2024
Jin Lab
Optical Imaging and Ultrafast Spectroscopy @ UC Santa Barbara
Recent Highlight IV:
Recent 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))
Recent Highlight III:
Recent 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: arXiv:2405.08074 (2024))
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: arXiv:2405.08074 (2024))
Recent Highlight II:
Recent 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))
Recent Highlight I:
Recent 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))
Welcome to our website!
Welcome to our website!
We develop optical spectroscopy and imaging techniques to "watch" quantum phenomena in space and time. Our current research interests lie in the interplay between dimensionality, many-body interaction, fluctuations, and competing orders. Examples include two-dimensional (2D) materials, moiré superlattices, spin systems, strongly correlated materials, topological systems, and their combinations.
We develop optical spectroscopy and imaging techniques to "watch" quantum phenomena in space and time. Our current research interests lie in the interplay between dimensionality, many-body interaction, fluctuations, and competing orders. Examples include two-dimensional (2D) materials, moiré superlattices, spin systems, strongly correlated materials, topological systems, and their combinations.