We study transport of heat, charge, and spin in materials by using light-matter interactions. We pursue fundamental understanding of heat transport carried by microscopic carriers and seek to answer the following questions:

  • How can we tailor time and length scales of transport of microscopic heat carriers to obtain desired macroscopic properties?
  • How can we utilize heat to enhance device operations? 
  • How can we develop experimental techniques that can lead to important scientific discovery? 

I. Nanoscale thermal transport

Cooling of small electronics has become one of the critical issues that limit the device performance. The solution requires knowledge of heat transport in materials and at interfaces. We explore phonon heat transport in materials of various shapes and compositions, and heat transport by other types of thermal excitations as well.

  • Thermal transport properties of various materials (e.g., metals, inorganic, organic materials, composites) and at interfaces
  • Thermal management of small electronics

In-plane and through-plane thermal conductivity of layered 2D materials measured by time-domain thermoreflectance (TDTR)

Jang et al., Adv. Mater. 29, 1700650 (2017) link

II. Thermally-induced charge and spin dynamics

Heat can be useful to induce charge and spin dynamics, which can potentially provide new mechanisms for device operation at ultrashort time scales and with higher energy efficiency. At ultrashort time scales (10-12 seconds), heat carriers are not in thermal equilibrium. We investigate how nonequilibrium evolves in time and space and how it is coupled to charge and spin dynamics.

  • Ultrafast spin dynamics in magnetic memory
  • Nonequilibrium carrier dynamics in optoelectronic devices

Nonequilibrium between electrons (e), magnons (m), and phonons (ph) at ultrashort time scales.

Jang et al., Phys. Rev. B, 101, 064304 (2020) link
Jang et al., Phys. Rev. Appl. 13, 024007 (2020) link

III. Advanced metrology

We aim to develop metrology that allows innovative research. For example, we are looking for a thermometer that can beat the diffraction-limited resolution and have a higher sensitivity to heat flux.

  • Time-domain thermoreflectance (TDTR)
  • Time-resolved magneto-optics
  • Microscopy

Optical setup for time-domain thermoreflectance