Interband State Transfer in Double-Gated Bilayer Graphene at High Electric Field

TL;DR

This study explores the effects of high electric fields on bilayer graphene using double ionic gating, revealing new in-gap state phenomena and transport behaviors when the interlayer potential exceeds the interlayer coupling energy.

Contribution

It demonstrates the ability to reach large interlayer potential differences in bilayer graphene and uncovers novel in-gap state phenomena at high electric fields.

Findings

Sharp change in resistance peak slope at Δ ≈ t⊥

Splitting and sign reversals in Hall resistance at high Δ

Emergence of hysteresis in transport measurements

Abstract

The band structure of Bernal-stacked bilayer graphene can be tuned using double-gated transistors to apply a perpendicular electric field that generates an interlayer potential energy difference $\Delta$. Dielectric breakdown limits the operation of conventional devices to the $\Delta \ll t_\perp \simeq 360$ meV regime. We employ double ionic gating to reach fields past $ 1$ V/nm, for which $\Delta > t_\perp$. We find that for $\Delta \simeq t_\perp$, the evolution of the longitudinal resistance ($R_{xx}$) peak as a function of applied gate voltages undergoes a sharp change in slope, exhibiting a pronounced "knee". Increasing $\Delta$ past the "knee" results in an unusual evolution transport properties: the peak in $R_{xx}$ decreases in magnitude, it exhibits a splitting concomitant with multiple sign reversals of the Hall resistance, and hysteresis in the peak position emerges. We explain the observed phenomenology in terms of in-gap bound states, whose energy strongly depends on the perpendicular electric field, and crosses the mid-gap level for sufficiently large $\Delta > t_\perp$. The phenomenon causes large changes in the electronic density of in-gap states that profoundly affect the evolution of the chemical potential. Our experimental results and their interpretation reveal unique aspects of the physics of in-gap states in Bernal bilayer graphene and demonstrate that double ionic gating enables investigating the large-$\Delta$ regime, which has remained experimentally inaccessible so far.