The first order phase transition and superconductivity in BaNi2As2 single crystals

We report the synthesis and physical properties of single crystals of stoichiometric BaNi2As2 that crystallizes in the ThCr2Si2 structure with lattice parameters a = 4.112(4) A and c = 11.54(2) A. The resistivity and heat capacity show a first order phase transition at T0 = 130 K with a thermal hysteresis of 7 K. The Hall coefficient is weakly temperature dependent from room temperature to 2 K where it has a value of -4 x 10-10 Ω cm Oe-1. The resistivity, ac susceptibility, and heat capacity provide evidence for bulk superconductivity at Tc = 0.7 K. The Sommerfeld coefficient at Tc is 11.6 ± 0.9 mJ mol-1 K-2. The upper critical field is anisotropic with initial slopes of dHc2c/dT = -0.19 T K-1 and dHc2ab/dT = -0.40 T K-1, as determined from the resistivity. (fast track communication)