Superconductivity in the YIr2Si2 and LaIr2Si2 Polymorphs

TL;DR

This study reveals that YIr2Si2 and LaIr2Si2 compounds exhibit superconductivity only in their high-temperature tetragonal polymorphs, with detailed analysis of their structural, magnetic, and electronic properties.

Contribution

It demonstrates the existence of superconductivity in specific polymorphs of YIr2Si2 and LaIr2Si2 and links structural phases to superconducting behavior through experimental and theoretical analysis.

Findings

Superconductivity occurs only in the high-temperature polymorphs.

Superconducting transition temperatures are 2.52 K for YIr2Si2 and 1.24 K for LaIr2Si2.

Both polymorphs behave as Pauli paramagnets.

Abstract

We report on existence of superconductivity in YIr2Si2 and LaIr2Si2 compounds in relation to crystal structure. The two compounds crystallize in two structural polymorphs, both tetragonal. The high temperature polymorph (HTP) adopts the CaBe2Ge2-structure type (space group P4/nmm) while the low temperature polymorph (LTP) is of the ThCr2Si2 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 900C 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 Tsc (= 2.52 K in YIr2Si2 and 1.24 K in LaIr2Si2). 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.