Behaviour of the energy gap near a commensurate-incommensurate transition in double layer quantum Hall systems at nu=1

TL;DR

This paper investigates how the energy gap behaves near a phase transition in double layer quantum Hall systems at filling factor nu=1, revealing a cusp in excitation energy related to vortex-antivortex pairs and string tension.

Contribution

It provides a detailed analysis of the energy gap behavior near the commensurate-incommensurate transition, including the role of vortex-antivortex pairs and disorder effects.

Findings

Energy gap drops as string lengthens approaching critical field

A sharp cusp appears in excitation energy at the transition

Disorder effects may influence tunneling and excitation energy minima

Abstract

The charged excitations in the system of the title are vortex-antivortex pairs in the spin-texture described in the theory by Yang et al which, in the commensurate phase, are bound together by a ``string''. It is shown that their excitation energy drops as the string lengthens as the parallel magnetic field approaches the critical value, then goes up again in the incommensurate phase. This produces a sharp downward cusp at the critical point. An alternative description based on the role of disorder in the tunnelling and which appears not to produce a minimum in the excitation energy is also discussed. It is suggested that a similar transition could also occur in compressible Fermi-liquid-like states.