phys. stat. sol. – 1 – Spin triplet superconductivity in Sr2RuO4 (original) (raw)

Spin triplet superconductivity in Sr2RuO4

physica status solidi (b), 2003

Sr 2 RuO 4 is at present the best candidate for being a superconducting analogue of the triplet superfluidity in 3 He. This material is a good (albeit correlated) Fermi liquid in the normal state and an exotic superconductor below Tc. The mechanism of superconductivity and symmetry of the order parameter are the main puzzling issues of on-going research. Here we present the results of our search for a viable description of the superconducting state realised in this material. Our calculations are based on a threedimensional effective three-band model with a realistic band structure. We have found a state with non-zero order parameter on each of the three sheets of the Fermi surface. The corresponding gap in the quasi-particle spectrum has line or point nodes on the α and β sheets and is complex with no nodes on the γ sheet. This state describes remarkably well a number of existing experiments including power low temperature dependence of the specific heat, penetration depth, thermal conductivity etc. The stability of the state with respect to disorder and different interaction parameters are also analyzed briefly.

Mechanism of Spin-Triplet Superconductivity in Sr2RuO4

Journal of the Physical Society of Japan, 2000

The unique Fermi surfaces and their nesting properties of Sr2RuO4 are considered. The existence of unconventional superconductivity is shown microscopically, for the first time, from the magnetic interactions (due to nesting) and the phonon-mediated interactions. The odd-parity superconductivity is favored in the α and β sheets of the Fermi surface, and the various superconductivities are possible in the γ sheet. There are a number of possible odd-parity gaps, which include the gaps with nodes, the breaking of time-reversal symmetry and d ẑ.

Electronic theory for superconductivity in Sr2RuO4: Triplet pairing due to spin-fluctuation exchange

EPL (Europhysics …, 2007

Using a two-dimensional Hubbard Hamiltonian for the three electronic bands crossing the Fermi level in Sr2RuO4 we calculate the band structure and spin susceptibility χ(q, ω) in quantitative agreement with nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS) experiments. The susceptibility has two peaks at Qi = (2π/3, 2π/3) due to the nesting Fermi surface properties and at qi = (0.6π, 0) due to the tendency towards ferromagnetism. Applying spin-fluctuation exchange theory as in layered cuprates we determine from χ(q, ω), electronic dispersions, and Fermi surface topology that superconductivity in Sr2RuO4 consists of triplet pairing. Combining the Fermi surface topology and the results for χ(q, ω) we can exclude s− and d−wave symmetry for the superconducting order parameter. Furthermore, within our analysis and approximations we find that f -wave symmetry is slightly favored over p-wave symmetry due to the nesting properties of the Fermi surface. 74.20.Mn, 74.25.Ha

Evaluation of Spin-Triplet Superconductivity in Sr2RuO4

Journal of the Physical Society of Japan, 2012

This review presents a summary and evaluations of the superconducting properties of the layered ruthenate Sr 2 RuO 4 as they are known in the autumn of 2011. This paper appends the main progress that has been made since the preceding review by Mackenzie and Maeno was published in 2003. Here, special focus is placed on the critical evaluation of the spin-triplet, odd-parity pairing scenario applied to Sr 2 RuO 4. After an introduction to superconductors with possible odd-parity pairing, accumulated evidence for the pairing symmetry of Sr 2 RuO 4 is examined. Then, significant recent progress on the theoretical approaches to the superconducting pairing by Coulomb repulsion is reviewed. A section is devoted to some experimental properties of Sr 2 RuO 4 that seem to defy simple explanations in terms of currently available spin-triplet scenario. The next section deals with some new developments using eutectic boundaries and micro-crystals, which reveals novel superconducting phenomena related to chiral edge states, odd-frequency pairing states, and half-fluxoid states. Some of these properties are intimately connected with the properties as a topological superconductor. The article concludes with a summary of knowledge emerged from the study of Sr 2 RuO 4 that are now more widely applied to understand the physics of other unconventional superconductors, as well as with a brief discussion of relatively unexplored but promising areas of ongoing and future studies of Sr 2 RuO 4 .

Three band model for superconductivity in Sr2RuO4

Arxiv preprint cond-mat/0105376, 2001

Abstract: We analyse the pairing symmetry of the order parameter in superconducting Sr2RuO4. Basing on a realistic three dimensional 3 band energy spectrum we have introduced effective attractive ellectron-electron interactions and found a solution which has line nodes in the gap in alpha and beta bands but not in gamma band. This state breaks time reversal symmetry and leads to the proper temperature dependence of the specific heat, in-plane penetration depth and thermal conductivity.

