Nontrivial doping evolution of electronic properties in Ising-superconducting alloys

TL;DR

This study investigates how the electronic properties of monolayer Nb$_{1- ext{delta}}$Mo$_{ ext{delta}}$Se$_2$ alloys evolve across the entire composition range, revealing nontrivial doping effects on superconductivity and electronic phases using advanced microscopy and theoretical calculations.

Contribution

It provides a detailed atomic-scale analysis of the electronic ground state evolution in 2D TMD alloys, highlighting the non-monotonic behavior of superconductivity with doping.

Findings

Superconducting transition temperature varies non-monotonically with doping.

Electronic phases like charge density wave and superconductivity are robust against disorder.

Bandgap and band shifts change monotonically with alloy composition.

Abstract

Transition metal dichalcogenides offer unprecedented versatility to engineer 2D materials with tailored properties to explore novel structural and electronic phase transitions. In this work, we present the atomic-scale evolution of the electronic ground state of a monolayer of Nb$_{1-\delta}$Mo$_{\delta}$Se$_2$ across the entire alloy composition range (0 < ${\delta}$ < 1) using low-temperature (300 mK) scanning tunneling microscopy and spectroscopy (STM/STS). In particular, we investigate the atomic and electronic structure of this 2D alloy throughout the metal to semiconductor transition (monolayer NbSe$_2$ to MoSe$_2$). Our measurements let us extract the effective doping of Mo atoms, the bandgap evolution and the band shifts, which are monotonic with ${\delta}$. Furthermore, we demonstrate that collective electronic phases (charge density wave and superconductivity) are remarkably robust against disorder. We further show that the superconducting TC changes non-monotonically with doping. This contrasting behavior in the normal and superconducting state is explained using first-principles calculations. We show that Mo doping decreases the density of states at the Fermi level and the magnitude of pair-breaking spin fluctuations as a function of Mo content. Our results paint a detailed picture of the electronic structure evolution in 2D TMD alloys, which is of utmost relevance for future 2D materials design.