1205.6667 (Michal Vališka et al.)

Superconductivity in the YIr$_{2}$Si$_{2}$ and
LaIr$_{2}$Si$_{2}$Polymorphs    [PDF]

Michal Vališka, Jiří Pospíšil, Jan Prokleška, Martin Diviš, Alexandra Rudajevová, Vladimír Sechovský

We report on existence of superconductivity in YIr$_{2}$Si$_{2}$ and LaIr$_{2}$Si$_{2}$ compounds in relation to crystal structure. The two compounds crystallize in two structural polymorphs, both tetragonal. The high temperature polymorph (HTP) adopts the CaBe$_{2}$Ge$_{2}$-structure type (space group P4/nmm) while the low temperature polymorph (LTP) is of the ThCr$_{2}$Si$_{2}$ type (I4/mmm). By studying polycrystals prepared by arc melting we have observed that the rapidly cooled samples retain the HTP even at room temperature (RT) and below. Annealing such samples at $\geq900^{\circ}\unit{C}$ followed by slow cooling to RT provides the LTP. Both, the HTP and LTP were subsequently studied with respect to magnetism and superconductivity by electrical resistivity, magnetization, AC susceptibility and specific heat measurements. The HTP and LTP of both compounds respectively, behave as Pauli paramagnets. Superconductivity has been found exclusively in the HTP of both compounds below $\mathrm{T_{SC}}$ (= 2.52 K in YIr$_{2}$Si$_{2}$ and 1.24 K in LaIr$_{2}$Si$_{2}$). The relations of magnetism and superconductivity with the electronic and crystal structure are discussed with comparing experimental data with the results of first principles electronic structure calculations.

View original: http://arxiv.org/abs/1205.6667