# Evidence for pairing states of composite fermions in double-layer graphene

## TL;DR

This paper presents experimental evidence for pairing states of composite fermions in double-layer graphene, revealing a new type of order involving CF pairing at half-filled levels, expanding understanding of quantum Hall states.

## Contribution

The study demonstrates the existence of pairing states of composite fermions in double-layer graphene, introducing a novel order beyond conventional models.

## Key findings

- Observation of fractional quantum Hall ground states in double-layer graphene
- Evidence for effective integer quantum Hall states of two-component composite fermions
- Detection of incompressible states at half-filled levels indicating CF pairing

## Abstract

Pairing interaction between fermionic particles leads to composite Bosons that condense at low temperature. Such condensate gives rise to long range order and phase coherence in superconductivity, superfluidity, and other exotic states of matter in the quantum limit. In graphene double-layers separated by an ultra-thin insulator, strong interlayer Coulomb interaction introduces electron-hole pairing across the two layers, resulting in a unique superfluid phase of interlayer excitons. In this work, we report a series of emergent fractional quantum Hall ground states in a graphene double-layer structure, which is compared to an expanded composite fermion model with two-component correlation. The ground state hierarchy from bulk conductance measurement and Hall resistance plateau from Coulomb drag measurement provide strong experimental evidence for a sequence of effective integer quantum Hall effect states for the novel two-component composite fermions (CFs), where CFs fill integer number of effective LLs (Lambda-level). Most remarkably, a sequence of incompressible states with interlayer correlation are observed at half-filled Lambda-levels, which represents a new type of order involving pairing states of CFs that is unique to graphene double-layer structure and beyond the conventional CF model.