Superconducting subphase and substantial Knight shift in Sr2RuO4

Abstract

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Distinguishing dxz+idyz and dx2−<

“…In conjunction with our previous finding [17] of a different high field phase diagram structure for helical pairing, the phase structure of the Pauli limiting regime would appear to represent a path to distinguish pairing symmetries in this material. While such upper and lower critical field phase lines have been observed in a number of previous experimental works [22,28,29], they have been found to be sensitive to disorder, with lower mean field path (i.e.…”

“…With p-wave pairing perhaps ruled out [9,15,16], as both chiral or helical pairing types appear not to be able to capture the very strong (∼ 80%) suppression of the Knight shift [17,18], attention has turned to even parity d-wave pairing [11,12,19]. The most natural d-wave candidates are the TRS breaking chiral d xz + id yz (E g ) and TRS preserving d x 2 −y 2 (B 1g ) order parameters.…”

“…One of the most fundamental properties of any material is its phase diagram: the structure of the phase boundaries, the nature of the transitions across them, and how they connect via multicritical points. The temperature-magnetic field phase diagram of Sr 2 RuO 4 has a well characterized bicritical point at T = 0.8 K and H = 1.2 Tesla at which the low field second order transition goes over to a first order Pauli limiting transition [17,[22][23][24][25][26][27]. Employing a realistic threedimensional tight-binding model that very well captures the normal state electronic structure, we explore the H-T phase diagram for the two even parity d-wave pairing types d xz + id yz and d x 2 −y 2 .…”

Possibility of mixed helical p-wave pairings in Sr$_2$RuO$_4$

“…We also discussed how these states may be compatible with several other key measurements. In addition, as shown in a recent study [64], the helical state may also explain the Pauli limiting behavior of the inplane H c2 and the first order phase transition observed in the H − T phase diagram at low T and at H near H c2 [65,67]. The most serious challenge for our proposal is probably the substantial Knight shift drop observed.…”

Superconducting Pairing Mechanism of Sr$_2$RuO$_4$

“…Very recently, ultrasound experiment reported a thermodynamic discontinuity in the shear elastic modulus c 66 and put further constraint on the pairing symmetry [20,21]. Candidate proposals of two-component TRSB order parameters include d x 2 −y 2 + ig [22,23], s + id x 2 −y 2 [24], s + id xy [25], chiral or helical or mixed p-wave [4,[26][27][28][29][30][31][32][33][34], d xz +id yz [35], and exotic interorbital pairings [36][37][38][39][40][41]. Among them, d xz + id yz and d x 2 −y 2 + ig can satisfy the ultrasound requirement.…”