Charge Imbalance and Bilayer 2D Electron Systems at $\nu_T = 1$

TL;DR

This study investigates how charge imbalance affects the phase stability of bilayer 2D electron systems at total filling factor ν_T=1, revealing complex phase transitions and the persistence of excitonic coherence under various conditions.

Contribution

It demonstrates that the excitonic ν_T=1 phase can survive significant charge imbalance and identifies new phase transition behaviors influenced by imbalance, temperature, and interlayer spacing.

Findings

Enhanced tunneling persists up to Δν=0.5

Phase transitions can be induced by increasing d/ℓ, T, or Δν

First observation of a direct transition between ν_T=1 and fractional quantum Hall states at Δν=1/3

Abstract

We use interlayer tunneling to study bilayer 2D electron systems at $\nu_T = 1$ over a wide range of charge density imbalance, $\Delta \nu =\nu_1-\nu_2$, between the two layers. We find that the strongly enhanced tunneling associated with the coherent excitonic $\nu_T = 1$ phase at small layer separation can survive at least up to an imbalance of $\Delta \nu$ = 0.5, i.e $(\nu_1, \nu_2)$ = (3/4, 1/4). Phase transitions between the excitonic $\nu_T = 1$ state and bilayer states which lack significant interlayer correlations can be induced in three different ways: by increasing the effective interlayer spacing $d/\ell$, the temperature $T$, or the charge imbalance, $\Delta \nu$. We observe that close to the phase boundary the coherent $\nu_T = 1$ phase can be absent at $\Delta \nu$ = 0, present at intermediate $\Delta \nu$, but then absent again at large $\Delta \nu$, thus indicating an intricate phase competition between it and incoherent quasi-independent layer states. At zero imbalance, the critical $d/\ell$ shifts linearly with temperature, while at $\Delta \nu$ = 1/3 the critical $d/\ell$ is only weakly dependent on $T$. At $\Delta \nu$ = 1/3 we report the first observation of a direct phase transition between the coherent excitonic $\nu_T = 1$ bilayer integer quantum Hall phase and the pair of single layer fractional quantized Hall states at $\nu_1$ = 2/3 and $\nu_2=1/3$.