Normal-state and superconducting properties of Sr2RuO4

Journal of Low Temperature Physics

We discuss some of the current issues on the copper-free layered perovskite superconductor Sr2Ru04, for which a sharp transition at Tc = 1.2 K has been reproducibly obtained. The normal state is character&ed as an essentially twodimensional Fermi liquid, and the coherent interlayer transport is established only at low temperatures. The cylindrical Fermi surface observed by de Haas-van Alphen experiments is consistent with other thermodynamic and transport properties. Although the specific heat jump across Tc confirms the bulk superconductivity, the large residual T-linear term which correlates with the variation in T c is unusual and suggestive of unconventional pairing.

Superconducting order of Sr2RuO4 from a three-dimensional microscopic model

Physical Review Research, 2019

We compute and compare even-and odd-parity superconducting order parameters of strontium ruthenate (Sr2RuO4) in the limit of weak interactions, resulting from a fully microscopic threedimensional model including spin-orbit coupling. We find that odd-parity helical and even-parity dwave order are favored for smaller and larger values of the Hund's coupling parameter J, respectively. Both orders are found compatible with specific heat data and the recently-reported nuclear magnetic resonance (NMR) Knight shift drop [A. Pustogow et al. Nature 574, 72 (2019)]. The chiral p-wave order, numerically very competitive with helical order, sharply conflicts with the NMR experiment.

Spin-Triplet Superconductivity in Sr2RuO4 Probed by Andreev Reflection

Physical Review Letters, 2000

The superconducting gap function of Sr2RuO4 was investigated by means of quasiparticle reflection and transmission at the normal conductor-superconductor interface of Sr2RuO4-Pt point contacts. We found two distinctly different types of dV /dI vs V spectra either with a double-minimum structure or with a zero-bias conductance anomaly. Both types of spectra are expected in the limit of high and low transparency, respectively, of the interface barrier between a normal metal and a spin-triplet superconductor. Together with the temperature dependence of the spectra this result strongly supports a spin-triplet superconducting order parameter for Sr2RuO4. 74.70.Dd, 71.20.Lp, 73.40.Jn, 74.80.Fp

Describing Sr 2RuO 4 superconductivity in a generalized Ginzburg–Landau theory

Physics Letters A, 2009

We propose a simple explanation of unconventional thermodynamical and magnetic properties observed for Sr2RuO4. Actually, our two-phase model of superconductivity, based on a straight generalization of the Ginzburg-Landau theory, does predict two jumps in the heat capacity as well as a double curve for the dependence of the critical temperature on an external magnetic field. Such theoretical previsions well agree with the currently available experimental data for Sr2RuO4. 74.20.De; 74.70.Pq; In a recent series of papers we have succeeded in obtaining a straightforward generalizations of the original Ginzburg-Landau (GL) theory [5] in order to describe s-wave superconductors endowed with two critical temperatures, or even spin-triplet one-phase superconductors. The basic idea has been to introduce two different order parameters represented by two charged scalar fields (really only one mean field with two distinct gauge representations, see below) describing Cooper pairs with electrons bound by a weaker or stronger attractive force, respectively. The resulting theoretical model is therefore able to describe superconductors with two distinct superconducting phases, since the two order parameters condensate, in general, at different critical temperatures. Peculiar thermal and magnetic properties of these kinds of superconductors have been discussed in . Here we only mention that an additional discontinuity in the specific heat is predicted, with respect to the conventional case, when passing from a superconducting phase to the other one. Moreover, at low temperature the London penetration length for the superconductors considered is strongly reduced, and the Ginzburg-Landau parameter κ becomes a function of temperature. Instead, in temperature region between the two phase transition, κ is constant and the system behaves as a type I or a type II superconductors depending on the ratio between the two critical temperatures. Such a ratio may be as large as 4/3 [2, 3] (that is, a maximum difference of ∼ 15% between the two critical temperatures) for very large selfinteraction of the Cooper pairs with respect to the electromagnetic coupling. By allowing a suitable non-linear interaction among the two scalar fields, the same theoretical model may as well account for rotational degrees of freedom in superconductivity, that is spin-triplet superconductors with a single phase (the two mutually interacting order parameters condensate simultaneously at a same temperature). In the corresponding model, the main thermodynamical and magnetic properties of these p-wave superconductors turn out to be essentially the same as for the conventional s-wave superconductors.

Superconducting Symmetries of Sr2RuO4 from First-Principles Electronic Structure

Physical Review Letters, 2019

Although correlated electronic-structure calculations explain very well the normal state of Sr2RuO4, its superconducting symmetry is still unknown. Here we construct the spin and charge fluctuation pairing interactions based on its correlated normal state. Correlations significantly reduce ferromagnetic in favor of antiferromagnetic fluctuations and increase inter-orbital pairing. From the normal-state Eliashberg equations, we find spinsinglet d-wave pairing close to magnetic instabilities. Away from these instabilities, where charge fluctuations increase, we find two time-reversal symmetry-breaking spin-triplets: an odd-frequency s-wave, and a doublydegenerate inter-orbital pairing between dxy and (dyz, dxz).