Quantum Physics

Stripes within crystals suggest electron activity in quantum systems.

According to an unexpected finding by RIKEN physicists, hidden stripes in a crystal may be able to shed some light on the puzzling behavior of electrons in some quantum systems, such as high-temperature superconductors.

Most materials have very weak electron-electron interactions. But in materials with strong electron interactions, physicists frequently notice intriguing properties. In these materials, the electrons frequently behave as particles when they are all together, creating “quasiparticles.”. “.

According to Christopher Butler of the RIKEN Center for Emergent Matter Science, “a crystal can be thought of as an alternative universe with different laws of physics that allow different fundamental particles to live there.”

“A crystal can be thought of as an alternate universe with different physical laws that allow different fundamental particles to live there,”

Christopher Butler of the RIKEN Center for Emergent Matter Science.

Butler and his coworkers investigated a crystal in which a layer of nickel atoms was arranged in a chessboard-like square lattice. Despite having a tiny mass on their own, individual electrons in this crystal appeared as massless quasiparticles.

Scanning tunneling microscopy was used by the team to investigate this peculiar effect, but it was difficult. The vacuum chamber where the walnut-sized microscope is located is filled with machinery that can produce conditions with low temperatures and ultralow pressures that are similar to those on the moon’s surface.

We try to cleave off a small flake, much like geologists do, to examine the crystals’ flawless surface, says Butler. However, since we must carry out this task in a vacuum, the crystals are prone to shattering into dust.

They finally succeeded after numerous failed attempts and used the microscope to scan the flake with a tiny needle that was similar to a record player and had a voltage applied to it. They could probe different features by varying the voltage.

The group verified that the arrangement of the nickel atoms resembled a chessboard. But to their surprise, the electrons had deviated from this pattern and were now arranged in striped alignment (Fig. 1). Nematicity is a phenomenon where the electrons exhibit less symmetry than the underlying material as a result of system interactions.

In comparison to throwing a pebble into a pond, Butler compares the discovery “You’d expect to see circular ripples, so if ripples started to appear in parallel lines, you’d know something weird is going on,” the author claims. “It necessitates an explanation.”.

These tests will allow physicists to compare various hypotheses for the behavior of quantum systems with numerous particle interactions, such as high-temperature superconductors. These new findings, for example, are consistent with theories put forth by the study’s co-authors at Nagoya University in Japan using a “density-wave” framework.

Butler claims that even with the use of supercomputers, the behavior of many interacting electrons is challenging to predict. However, we can at least see what they are doing under a microscope. “.

The results have been reported in the Proceedings of the National Academy of Sciences.

More information: Christopher John Butler et al, Correlation-driven electronic nematicity in the Dirac semimetal BaNiS 2, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2212730119

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