Welcome! Our laboratory is hosted by the Department of Physics, The Chinese University of Hong Kong. We investigate a wide range of quantum materials under extreme conditions. The group is led by Prof. Swee K. Goh (Associate Professor).

Recent topics:

February 2023 The kagome metal CsV3Sb5 features an unusual competition between the charge-density-wave (CDW) order and superconductivity. Evidence for time reversal symmetry breaking (TRSB) inside the CDW phase has been accumulating. Hence, the superconductivity in CsV3Sb5 emerges from a TRSB normal state, potentially resulting in an exotic superconducting state. To reveal the pairing symmetry, we first investigate the effect of nonmagnetic impurity. Our results show that the superconducting critical temperature is insensitive to disorder, pointing to conventional s-wave superconductivity. Next, our measurements of the self-field critical current (Ic,sf), which is related to the London penetration depth, also confirm conventional s-wave superconductivity with strong coupling. Finally, we measure Ic,sf where the CDW order is removed by pressure and superconductivity emerges from the pristine normal state. Our results show that s-wave gap symmetry is retained, providing strong evidence for the presence of conventional s-wave superconductivity in CsV3Sb5 irrespective of the presence of the TRSB. This work is published in Nano Letters.

February 2020 As a leading candidate of type-II Weyl semimetal, Td-MoTe2 has attracted a lot of attention. Thus, the understanding of its Fermiology is important. The bulk electronic structure of Td-MoTe2 features large hole pockets at the Brillouin zone center, which have never been conclusively detected in quantum oscillations. The existence of these hole pockets is important for understanding the Weyl physics. Here, we successfully solve this puzzle by detecting these elusive hole pockets in our quantum oscillation measurements. Combining with the high-pressure quantum oscillation study and the DFT + U calculations, we reveal that the hole pockets have a large Fermi surface curvature at ambient pressure, making the associated quantum oscillation signals weak. This probably explains their absence in previous quantum oscillation experiments. This work is published in Physical Review Letters.

December 2019 To measure the diamagnetism associated with the superconductivity under high pressure is not an easy task. In collaboration with Sen Yang's group, we accomplish this mission by utilising the nitrogen vacancies in diamond particles as a local sensor of magnetic field. We successfully detected the Tc, Hc1 and Hc2 in BaFe2(As0.59P0.41)2 under pressure with spatial resolution. Depending on the positions of diamond particles relative to the sample, the effects "felt" by the NV centres can be different, enabling the magnetic field profile around the superconductor to be extracted. The crystals used were prepared and characterised by the teams at Kyoto University and The University of Tokyo. This work is published in Science. See press coverage at CUHK's CPR office, Physics World and HK China News Agency (in Chinese).

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