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Register a new userShot noise of charge and spin transport in a junction with a precessing molecular spin
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Magnetic molecules and nanomagnets can be used to influence the electronic transport in mesoscopic junction. In a magnetic field the precessional motion leads to resonances in the dc- and ac-transport properties of a nanocontact, in which the electrons are coupled to the precession. Quantities like the dc-conductance or the ac-response provide valuable information like the level structure and the coupling parameters. Here, we address the current noise properties of such contacts. This encompasses the charge current and spin-torque shot noise, which both show a step-like behavior as functions of bias voltage and magnetic field. The charge current noise shows pronounced dips around the steps, which we trace back to interference effects of electron in quasienergy levels coupled by the molecular spin precession. We show that some components of the noise of the spin-torque currents are directly related to the Gilbert damping and, hence, are experimentally accessible. Our results show that the noise characteristics allow to investigate in more detail the coherence of spin transport in contacts containing magnetic molecules.
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We address the shot noise in the tunneling current through a localized spin, pertaining to recent experiments on magnetic adatoms and single molecular magnets. We show that both uncorrelated and spin-correlated scattering processes contribute vitally to the noise spectrum. The spin-correlated scattering processes provide an additional contribution to the Landauer-Buttiker shot noise expression, accounting for correlations between the tunneling electrons and the localized spin moment. By calculating the Fano factor, we show that both super- and sub-Poissonian shot noise can be described within our approach. Our theory provides transparent insights to noise spectroscopy, consistent with recent experiments using local probing techniques on magnetic atoms.
An in-plane magnetic field applied to an Ising superconductor converts spin-singlet Cooper pairs to spin-triplet ones. In this work, we study a Josephson junction formed by two Ising superconductors that are proximitized by ferromagnetic layers. This leads to highly tunable spin-triplet pairing correlations which allow to modulate the charge and spin supercurrents through the in-plane magnetic exchange fields. For a junction with a nonmagnetic barrier, the charge current is switchable by changing the relative alignment of the in-plane exchange fields, and a $pi$-state can be realized. Furthermore, the charge and spin current-phase relations display a $phi_0$-junction behavior for a strongly spin-polarized ferromagnetic barrier.
We investigate effects of spin-orbit splitting on electronic transport in a spin valve consisting of a large quantum dot defined on a two-dimensional electron gas with two ferromagnetic contacts. In the presence of both structure inversion asymmetry (SIA) and bulk inversion asymmetry (BIA) a giant anisotropy in the spin-relaxation times has been predicted. We show how such an anisotropy affects the electronic transport properties such as the angular magnetoresistance and the spin-transfer torque. Counterintuitively, anisotropic spin-relaxation processes sometimes enhance the spin accumulation.
We report the theoretical investigation of noise spectrum of spin current and spin transfer torque for non-colinear spin polarized transport in a spin-valve device which consists of normal scattering region connected by two ferromagnetic electrodes. Our theory was developed using non-equilibrium Greens function method and general non-linear $S^sigma-V$ and $S^tau-V$ relations were derived as a function of angle $theta$ between magnetization of two leads. We have applied our theory to a quantum dot system with a resonant level coupled with two ferromagnetic electrodes. It was found that for the MNM system, the auto-correlation of spin current is enough to characterize the fluctuation of spin current. For a system with three ferromagnetic layers, however, both auto-correlation and cross-correlation of spin current are needed to characterize the noise spectrum of spin current. Furthermore, the spin transfer torque and the torque noise were studied for the MNM system. For a quantum dot with a resonant level, the derivative of spin torque with respect to bias voltage is proportional to $sintheta$ when the system is far away from the resonance. When the system is near the resonance, the spin transfer torque becomes non-sinusoidal function of $theta$. The derivative of noise spectrum of spin transfer torque with respect to the bias voltage $N_tau$ behaves differently when the system is near or far away from the resonance. Specifically, the differential shot noise of spin transfer torque $N_tau$ is a concave function of $theta$ near the resonance while it becomes convex function of $theta$ far away from resonance. For certain bias voltages, the period $N_tau(theta)$ becomes $pi$ instead of $2pi$. For small $theta$, it was found that the differential shot noise of spin transfer torque is very sensitive to the bias voltage and the other system parameters.
We measured the Josephson radiation emitted by an InSb semiconductor nanowire junction utilizing photon assisted quasiparticle tunneling in an AC-coupled superconducting tunnel junction. We quantify the action of the local microwave environment by evaluating the frequency dependence of the inelastic Cooper-pair tunneling of the nanowire junction and find the zero frequency impedance $Z(0)=492,Omega$ with a cutoff frequency of $f_0=33.1,$GHz. We extract a circuit coupling efficiency of $etaapprox 0.1$ and a detector quantum efficiency approaching unity in the high frequency limit. In addition to the Josephson radiation, we identify a shot-noise contribution with a Fano factor $Fapprox1$, consistently with the presence of single electron states in the nanowire channel.
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