Anisotropy in the optical properties of bulk and layered transition metal dichalcogenide ReS$_{2}$

Unlike most transition metal dichalcogenides, ReS$_{2}$ in the distorted 1T$^{\prime}$ phase, is a direct gap semiconductor. We measured the temperature dependent photoluminescence in both bulk and layered ReS$_{2}$ and examined the evolution of the peaks with the number of layers. We obtained strong signatures of optical anisotropy in the absorption spectroscopy and photocurrent response which makes this material a potential candidate for optoelectronic applications. Many body calculations including electron-hole interactions as implemented in the GW+BSE approach, agrees with the strong anisotropy in the optical properties of bulk and monolayer ReS$_{2}$. A shift in the excitonic peaks by about 0.8 eV introduced by solving the Bethe-Salpeter equation indicates strong contribution from excitonic bound states in this transition metal dichalcogenide.