Incipient Formation of Wigner Crystal in Strongly Interacting 2D Holes

Published January 19, 2021

(Left) Schematic phase diagram of interacting 2D electrons or holes. (Right) Wigner crystallization appears as a reentrant insulating phase (RIP) in the magneto-resistance traces of 2D holes at low temperatures

Xuan Gao - Case Western Reserve University

This highlight reports on the still poorly understood transition to an electron crystalline state (the Wigner crystal) in a two-dimensional system at extremely low densities, observable at low temperatures as a function of magnetic field. This experiment finds a surprising stabilization of the Wigner crystal arising from magnetic-field-induced spin alignment. Such electrically-delicate samples require the ultra-low-noise environment and experimental techniques available at the High B/T facility.

What did scientists discover?

Charged carriers (negatively charged electrons or positively charged “holes”) confined to move in only two dimensions (2D) within a semiconductor structure can interact with each other to form a variety of phases when the carrier density, temperature, or an applied magnetic field is tuned. In this work, MagLab users found evidence for the emergence of a crystal phase inside the liquid phase of 2D hole carriers and, furthermore, discovered that polarizing the carriers’ spin promotes the crystal formation.

Why is this important?

Two-dimensional semiconductor electronic devices find applications in high-speed electronics. They also provide an nearly ideal platform for settling scientific questions about electronic correlations that are of fundamental interest and of relevance to other materials with novel electronic or magnetic properties.

Who did the research?

R. L.J. Qiu, C.W. Liu, X. P.A. Gao¹, A. J. Woods, A. Serafin, J.S. Xia², L.N. Pfeiffer, K.W. West³

¹Case Western Reserve University ; ²National MagLab; ³Princeton University

Why did they need the MagLab?

High-quality 2D electron and hole systems are incredibly susceptible to deleterious impact of electromagnetic interference. The ultra-low-noise environment of the MagLab’s High B/T facility provides a unique opportunity to investigate the electrical transport behavior of the 2D hole system at low temperatures, subject to tunable perpendicular and parallel magnetic fields by rotating the sample in the magnetic field. Sample rotation enables separate control of the interactions between carriers and their spin polarization, important to understand the origin of the Wigner crystal phase transition.