Giant gate-tunable renormalization of spin-correlated flat-band states and bandgap in a 2D magnetic insulator

TL;DR

This study demonstrates that electrostatic gating can significantly tune the flat-band states and bandgap in 2D magnetic CrBr3 monolayers, impacting spin interactions and magnetic properties for spintronics applications.

Contribution

It reveals a giant, gate-tunable renormalization of flat-band states and bandgap in 2D CrBr3, highlighting a new method to control Coulomb interactions in magnetic 2D materials.

Findings

Gate voltage modulates flat-band spacing by 120 meV.

Bandgap can be tuned by 240 meV through electrostatic doping.

Self-screening effects dominate over substrate screening in CrBr3.

Abstract

Emergent quantum phenomena in two-dimensional van der Waal (vdW) magnets are largely governed by the interplay between the exchange and Coulomb interactions. The ability to tune the Coulomb interaction in such strongly correlated materials enables the precise control of spin-correlated flat-band states, bandgap (Eg) and unconventional magnetism, all of which are crucial for next-generation spintronics and magnonics applications. Here, we demonstrate a giant gate-tunable renormalization of spin-correlated flat-band states and bandgap in magnetic chromium tribromide (CrBr3) monolayers grown on graphene. Our gate-dependent scanning tunneling spectroscopy (STS) studies reveal that the inter-flat-band spacing and bandgap of CrBr3 can be continuously tuned by 120 meV and 240 meV respectively via electrostatic injection of carriers into the hybrid CrBr3/graphene system, equivalent to the modulation of the Cr on-site Coulomb repulsion energy by 500 meV. This can be attributed to the self-screening of CrBr3 arising from the gate-induced carriers injected into CrBr3, which dominates over the opposite trend from the remote screening of the graphene substrate. Precise tuning of the spin-correlated flat-band states and bandgap in 2D magnets via electrostatic modulation of Coulomb interactions not only provides new strategies for optimizing the spin transport channels but also may exert a crucial influence on the exchange energy and spin-wave gap, which could raise the critical temperature for magnetic order.