Spontaneous "Valley Magnetization" in an Atomically-Thin Semiconductor

Published November 18, 2020

Left: The tungsten di-selenide (WSe2) monolayer-on-fiber assembly used for optical absorption studies in 60 tesla magnetic fields., Right: Discrete jumps in the absorption indicate emptying and spontaneous filling of specific quantum states (the “valley”states).

Jing Li

Interactions between electrons underpin some of the most interesting – and useful -- effects in materials science and condensed-matter physics. This work demonstrates that, in the new family of so-called "monolayer semiconductors" that are only one atomic layer thick, electron-electron interactions can lead to the sudden and spontaneous formation of a magnetized state, analogous to the appearance of magnetism in conventional materials like iron.

What did scientists discover?

In a single atomically-thin layer of the semiconductor WSe₂, optical studies have shown that all of the electrons in the material can spontaneously "polarize" – or suddenly jump to the same quantum state (or "valley") in the material. This a phenomenon is directly analogous to magnetization.

Why is this important?

Interactions between electrons are the root of some of the most interesting effects in condensed-matter physics (including magnetism). In two-dimensional ‘sheets’ of electrons in very high-quality semiconductors, interactions can result in the discovery of important new phenomena, such as the Fractional Quantum Hall Effect (for which a Nobel prize was awarded in 1998). The electron-electron interactions here could yield a new way to use valleytronic controls in magnetic information storage or other exciting applications.

Who did the research?

J. Li¹, M. Goryca¹, N. P. Wilson², A. V. Stier¹, X. Xu², S. A. Crooker¹

¹National MagLab, Los Alamos National Laboratory; ²University of Washington

Why did they need the MagLab?

Large magnetic fields up to 60 T were essential for creating conditions wherein the 'valley magnetization' could spontaneously occur in the WSe₂ monolayer semiconductor. Large fields were also needed to separate the different energy levels, so that they could be experimentally distinguished using light.

Details for scientists

View or download the expert-level Science Highlight, Spontaneous "valley magnetization" in an atomically-thin semiconductor
Read the full-length publication Spontaneous Valley Polarization of Interacting Carriers in a Monolayer Semiconductor, in Phys. Rev. Lett..

Funding

This research was funded by the following grants: G.S. Boebinger (NSF DMR-1644779) S. A. Crooker (DOE BES ‘Science of 100T’, Los Alamos LDRD); X. Xu (DOE DE-SC0018171)

For more information, contact Scott A Crooker.