LMU Seminars

Superconductivity and Charge Order on the Correlated Kagome Lattice

by Mr Charles Mielke (LMU/PSI)



One of the most well-known and versatile playgrounds for condensed matter physics research is the structural motif composed of an interlocking network of corner-sharing triangles known as the kagome lattice, taking its name from a traditional japanese style of basket weaving. Kagome lattice metals have long been predicted to be the ideal platform for hosting unconventional phases, given the band structure arising from the geometric frustration featuring flat bands, van Hove singularities, and topological Dirac points [1,2]. In this regard, muon spin relaxation/rotation (μSR) provides the ideal technique to investigate the unconventional quantum phases which arise from this unique structural motif. We have found a systematic set of unconventional features of superconductivity arising from the kagome band structures in LaRu3Si2 and the AV3Sb5 (A = K, Rb, Cs) family, gaining a rich understanding of the unconventional effects that hydrostatic pressure and chemical substitution have on the superconducting gap symmetry [3-6]. Importantly, μSR has proved to be one of the most sensitive techniques in the detection of time-reversal symmetry-breaking (TRSB). We have utilized the powerful combination of zero-field and high-field μSR to discover TRSB charge order in the AV3Sb5 family [5,6]. This discovery gave way to the observation of TRSB charge ordered phases in other kagome materials (such as ScV6Sn6, FeGe, and LaRu3Si2 [5-7]) which hints at a nearly universal unconventional chiral charge order arising from the kagome lattice which may host orbital currents. Such diverse quantum phases hosted on the kagome lattice provide an exquisite and tantalizing step towards control and comprehension of the complex interplay between competing states in condensed matter physics.
[1] Kiesel & R. Thomale. “Sublattice interference in the kagome Hubbard model.” Phys. Rev. B 86, 121105(R) (2012).
[2] W.-S. Wang, Z.-Z. Li, Y.-Y. Xiang, & Q.-H. Wang. “Competing electronic orders on kagome lattices at van Hove filling.” Phys. Rev. B 87, 115135 (2013).
[3] C. Mielke III et al. & Z. Guguchia. “Nodeless kagome superconductivity in LaRu3Si2.” Phys. Rev. Mat. 5, 034803 (2021).
[4] C. Mielke III et al. & Z. Guguchia. “Microscopic study of the impurity effect in the kagome superconductor La(Ru1-xFex)3Si2.” Phys. Rev. B 109, 134501 (2024).
[5] C. Mielke III et al. & Z. Guguchia.  “Time-reversal symmetry-breaking charge order in a kagome superconductor.” Nature 602, 245 (2022).
[6] Z. Guguchia, C. Mielke III et al. “Tunable unconventional kagome superconductivity in charge ordered RbV3Sb5 and KV3Sb5.” Nat. Comm. 14, 153 (2023).
[7] C. Mielke III et al. & Z. Guguchia. “Charge orders with distinct magnetic response in a prototypical kagome superconductor LaRu3Si2.” arxiv:2402.16219 (2024)
Organized by

Zaher Salman

Zaher Salman