Sudden reversal in the pressure dependence ofTcin the iron-based superconductor CsFe2As2: A possible link between inelastic scattering and pairing symme

Abstract

We report a sudden reversal in the pressure dependence of T c in the iron-based superconductor CsFe 2 As 2 , similar to that discovered recently in KFe 2 As 2 [Tafti et al., Nat. Phys. 9, 349 (2013)]. As in KFe 2 As 2 , we observe no change in the Hall coefficient at T → 0, again ruling out a Lifshitz transition across the critical pressure P c . We interpret the T c reversal in the two materials as a phase transition from one pairing state to another, tuned by pressure, and we investigate which parameters control this transition. Comparing samples of different residual resistivity ρ 0 , we find that a sixfold increase in impurity scattering does not shift P c . From a study of x-ray diffraction on KFe 2 As 2 under pressure, we report the pressure dependence of lattice constants and As-Fe-As bond angle. The pressure dependence of the various lattice parameters suggests that P c should be significantly higher in CsFe 2 As 2 than in KFe 2 As 2 , but we find on the contrary that P c is lower in CsFe 2 As 2 , indicating that other factors control T c . Resistivity measurements under pressure reveal a change of regime across P c , suggesting a possible link between inelastic scattering and pairing symmetry.

Universal V-shaped temperature-pressure phase diagram in the iron-based superconductorsKFe2As2,RbFe2As2, andTafti1, Ouellet2, Juneau-Fecteau3 et al. 2015Phys. Rev. BSelf Cite

“…These ideas gained experimental relevance with our recent discovery of a V-shaped T -P phase diagram in KFe 2 As 2 and CsFe 2 As 2 , where T c decreases initially as a function of pressure, then at a critical pressure P c , it suddenly changes direction and increases. 5,6 Our results on KFe 2 As 2 have been reproduced by other groups. [7][8][9] We interpreted the transition at P c as a change of pairing state, possibly from d to s ± , where the decreasing T c of the former meets the growing T c of the latter at P c , resulting in a V-shaped phase diagram.…”

“…a Lifshitz transition. 5,6 We concluded that the phase transition at P c is not triggered by some change in the Fermi surface, and is instead associated with a change in the superconducting state itself. This was confirmed by quantum oscillation measurements on KFe 2 As 2 under pressure, which found a smooth evolution of the oscillation frequencies and cyclotron masses across P c .…”

“…Through the same procedure, we extracted ρ 0 and ρ(T = 20K) as a function of pressure in KFe 2 As 2 and CsFe 2 As 2 , from published data. 5,6 In Fig. 11, the inelastic resistivity ρ(T = 20K) − ρ 0 is plotted as a function of P −P c .…”

“…[6] that it takes about 30 kbar to tune the unit cell volume and the As-Fe-As bond angle of CsFe 2 As 2 to match those of KFe 2 As 2 . Therefore, if the structural parameters directly controlled P c , one would expect the critical pressure of CsFe 2 As 2 to be 30 kbar larger than that of KFe 2 As 2 .…”

Strong enhancement ofs-wave superconductivity near a quantum critical point ofCa3Ir4Sn13

“…For instance the dependence of T c on pressure for MgB 2 indicated a mediating electron-phonon coupling [35]. Recently, in Bi 2 Se 3 an anomalously saturating p dependence of T c (for p > 30.0 GPa) suggested the presence of an unconventional pressure-induced superconducting pairing state in this topological insulator [36] and pressure-induced reversal of the dependence of T c on pressure in KFe 2 As 2 indicated a pairing state transition [37]. Investigations have mainly focussed on the study of T c (p) [38].…”