Superconducting transitions of intrinsic arrays of weakly coupled 1D superconducting chains: The case of the extreme quasi-1D superconductor Tl2Mo6Se6

TL;DR

This study investigates the complex superconducting transition in Tl2Mo6Se6, revealing a multi-stage process involving phase coherence establishment in a quasi-1D superconductor, akin to a Josephson junction array.

Contribution

It provides detailed experimental evidence of a multi-stage superconducting transition in Tl2Mo6Se6, modeling it as an intrinsic array of weakly coupled 1D superconducting chains.

Findings

Superconducting transition occurs in multiple stages with distinct features.

Global phase coherence develops gradually in the array.

Transition resembles a Berezinskii-Kosterlitz-Thouless transition.

Abstract

Tl2Mo6Se6 represents a model system for quasi-one-dimensional superconductors. We investigate its superconducting transition in detail by means of electrical transport experiments on high-quality single crystalline samples with onset Tc = 6.8 K. Our measurements indicate a highly complex superconducting transition which occurs in different stages, with a characteristic bump in the resistivity and distinct plateau structures in the supercurrent gap imaged by V-I curves. We interpret these features as fingerprints of the gradual establishment of global phase coherence in an array of weakly coupled parallel one-dimensional (1D) superconducting bundles. In this way, we demonstrate that superconducting Tl2Mo6Se6 behaves like an intrinsic array of Proximity or Josephson junctions, undergoing a complex superconducting phase-ordering transition at 4.5 K which shows many similarities to the Berezinskii-Kosterlitz-Thouless transition.