Quantum bubble defects in the lowest Landau level crystal

TL;DR

This paper investigates quantum bubble defects in the lowest Landau level crystal, revealing a new type of defect with significantly lower energy that explains experimental activation gaps.

Contribution

It introduces a hyper-correlated bubble interstitial defect, reducing the energy discrepancy between theory and experiment in Landau level crystals.

Findings

The lowest energy defect is a six-fold symmetric bubble interstitial.

The bubble defect's energy is about three times lower than Hartree-Fock predictions.

Quantum correlations significantly lower defect energies, explaining experimental gaps.

Abstract

A longstanding puzzle for the lowest Landau level crystal phase has been an order of magnitude discrepancy between the theoretically calculated energy of the defects and the measured activation gap. We perform an extensive study of various kinds of defects in the correlated composite fermion crystal and find that the lowest energy defect is a six-fold symmetric "hyper-correlated bubble interstitial," in which an interstitial particle forms a strongly correlated bound state with a particle of the crystal. The energy of the bubble defect is a factor of $\sim$3 smaller than that of the lowest energy defect in a Hartree-Fock crystal. The anomalously low activation energies measured in transport experiments are thus a signature of the unusual quantum nature of the crystal and its defects.