Effect of Nominal Composition on Transport, Optical, Magnetic, and Thermodynamic Properties of SmS Single Crystals

Abstract

We have grown single crystals of SmS and investigated effects of nominal composition on the electrical resistivity, optical reflectivity, magnetoresistance, dc magnetization, and specific heat. We report that nominally stoichiometric and S-excess samples have an energy gap (E_g) of about 950 (±100) K while Sm-excess samples possess E_g of about 1500 (±100) K, and further that these values of E_g correlate with the lattice constant. These findings were interpreted as the chemical pressure effect. As an external magnetic field is increased, E_g monotonically decreases albeit in the nonmagnetic black phase, which can be an origin of reported negative magnetoresistance. The low-temperature specific heat under pressure shows the presence of an intrinsic γ-term in the golden phase in addition to a spurious
γ-coefficient arising from secondary phases such as Sm₃S₄.