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Mapping How Electron Energies Vary Between Regions in Specific Quantum State

The way energies of electrons differ from one region to another in a specific quantum state has now been mapped by a group of physicists with unmatched clarity.

Image Credit: Pobytov/Getty Images.

This insight unravels a fundamental mechanism, called quantum “hybridization,” through which electrons affect each other. This mechanism had not been observed in earlier experiments.

The outcomes of the study, by researchers from New York University, the Lawrence Berkeley National Laboratory, Rutgers University, and MIT, have been described in the Nature Physics journal.

This sort of relationship is essential to understanding a quantum electron system—and the foundation of all movement—but had often been studied from a theoretical standpoint and not thought of as observable through experiments. Remarkably, this work reveals a diversity of energetic environments inside the same material, allowing for comparisons that let us spot how electrons shift between states.

Andrew Wray, Assistant Professor, Department of Physics, New York University

Wray is one of the co-authors of the paper.

The focus of the study was on bismuth selenide (Bi2Se3), a material that has been studied intensely in the past decade as the foundation of sophisticated information and quantum computing technologies. In 2008 and 2009, various studies unraveled that Bi2Se3 hosts a rare “topological insulator” quantum state that alters how electrons at its surface interact with and store information.

From that time, research works have confirmed several theoretically motivated concepts related to topological insulator surface electrons. But since these particles are located on the surface of a material, they are prone to environmental factors that do not exist in the bulk of the material, making them manifest and shift in different ways from one region to another.

The ensuing gap in the knowledge, along with analogous challenges for other classes of materials, has inspired researchers to devise methods for evaluating electrons with micron- or nanometer-scale spatial resolution. This has enabled then to investigate electron interaction without any external interference.

The Nature Physics study is the first of its kind to employ these latest experimental tools, called “spectromicroscopy”—and the first spectromicroscopy analysis of Bi2Se3. This process has the capability to track the difference in the motion of surface electrons within a material from one region to another.

Instead of focusing on average electron activity across a single huge region on the surface of a sample, the researchers gathered data from almost 1,000 smaller regions.

Using this approach, the researchers widened the terrain and thus could notice signatures of quantum hybridization in the relationships between moving electrons, for example, a repulsion between electronic states that get close to each other in energy. Measurements performed using this technique threw light on the changes in electronic quasiparticles over the material surface.

Looking at how the electronic states vary in tandem with one another across the sample surface reveals conditional relationships between different kinds of electrons, and it’s really a new way of studying a material. The results provide new insight into the physics of topological insulators by providing the first direct measurement of quantum hybridization between electrons near the surface.

Erica Kotta, Study First Author and Graduate Student, New York University

Yishuai Xu, a doctoral candidate, and Lin Miao, a postdoctoral fellow when the study was performed, are the other NYU researchers who were part of the study.

The study was financially supported by the U.S. Department of Energy (DE-AC02-05CH11231), and also by the MRSEC Program of the National Science Foundation (DMR-1420073), the National Science Foundation (DMR-1506618), and the Office of Naval Research (N00014-17-1-2883).


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