Giant Rashba Splitting and Enhanced Nonlinear Berry-Phase Responses in Sliding-Tunable vdW MXene Heterostructures

TL;DR

This study explores tunable Rashba splitting and nonlinear Berry-phase responses in van der Waals MXene heterostructures, revealing how stacking and sliding control emergent magnetic and topological phases.

Contribution

It introduces M2CS2/CrBr3 heterostructures with mechanically tunable exchange and spin-orbit effects, advancing control over topological and nonlinear electronic properties.

Findings

Rashba splitting up to 2.53 eV Å in monolayers

High shift current density in bilayer Ta2CS2 (~5 A/mA/V^2)

Emergent quantum anomalous Hall phase driven by stacking geometry

Abstract

Chalcogen-terminated van der Waals MXenes (M2CX2; M = Nb, Ta; X = S, Se) provide a robust platform for exploring strong spin-orbit coupling and proximity engineering. To probe their tunability and guide optimization of emergent properties, we systematically examine sister compounds and propose M2CS2/CrBr3 heterostructures that break time-reversal symmetry via proximity exchange coupling, enabling combined intrinsic magnetic and mechanical control. First-principles calculations reveal Rashba splitting up to 2.53 eV A and valley-contrasting spin polarization in monolayers. These features drive strong second-order nonlinear responses, with pristine bilayer Ta2CS2 reaching a shift current of |sigma|_max approx 5 A mA/V^2 and Nb2CS2/CrBr3 attaining |D|_max approx 18.44 A. In M2CS2/CrBr3 heterostructures, the ferromagnetic substrate induces a magnetization-reversible proximity exchange field with valley-selective conduction-band renormalization (Delta_val approx 50 meV). Crucially, interfacial geometry, controlled by stacking inversion and lateral sliding, acts as a mechanical knob that continuously tunes the exchange-SOC interplay and bandgap, driving an emergent quantum anomalous Hall phase in the bilayer.