We successfully synthesized the BaPt$_2$As$_2$ single crystals and studied their structural and physical properties at low temperatures. BaPt$_2$As$_2$ crystallizes in the CaBe$_2$Ge$_2$-type tetragonal structure (P4/nmm) at room temperature and unde
rgoes a first-order structural transition at $T_Ssimeq 275$ K, which is likely associated with a charge-density-wave (CDW) instability. BCS-type superconductivity with two subsequent transitions at $T_{c1}=1.67$K and $T_{c2}$=1.33K are observed in this compound. Thus, BaPt$_2$As$_2$ may serve as a new system for studying the interplay of superconductivity and the CDW order.
We measure the magnetic penetration depth $Deltalambda(T)$ for NdO$_{1-x}$F$_{x}$BiS$_{2}$ ($x$ = 0.3 and 0.5) using the tunnel diode oscillator technique. The $Deltalambda(T)$ shows an upturn in the low-temperature limit which is attributed to the p
aramagnetism of Nd ions. After subtracting the paramagnetic contributions, the penetration depth $Deltalambda(T)$ follows exponential-type temperature dependence at $Tll T_c$. Both $Deltalambda(T)$ and the corresponding superfluid density $rho_s(T)$ can be described by the BCS model with an energy gap of $Delta(0)$ $approx$ 2.0 $k_BT_c$ for both $x$ = 0.3 and 0.5, suggesting strong-coupling BCS superconductivity in the presence of localized moments for NdO$_{1-x}$F$_{x}$BiS$_{2}$.
