We report Shubnikov-de Haas oscillations measurements revealing experimental signatures of an annular Fermi sea that develops near the energy band edge of the excited subband of two-dimensional holes confined in a wide GaAs quantum well. As we increase the hole density, when the Fermi level reaches the excited subband edge, the low-field magnetoresistance traces show a sudden emergence of new oscillations at an unexpectedly large frequency whose value does not correspond to the (negligible) density of holes in the excited subband. There is also a sharp and significant increase in zero-field resistance near this onset of subband occupation. Guided by numerical energy dispersion calculations, we associate these observations with the unusual shape of the excited subband dispersion which results in a "ring of extrema" at finite wavevectors and an annular Fermi sea. Such a dispersion and Fermi sea have long been expected from energy band calculations in systems with strong spin-orbit interaction but their experimental signatures have been elusive.
@article{arxiv.1607.01463,
title = {Signatures of an annular Fermi sea},
author = {Insun Jo and Yang Liu and L. N. Pfeiffer and K. W. West and K. W. Baldwin and M. Shayegan and R. Winkler},
journal= {arXiv preprint arXiv:1607.01463},
year = {2017}
}