Magnetization amplification in the interlayer pairing superconductor 4Hb-TaS$_2$

TL;DR

This paper proposes a theoretical mechanism explaining the observed magnetization amplification and time-reversal symmetry breaking in the superconductor 4Hb-TaS$_2$, linking it to a unique interlayer, equal-spin pairing state with a specific phase winding.

Contribution

It introduces a novel superconducting state with a 6π phase winding in 4Hb-TaS$_2$, explaining its magnetic memory and symmetry-breaking features.

Findings

Superconductivity in 4Hb-TaS$_2$ involves interlayer, equal-spin pairing.

The phase of the gap function winds by 6π along the Fermi surface.

Magnetization enhancement in the superconducting state accounts for magnetic memory.

Abstract

A recent experiment on the bulk compound 4Hb-TaS$_2$ reveals an unusual time-reversal symmetry-breaking superconducting state that possesses a magnetic memory not manifest in the normal state. Here we provide a mechanism for this observation by studying the magnetic and electronic properties of 4Hb-TaS$_2$. We discuss the criterion for a small magnetization in the normal state in terms of spin and orbital magnetizations. Based on an analysis of lattice symmetry and Fermi surface structure, we propose that 4Hb-TaS$_2$ realizes superconductivity in the interlayer, equal-spin channel with a gap function whose phase winds along the Fermi surface by an integer multiple of $6\pi$. The enhancement of the magnetization in the superconducting state compared to the normal state can be explained if the state with a gap winding of $6\pi$ is realized, accounting for the observed magnetic memory. We discuss how this superconducting state can be probed experimentally by spin-polarized scanning tunneling microscopy.