Model for Unconventional Superconductivity ofSr2RuO4: Effect of Impurity Scattering on Time-Reversal Breaking Triplet Pairing with a Tiny Gap

Abstract

A model for unconventional superconductivity of Sr 2 RuO 4 is presented to resolve its puzzle. It is shown that the short-range ferromagnetic spin fluctuations give rise to the triplet pairing with p-like symmetry which is breaking the time-reversal symmetry and has a tiny gap due to the salient shape of the Fermi surface characteristic to Sr 2 RuO 4 . The effect of nonmagnetic-impurity scattering in the unitarity limit is shown to fill up easily the tiny gap giving rise to an appreciable residual density of states, which explains consistently the puzzling properties observed so far.

Charge current in ferromagnet-triplet- superconductor junctions

“…8 a,b, for the nodeless pairing states, isotropic pwave, and p-wave, proposed by K. Miyake, and O. Narikiyo, [21] respectively. The orientation of the superconductor is chosen as β = 0.…”

Hall Conductivity of a Spin-Triplet Superconductor

“…In fact, its location is ω/∆ 0 = 1 + | cos(ϕ)|. As mentioned early, the DOS illustrates a tiny gap obtained in a different context [16]. When ϕ ≃ 5π/6, the tiny (minimum) gap is about 0.3∆ 0 while the maximum gap (peak) about 1.37∆ 0 .…”

“…We also discuss the chirality [14,15] and the density of states (DOS) for these gaps. The DOS of the p-wave gap provides a mapping of ϕ onto a tiny gap [16] associated with the shape of the Fermi surface in Sr 2 RuO 4 .…”

Edge states and determination of pairing symmetry in superconductingSr2RuO4

“…[16], the pairing potential and the energy dispersion are where a is the lattice constant, and k (s) F a = 0.9πh. Substituting Eqs.…”

“…However, the power-law temperature dependences found in specific heat [9], nuclear relaxation rate [10], penetration depth [11], thermal conductivity [12], and ultrasonic attenuation [13,14] indicate nodes in the energy gap. In response to these experiments, the following alternative order parameters were proposed [15]: anisotropic p-wave [16], p-wave with horizontal lines of nodes [17], and fwaves with vertical [17,18] or horizontal lines of nodes [19]. It was also proposed that the α and β bands of Sr 2 RuO 4 are either not superconducting [20] or have horizontal lines of nodes [21].…”