Research
Research
We are interested in probing and controlling light-matter interaction in the low-dimensional quantum material heterostructures using ultrafast optical microscopy. Over the past few years, we have developed various ultrafast nonlinear optical microscopic techniques and established the significance of ultrafast optical spectroscopy in revealing the unique quantum dynamics in various low-dimensional systems, such as semiconducting nanowires, organic molecules, and atomically thin quantum materials. Recently, the ability to isolate the materials into atomically thin layer in various van der Waals materials, such as graphene and transition metal dichalcogenides (TMD), has provided a unique platform to explore various light-driven quantum phenomena in a custom-tailored quantum system - the van der Waals heterostructures - with unprecedented flexibility and control. This enables the design and creation of functional 2D heterostructures that combine extremely different properties, something that is not possible in other conventional material systems. Our research focus on both fundamental quantum science research and development of nanoscale quantum technology through investigating:
1. Exciton Physics: Strong confinement of electronic wavefunction in atomically thin 2D materials greatly enhances the Coulomb correlation, giving rise to the formation of strongly bound exciton, trion and biexciton quasi-particles that govern the optical transition. Such strong interaction even breaks-down the optical selection rules based on non-interacting exciton picture, opens up new windows for the coherent manipulation of quantum states using light. We are interested to develop ultrafast nonlinear optical spectroscopy to explore the novel exciton physics emerge from the combination of van der Waals stacking, prominent Coulomb-correlation, and wavefunction engineering.
Biexcitonic Optical Stark Effects in Monolayer Molybdenum Diselenide Nature Physics (2018) Link
Valley-Dependent Exciton Fine Structure and Autler-Townes Doublets from Berry Phases in Monolayer MoSe2 Nature Materials (2019) Link
2. Many-body interactions: Quantum particles with competing long-range interactions are ubiquitous in physics, giving rise to rich quantum many-body ground states that challenge theory. For example, the competing electron-electron and electron-phonon interactions govern the formation of charge-density wave (CDW), superconductivity, Mott insulator, Wigner crystal and moiré exciton. Atomically thin 2D heterostructure provide a unique platform to explore the intriguing quantum states of matters arise from such long-range interactions. In-particular, the ability to control the orbital overlap at the proximity of 2D heterostructure opens up rich possibilities to engineer the correlation energy. However, the ability to simultaneously probe and control the dynamics of these interactions are challenging and calls for novel spectroscopic technique. We aim to improve the sample quality and develop optical measurements to reveal the unique quantum states of matters arise from twisting the atomic interface of 2D heterostructures.
Proximity control of the interlayer exciton-phonon hybridization in van der Waals heterostructures Nature Communications (2021) Link
Twist-tailoring Coulomb correlation in van der Waals homobilayers
Nature Communications (2020) Link
3. Ultrafast manipulation of quantum states of matters: The combination of prominent light-matter interaction, spin-orbit coupling and strong confinement of electronic wavefunctions in 2D heterostructure provide a unique platform to realize all-optical manipulation of electronic states, spin, valley, phonon and their interplays in the system, with application relevant to the quantum computing and information processing. We aim to advance the ultrafast nonlinear optical microscopy based on phase-locked femtosecond laser pulses to explore the coherent control of quantum states of matters, paving way to realize the ultimate limits of electron dynamics in the quantum devices.
Valley-Dependent Exciton Fine Structure and Autler-Townes Doublets from Berry Phases in Monolayer MoSe2 Nature Materials (2019) Link
4. Light-induced quantum phase transitions: By advancing the ultrafast THz spectroscopy, we aim to understand and control the microscopic interplay between elementary degrees of freedom that govern the quantum phase transitions in atomically thin quantum materials. In-particular, as the material thicknesses are reduced to single atomic layer, the interplays among electronic wavefunction, lattice, and environments can give rise to various quantum ground states. Even more exciting is the ability to quantum design the system through the highly flexible interlayer proximity control, electrostatic doping and moiré superlattice engineering. We are interested to explore the novel light-induced quantum phase transition and novel electron dynamics in these systems using intense fs-laser pulses.
Proximity control of the interlayer exciton-phonon hybridization in van der Waals heterostructures Nature Communications (2021) Link
As the essential toolbox, our laboratory develops ultrafast optical microscopy based on highly-intense ultrashort laser pulses with energy spans from visible to THz. Similarly, to an extremely slow-motion camera, our approaches enable the simultaneous observation and control of the elementary quantum dynamics on the femtosecond timescale (1fs = 10-15s), providing new physical insights on the properties of quantum materials stroboscopically that are otherwise impossible using other techniques. Exploiting the quantum physics and optical phenomena in the atomically thin 2D material heterostructures provide exciting pathways to implement these materials as building blocks in quantum optoelectronics, quantum computing and quantum information technology.