Superconductivity and structural distortion in BaPt₂As₂

Abstract

We report the synthesis of BaPt2As2 single crystals and the discovery of superconductivity and a structural phase transition in this compound by measuring the electrical resistivity, magnetic susceptibility and specific heat as well as the x-ray diffraction at low temperatures. BaPt2As2 crystallizes in the CaBe2Ge2-type tetragonal structure (P4/nmm) at room temperature and undergoes a first-order structural transition at TS ≃ 275 K, which is likely to be associated with a charge-density-wave (CDW) instability. BCS-like superconductivity with two subsequent transitions Tc1 ≃ 1.67 K and Tc2 ≃ 1.33 K is observed. Our results demonstrate that BaPt2As2 may serve as a new system for studying the interplay of superconductivity and the CDW order.

Possibility of charge density wave transition in a SrPt2Sb2superconductor

“…This is consistent with optical conductivity results in SrPt 2 As 2 [24] and the quasi-nesting features obtained by band structure calculations in SrPt 2 As 2 [26]. The negative curvature of the electrical resistivity temperature dependence (d 2 ρ/dT 2 < 0) [24,25,20,32,27] indicates strong electron-phonon interaction [34,35,36]. These results suggest that the CDW instability originates from momentum-dependent electron-phonon coupling.…”

“…The coexistence of the CDW and superconductivity has been proposed for some of these superconductors: SrPt 2 As 2 , BaPt 2 As 2 and LaPt 2 Si 2 . In these compounds, orthorhombic distortion from the CaBe 2 Ge 2 -type tetragonal structure was observed and associated with the CDW order [19,23,24,25,20,21,32]. SrPt 2 Sb 2 showed a transition from the monoclinic to a modulated orthorhombic structure.…”

“…An increase in the electrical resistivity is caused by a decrease in the DOS at the Fermi energy and/or an increase in electron scattering by phonons. The magnetic susceptibility remains unchanged with decreasing temperature for BaPt 2 As 2 [20], whereas it decreases for LaPt 2 Si 2 [32] and increases for SrPt 2 Sb 2 . To the best of our knowledge, the magnetic susceptibility of SrPt 2 As 2 near T 0 has not been reported to date.…”

“…The coexistence of CDW and superconductivity was observed in the Pt-based 122 compounds, such as SrPt 2 As 2 [19], BaPt 2 As 2 [20], and LaPt 2 Si 2 [21]. For example, SrPt 2 As 2 exhibits superconductivity at the critical temperature T c = 5.2 K [19,22], and the CDW order at the transition temperature T 0 = 470 K [23,24,25].…”

Superconductivity in 122-Type Pnictides without Iron

“…On the other hand, SC is also observed in other 122-type compounds formulated with AT 2 Pn 2 (A = alkaline-earth or rare-earth; T = transition metals; Pn = P, As or Sb) without iron [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. It has been reported that these 122-compounds show a variety of interesting phenomena, such as SC [1], heavy fermion [26], densed Kondo behavior [27], coexistence of SC and anti-ferromagnetism (AFM)/ferromagnetism (FM) /spin-density-wave (SDW) or charge density wave (CDW) [1,13,28].…”