Superconducting dome by tuning through a Van Hove singularity in a two-dimensional metal

TL;DR

This study demonstrates how minute electron doping in single-layer TaSe2 induces a superconducting dome by tuning through a Van Hove singularity, revealing the interplay between doping, density of states, and emergent phases.

Contribution

It provides experimental evidence of a superconducting dome in a 2D material driven by Van Hove singularity tuning via chemical doping, and tracks the development of a Coulomb glass phase.

Findings

Superconductivity appears in TaSe2 with electron doping from W substitution.

Maximum T_C of 0.9 K occurs near the Van Hove singularity.

Disorder from W dopants induces a Coulomb glass phase.

Abstract

Chemical substitution is a promising route for the exploration of a rich variety of doping- and/or disorder-dependent collective phenomena in low-dimensional quantum materials. Here we show that transition metal dichalcogenide alloys are ideal platforms to this purpose. In particular, we demonstrate the emergence of superconductivity in the otherwise metallic single-layer TaSe$_{2}$ by minute electron doping provided by substitutional W atoms. We investigate the temperature- and magnetic field-dependence of the superconducting state of Ta$_{1-\delta}$W$_\delta$Se$_2$ with electron doping ($\delta$) using variable temperature (0.34 K - 4.2 K) scanning tunneling spectroscopy (STS). We unveil the emergence of a superconducting dome spanning 0.003 < $\delta$ < 0.03 with a maximized critical temperature of 0.9 K, a significant increase from that of bulk TaSe$_{2}$ (T$_C$ = 0.14 K). Superconductivity emerges from an increase of the density of states (DOS) as the Fermi surface approaches a van Hove singularity due to doping. Once the singularity is reached, however, the DOS decreases with $\delta$, which gradually weakens the superconducting state, thus shaping the superconducting dome. Lastly, our doping-dependent measurements allow us to unambiguously track the development of a Coulomb glass phase triggered by disorder due to W dopants.