arXiv subjects

K. Michaeli

Publications and source records attributed to K. Michaeli.

6 recordsLinked to original sources

arXiv2023

Planar Hall effect from superconducting fluctuations

We investigate the planar Hall effect (PHE) in two-dimensional (2D) superconductors with spin-orbit interactions, where transport anisotropy is induced by an in-plane magnetic field. While PHE typically arises from the breaking of basal mirror symmetry, when the field exclusively couples to spin degrees of freedom, it remains negligible in non-interacting systems. In this study, we explore anisotropic paraconductivity as an alternative mechanism for PHE observed in 2D superconductors in the normal state. Due to the momentum dependence of spin-orbit interactions, the field-induced pair breaking exhibits anisotropy. To elucidate this phenomenon, we compute the PHE for the Rashba spin-orbit interaction. Our analysis reveals that Cooper pairs propagating along the field experience stronger pair breaking compared to those moving perpendicular to the field. This physical insight is corroborated by explicit calculations of paraconductivity.

cond-mat.supr-con↗

arXiv2018

Quantum meets classical phase transition: Low-temperature anomaly in disordered superconductors near $B_{c2}$

Strongly disordered superconductors in a magnetic field display many characteristic properties of type-II superconductivity--- except at low temperatures where an anomalous linear $T$-dependence of the resistive critical field $B_{c2}$ is routinely observed. This behavior violates the conventional theory of superconductivity, and its origin remains a long-standing puzzle. Here we report on systematic measurements of the critical magnetic field and current on amorphous indium oxide films of various levels of disorder. Surprisingly, our measurements show that the $B_{c2}$ anomaly near zero-temperature is accompanied by a clear mean-field like scaling behavior of the critical current. We demonstrate theoretically that these are consequences of the vortex-glass ground state and its thermal fluctuations. This theory further predicts the linear-$T$ anomaly to occur in films as well as bulk superconductors with a slope that depends on the normal-state sheet resistance---in agreement with experimental data. Thus, our combined experimental and theoretical study reveals universal low-temperature behavior of $B_{c2}$ in a large class of disordered superconductors.

cond-mat.supr-con↗

arXiv2007

Suppression of Tunneling of Superconducting Vortices Caused by a Remote Gate: Example of an Extended Object Tunneling

We discuss a recent experiment in which the resistance of a superconducting film has been measured in magnetic field. A strong decrease of the superconducting film resistance has been observed when a metallic gate is placed above the film. We study how the magnetic coupling between vortices in a thin superconducting film and electrons in a remote unbiased gate suppresses the tunneling rate of the vortices. We examine two general approaches to analyze tunneling in the presence of slow low-energy degrees of freedom: the functional-integral and scattering formalisms. In the first one, the response of the electrons inside the metallic gate to a change in the vortex position is described by the "tunneling with dissipation". We consider the Eddy current induced in the gate by the magnetic flux of the vortex as a result of tunneling. In the second approach, the response is given in terms of scattering of the electrons by the magnetic flux of the vortex in a way similar to the Aharonov-Bohm scattering. A sudden change in the vortex position leads to the Orthogonality Catastrophe that opposes the vortex tunneling. We show that the magnetic coupling between the vortices and the electrons inside the gate can lead to a dramatic suppression of the vortex tunneling, restoring the superconducting property in accord with the experiment.

cond-mat.supr-con↗

arXiv2006

Metal-Insulator Transition in a System of Superconducting Vortices Caused by a Metallic Gate

We address a recent experiment in which a strong decrease of the resistance of a superconducting film has been observed when a remote unbiased gate was placed above the film. Here we explain the experimental finding as a suppression of the vortex tunneling due to the Orthogonality Catastrophe of the electrons inside the gate. We interpret the change in the resistance of the film as a "metal-insulator" transition in the system of vortices induced by the gate.

cond-mat.supr-con↗

arXiv2006

Advances in Thick GEM-like gaseous electron multipliers. Part II: low-pressure operation

We present results on THGEM operation at low gas pressures, in the range 0.5-50 Torr. Gaseous gain up to 100000 was recorded at 10 Torr of Isobutane in a single multiplier element, with pulses rise-time in the few ns range. Cascaded operation of two THGEMs is reported, with similar total gain but at lower voltages on each element. The present work encompasses a large variety of THGEM geometries and includes electric-field distribution calculations and electron transport simulations. We discuss the operation mechanism and some possible applications of THGEMs at low gas pressures.

physics.ins-det↗

arXiv2006

Advances in Thick GEM-like gaseous electron multipliers. Part I: atmospheric pressure operation

Thick GEM-like (THGEM) gaseous electron multipliers are made of standard printed-circuit board perforated with sub-millimeter diameter holes, etched at their rims. Effective gas multiplication factors of 100000 and 10000000 and fast pulses in the few nanosecond rise-time scale were reached in single- and cascaded double-THGEM elements, in atmospheric-pressure standard gas mixtures with single photoelectrons. High single-electron detection efficiency is obtained in photon detectors combining THGEMs and semitransparent UV-sensitive CsI photocathodes or reflective ones deposited on the top THGEM face; the latter benefits of a reduced sensitivity to ionizing background radiation. Stable operation was recorded with photoelectron fluxes exceeding MHz/mm2. The properties and some potential applications of these simple and robust multipliers are discussed.

physics.ins-det↗