tends to 1.
The presence of edges locally breaks the inversion symmetry of heterostructures and gives rise to lateral (edge) spin-orbit coupling (SOC), which, under some conditions, can lead to the formation of helical edge states. If the edge SOC is strong enough, the helical edge states can penetrate the band-gap and be energetically isolated from the bulk-like states. As a result backward scattering is suppressed, dissipationless helical edge channels protected against time-inversion symmetric perturbations emerge, and the system behaves as a 2D topological insulator (TI). However, unlike in previous works on TIs, the mechanism proposed here for the creation of protected helical edge states relies on the strong edge SOC rather than on band inversion.
This is the reply to the comment by I. S. Burmistrov, P. D. Kurilovich, and V. D. Kurilovich [arXiv:1903.047241] on our paper Noise in the helical edge channel anisotropically coupled to a local spin [JETP Lett. 108, 664 (2018), arXiv:1810.05831].
Spin-orbit interaction (SOI) leads to spin precession about a momentum-dependent spin-orbit field. In a diffusive two-dimensional (2D) electron gas, the spin orientation at a given spatial position depends on which trajectory the electron travels to that position. In the transition to a 1D system with increasing lateral confinement, the spin orientation becomes more and more independent on the trajectory. It is predicted that a long-lived helical spin mode emerges. Here we visualize this transition experimentally in a GaAs quantum-well structure with isotropic SOI. Spatially resolved measurements show the formation of a helical mode already for non-quantized and non-ballistic channels. We find a spin-lifetime enhancement that is in excellent agreement with theoretical predictions. Lateral confinement of a 2D electron gas provides an easy-to-implement technique for achieving high spin lifetimes in the presence of strong SOI for a wide range of material systems.
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