Spin Gating of Mesoscopic Devices

Inefficient screening of electric fields in nanoconductors makes electric manipulation of electronic transport in nanodevices possible. Accordingly, electrostatic (charge) gating is routinely used to affect and control the Coulomb electrostatics and quantum interference in modern nanodevices. Besides their charge, another (quantum mechanical) property of electrons - their spin - is at the heart of modern spintronics, a term implying that a number of magnetic and electrical properties of small systems are simultaneously harvested for device applications. In this review the possibility to achieve "spin gating" of mesoscopic devices, i.e. the possibility of an external spin control of the electronic properties of nanodevices is discussed. Rather than the Coulomb interaction, which is responsible for electric-charge gating, we consider two other mechanisms for spin gating. These are on the one hand the magnetic exchange interaction in magnetic devices and on the other hand the spin-orbit coupling ("Rashba effect"), which is prominent in low dimensional conductors. A number of different phenomena demonstrating the spin gating phenomenon will be discussed, including the spintro-mechanics of magnetic shuttling, Rashba spin splitting, and spin-gated weak superconductivity.Comment: Submitted to a special issue of "Synthetic Metals" to appear in March 201

Nonlinear conductance of nanowires - A signature of Luttinger liquid effects?

We analyze recent measurements of the room temperature current-voltage characteristics of gold nanowires, whose zero current conductance is quantized in units of $2e^2/h$. A faster than linear increase of current with voltage was observed at low voltages beginning from $V_c=0.1$V. We analyze the nonlinear behavior in terms of a dynamic Coulomb blockade of conducting modes and show that it may be explained as a Luttinger-liquid effect.Comment: 13 pages, latex with supplied stylefile, 3 figures in eps format, submitted to Superlattices and Microstructure

Giant conductance oscillations in a normal mesoscopic ring induced by an SNS Josephson current

A theoretical explanation of giant conductance oscillations observed in normal mesoscopic rings with superconducting ``mirrors" is proposed. The effect is due to resonant tuning of Andreev levels to the Fermi level, which enhances the transparency of the system to the normal current. The mechanism is demonstrated for a one-dimensional model system.Comment: 10 pages, RevTeX, 3 fig. available upon request, Appl. Phys. Report 94-

Rashba splitting of Cooper pairs

We investigate theoretically the properties of a weak link between two superconducting leads, which has the form of a non-superconducting nanowire with a strong Rashba spin-orbit coupling caused by an electric field. In the Coulomb blockade regime of single-electron tunneling, we find that such a weak link acts as a "spin splitter" of the spin states of Cooper pairs tunneling through the link, to an extent that depends on the direction of the electric field. We show that the Josephson current is sensitive to interference between the resulting two transmission channels, one where the spins of both members of a Cooper pair are preserved and one where they are both flipped. As a result, the current is a periodic function of the strength of the spin-orbit interaction and of the bending angle of the nanowire (when mechanically bent); an identical effect appears due to strain-induced spin-orbit coupling. In contrast, no spin-orbit induced interference effect can influence the current through a single weak link connecting two normal metals.Comment: 5 pages 3 figures. arXiv admin note: text overlap with arXiv:1306.512

Suppression of stochastic fluctuations of suspended nanowires by temperature-induced single-electron tunnelling

We investigate theoretically the electromechanical properties of freely suspended nanowires that are in tunnelling contact with the tip of a scanning tunnelling microscope (STM) and two supporting metallic leads. The aim of our analysis is to characterize the fluctuations of the dynamical variables of the nanowire when a temperature drop is mantained between the STM tip and the leads, which are all assumed to be electrically grounded. By solving a quantum master equation that describes the coupled dynamics of electronic and mechanical degrees of freedom we find that the stationary state of the mechanical oscillator has a Gaussian character, but that the amplitude of its root-mean square center-of-mass fluctuations is smaller than would be expected if the system were coupled only to the leads at thermal equilibrium.Comment: Published versio

Rashba proximity states in superconducting tunnel junctions

We consider a new kind of superconducting proximity effect created by the tunneling of "spin split" Cooper pairs between two conventional superconductors connected by a normal conductor containing a quantum dot. The difference compared to the usual superconducting proximity effect is that the spin states of the tunneling Cooper pairs are split into singlet and triplet components by the electron spin-orbit coupling, which is assumed to be active in the normal conductor only. We demonstrate that the supercurrent carried by the spin-split Cooper pairs can be manipulated both mechanically and electrically for strengths of the spin-orbit coupling that can realistically be achieved by electrostatic gates.Comment: Accepted for publication in Fiz. Niz. Temp./Low Temp. Phys. vol. 44, no. 6, 2018. arXiv admin note: text overlap with arXiv:1709.0802