Coexistence of Superconductivity and Charge Density Wave in SrPt₂As₂

Abstract

SrPt 2 As 2 is a novel arsenide superconductor, which crystallizes in the CaBe 2 Ge 2 -type structure as a different polymorphic form of the ThCr 2 Si 2 -type structure. SrPt 2 As 2 exhibits a charge-density-wave (CDW) ordering at about 470 K and enters into a superconducting state at T c ¼ 5:2 K. The coexistence of superconductivity and CDW refers to Peierls instability with a moderately strong electron-phonon interaction. Thus SrPt 2 As 2 can be viewed as a nonmagnetic analog of iron-based superconductors, such as doped BaFe 2 As 2 , in which superconductivity emerges in close proximity to spin-density-wave ordering.KEYWORDS: non-iron-based pnictide, superconductivity, charge-density wave, SrPt 2,3) BaFe 2 As 2 is the compound most studied among the iron-based families so far and is widely thought to represent the generic features of the iron-based superconductors.2,3) BaFe 2 As 2 exhibits AFM ordering below T N ¼ 140 K.4) The partial chemical substitution of either Ba, Fe, or As ions with a different element suppresses the AFM ordering and induces superconductivity.5-8) The maximum superconducting transition temperature, T c ¼ 38 K for (Ba 1Àx K x )Fe 2 As 2 , 5) is obtained near the critical concentration where AFM ordering is completely suppressed.It has been widely thought that AFM ordering in ironbased superconductors originates from the spin-densitywave (SDW) instability due to the nesting of two Fermi pockets, a hole pocket centered at the À point and an electron pocket centered at the M point, which are connected by the nesting vector Q ¼ ð; Þ.9-12) This characteristic electronic structure is believed to be a key ingredient of the high-temperature superconductivity due to AFM spin fluctuations in iron-based families. 2,3,13,14) Moreover, it has been theoretically proposed that the nesting determines the symmetry of Cooper pairs in the iron-based superconductors, in which a node locates either away from the Fermi surfaces (s AE -wave) 13,14) or directly at the Fermi surface (d-wave).14)The charge-density-wave (CDW) instability is another consequence of Fermi-surface nesting when electron-phonon interaction remains important. CDW ordering, as well as SDW ordering, competes with or coexists with superconductivity. [15][16][17][18][19][20] In this letter, we demonstrate that superconductivity at T c ¼ 5:2 K coexists with CDW in platinumbased 122 arsenide SrPt 2 As 2 . The superconducting transition temperature of SrPt 2 As 2 is considerably high compared with those of other non-iron-based 122 arsenides such as SrNi 2 As 2 (T c ¼ 0:62 K) 21) and BaNi 2 As 2 (T c ¼ 0:7 K). 22)Our observation suggests that Fermi-surface nesting is a key ingredient of the relatively high superconducting transition temperature of SrPt 2 As 2 . SrPt 2 As 2 crystallizes in a tetragonal CaBe 2 Ge 2 -type structure with the space group P4=nmm (#129), 23) as shown in Fig. 1(a). The structure is different from another polymorphic form of 122, a ThCr 2 Si 2 -type structure with the space group I4=mmm (#139), in which BaFe 2 As 2 cryst...

Electronic structure of new iron-based superconductors: From pnictides to chalcogenides and other similar systems

“…The value of density of states at the Fermi level N(E F ), obtained in our calculations is equal to 5.6 states/eV/cell. Then the coefficient of linear temperature contribution to specific heat following from the results of LDA calculations will be γ b = π 2 3 N (E F )= 13.1 mJ/mole/K 2 , which is in reasonable agreement with experimental estimates giving 9.7 mJ/mole/K 2 [8]. Let us estimate the pairing coupling constant λ in BCS expression for T c = 1.14ω D e −1/λ , using the experimental value of Debye frequency ω D .…”

“…Let us estimate the pairing coupling constant λ in BCS expression for T c = 1.14ω D e −1/λ , using the experimental value of Debye frequency ω D . For ω D =200K and T c =5.2K [8] we get for SrPt 2 As 2 λ=0.26. Then we can estimate T c for isovalent superconducting systems BaNi 2 As 2 [6] and SrNi 2 As 2 [7] with T c equal to 0.7K [6] and 0.62K [7] respectively.…”

“…such as BaNi 2 As 2 [6], SrNi 2 As 2 [7], SrPt 2 As 2 [8], SrPtAs [9]. However, these systems possess rather low superconducting transition temperature T c .…”

Evidence for two energy gaps and Fermi liquid behavior in the SrPt2As2superconductor

“…While in iron-based pnictides, the role played by antiferromagnetic spin fluctuations is largely dependent on the strength of the iron 3d electron correlation and remains controversial albeit a sign-reversing s ± gap structure and multiple energy gaps have been reported [2,3]. In this regard, it is of fundamental importance to identify the gap structure in understanding the underlying mechanism for the superconducting pairing glue.Recently, motivated by the discovery of high T c superconductivity in ThCr 2 Si 2 -type pnictides AFe 2 As 2 (where A represents alkaline-earth metals)[4], a 5d-transition metal platinum-based 122 arsenide SrPt 2 As 2 was found to be superconducting below T c ∼ 5K [5][6][7]. In contrast to other 122 Fe-based superconductors, this ironfree SrPt 2 As 2 adopts a different CaBe 2 Ge 2 -type structure.…”

Possibility of charge density wave transition in a SrPt2Sb2superconductor

“…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.…”