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Revealing correlation and topology in Kagome lattices using STM

Hong Li, Boston College
Thursday, February 1, 2024 - 12:30pm to 1:30pm
PAB B421

The discovery of high-Tc superconductors (SC) and quantum Hall effects years ago marked significant milestones in condensed matter physics. The former, shaped by strong correlation, and the latter, driven by topology, continue to unveil mysterious phenomena not fully understood until today. Like machine learning extracts laws from extensive data, we seek diverse platforms with correlated and topological states to better grasp the universal driving mechanism. In this presentation, I will demonstrate the Kagome lattice as an exceptional novel host for both strong Coulomb interactions and symmetry-broken/protected topology with our STM experiments, expanding the scope beyond previously limited platforms. Specifically, similar to nematic quantum fluids in high Tc SCs and quantum Hall liquids, spontaneous rotation symmetry breaking occurs in electronic states due to Coulomb interactions in Kagome crystals such as AV3Sb5 and ATi3Bi5 (A=Cs, K, Rb). Surprisingly, a unidirectional coherent state emerges above Tc as a condensation crossover from the normal state to the SC phase. In cases where interactions play a neglected role, such as some kagome RT6E6 (R = rare earth; T = transition metals; and E = Sn, Ge, etc), we have discovered both Chern bands and a  magnetic phase. In both scenarios, non-zero (spin) Berry curvature induces a huge orbital Zeeman effect, allowing us, for the first time, to validate the Modern orbital magnetization theory directly. All these findings demonstrate Kagome lattices as an extraordinary environment for delving into and unraveling correlation and topology.

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