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Quest for Novel States of Quantum Matter
Speaker Prof. Gang Cao, University of Colorado at Boulder
Date 13 June 2024 (Thursday)
Time 10:00 - 11:30
Venue Room 5508, Academic Building, HKUST (Lifts 25-26)

Our research has focused on the discovery, synthesis, and study of novel quantum materials [1]. Here, I report two of our most recent discoveries: (1) A chiral-orbital-currents state that underpins a novel colossal magnetoresistance and a strongly current-sensitive Hall effect in ferrimagnetic Mn3Si2Te6 [2, 3], and (2) A heavy Fermi surface of charge-neutral spinons that supports both a heavy-fermion strange metal and adjacent quantum-spin-liquid phases in the 4d-electron trimer lattice Ba4Nb1-xRu3+xO12 (without f electrons). The extraordinarily large entropy, linear heat capacity and thermal conductivity of both phases extend into milli-Kelvin temperatures, which is best explained by charge and spin dissociation. The insulating spin liquid is a much better thermal conductor than the heavy-fermion strange metal that is separately observed to strongly violate the Wiedemann-Franz law [4]. The novel phenomenology potentially offers an unprecedented paradigm of correlated quantum matter.



  1. Physics of Spin-Orbit-Coupled Oxides, Gang Cao and Lance E. De Long, Oxford University Press; Oxford, 2021.
  2. Control of chiral orbital currents in a colossal magnetoresistance material, Yu Zhang, Yifei Ni, Hengdi Zhao, Sami Hakani, Feng Ye, Lance DeLong, Itamar Kimchi, and Gang Cao, Nature 611, 467–472 (2022).
  3. Current-sensitive Hall effect in a chiral-orbital-current state, Yu Zhang, Yifei Ni, Pedro Schlottmann, Rahul Nandkishore, Lance E. DeLong, and Gang Cao, Nature Communications 15, 3579 (2024)
  4. Transition between heavy-fermion-strange-metal and spin liquid in a 4d-electron trimer lattice, Hengdi Zhao, Yu Zhang, Pedro Schlottmann, Rahul Nandkishore and Gang Cao, Phys. Rev. Lett. 132, 226503 (2024).

    Please contact phweb@ust.hk should you have questions about the talk.