Pressure-Driven Metallicity in {\AA}ngstr\"om-Thickness 2D Bismuth and Layer-Selective Ohmic Contact to MoS2

TL;DR

This paper reveals that pressure-induced structural changes cause metallicity in 2D bismuth and introduces a layer-selective Ohmic contact in MoS2-Bi heterostructures, enabling spatial charge injection and layertronic device potential.

Contribution

It uncovers the pressure-driven transition from semiconducting to metallic phases in 2D bismuth and demonstrates a novel layer-selective Ohmic contact in MoS2-Bi heterostructures.

Findings

Pressure induces buckled-to-flat transition in 2D Bi, changing its electronic phase.

Layer-selective Ohmic contact can be switched via external gate polarity.

Charge can be spatially injected into different MoS2 layers in heterostructures.

Abstract

Recent fabrication of two-dimensional (2D) metallic bismuth (Bi) via van der Waals (vdW) squeezing method opens a new avenue to ultrascaling metallic materials into the {\aa}ngstr\"om-thickness regime [Nature 639, 354 (2025)]. However, freestanding 2D Bi is typically known to exhibit a semiconducting phase [Nature 617, 67 (2023), Phys. Rev. Lett. 131, 236801 (2023)], which contradicts with the experimentally observed metallicity in vdW-squeezed 2D Bi. Here we show that such discrepancy originates from the pressure-induced buckled-to-flat structural transition in 2D Bi, which changes the electronic structure from semiconducting to metallic phases. Based on the experimentally fabricated MoS2-Bi-MoS2 trilayer heterostructure, we demonstrate the concept of layer-selective Ohmic contact in which one MoS2 layer forms Ohmic contact to the sandwiched Bi monolayer while the opposite MoS2 layer exhibits a Schottky barrier. The Ohmic contact can be switched between the two sandwiching MoS2 monolayers by changing the polarity of an external gate field, thus enabling charge to be spatially injected into different MoS2 layers. The layer-selective Ohmic contact proposed here represents a layertronic generalization of metal/semiconductor contact, paving a way towards layertronic device application.