Inhomogeneity-driven multiform Spontaneous Hall Effect in conventional and unconventional superconductors

TL;DR

This paper investigates the spontaneous Hall effect in superconductors, proposing that spatial inhomogeneities in critical temperature due to material disorder can explain the observed phenomena across different types of superconductors.

Contribution

It introduces a unified explanation for the spontaneous Hall effect in superconductors based on inhomogeneity-driven mechanisms supported by experimental and simulation data.

Findings

SHE peaks are observed near the superconducting transition in different materials.

Inhomogeneities in critical temperature can account for SHE characteristics.

Simulations support a common origin of SHE related to Tc-distribution.

Abstract

The spontaneous Hall effect (SHE), a finite voltage occurring transversal to the electrical current in zero-magnetic field, has been observed in both conventional and unconventional superconductors, appearing as a peak near the superconducting transition temperature. The origin of SHE is strongly debated, with proposed explanations ranging from intrinsic and extrinsic mechanisms such as spontaneous symmetry breaking and time-reversal symmetry breaking (BTRS), Abrikosov vortex motion, or extrinsic factors like material inhomogeneities, such as non-uniform critical temperature (Tc) distributions or structural asymmetries. This work is an experimental study of the SHE in various superconducting materials. We focused on conventional, low-Tc, sharp transition Nb and unconventional, intermediate-Tc, smeared transition Fe(Se,Te). Our findings show distinct SHE peaks around the superconducting transition, with variations in height, sign and shape, indicating a possible common mechanism independent of the specific material. We propose that spatial inhomogeneities in the critical temperature, caused by local chemical composition variations, disorder, or other forms of electronic spatial inhomogeneities could explain the appearing of the SHE. This hypothesis is supported by comprehensive finite elements simulations of randomly distributed Tc by varying Tc-distribution, spatial scale of disorder and amplitude of the superconducting transition. The comparison between experimental results and simulations suggest a unified origin for the SHE in different superconductors, whereas different phenomenology can be explained in terms of amplitude of the transition temperature in respect to Tc-distribution.