In condensed matter physics, the new paradigm to achieve truly disruptive innovation is to go beyond the usual quantum properties of an electron related to charge and spin, and to use topological properties embedded in the electronic wave function of a solid.
Kagome metals AV
3Sb
5 (A=K, Rb, Cs), whose electronic band structure naturally hosts van Hove singularities, Dirac points and flat bands, serve as an ideal platform to investigate the interplay between topologically nontrivial states and the electronic correlation. Due to the correlation effects, an abundance of instabilities, including charge density wave, nematicity and superconductivity, have been realized in AV
3Sb
5. Hence, AV
3Sb
5 metals exhibit various quantum states that are actively explored in modern condensed matter research.
In collaboration with a team from the Chinese University of Hong Kong and the high magnetic field laboratory LNCMI of the CNRS in Grenoble, we conducted a detailed study of the Fermi surface of CsV3Sb5, a member of the kagome family. In this material, the Fermi surface is reconstructed due to the charge density wave instability. For a further insight into this material, it is crucial to know the Fermi surface of the “pristine” metal, before the electronic instability sets in. Therefore, we determined the CsV3Sb5 Fermi surface by probing it as a function of hydrostatic pressure up to 30 kbar and in high magnetic fields up to 30 T.
The first outcome is the discovery of a large Fermi surface, which is a signature of the pristine state and absent in the reconstructed Fermi surface at ambient pressure. For the first time such a strong effect of the charge density wave instability on the Fermi surface is directly demonstrated by quantum oscillations. Another important result is that the effective mass of the charge carriers is noticeably enhanced near the critical pressure where the charge density instability is suppressed. Both findings emphasize the influence of the charge density wave on the electronic structure, together with the sensitivity of the electronic correlations driving this electronic instability to a modest pressure.
Fig. 1: Schematics of the charge order and superconductivity detected in kagome superconductors AV3Sb5. The dark and light-blue spheres form the kagome lattice. The shade of the color represents the unusual distribution pattern of the charge order. The large red and blue spheres with arrows represent Cooper pairing of the superconductivity (from J. X. Yin et al.
Nature 612-647 2022).
Fig. 2. Physical-pressure- or chemical-doping-based phase diagram, showing the competition between charge order and superconductivity (from J. X. Yin et al.
Nature 612-647 2022)
For more details:W. Zhang et al. Large Fermi surface and enhanced quasiparticle effective masses in pristine kagome metal CsV3Sb5
PNAS 121 2024