Gate-Tunable Renormalization of Spin-Correlated Flat-Band States and Bandgap in a 2D Magnetic Insulator

Abstract

Emergent quantum phenomena in two-dimensional van der Waal (vdW) magnets are largely governed by the interplay between exchange and Coulomb interactions. The ability to precisely tune the Coulomb interaction enables the control of spin-correlated flat-band states, band gap, and unconventional magnetism in such strongly correlated materials. Here, we demonstrate a 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 interflat-band spacing and bandgap of CrBr3 can be continuously tuned by 120 and 240 meV, respectively, via electrostatic injection of carriers into the hybrid CrBr3/graphene system. This can be attributed to the self-screening of CrBr3 arising from the gate-induced carriers injected into CrBr3, which dominates over the weakened remote screening of the graphene substrate due to the decreased carrier density in graphene. Precise tuning of the spin-correlated flat-band states and bandgap in 2D magnets via electrostatic modulation of Coulomb interactions not only provides effective 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.

Out-of-plane pressure and electron doping inducing phase and magnetic transitions in GeC/CrS2/GeC van der Waals heterostructure

“…Electron doping is an effective method to modulate the magnetic properties and phase transition as reported by recent studies. 28–31 In addition to the out-of-plane compression, we tested the effect of electron doping into GeC/CrS 2 /GeC vdWHs trying to trigger magnetic and phase transitions. We find that electron doping can trigger 1T′-FM to 1T-AFM in GeC/CrS 2 /GeC vdWHs.…”

“…34 The electron doping could be realized by many methods. 28,35 For example, a gate electric field to drive Li ions in and out of the layered 1T-TaS 2 has been realized in experiments. This method will introduce higher doping levels (∼0.2 electrons from Li) in each atomic layer.…”

Scanning tunneling microscope studies on low-dimensional transition-metal halides

“…Equipped with the miscellaneous synthesis and micro-nano machining techniques, many ingenious devices of LDTMHs have been fabricated [Figs. 1(d) and 1(e)], 19,20) allowing the tuning of various parameters to study correlated electronic and magnetic properties (details are discussed later).…”

“…3(a), the 3d 3 electrons of Cr 3+ ions fully fill the t 2g levels of the majority channel, giving an S = 3/2 high-spin semiconducting state. 19) The exchange splitting pushes the minority channels into higher energy positions, leaving the lowest occupied band to be the majority e g levels and a bandgap determined by the crystal field, spin exchange, and Hubbard correlation. The right panel of Fig.…”

Mapping the phase-separated state in a 2D magnet

“…What we need is to choose the visualization technique and the material for the study. On the one hand, scanning tunnelling microscopy has been applied to Cr-based 2D magnets, to explore the layer-dependent magnetism in CrBr 3 down to a single monolayer, 38,39 the AFM order in 1 ML CrTe 2 , 40 the AFM-to-FM transition in few-layer CrI 3 . 41 On the other hand, nanoscale magnetic imaging techniques are natural candidates to probe the spatial variation of order parameters in 2D systems due to advantageous combination of high spatial resolution and high magnetic field sensitivity.…”