Thermodynamic evidence for a two-component superconducting order parameter in Sr2RuO4

The symmetry of superconducting Sr2RuO4

“…While this constrains the order parameter symmetry, it still allows many possibilities. This is apparent in the conclusions of Benhabib et al 6 and Ghosh et al 5 , who propose different pairing states consistent with their data. It is conventional to describe these states using a notation akin to that of atomic orbitals, and the pertinent ones are sketched in Fig.…”

“…This allowed a measurement of its velocity, from which the c 66 modulus was calculated. In contrast, Ghosh et al 5 , observed the frequencies of the natural shape resonances of the crystal and deduced all the elastic moduli from this information. Two different experiments revealed a jump in the same c 66 modulus, which is strong evidence for a multicomponent superconducting order parameter.…”

“…However, more recent measurements 3 led to the re-examination of this conclusion, and modernized nuclear magnetic resonance experiments 4 showed that the Cooper pairs must be in a singlet state of some form, and reopened the debate about the nature of the superconductivity. Now, reporting in Nature Physics, Ghosh et al 5 and Benhabib et al 6 show ultrasound measurements that make an important step towards identifying the underlying symmetry of the Cooper pairs. In particular, they reveal that they must have at least two components -unlike the single-component singlet Cooper pair wave functions of usual superconductors.…”

Superconducting subphase and substantial Knight shift in Sr2RuO4

“…Such superposition states are worthy of future study as, in addition to possibly capturing the superconducting subphase described in this work, they may plausibly (i) yield a non-zero Kerr effect and finite orbital magnetic moment similar to those found in the chiral state 60,61 , and (ii) may resolve the contradiction of the absence of edge super-currents, as the occurrence of such currents for TRSB helical states is unclear (in contrast to the TRSB chiral state in which they are expected). Such pairing states are also interesting as degeneracies among helical states could explain the recently reported anomaly in the B 2g channel 62,63 , interpreted as x indicating multiple order parameters (which of course is also consist with chiral p-wave, or d + id pairing). Furthermore, experiments indicating possible half-flux vortices 31,32 imply a non-abelian gauge symmetry, also requiring a multiple component order parameter.…”

Spin triplet superconductors

“…因此, Sr 2 RuO 4 的超导自旋三重态配对形式受到了 很多质疑, 但是人们依然相信超导态的时间反演对称 性发生了破缺且超导能隙存在节点. 在这一背景下, 研究人员测量了超声波共振谱 [81] 及超声波传播速度 [82] 在样品中的变化, 证实了Sr 2 RuO 4 的超导序参量含有两 个组成部分, 可能的能隙方程为d+id, 甚至d+ig形式.…”