Engineering Emergent Correlated States with Complex Quantum Materials
New electronic states often emerge at atomically clean interfaces between parent states hosted in distinct crystalline lattices. Yet some of the most interesting strongly correlated parent states exist only in complex materials which are difficult to handle.
In this talk, I will demonstrate two different strategies for realizing emergent correlated electronic states by design. First, using a novel cryogenic van der Waals stacking technique, we created twist Josephson junctions between high temperature Bi2Sr2CaCu2O8+x superconductors with quality approaching that between CuO2 layers within single crystals. At 45 degree twist angle, we observe half-integer Shapiro steps and spontaneous time-reversal symmetry breaking, consistent with the emergence of predicted interfacial high-temperature topological superconductivity. Next, I discuss our discovery of the single-crystal superconductor BaTa2S5, whose superlattice of weakly coupled H-TaS2 monolayers achieve high electronic mobility while breaking inversion symmetry of the parent 2H-TaS2 compound. Using multiple independent experimental probes, we uncover a magnetic field induced phase transition between distinct superconducting states, one of which survives well beyond 60 T, at least 12 times the Pauli limit. This phase boundary intersects the superconducting-normal boundary exactly at an upturn in HC2(T), pointing to the emergence of field-induced spin-triplet superconductivity.
Bio: Frank Zhao earned his B.Sc. (Honors) degree at University of Toronto, where he studied mathematics and physics. For his doctoral research, he studied emergent quantum phenomena at atomically clean interfaces between air sensitive 2D materials in mesoscopic devices, with Philip Kim at Columbia and Harvard University. He continued his research at MIT with Joe Checkelsky where he synthesized new unconventional superconductors, which he measured using structural, transport and magnetic probes at low temperature and high magnetic field. He will combine material synthesis and cryogenic van der Waals stacking techniques to discover emergent phenomena at the interface between quantum materials.