Relaxation dynamics of photoexcited carriers in hBN-encapsulated graphene*

Relaxation of photo-excited carriers is a key dynamic process to reveal coupling between electrons, phonons, and impurities in condensed matter systems. In monolayer graphene, a 'phonon bottleneck' limits efficient cooling when the electrons are cooled to a certain temperature, and 'supercollision' dominates the further cooling process. While this hypothesis is supported by experiments on low-quality graphene on SiO2 substrate, charge dynamics in high-quality hBN-encapsulated graphene has not been explored much. In this talk, I will report on our temperature-dependent near-infrared pump mid-infrared probe measurement of hBN-encapsulated monolayer graphene. We observed a significantly longer lifetime of photo-excited carriers than shown before. I will discuss its implications on scattering mechanisms involving different degrees of freedom in this system.