arXiv subjects

F. Sebastián Bergeret

Publications and source records attributed to F. Sebastián Bergeret.

22 records · Page 2Linked to original sources

arXiv2016

Semiclassical quantization of spinning quasiparticles in ballistic Josephson junctions

A Josephson junction made of a generic magnetic material sandwiched between two conventional superconductors is studied in the ballistic semi-classic limit. The spectrum of Andreev bound states is obtained from the single-valuedness of a particle-hole spinor over closed orbits generated by electron-hole reflections at the interfaces between superconducting and normal materials. The semiclassical quantization condition is shown to depend only on the angle mismatch between initial and final spin directions along such closed trajectories. For the demonstration, an Andreev-Wilson loop in the composite position/particle-hole/spin space is constructed, and shown to depend on only two parameters, namely a magnetic phase shift and a local precession axis for the spin. The details of the Andreev-Wilson loop can be extracted via measuring the spin-resolved density of states. A Josephson junction can thus be viewed as an analog computer of closed-path-ordered exponentials.

cond-mat.supr-con↗

arXiv2015

Theory of the spin-galvanic effect and the anomalous phase-shift $φ_{0}$ in superconductors and Josephson junctions with intrinsic spin-orbit coupling

Due to the spin-orbit coupling (SOC) an electric current flowing in a normal metal or semiconductor can induce a bulk magnetic moment. This effect is known as the Edelstein (EE) or magneto-electric effect. Similarly, in a bulk superconductor a phase gradient may create a finite spin density. The inverse effect, also known as the spin-galvanic effect, corresponds to the creation of a supercurrent by an equilibrium spin polarization. Here, by exploiting the analogy between a linear-in-momentum SOC and a background SU(2) gauge field, we develop a quasiclassical transport theory to deal with magneto-electric effects in superconducting structures. For bulk superconductors this approach allows us to easily reproduce and generalize a number of previously known results. For Josephson junctions we establish a direct connection between the inverse EE and the appearance of an anomalous phase-shift $φ_{0}$ in the current-phase relation. In particular we show that $φ_{0}$ is proportional to the equilibrium spin-current in the weak link. We also argue that our results are valid generically, beyond the particular case of linear-in-momentum SOC. The magneto-electric effects discussed in this study may find applications in the emerging field of coherent spintronics with superconductors.

cond-mat.mes-hall↗

arXiv2010

Linear AC Response of Diffusive SNS Junctions

We explore the behavior of the ac admittance of superconductor-normal metal-superconductor (SNS) junctions as the phase difference of the order parameters between the superconductors is varied. We find three characteristic regimes, defined by comparing the driving frequency $ω$ to the inelastic scattering rate $Γ$ and the Thouless energy $E_T$ of the junction (typically $\hbarΓ\ll E_T$). Only in the first regime $ω\ll Γ$ the usual picture of the kinetic inductance holds. We show that the ac admittance can be used to directly access some of the characteristic quantities of the SNS junctions, in particular the phase dependent energy minigap and the typically phase dependent inelastic scattering rate. Our results partially explain the recent measurements of the linear response properties of SNS Superconducting Quantum Interference Devices (SQUIDs) and predict a number of new effects.

cond-mat.supr-con↗

arXiv2010

Theory of Microwave-Assisted Supercurrent in Diffusive SNS Junctions

The observation of very large microwave-enhanced critical currents in superconductor-normal metal-superconductor (SNS) junctions at temperatures well below the critical temperature of the electrodes has remained without a satisfactory theoretical explanation for more than three decades. Here we present a theory of the supercurrent in diffusive SNS junctions under microwave irradiation based on the quasiclassical Green's function formalism. We show that the enhancement of the critical current is due to the energy redistribution of the quasiparticles in the normal wire induced by the electromagnetic field. The theory provides predictions across a wide range of temperatures, frequencies, and radiation powers, both for the critical current and the current-phase relationship.

cond-mat.supr-con↗