Theory of superconductivity in a three-orbital model of Sr₂RuO₄

¹ National Laboratory of Solid State Microstructures, Nanjing University - Nanjing, 210093, China
² Theoretical Physics, University of Würzburg - D-97074 Würzburg, Germany
³ Institute for Theoretical Solid State Physics, RWTH Aachen University - D-52056 Aachen, Germany
⁴ JARA - FIT Fundamentals of Future Information Technology - Germany
⁵ Department of Physics, and Center of Theoretical and Computational Physics, The University of Hong Kong - Hong Kong, China
⁶ Department of Physics, Zhejiang University - Hangzhou, China
⁷ Institute for Theoretical Physcis, ETH Zurich - CH-8093 Zürich, Switzerland
⁸ Institut de théorie des phénomènes physiques, École Polytechnique Fédérale de Lausanne CH-1015 Lausanne, Switzerland

Received: 13 September 2013
Accepted: 13 October 2013

Abstract

In conventional and high transition temperature copper oxide and iron pnictide superconductors, the Cooper pairs all have even parity. As a rare exception, Sr₂RuO₄ is the first prime candidate for topological chiral p-wave superconductivity, which has time-reversal breaking odd-parity Cooper pairs known to exist before only in the neutral superfluid ³He. However, there are several key unresolved issues hampering the microscopic description of the unconventional superconductivity. Spin fluctuations at both large and small wave vectors are present in experiments, but how they arise and drive superconductivity is not yet clear. Spontaneous edge current is expected but not observed conclusively. Specific experiments point to highly band- and/or momentum-dependent energy gaps for quasiparticle excitations in the superconducting state. Here, by comprehensive functional renormalization group calculations with all relevant bands, we disentangle the various competing possibilities. In particular, we show the small wave vector spin fluctuations, driven by a single two-dimensional band, trigger p-wave superconductivity with quasi-nodal energy gaps.