arXiv subjects

Edouard Sonin

Publications and source records attributed to Edouard Sonin.

8 recordsLinked to original sources

arXiv2026

Theory of ballistic SNS junctions revisited

The recently suggested theory of planar ballistic SNS junctions demonstrated that in junctions without normal scattering (the case of equal Fermi velocities and effective masses in all layers) phase gradients in superconducting leads cannot be ignored. The revision of the previous theory ignoring them essentially changes the current-phase relation (CPR) of short junctions at $T=0$. It transforms it from forward-skewed to backward-skewed. The CPR at temperatures exceeding the energy spacing between Andreev levels but less than the critical temperature was also calculated. The current at these temperatures is temperature independent and decreases with growing $L$ as $1/L^4$. The previous theory predicted the current exponentially decreasing with growing $T$ and $L$. The SNS junctions with normal scattering (non-equal Fermi velocities in leads and inside the junction) were also analyzed. At strong mismatch of Fermi velocities the planar ballistic SNS junction becomes a common Josephson junction, which is a weak link and satisfies the Ambegaokar--Baratoff relation. Implications of the analysis for non-planar junctions (narrow normal bridge between two bulk superconductors) are also discussed. A qualitative explanation of experimental observation of backward-skewed CPR in short InAs nanowire bridge junctions was suggested.

cond-mat.supr-con↗

arXiv2024

Comment on "Square-well model for superconducting pair-potential"

The current-phase relation for a ballistic SNS junction in a 1D wire at T = 0 was derived by Thuneberg [1] neglecting phase gradients in superconducting leads. This invalidates the derivation, since the charge conservation law is violated. The theory of Ref. [1] predicts an unphysical phase jump in the limit of zero normal-layer thickness. In this limit the SNS junction becomes an ideal uniform superconductor, in which the currentis supported by a constant phase gradient without any phase jump.

cond-mat.supr-con↗

arXiv2024

Andreev reflection, Andreev states, and long ballistic SNS junction

The analysis in the present paper is based on the most known concept introduced by the brilliant physicist Alexander Andreev: Andreev bound states in a normal metal sandwiched between two superconductors. The paper presents results of direct calculations of {\em ab initio} expressions for the currents in a long ballistic SNS junction. The expressions are expanded in $1/L$ ($L$ is the thickness of the normal layer). The main contribution $\propto 1/L$ to the current agrees with the results obtained in the past, but the analysis suggests a new physical picture of the charge transport through the junction free from the problem with the charge conservation law. The saw-tooth current-phase relation at $T=0$ directly follows from the Galilean invariance of the Bogolyubov-de Gennes equations proved in the paper. The proof is valid for any variation of the energy gap in space if the Andreev reflection is the only scattering process. The respective roles of the contributions of bound and continuum states to the current are clarified. They depend on the junction dimensionality.

cond-mat.supr-con↗

arXiv2023

Joe Vinen and transverse force on vortex

The paper gives a glimpse on the problem of transverse force on a vortex, its proper determination in general and the role in the process of quantum vortex nucleation. Investigation of this problem is an essential part of the scientific heritage of Joe Vinen as an experimentalist and a theoretician.

cond-mat.other↗

arXiv2017

Gyrotropic Zener tunneling and nonlinear IV curves in the zero-energy Landau level of graphene in a strong magnetic field

We have investigated tunneling current through a suspended graphene Corbino disk in high magnetic fields at the Dirac point, i.e. at filling factor $ν$ = 0. At the onset of the dielectric breakdown the current through the disk grows exponentially before ohmic behaviour, but in a manner distinct from thermal activation. We find that Zener tunneling between Landau sublevels dominates, facilitated by tilting of the source-drain bias potential. According to our analytic modelling, the Zener tunneling is strongly affected by the gyrotropic force (Lorentz force) due to the high magnetic field

cond-mat.mes-hall↗

arXiv2017

Observation of spin superfluidity: YIG magnetic films and beyond

From topology of the order parameter of the magnon condensate observed in yttrium-iron-garnet (YIG) magnetic films one must not expect energetic barriers making spin supercurrents metastable. But we show that some barriers of dynamical origin are possible nevertheless until the gradient of the phase (angle of spin precession) does not exceed the critical value (analog of the Landau critical velocity in superfluids). On the other hand, recently published claims of experimental detection of spin superfluidity in YIG films and antiferromagnets are not justified, and spin superfluidity in magnetically ordered solids has not yet been experimentally confirmed.

cond-mat.other↗

arXiv2015

Contact doping, Klein tunneling, and asymmetry of shot noise in suspended graphene

The inherent asymmetry of the electric transport in graphene is attributed to Klein tunneling across barriers defined by $\textit{pn}$-interfaces between positively and negatively charged regions. By combining conductance and shot noise experiments we determine the main characteristics of the tunneling barrier (height and slope) in a high-quality suspended sample with Au/Cr/Au contacts. We observe an asymmetric resistance $R_{\textrm{odd}}=100-70$ $Ω$ across the Dirac point of the suspended graphene at carrier density $|n_{\rm G}|=0.3-4 \cdot 10^{11}$ cm$^{-2}$, while the Fano factor displays a non-monotonic asymmetry in the range $F_{\textrm{odd}} \sim 0.03 - 0.1$. Our findings agree with analytical calculations based on the Dirac equation with a trapezoidal barrier. Comparison between the model and the data yields the barrier height for tunneling, an estimate of the thickness of the $\textit{pn}$-interface $d < 20$ nm, and the contact region doping corresponding to a Fermi level offset of $\sim - 18$ meV. The strength of pinning of the Fermi level under the metallic contact is characterized in terms of the contact capacitance $C_c=19 \times 10^{-6}$ F/cm$^2$. Additionally, we show that the gate voltage corresponding to the Dirac point is given by the work function difference between the backgate material and graphene.

cond-mat.mes-hall↗

arXiv2004

Peak-effect and surface crystal-glass transition for surface-pinned vortex array

We present a theoretical and experimental study of the peak effect in the surface pinning of vortices. It is associated with a sharp transition in the vortex slippage length which we relate to a crossover from a weakly disordered crystal to a surface glass state. Experiments are performed on ion-beam etched Nb crystals. The slippage length is deduced from 1kHz-1MHz linear AC penetration depth measurements.

cond-mat.mes-hall↗