Universal V-shaped temperature-pressure phase diagram in the iron-based superconductorsKFe2As2,RbFe2As2, and

Fazel Tafti

¹

,

A. Ouellet

²

,

A. Juneau-Fecteau

³

et al.

Abstract

We report a sudden reversal in the pressure dependence of Tc in the iron-based superconductor RbFe2As2, at a critical pressure Pc = 11 kbar. Combined with our prior results on KFe2As2 and CsFe2As2, we find a universal V-shaped phase diagram for Tc vs P in these fully hole-doped 122 materials, when measured relative to the critical point (Pc, Tc). From measurements of the upper critical field Hc2(T ) under pressure in KFe2As2 and RbFe2As2, we observe the same two-fold jump in (1/Tc)(−∂Hc2/∂T) Tc across Pc, compelling evidence for a sudden change in the structure of the superconducting gap. We argue that this change is due to a transition from one pairing state to another, with different symmetries on either side of Pc. We discuss a possible link between scattering and pairing, and a scenario where a d-wave state favoured by high-Q scattering at low pressure changes to a state with s± symmetry favoured by low-Q scattering at high pressure.

Observation of two superconducting domes under pressure in tetragonal FeS

“…46 Previously, two superconducting domes in the T-P phase diagram were reported in two other IBS systems. 37,[47][48][49][50][51] For (K/Tl/ Rb) x Fe 2-y Se 2 , the T c has a maximum value of 32 K at 1 GPa within the first dome, and a maximum T c of 48.7 K in the second dome Fig. 4 a The pressure dependence of phase contents around the structure transition, which are obtained through refinements.…”

Highly responsive ground state of PbTaSe2 : Structural phase transition and evolution of superconductivity under pressure

“…19, 22,23 Additionally, motivated by a clear signature of a structural phase transition appearing in the low temperature results discussed below, ambient pressure x-ray diffraction and transmission electron microscopy measurements at elevated temperatures were performed.…”

High-temperature superconductivity stabilized by electron-hole interband coupling in collapsed tetragonal phase ofKFe2As2under high pressure

“…In the iron superconductors, a wide versatility is found in the symmetry of the superconducting (SC) gap function, including sign-reversed full gap (s ± ) [2][3][4][5] and symmetry-imposed (d) [6] or accidental nodal states (nodal s ± ) [7,8]. These paring symmetries have indeed been considered theoretically and experimentally [9,10], and can undergo a transition from one to another by chemical substitution or pressure [8,[11][12][13]. Capturing universal traits in these symmetries is widely thought to give us the key to understanding high-temperature superconductivity in these fascinating materials.…”

“…While in (Ba,K)Fe 2 As 2 , the gap symmetry is believed to be of the fully-gapped s-wave type [5,15], in KFe 2 As 2 both symmetry-imposed [6] and accidental nodal [7,8] gap functions have been reported, which suggests a transition or crossover of SC gap function with chemical doping. In addition to chemical manipulation, recent pressure studies on KFe 2 As 2 have proposed a possible symmetry change from d-to s ± -wave state to explain the sudden reversal of T c pressure dependence at P c ∼ 2 GPa [12,13].…”

“…The enhancement (rather than suppression) of T c in SC1 can be possibly explained by the reduction in hydrostatic pressure conditions produced by the steatite powder in our DAC experiment, as compared to the previous clamp-cell experiments. While the level of hydrostaticity at low pressures is generally con- sidered good in this configuration, the sensitivity of T c in KFe 2 As 2 to uniaxial components may be susceptible to such differences and may explain the variation of T c values reported at low pressures [12,13,[16][17][18]. We can estimate the slope of T c as a function of uniaxial pressure by using the thermodynamic relation for the second-order transition, or the Ehrenfest relation [25,26],…”