Berry Phase and Anomalous Transport of the Composite Fermions at the Half-Filled Landau Level

TL;DR

This paper provides experimental evidence for a π Berry phase in composite fermions at half-filling in the fractional quantum Hall effect, revealing novel topological properties and anomalous transport behaviors.

Contribution

First experimental detection of the Berry phase of composite fermions at half-filling, supporting theoretical predictions and revealing new transport phenomena.

Findings

Detection of π Berry phase in composite fermions

Linear density dependence of CF conductivity at ν=1/2

Confirmation of Fermi surface and Fermi wave vector in CFs

Abstract

The fractional quantum Hall effect (FQHE) in two-dimensional electron system (2DES) is an exotic, superfluid-like matter with an emergent topological order. From the consideration of Aharonov-Bohm interaction of electrons and magnetic field, the ground state of a half-filled lowest Landau level is mathematically transformed to a Fermi sea of composite objects of electrons bound to two flux quanta, termed composite fermions (CFs). A strong support for the CF theories comes from experimental confirmation of the predicted Fermi surface at $\nu$ = 1/2 (where $\nu$ is the Landau level filling factor) from the detection of the Fermi wave vector in the semi-classical geometrical resonance experiments. Recent developments in the theory of CFs have led to a prediction of a $\pi$ Berry phase for the CF circling around the Fermi surface at half-filling. In this paper we provide the first experimental evidence for the detection of the Berry phase of CFs in the fractional quantum Hall effect. Our measurements of the Shubnikov-de Haas oscillations of CFs as a function carrier density at a fixed magnetic field provide a strong support for an existence of a $\pi$ Berry phase at $\nu$ = 1/2. We also discover that the conductivity of composite fermions at $\nu$ = 1/2 displays an anomalous linear density dependence, whose origin remains mysterious yet tantalizing.