Alloying 2D VSe2 with Pt: from a charge density wave state to a disordered insulator

TL;DR

This study investigates how alloying VSe2 monolayers with platinum affects their electronic and structural properties, revealing a transition from a charge density wave state to a disordered insulating phase with nanoscale gap variations.

Contribution

It provides detailed atomic and electronic characterization of VSe2-Pt alloys across different compositions, highlighting the preservation and destruction of charge density wave order and the emergence of a disordered insulator.

Findings

Charge density wave order persists at low Pt concentrations.

A disordered insulating phase forms at higher Pt concentrations.

Significant substrate interaction observed at certain compositions.

Abstract

We have analyzed by means of scanning tunneling microscopy and spectroscopy the atomic and electronic structure of monolayers of 1T-VxPt1-xSe2 alloys grown by molecular beam epitaxy on epitaxial graphene substrates. We have focused on the composition range (0.1<x<0.35) where ferromagnetic behaviour has recently been demonstrated. For low Pt concentration, (x=0.07 and x=0.21), small domains (a few nanometres in diameter) exhibiting the characteristic superstructure of the charge density wave (CDW) state of pristine VSe2 monolayer remain visible on most of the sample surface. Thus alloying preserves the short range order of the CDW phase, although it destroys its long range order. For higher Pt concentration (x=0.35) a disordered alloy forms. It presents a fully developped gap (a few tens meV in width) at the Fermi level and is thus a disordered insulator. This gap exhibits strong variations at the nanometer scale, reflecting the local fluctuations in the composition. An unexpectedly large interaction of the TMD layer with the graphene substrate sets in for this composition range.