Research

Prof. Liu’s research helped establish superconductivity at KTaO₃ interfaces, where two-dimensional electron gases exhibit a strong dependence of superconductivity on crystallographic orientation and carrier density. These systems provide a platform for investigating how interfacial symmetry and strong spin–orbit coupling shape superconducting and normal-state electronic properties.

Building on this foundation, the Liu Group investigates how interface structure, symmetry, spin–orbit coupling, and electronic tuning govern superconductivity and transport in KTaO₃-based heterostructures. A particular focus is the use of interface engineering, including magnetic exchange coupling, as a controlled probe of the spin and symmetry structure of the superconducting electron gas.

Research topics: superconducting oxide interfaces · two-dimensional superconductivity · spin–orbit coupling · interfacial symmetry · exchange coupling · nonlinear and quantum transport

Selected related publications

J. Yang*, C. Liu*, et al. “Uniaxial spin texture in a superconducting electron gas revealed by exchange interactions.”
Science Advances 12, eaeb1601 (2026).

Q. Du*, J. Yang*, et al. “Tuning kinetic inductance with doping in superconducting electron gases at the KTaO₃ (111) interface.”
Nano Letters 25, 7234–7240 (2025).

C. Liu et al. “Tunable superconductivity and its origin at KTaO₃ interfaces.”
Nature Communications 14, 951 (2023).

M. Yu, C. Liu, et al. “Nanoscale control of the metal–insulator transition at LaAlO₃/KTaO₃ interfaces.”
Nano Letters 22, 6062–6068 (2022).

C. Liu*, X. Yan*, et al. “Two-dimensional superconductivity and anisotropic transport at KTaO₃ (111) interfaces.”
Science 371, 716–721 (2021).

Our group is developing epitaxial thin films of rare-earth intermetallic compounds in the MA₄ family, where M is a rare-earth element and A is Al or Ga. These materials adopt the BaAl₄-type tetragonal structure and provide a versatile platform in which localized rare-earth moments interact with itinerant electronic states.

By bringing MA₄ materials into thin-film form, we aim to introduce new control parameters—including crystalline orientation, epitaxial strain, thickness, and interface design—that are difficult to access in bulk crystals. Molecular beam epitaxy allows us to investigate how these structural degrees of freedom influence phase formation and the underlying electronic and magnetic properties.

A particular interest is the interplay between charge-density-wave order and complex magnetism, exemplified by EuAl₄ and related compounds. The presence of multiple competing magnetic states provides an opportunity to study how charge order, magnetic interactions, and external fields combine to produce tunable quantum phases.

Research topics: rare-earth intermetallics · molecular beam epitaxy · charge-density waves · correlated magnetism · field-tunable phases · magnetic heterostructures

Prof. Liu’s prior research explored how magnetic order, interfacial symmetry, and external control parameters govern spin transport in magnetic quantum materials. A central focus was antiferromagnetic insulators, where thermally excited magnons can carry spin angular momentum without accompanying charge transport.

Using epitaxial Cr₂O₃ as a model antiferromagnet, this work demonstrated that the spin Seebeck effect can electrically resolve magnetic sublattices and that magnon spin currents can be controlled by an applied electric field through magnetoelectric coupling. These studies established spin-caloritronic transport as a sensitive probe of antiferromagnetic order and interfacial magnetic states.

This foundation motivates the Liu Group’s current efforts to synthesize and investigate new magnetic quantum materials and heterostructures, with particular interest in how magnetic symmetry, competing ordered states, and interfaces can be used to control electronic and spin transport.

Research topics: antiferromagnetic spin transport · magnon spin currents · spin Seebeck effect · magnetic symmetry · magnetoelectric control · magnetic heterostructures

Selected related publications

C. Liu*, Y. Luo*, et al.
“Electric field control of magnon spin currents in an antiferromagnetic insulator.”
Science Advances 7, eabg1669 (2021).

Y. Luo*, C. Liu*, et al.
“Distinguishing antiferromagnetic spin sublattices via the spin Seebeck effect.”
Physical Review B 103, L020401 (2021), Editor’s Suggestion.

Our research integrates thin-film synthesis, materials characterization, and low-temperature quantum transport. Molecular beam epitaxy provides control over composition, orientation, interface structure, and defect profiles, while cryogenic electrical measurements connect these synthesis parameters to superconducting, magnetic, nonlinear, and symmetry-dependent transport phenomena.