Quantum Transport in Bismuth Two-Dimensional Electron System

Two-dimensional electron systems (2DESs) have represented an ever-expanding frontier in condensed matter physics. Over the past two decades, this growth has primarily been propelled by the emergence of novel 2DESs, exemplified by graphene and other two-dimensional (2D) crystals, each exhibiting distinctive properties. In this study, we synthesize high-quality <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>β</a:mi> </a:math> -phase bismuth thin films on exfoliated hexagonal boron nitride (hBN) and establish that bismuth surface states form a high-mobility 2DES with strong spin-orbit coupling (SOC). The extreme two dimensionality of the 2DES is characterized by an out-of-plane to in-plane effective-mass-anisotropy lower bound exceeding <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mrow> <c:msup> <c:mrow> <c:mn>10</c:mn> </c:mrow> <c:mrow> <c:mn>3</c:mn> </c:mrow> </c:msup> </c:mrow> </c:math> . We further demonstrate that the spin degeneracy of the hole pockets is completely lifted, providing unambiguous transport evidence that they originate from Rashba states induced by strong SOC in the bismuth thin film. Under magnetic fields up to 40 Tesla, electrostatic gating drives the carriers into the lowest Landau levels, revealing signatures of rotational symmetry breaking and electronic nematicity. These findings position the bismuth 2DES as a compelling platform for exploring topological quantum phenomena in systems with strong SOC and high carrier mobility.