Using equilibrium and nonequilibrium molecular dynamics simulations, we determine the Kapitza resistance (or thermal contact resistance) at a model liquid solid interface. The Kapitza resistance (or the associated Kapitza length) can reach appreciable values when the liquid does not wet the solid. The analogy with the hydrodynamic slip length is discussed.

Dipolar excitons offer a rich playground for both design of novel optoelectronic devices and fundamental many-body physics. Wide GaN/(AlGa)N quantum wells host a new and promising realization of dipolar excitons. We demonstrate the inplane confinement and cooling of these excitons, when trapped in the electrostatic potential created by semitransparent electrodes of various shapes deposited on the sample surface. This result is a prerequisite for the electrical control of the exciton densities and fluxes, as well for studies of the complex phase diagram of these dipolar bosons at low temperature. Keywords exciton fluid, electrostatic traps, cooling, gallium nitride Dipolar excitons, Coulomb-bound but spatially separated electron-hole pairs, have a long life-time and a built-in dipole moment that offer an opportunity for the cooling and electrical 1 arXiv:1902.02974v1 [physics.app-ph] 8 Feb 2019 control of exciton fluids. 1-7 Various intriguing quantum phenomena including Bose-Einsteinlike condensation, darkening and superfluidity of excitons have been recently reported. 8-15Albeit demonstrated at very low temperatures, those phenomena are promising for better understanding of new states of matter, but also for potential applications in excitonic devices with novel functionalities. 7The recent emergence of high quality wide-bandgap semiconductor quantum wells (QWs) and two-dimensional Van der Waals heterostructures, hosting dipolar excitons with large exciton binding energies and built-in electric fields, has given a new impetus to this research. [16][17][18][19][20] Room temperature exciton transport in GaN/(AlGa)N QWs has been demonstrated, 17 as well as its electrical control in MoS 2 −WSe 2 heterostructures. 20 The latter is

The Mott transition from a dipolar excitonic to an electron-hole plasma state is demonstrated in a wide GaN/(Al,Ga)N quantum well at T = 7 K by means of spatially resolved magnetophotoluminescence spectroscopy. Increasing optical excitation density, we drive the system from the excitonic state, characterized by a diamagnetic behavior and thus a quadratic energy dependence on the magnetic field, to the unbound electron-hole state, characterized by a linear shift of the emission energy with the magnetic field. The complexity of the system requires taking into account both the density dependence of the exciton binding energy and the exciton-exciton interaction and correlation energy that are of the same order of magnitude. We estimate the carrier density at Mott transition as n Mott ≈ 2 × 10 11 cm −2 and address the role played by excitonic correlations in this process. Our results strongly rely on the spatial resolution of the photoluminescence and the assessment of the carrier transport. We show that in contrast to GaAs/(Al,Ga)As systems, where transport of dipolar magnetoexcitons is strongly quenched by the magnetic field due to exciton mass enhancement, in GaN/(Al,Ga)N the band parameters are such that the transport is preserved up to 9 T.