Topological Magnetism, Superconductivity, and Charge Order on the Correlated Kagome Lattice

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. In particular, we have utilized μSR to investigate the interplay between magnetism and topologically nontrivial electronic structures in TbMn6Sn6, a topological Chern magnet [3]. We uncover a volume-wise crossover at low temperatures which experiences significant tunability through the application of hydrostatic pressure. We have also 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 [4-7]. Finally, 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 [6,7]. This discovery gave way to the observation of TRSB charge ordered phases in other kagome materials (such as ScV6Sn6, FeGe, and LaRu3Si2 [6-8]) 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. “Low-temperature magnetic crossover in the topological kagome magnet TbMn6Sn6.” Comm. Phys. 5, 107 (2022).
[4] C. Mielke III et al. & Z. Guguchia. “Nodeless kagome superconductivity in LaRu3Si2.” Phys. Rev. Mat. 5, 034803 (2021).
[5] 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).
[6] C. Mielke III et al. & Z. Guguchia. “Time-reversal symmetry-breaking charge order in a kagome superconductor.” Nature 602, 245 (2022).
[7] Z. Guguchia, C. Mielke III et al. “Tunable unconventional kagome superconductivity in charge ordered RbV3Sb5 and KV3Sb5.” Nat. Comm. 14, 153 (2023).
[8] C. Mielke III et al. & Z. Guguchia. “Charge orders with distinct magnetic response in a prototypical kagome superconductor LaRu3Si2.” arxiv:2402.16219 (2024).

Charles Mielke III has dedicated his career to the exploration of novel materials properties. Originally from Los Alamos, New Mexico, he held internships at the Los Alamos National Laboratory in the Materials Science and Technology division with Dr. Jason Cooley while completing his Bachelor’s in Mechanical Engineering. He then moved to the Università di Torino in Italy for his Master’s studies as part of the MaMaSELF Erasmus Mundus program. This mobility program took him to Université de Montpellier in France and the Paul Scherrer Institute in Switzerland for his Master’s Thesis investigating the metal-to-insulator transition via chemical substitution with Dr. Dariusz Gawryluk in the Laboratory for Multiscale materials eXperiments. Since 2020 he has been working on his doctoral research in the Bulk μSR Group with Dr. Zurab Guguchia at the Paul Scherrer Institute. During his doctoral studies, his research interests have concentrated on magnetism and correlated electron systems, in particular kagome lattice materials, studying such systems using primarily the muon spin rotation/relaxation technique complemented by several other techniques.

If you would like to meet with Charles during his visit, please contact Susan LaMoreaux.