Superconductivity and Physical Properties of CaPd2Ge2 Single Crystals

We present the superconducting and normal state properties of CaPd2Ge2 single crystal investigated by magnetic susceptibility \chi, isothermal magnetization M, heat capacity C_p, in-plane electrical resistivity \rho and London penetration depth \lambda versus temperature T and magnetic field H measurements. Bulk superconductivity is inferred from the \rho(T) and C_p(T) data. The \rho(T) data exhibit metallic behavior and undergoes a superconducting transition with T_c onset = 1.98 K and zero resistivity state at T_c 0 = 1.67 K. The \chi(T) reveal the onset of superconductivity at 2.0 K. For T>2.0 K, the \chi(T) and M(H) are weakly anisotropic paramagnetic with \chi_ab > \chi_c. The C_p(T) confirm the bulk superconductivity below T_c = 1.69(3) K. The superconducting state electronic heat capacity is analyzed within the framework of a single-band \alpha-model of BCS superconductivity and various normal and superconducting state parameters are estimated. Within the \alpha-model, the C_p(T) data and the ab plane \lambda(T) data consistently indicate a moderately anisotropic s-wave gap with \Delta(0)/k_B T_c ~ 1.6, somewhat smaller than the BCS value of 1.764. The relationship of the heat capacity jump at T_c and the penetration depth measurement to the anisotropy in the s-wave gap is discussed.