Ning WANG

Chair Professor of Physics

School of Science

Tel: 2358-7489

Email: phwang@ust.hk

Office: Room 4442, Lift 25-26, HKUST, Clear Water Bay, HK

Recent 2D research

• Berry curvature dipole induced intrinsic nonlinear Hall effect

We reported a Berry curvature dipole induced intrinsic nonlinear Hall effect in high-quality twisted bilayer graphene. We discover that the application of the displacement field substantially changes the direction and amplitude of the nonlinear Hall voltages, as a result of a field-induced sliding of the Berry curvature hotspots. The Berry curvature dipole could play a dominant role in generating the intrinsic nonlinear Hall signal in graphene moire superlattices with low disorder densities. Phys. Rev. Lett. 131 (2023) 066301 (Editor's Suggestion paper).

• Unconventional ferroelectricity in twisted WSe₂

We observed an abnormal electronic polarization in twisted double bilayer WSe2 in antiparallel interface stacking geometry, where local centrosymmetry of atomic registries at the twist interface does not favor the spontaneous electronic polarizations. The ferroelectric behaviors occur at half-filling insulating states at cryogenic temperatures. Our work highlights the prominent role of many-body electronic interaction in fostering novel electronic states in moire supperlattices. National Science Open 2 (2023)20220033.

• Bridging the gap between TMDCs and metals

We developed a new strategy to achieve nearly barrier-free electrical contacts with few-layer TMDSCs. The carrier-injection efficiency is substantially increased with robust ohmic behaviors from room to cryogenic temperatures. We achieved ultra low contact resistance (down to 90 Ωµm in MoS2) and ultra high field-effect mobility (up to 358,000 cm^2/Vs in WSe2). Nature Comm. 13, 1777 (2022). (Xiangbin Cai, Hong Kong PHD Fellowship Winner)

• Giant Nonlinear Hall Transport in Twisted WSe₂

Twisted WSe₂ shows highly tunable giant nonlinear Hall effects (NHE). No specific twist angles for generating such a NHE. The extracted Berry curvature dipole in twisted WSe₂ is among the highest of all materials ever explored. The electron correlation effects may play a significant role in generating the record high responsivity. National Science Review 10 (2023) nwac232. (Meizhen Huang, Hong Kong PHD Fellowship Winner)

• Reconstruction and flat bands in twisted WSe2

We uncovered the interface reconstruction of twisted WSe2, which exhibits a strong dependence on the constituent layer number and twist angles. The competition between the interlayer interaction leads to rich superlattice motifs and strain modulation. The number of ultra-flat bands and spatial distribution of the wavefunctions match well with the theoretical predictions, providing a foundation for further study of correlated electronic phases. (Nature Comm. 12, 5601 (2021); Nanoscale 13,13624 (2021)). 

• Superconductivity Signatures in Twisted WSe₂

Working together with collaborators, we detected superconductivity signatures in twisted WSe₂. Enhanced interlayer interaction and flat band properties are observable at twist angles ranging from 1 to 4 degrees. Reconstructed domains formed in a conventional moiré superlattice. Different from graphene, there is no specific magic angle for twisted WSe₂. Nanoscale Horizons, 2020, 5, 1309. (Dr. An has joined in NTU)

•  Intrinsic Valley Hall Transport in MoS₂

We observed intrinsic valley Hall transport in the non-centrosymmetric monolayer and trilayer MoS2, without any extrinsic symmetry breaking. Such a hallmark survives even at room temperature. Our work elucidates the topological origin of valley Hall effects and marks a significant step towards the purely electrical control of valley degree of freedom in topological valleytronics. See Nature Comm. 10(2019)611. (Dr. Wu has joined in Prof. Andre Geim group @ Manchester).

• Enhanced Valley Susceptibility in Spin-Valley-Locked MoS₂

We probed many-body interaction effects in MoS2 and unambiguously determined the density-dependent valley susceptibility and the interaction enhanced g-factor from 12.7 to 23.6. Near integer ratios of Zeeman-to-cyclotron energies, we discovered LL anticrossings due to the formation of Hall Ising ferromagnets, Nano Lett. 2019, 19, 3, 1736. ( Xiazi Linjiang, Hong Kong PHD Fellowship Winner,  now joined Brown University).

• Giant Spin Sussceptibility in WSe₂

High-mobility p-type few-layer WSe2 FETs show surprisingly a serious of Hall states following an unconventional sequence predominated by odd-integer states. We observe a very large Zeeman energy that is almost three times as large as the cyclotron energy. Phys. Rev. Lett. 118 (2017) 067702 (Editor's Suggestion paper) (Dr. Xu joined in Prof. Andre Geim group @ Manchester).

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