Center for Artificial Low Dimensional Electronic Systems

The nontrivial topology of magnetic systems is one of the most active research fields of modern condensed matter physics. The topological phases are characterized by the Chern number or Z2 topological number, which classifies the topological magnetic semimetals (TMSs). The hallmark of TMSs is bulk gapless topological states with broken time-reversal symmetry. It is theoretically predicted that TMSs can host various topological states depending on the spin configurations, such as a single gapless Dirac cone for antiferromagnetism and quantum anomalous Hall effect state with chiral edge state for out-of-plane ferromagnetism. In this vein, the interplay between magnetism and topology plays a vital role in the emergence of topological phenomena. We currently focus on understanding their subtle interplay in various TMSs using local probe techniques, such as muon spin relaxation/rotation, electron spin resonance, and nuclear magnetic resonance.

When a magnetic impurity is introduced into a metal, conduction electrons interact with the local magnetic moment. At temperatures below the so-called Kondo temperature, the impurity spin becomes effectively screened by the surrounding conduction electrons, creating a many-body entanglement cloud. Beyond normal metals, the purview of Kondo physics has expanded into various materials, including quantum dots, graphene, topological insulators, and Weyl semimetals. It is also envisioned that the Kondo effect may occur in quantum spin liquids (QSLs) that constitute highly entangled quantum states harboring fractionalized spinon excitations, an emergent gauge structure, and topological order. In addition, magnetic impurities incorporated into QSLs may be subject to RKKY-type interactions mediated by spinons or gauge fluctuations. We currently explore the Kondo effect in various QSL candidates using local probes.