Search for unconventional superconductors among the YTE₂Si₂compounds (TE  =  Cr, Co, Ni, Rh, Pd, Pt)

Abstract

Motivated by the recent discovery of exotic superconductivity in YFeGe we undertook reinvestigation of formation and physical properties of yttrium-based 1:2:2 silicides. Here we report on syntheses and crystal structures of the YTE Si compounds with TE = Cr, Co, Ni, Rh, Pd and Pt, and their low-temperature physical properties measurements, supplemented by results of fully relativistic full-potential local-orbital minimum basis band structure calculations. We confirm that most of the members of that family crystallize in a tetragonal ThCrSi-type structure (space group I4/mmm) and have three-dimensional Fermi surface, while only one of them (YPtSi) forms with a closely-related primitive CaBeGe-type unit cell (space group P4/nmm) and possess quasi-two-dimensional Fermi surface sheets. Physical measurements indicated that BCS-like superconductivity is observed only in YPtSi (T = 1.54 K) and YPdSi (T = 0.43 K), while no superconducting phase transition was found in other systems at least down to 0.35 K. Thermal analysis showed no polymorphism in both superconducting phases. No clear relation between the superconductivity and the crystal structure (and dimensionality of the Fermi surface) was observed.

Composition dependence of bulk superconductivity in YFe2Ge2

“…Further interest in this material derives from theoretical proposals for the superconducting state, which include s ± [3] or triplet pair wavefunctions [4] and from its striking similarities to some of the iron pnictide superconductors [8,9]. Moreover, several structurally and electronically related materials have recently been examined, some of which were found to superconduct at low temperatures [10][11][12][13], including a new iron-based superconductor, LaFeSiH [14].…”

Crystal Growth and Physical Properties of the YPd2Si2 Superconductor

“…Since our DTA analysis of polycrystalline YPd 2 Si 2 (reported in ref ) has shown that the compound forms at about 1150 °C, we considered the binary compound PdSi with melting temperature of about 900 °C as an alternative flux for synthesizing single-crystalline YPd 2 Si 2 . In the first step, high-purity elemental Pd and Si were arc-melted under protective purified-argon atmosphere to form equiatomic binary compound PdSi.…”

“…The findings reported for YFe 2 Ge 2 motivated us to perform systematic reinvestigation of other d-electron 1:2:2 silicides and germanides. − Among the compounds being studied in this project is YPd 2 Si 2 , which has been briefly mentioned in the literature as a superconductor . Also in our recent report on crystal structure and basic physical properties of Y TE 2 Si 2 systems ( TE = transition element), we have only briefly described polycrystalline samples of YPd 2 Si 2 .…”

“…The findings reported for YFe 2 Ge 2 motivated us to perform systematic reinvestigation of other d-electron 1:2:2 silicides and germanides. − Among the compounds being studied in this project is YPd 2 Si 2 , which has been briefly mentioned in the literature as a superconductor . Also in our recent report on crystal structure and basic physical properties of Y TE 2 Si 2 systems ( TE = transition element), we have only briefly described polycrystalline samples of YPd 2 Si 2 . In particular, we have analyzed results of X-ray diffraction (XRD) and differential thermal analysis (DTA), which confirmed that the system crystallizes in the tetragonal ThCr 2 Si 2 -type structure and revealed that it does not form as the CaBe 2 Ge 2 -type derivative.…”

First Principles Calculations of Superconducting Critical Temperature of ThCr$_2$Si$_2$-Type Structure

“…8), we found that both of compounds adopted the tetragonal ThCr2Si2-type structure having three-dimentional electron-like and hole-like multiband FS's as most of the same type compounds have 45,46 . Finally, the two compounds appear to be typical of superconductors mediated by phonons (BSC-type superconductor) exhibing a superconductivity at low temperature (however, it is high compared to another compounds having the same structure) and it is not required any special dimensionality of Fermi surface requiring possible nesting vector which can favor electron's pairscoming from different conduction band 47 .…”