Research directions:
Research directions:
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Imaging patterns of correlated states
Imaging patterns of correlated states
Pattern formation and domain configuration encode important information about correlated phases. We developed optical techniques that enable high-throughput, wide-field imaging of spatial patterns, which allows us to monitor their evolution dynamically. See here
Ultrafast space-time imaging
Ultrafast space-time imaging
Quantum materials often host excitations with exotic properties, such as dissipation-less transport, unconventional statistics, superfluidity, etc. We developed an ultrafast imaging technique to directly watch their propagation in space and time. See here
Watching fluctuations
Watching fluctuations
Thermal and quantum fluctuations are the driving force behind phase transitions. However, their stochastic nature prohibits averaging, making their direct observation challenging. We developed a fast and sensitive imaging technique and successfully captured them in real-time. See here
2D moiré superlattices
2D moiré superlattices
2D moiré superlattices combines the scalability of natural crystals and the tunability of cold atoms, providing unprecedented opportunities to engineer and investigate quantum phenomena. The sensitivity and versatility of optical spectroscopies allow us to unravel many layers of information with various techniques. See here and here
Research Highlight I:
Research Highlight I:
We observed a bosonic correlated insulator in WSe2/WS2 moiré superlattices composed of excitons, tightly bound electron-hole pairs. In our experiment, we built a novel optical pump probe technique, which is an optical counterpart of electrical capacitance measurement and distinctively different from conventional pump probe concepts. We directly obtained exciton chemical potential depending on exciton density and identified an incompressible state of exciton at filling νex = 1: the hallmark of a bosonic correlated insulator. By further varying charge density with gate, we also observed a mixed correlated insulator involving both fermionic electrons and bosonic excitons. These observations are well captured by a Bose-Fermi-Hubbard model. (Read more: Science (2023))
We observed a bosonic correlated insulator in WSe2/WS2 moiré superlattices composed of excitons, tightly bound electron-hole pairs. In our experiment, we built a novel optical pump probe technique, which is an optical counterpart of electrical capacitance measurement and distinctively different from conventional pump probe concepts. We directly obtained exciton chemical potential depending on exciton density and identified an incompressible state of exciton at filling νex = 1: the hallmark of a bosonic correlated insulator. By further varying charge density with gate, we also observed a mixed correlated insulator involving both fermionic electrons and bosonic excitons. These observations are well captured by a Bose-Fermi-Hubbard model. (Read more: Science (2023))
Research Highlight II:
Research Highlight II:
We demonstrate exciton-filling and magnetic field tunable exciton valley-pseudospin orders in a doped correlated insulator of excitons. We find evidence of an in-plane order of exciton “spin” – here, valley pseudospin – around exciton filling vex = 1, which strongly suppresses the out-of-plane “spin” polarization. Upon increasing vex or applying a small magnetic field of ~10 mT, it transitions into an out-of-plane ferromagnetic spin order that spontaneously enhances the “spin” polarization, i.e., the circular helicity of emission light is higher than the excitation. The phase diagram is qualitatively captured by a spin-1/2 Bose–Hubbard model. (Read more: Nature Communications (2024))
We demonstrate exciton-filling and magnetic field tunable exciton valley-pseudospin orders in a doped correlated insulator of excitons. We find evidence of an in-plane order of exciton “spin” – here, valley pseudospin – around exciton filling vex = 1, which strongly suppresses the out-of-plane “spin” polarization. Upon increasing vex or applying a small magnetic field of ~10 mT, it transitions into an out-of-plane ferromagnetic spin order that spontaneously enhances the “spin” polarization, i.e., the circular helicity of emission light is higher than the excitation. The phase diagram is qualitatively captured by a spin-1/2 Bose–Hubbard model. (Read more: Nature Communications (2024))
Research Highlight III:
Research Highlight III:
We describe an optical technique that sensitively and selectively detects flavor textures via the exciton response of a proximal transition metal dichalcogenide layer. Through a systematic study of rhombohedral and rotationally faulted graphene bilayers and trilayers, we show that when the semiconducting dichalcogenide is in direct contact with the graphene, the exciton response is most sensitive to the large momentum rearrangement of the Fermi surface, and thus flavor orders. The wide-field imaging capability of optical probes allows us to obtain spatial maps of flavor orders with high throughput, and with broad temperature and device compatibility. (Read more: Nature Communications (2025))
We describe an optical technique that sensitively and selectively detects flavor textures via the exciton response of a proximal transition metal dichalcogenide layer. Through a systematic study of rhombohedral and rotationally faulted graphene bilayers and trilayers, we show that when the semiconducting dichalcogenide is in direct contact with the graphene, the exciton response is most sensitive to the large momentum rearrangement of the Fermi surface, and thus flavor orders. The wide-field imaging capability of optical probes allows us to obtain spatial maps of flavor orders with high throughput, and with broad temperature and device compatibility. (Read more: Nature Communications (2025))
Research Highlight IV:
Research Highlight IV:
Combining optical flavor sensing and pump probe technique, we demonstrate long-lived isospin excitations in a broad filling range around filling ν = 2 and between ν = −3 and −2 in magic angle twist bilayer graphene. The slow dynamics indicates the existance of collective isospin modes and strong isospin fluctuations, consistent with an intervalley coherent or incommensurate Kekulé spiral ground state. Considering superconductivity is widely observed in a similar filling range of ν= −2 ~ −3, our observation also suggests isospin fluctuations as a potential pairing glue for superconductivity. Our study paves the way for understanding many-body flat-band physics and actively controlling non-equilibrium phenomena in moiré systems. (Read more: Nature (2024))
Combining optical flavor sensing and pump probe technique, we demonstrate long-lived isospin excitations in a broad filling range around filling ν = 2 and between ν = −3 and −2 in magic angle twist bilayer graphene. The slow dynamics indicates the existance of collective isospin modes and strong isospin fluctuations, consistent with an intervalley coherent or incommensurate Kekulé spiral ground state. Considering superconductivity is widely observed in a similar filling range of ν= −2 ~ −3, our observation also suggests isospin fluctuations as a potential pairing glue for superconductivity. Our study paves the way for understanding many-body flat-band physics and actively controlling non-equilibrium phenomena in moiré systems. (Read more: Nature (2024))
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