Observation of soft magnetorotons in bilayer quantum Hall ferromagnets

TL;DR

This paper reports the observation of soft magnetorotons in bilayer quantum Hall ferromagnets, revealing their role in phase transitions and excitonic interactions through inelastic light scattering experiments.

Contribution

It provides the first experimental evidence of soft magnetorotons in bilayer quantum Hall systems and links them to quantum phase transitions.

Findings

Deep magnetoroton observed in charge-density excitations

Magnetoroton softens and sharpens near phase boundary

Hartree-Fock calculations connect soft magnetorotons to Coulomb interactions

Abstract

Inelastic light scattering measurements of low-lying collective excitations of electron double layers in the quantum Hall state at total filling nu_T=1 reveal a deep magnetoroton in the dispersion of charge-density excitations across the tunneling gap. The roton softens and sharpens markedly when the phase boundary for transitions to highly correlated compressible states is approached. The findings are interpreted with Hartree-Fock evaluations that link soft magnetorotons to enhanced excitonic Coulomb interactions and to quantum phase transitions in the ferromagnetic bilayers.