Exciton diffusion in hBN-encapsulated monolayer MoSe2

Excitons, quasiparticles composed of an electron and a hole, play an important role in optical responses in low-dimensional nanostructures. In this work, we have investigated exciton diffusion in monolayer $\mathrm{Mo}{\mathrm{Se}}_{2}$ encapsulated between flakes of hexagonal boron nitride ($h\mathrm{BN}/\mathrm{MoS}{\mathrm{e}}_{2}/h\mathrm{BN}$). Through photoluminescence imaging and numerical solution of the two-dimensional diffusion equation, we revealed that temperature dependence of exciton mobility, ${\ensuremath{\mu}}_{\mathrm{ex}}$, in $h\mathrm{BN}/\mathrm{MoS}{\mathrm{e}}_{2}/h\mathrm{BN}$ shows a nonsaturating increase at low temperature, which is qualitatively different from those of quantum wells composed of compound semiconductors. The ultraflat structure of monolayer $\mathrm{Mo}{\mathrm{Se}}_{2}$ in $h\mathrm{BN}/\mathrm{MoS}{\mathrm{e}}_{2}/h\mathrm{BN}$ probably leads to the suppression of charged-impurity scattering and surface-roughness scattering.