Integer and Fractional Quantum Hall effect in Ultra-high Quality Few-layer Black Phosphorus Transistors

TL;DR

This study demonstrates the observation of integer and fractional quantum Hall effects in high-mobility few-layer black phosphorus transistors, revealing linear Landau level gaps and new fractional states, thus advancing the understanding of anisotropic 2D quantum phenomena.

Contribution

It reports the first measurement of Landau level gaps over a wide magnetic field range in black phosphorus, confirming their linear dependence, and identifies fractional quantum Hall states in this material.

Findings

Landau level gaps are linear in magnetic field B.

Observation of fractional quantum Hall state at ν ≈ -4/3.

Detection of an additional feature at -0.56±0.1, indicating electron interactions.

Abstract

As a high mobility two-dimensional semiconductor with strong structural and electronic anisotropy, atomically thin black phosphorus (BP) provides a new playground for investigating the quantum Hall (QH) effect, including outstanding questions such as the functional dependence of Landau level (LL) gaps on magnetic field B, and possible anisotropic fractional QH states. Using encapsulating few-layer BP transistors with mobility up to 55,000 cm2/Vs, we extract LL gaps over an exceptionally wide range of B for QH states at filling factors {\nu}=-1 to -4, which are determined to be linear in B, thus resolving a controversy raised by its anisotropy. Furthermore, a fractional QH state at {\nu}~ -4/3 and an additional feature at -0.56+/- 0.1 are observed, underscoring BP as a tunable 2D platform for exploring electron interactions.