KIM GROUP · POSTECH

Research

Understanding quantum materials through light.

Our research group investigates optical and electronic phenomena in low-dimensional nanoscale materials using ultrafast imaging and laser spectroscopy. We focus in particular on van der Waals (vdW) layered materials, whose atomically thin layers enable precise control of atomic structure, flexible heterostructure design, and moiré engineering. The materials include graphene, transition metal dichalcogenides, hexagonal boron nitride, black phosphorus, and their heterostructures. These unique characteristics provide an ideal platform for exploring strong Coulomb interactions, emergent quantum phenomena, and novel light–matter interactions beyond the limits of conventional semiconductors. Ultrafast laser imaging and spectroscopy, together with the development of advanced device fabrication and material synthesis techniques, form the core experimental approaches of our research.

1. Light-matter interactions in vdW quantum materials

Van der Waals quantum materials offer unprecedented control over layered structures with atomically thin and sharply defined interfaces. By engineering vdW stacking sequences and twist angles, it is possible to confine electrons within tunable atomic-scale and periodic potentials that do not exist in naturally occurring crystals. This level of structural control fundamentally reshapes light–matter interactions, enabling the enhancement and manipulation of optical processes such as light absorption, scattering, and emission. Our research seeks to uncover how these engineered electronic states interact with light at ultrafast time scales and to establish design principles for controlling optical responses in vdW quantum materials.

2. Device physics of vdW quantum materials

Novel light emission and absorption properties of vdW quantum materials opens new opportunities for transformative optoelectronic devices that go beyond the foundations of conventional semiconductor technology. vdW quantum materials enable the realization of ultrathin, highly efficient light-emitting and photodetecting devices. Moreover, their unique electronic structures allow access to new spectral regimes—from deep-ultraviolet to infrared frequencies. We fabricate optoelectronic devices based on vdW quantum materials using established semiconductor processing techniques to electrically control optical responses. In addition, we integrate nanophotonic structures, such as optical cavities, to enhance and tailor light–matter interactions at the device level.

3. In-situ ultrafast laser imaging of materials and devices

Directly observing the motion of charge carriers, excitons, ions, phonons, and atomic-scale structures in materials and operating devices provides fundamental insight into the microscopic processes that govern material properties. We develop novel in situ ultrafast laser imaging techniques that leverage key capabilities of ultrafast lasers, including wavelength tunability for resonant excitation and extremely short optical pulses, enabling real-time visualization of dynamic processes in materials and devices with high sensitivity and temporal resolution.