The Unusual Suppression of Superconducting Transition Temperature in Double-Doping 2H-NbSe$_2$

TL;DR

This study investigates how double-doping with Cu and S in 2H-NbSe2 affects its superconducting transition temperature, revealing an unusual suppression and plateauing behavior not seen in single-doping systems.

Contribution

It provides the first systematic analysis of double-doping effects on 2H-NbSe2's superconductivity and constructs phase diagrams contrasting with single-ion doping.

Findings

Tc decreases with increasing Cu and S content

At high doping levels, Tc stabilizes near 2 K

Double-doping suppresses Tc faster than single doping

Abstract

2H-NbSe2 is one of the most widely researched transition metal dichalcogenide (TMD) superconductors, which undergoes charge-density wave (CDW) transition at TCDW about 33 K and superconducting transition at Tc of 7.3 K. To explore the relation between its superconductivity and Fermi surface nesting, we combined S substitution with Cu intercalation in 2H-NbSe2 to make CuxNbSe2-ySy. Upon systematic substitution of S and intercalation of Cu ions into 2H-NbSe2, we found that when the Cu and S contents increases, the Tc decreases in CuxNbSe2-ySy. While at higher x and y values, Tc keeps a constant value near 2 K, which is not commonly observed for a layered TMD. For comparison, we found the simultaneous substitution of Nb by Cu and Se by S in CuxNb1-xSe2-ySy lowered the Tc substantially faster. We construct a superconducting phase diagrams for our double-doping compounds in contrast with the related single-ions doping systems.