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The overarching theme of our lab is to discover novel quantum-optical phenomena by engineering light-matter and matter-matter interactions.
Light-matter interactions are central to spectroscopy, which provides us with fingerprints of physical processes in matter. We extend the concept of spectroscopy and control the behavior of electrons and atoms using light.
Matter-matter interactions determine the properties of materials. We design novel material structures to enhance the effect of these interactions, thereby achieve strong correlations and unconventional properties.
To accomplish this goal, we explore a wide range of scientific topics, including but not limited to the following:
Systems
Engineered van der Waals heterostructures
We engineer van der Waals heterostructures to obtain desired properties that are not available in nature. For example, we stack two-dimensional (2D) materials with a precise twist angle to induce moiré patterns, or we insert an atomically thin spacer layer between host layers to induce dipolar interactions.
Quantum materials in a cavity
By integrating quantum materials in photonic cavities, we manipulate light-matter interactions and light-mediated interactions between distant quantum systems. Such photonic interfaces allow us to design practical quantum-photonic devices.
Properties
Ultrafast dynamics in space, time, and energy
The natural timescale of electron motions and interactions range from femtoseconds to picoseconds. We use low-temperature transient reflectance microscopy to study the ultrafast dynamics of electrons, excitons, phonons, magnons, polarons, and polaritons in various quantum materials.
Coherent control of material properties
Coherent control of material properties using laser pulses has been a long-standing challenge. We address this by employing a series of tailored ultrafast pulses—precisely tuned in timing, polarization, frequency, and intensity—to drive phase transitions and reveal hidden nonequilibrium phases. THz pulses are particularly promising, as atomic vibrations naturally resonate at THz frequencies, allowing atoms to respond directly to THz electric fields.
Nanomechanical oscillations
We use few-layer graphene (FLG) as an ultrabroadband transducer that converts optical pulses to mechanical (phonon) pulses. These phonon pulses allow us to interrogate mechanical properties of materials (phononic spectroscopy) or to drive atoms/layers far from their equilibrium positions (nonlinear phononics).
Techniques
Ultrafast pump-probe spectroscopy
We use pump pulses to create excitations in our samples and use time-delayed probe pulses to analyze the changes induced by the pump. This approach allows us to track various physical processes over time.
Strong THz field generation & detection
THz pulses generated using the tilted-pulse-front method exhibit the unique characteristic of being close to half-cycle pulses on the 1 ps time sale. Under a peak THz field strength of 300 kV/cm, an electron accelerates and gains energy of 1 eV within the half cycle of the THz pulse, far surpassing the moiré potential depth or exciton binding energy. Such strong THz fields allow us to exert forces on electrons and overcome various energy barriers.
Exciton sensing
Excitons are highly sensitive to their surrounding environment. Both tightly bound excitons and extended Rydberg excitons can serve as sensors to detect phonons, electrons (particularly correlated electronic states), spins, magnons, and disorder. Remarkably, excitons can discern nanoscale features, despite being optically excited at the diffraction limit.
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