Low-temperature thermal conductivity of bulk and film-like rubrene single crystals

Abstract

Thermal conductivity of rubrene single crystals is measured for both bulk and film-like crystals down to 0.5 K in order to estimate the density of crystalline defects quantitatively from their phonon mean-free paths. The temperature profile of the rubrene crystals exhibit a pronounced peak at $~$ 10 K in the thermal conductivity due to very long mean-free paths of their phonons, which indicates extremely low-level defect density in the region of 10${}^{15}$--10${}^{16}$ cm${}^{\ensuremath{-}3}$ depending on different growth methods. The crystals grown from the gas phase tend to have less defects than those grown from solution. The method is applied even for micrometer-thick crystals used for field-effect transistors developed for a new membrane device for thermal-conductivity measurement of film-like samples.