
For each field pulse, a tiny crystal of CsV3Sb5 was rotated to different precise angles for each pulse. The angles are shown at right. Wiggles are seen in the frequency, and their amplitude varies with the crystal’s angle in a distinctive way. Image published in Communications Materials and used via Creative Commons license.
The recently discovered kagome metal CsV3Sb5 has attracted considerable attention because it is thought to host small Chern Fermi pockets that possess spontaneous orbital currents and large orbital magnetic moments. Chern pockets are a key indicator of a quantum mechanical property known as topology, which promises to be invaluable in future electronic devices that will work on completely new quantum principles. In work described in Communications Materials, a research team probed the material’s properties using high magnetic fields generated at Los Alamos’ Pulsed Field Facility of the National High Magnetic Field Laboratory.
Until the present measurement, the presence of Chern Fermi pockets in CsV3Sb5 has proven impossible to definitively detect because the pockets align antiferromagnetically. That is, Chern pockets with oppositely circulating currents pair up, cancelling out their magnetic fields. Studying CsV3Sb5, under pulsed magnetic fields of up to 75 Tesla, the experiment recorded the electrical conductivity of CsV3Sb5 via its effect on the frequency f of an oscillator. For each field pulse, a tiny crystal of CsV3Sb5 was rotated to different precise angles; wiggles are seen in the frequency, their amplitude varying with the crystal’s angle in a distinctive way.
The high fields cause electrons to tunnel out of the Chern pockets onto more conventional bands in CsV3Sb5 and then back again; this repetitive back-and-forth motion leads to the wiggles. Because the two types of Chern pocket have opposite currents, their tunneling processes are not quite the same, producing two sets of wiggles with slightly different frequencies. These frequencies vary differently as the angle of the crystal in the field changes; as a result, the two sets of wiggles go in and out of phase, leading to an overall amplitude that goes up and down. It is this variation of the wiggle amplitude — visible in the raw data — that definitively identifies the orbital moments of the Chern pockets. This visible manifestation is a remarkable example of the interplay between topological effects and more conventional electronic bands in quantum materials, giving hope for future devices in which topology is writ large.
Funding and mission
This work is supported by the National Science Foundation; the U.S. Department of Energy, including the Basic Energy Sciences office, and including the Basic Energy Sciences program “Science at 100 T”; the Institute for Complex Adaptive Matter; and the Gordon and Betty Moore Foundation. The work supports the Global Security mission area and the Materials for the Future capability pillar.
Reference
“Magnetic breakdown and spin-zero effect in quantum oscillations in kagome metal CsV3Sb5,” Communications Materials, 4 (2023); DOI: 10.1038/s43246-023-00422-y. Authors: Kuan-Wen Chen, Guoxin Zheng, Dechen Zhang, Aaron Chan, Yuan Zhu, Kaila Jenkins and Lu Li (University of Michigan); Fanghang Yu, Mengzhu Shi, Jianjun Ying and Xianhui Chen (University of Science and Technology of China); Ziji Xiang (University of Michigan, University of China); Ziqiang Wang (Boston College); and John Singleton (Los Alamos National Laboratory).
Technical contact: John Singleton (MPA-MAGLAB)