Using controlled disorder to probe the interplay between charge order and superconductivity in NbSe2

TL;DR

This study uses controlled disorder via electron irradiation to investigate how charge density waves and superconductivity interact in NbSe2, revealing that disorder suppresses CDW order while initially competing with but eventually aiding superconductivity.

Contribution

It introduces a systematic way to probe the interplay between charge order and superconductivity in NbSe2 through controlled disorder and detailed measurements.

Findings

CDW order decreases monotonically with disorder

Superconducting transition temperature varies nonmonotonically

Short-range CDW persists beyond long-range order disappearance

Abstract

The interplay between superconductivity and charge density waves (CDW) in $H$-NbSe2 is not fully understood despite decades of study. Artificially introduced disorder can tip the delicate balance between two competing forms of long-range order, and reveal the underlying interactions that give rise to them. Here we introduce disorders by electron irradiation and measure in-plane resistivity, Hall resistivity, X-ray scattering, and London penetration depth. With increasing disorder, $T_{\textrm{c}}$ varies nonmonotonically, whereas $T_{\textrm{CDW}}$ monotonically decreases and becomes unresolvable above a critical irradiation dose where $T_{\textrm{c}}$ drops sharply. Our results imply that CDW order initially competes with superconductivity, but eventually assists it. We argue that at the transition where the long-range CDW order disappears, the cooperation with superconductivity is dramatically suppressed. X-ray scattering and Hall resistivity measurements reveal that the short-range CDW survives above the transition. Superconductivity persists to much higher dose levels, consistent with fully gapped superconductivity and moderate interband pairing.