A review of some new perspectives on the theory of superconducting Sr₂RuO₄ *

Abstract

The nature of the Cooper pairing in the paradigmatic unconventional superconductor Sr 2 RuO 4 is an outstanding puzzle in condensed matter physics. Despite the tremendous efforts made in the past twenty-seven years, neither the pairing symmetry nor the underlying pairing mechanism in this material has been understood with clear consensus. This is largely due to the lack of a superconducting order that is capable of interpreting in a coherent manner the numerous essential experimental observations. At this stage, it may be desirable to reexamine our existing theoretical descriptions of superconducting Sr 2 RuO 4 . This review focuses on several recent developments that may provide some clues for future study. We highlight three separate aspects: 1) any pairing in the E u symmetry channel, with which the widely discussed chiral p-wave is associated, shall acquire a 3D structure due to spin-orbit entanglement; 2) if the reported Kerr effect is a superconductivity-induced intrinsic bulk response, the superconductivity must either exhibit a chiral character, or be complex mixtures of certain set of helical p-wave pairings; 3) when expressed in a multiorbital basis, the Cooper pairing could acquire numerous exotic forms that are inaccessible in single-orbital descriptions. The implications of each of these new perspectives are briefly discussed in connection with selected experimental phenomena.

Topological superconductivity in Janus monolayer transition metal dichalcogenides

“…Topological superconductors (TSCs), which are characterized by a full-gap bulk and robust gapless surface (edge) states, have gained much attention for their novel topological properties in recent years. [1][2][3][4][5][6][7][8][9] Several superconductors are considered to be unconventional and even topologically nontrivial, including Sr 2 RuO 4 [10][11][12][13] and heavy fermion compounds. [14][15][16] There are also theoretical proposals for artificially realizing the topological superconducting states by using the s-wave superconductor together with spin-orbit coupling (SOC).…”

Frequency-dependent Inter-pseudospin Solutions to Superconducting Strontium Ruthenate

“…Usually, the symmetry of the SCOP of new systems is identified rather quickly. It is thus surprising that after several decades of work and recent remarkable progress of experimental probes, the symmetry of the SCOP of Sr 2 RuO 4 (SRO) has not yet been unambiguously established [3,4]. The reason is that certain measurements appear contradictory.…”