Emptying Dirac valleys in bismuth using high magnetic fields

TL;DR

This paper reports the discovery of a new magnetic field threshold in bismuth where one or two electron valleys become completely empty, significantly enhancing conductance and revealing novel valley dynamics under high magnetic fields.

Contribution

It introduces the observation of a previously unreported threshold magnetic field in bismuth that empties specific electron valleys, affecting its electronic transport properties.

Findings

Valley-specific electron depletion occurs above a new magnetic field threshold.

Magnetoresistance drops sharply across this threshold due to carrier transfer between valleys.

Field-dependent mobility explains most observed phenomena, with Coulomb interactions possibly influencing fine details.

Abstract

The Fermi surface of elemental bismuth consists of three small rotationally equivalent electron pockets, offering a valley degree of freedom to charge carriers. A relatively small magnetic field can confine electrons to their lowest Landau level. This is the quantum limit attained in other dilute metals upon application of sufficiently strong magnetic field. Here, we report on the observation of another threshold magnetic field never encountered before in any other solid. Above this field, $B_{\rm{empty}}$, one or two valleys become totally empty. Drying up a Fermi sea by magnetic field in the Brillouin zone leads to a manyfold enhancement in electric conductance. We trace the origin of the large drop in magnetoresistance across $B_{\rm{empty}}$ to transfer of carriers between valleys with highly anisotropic mobilities. The non-interacting picture of electrons with field-dependent mobility explains most results. Coulomb interaction may play a role in shaping the fine details.