Interorbital topological superconductivity in spin-orbit coupled superconductors with inversion symmetry breaking

Abstract

We study the superconducting state of multi-orbital spin-orbit coupled systems in the presence of an orbitally driven inversion asymmetry assuming that the inter-orbital attraction is the dominant pairing channel. Although the inversion symmetry is absent, we show that superconducting states that avoid mixing of spin-triplet and spin-singlet configurations are allowed, and remarkably, spintriplet states that are topologically nontrivial can be stabilized in a large portion of the phase diagram. The orbital-dependent spin-triplet pairing generally leads to topological superconductivity with point nodes that are protected by a nonvanishing winding number. We demonstrate that the disclosed topological phase can exhibit Lifshitz-type transitions upon different driving mechanisms and interactions, e.g., by tuning the strength of the atomic spin-orbit and inversion asymmetry couplings or by varying the doping and the amplitude of order parameter. Such distinctive signatures of the nodal phase manifest through an extraordinary reconstruction of the low-energy excitation spectra both in the bulk and at the edge of the superconductor.

Magnetoelectrically tunable Andreev bound state spectra and spin polarization in p -wave Josephson junctions

“…For instance, this is the case for the organic Bechgaard salts [88,89], the purple molybdenum bronze Li 0.9 Mo 6 O 17 [90], and more recently the Cr-based pnictide superconductors [91,92]. Moreover, we remark that the design of spinful triplet superconductivity can also rely on harnessing the orbital degrees of freedom, as it has been demonstrated for 2D electron gases [103] and multi-orbital optical-lattice systems exhibiting superfluidity [104].…”

Nanopatterning of oxide 2-dimensional electron systems using low-temperature ion milling

“…The nature of the superconducting ground state in the LAO/STO system, for example, is still not completely understood. Several theoretical [22][23][24][25] and experimental [18,26,27] works indicate an unconventional superconducting ground state for this 2DES, but a final proof of the superconducting order parameter symmetry is still lacking. A direct way to probe the order parameter symmetry would be to couple the 2DES with a conventional superconductor, as for example has been done to study the order parameter symmetry of high temperature superconductors (HTS) [28].…”

Gate-tunable pairing channels in superconducting non-centrosymmetric oxides nanowires

“…S14). Then, the π channel can be linked to both intra-orbital spin-singlet states with superconducting order parameters with opposite sign 9,18,19 or inter-orbital spin-triplet pairs 8 and can be generally stable in the presence of inhomogeneous spatial conditions as well as inversion symmetry breaking. This implies that a time-reversal invariant superconductor with local intra-orbital singlet and triplet pairs is compatible with the occurrence of independent π and φ 0 channels that are gate tunable.…”

“…Twodimensional (2D) superconductors offer new opportunities to study and tailor unconventional superconducting order parameters as they inherently lack inversion symmetry in the presence of Rashba-type spin-orbit coupling and allow large electrostatic tuning of charge carrier density and bands occupation [2][3][4][5] . The 2D electron systems in SrTiO 3 based heterostructures, such as LaAlO 3 / SrTiO 3 (LAO/STO) 6,7 , are a versatile platform for studying noncentrosymmetric multi-orbital superconductivity [8][9][10] due to the ability to modulate by electrostatic gating the superconducting critical temperature [11][12][13] together with the strength of the Rashba spin-orbit coupling 14,15 and the occupation of the Ti 3d orbitals (d xy ,d xz ,d yz ) 16,17 . Remarkably, the combination of inversion symmetry breaking and multiple orbital degrees of freedom can yield a superconducting order parameter that goes beyond the canonical singlet-triplet mixed parity, with an inter-band antiphase pairing (e.g., s +− ) 9 or pure even-parity inter-orbital spintriplet pairs 8 .…”

“…The 2D electron systems in SrTiO 3 based heterostructures, such as LaAlO 3 / SrTiO 3 (LAO/STO) 6,7 , are a versatile platform for studying noncentrosymmetric multi-orbital superconductivity [8][9][10] due to the ability to modulate by electrostatic gating the superconducting critical temperature [11][12][13] together with the strength of the Rashba spin-orbit coupling 14,15 and the occupation of the Ti 3d orbitals (d xy ,d xz ,d yz ) 16,17 . Remarkably, the combination of inversion symmetry breaking and multiple orbital degrees of freedom can yield a superconducting order parameter that goes beyond the canonical singlet-triplet mixed parity, with an inter-band antiphase pairing (e.g., s +− ) 9 or pure even-parity inter-orbital spintriplet pairs 8 . Recently, several experimental observations have been considered as a direct manifestation of an s +− pairing or as a generic indication of an unconventional type of superconductivity.…”