Anomalous Josephson coupling and high-harmonics in non-centrosymmetric superconductors with S-wave spin-triplet pairing

Abstract

We study the Josephson effects arising in junctions made of non-centrosymmetric superconductors with spin-triplet pairing having s-wave orbital-singlet symmetry. We demonstrate that the orbital dependent character of the spin-triplet order parameter determines its non-trivial texture in the momentum space due to the inversion symmetry breaking and spin-orbit interactions. The emergence of this pattern is responsible for the occurrence of an anomalous Josephson coupling and a dominance of high-harmonics in the current phase relation. Remarkably, due to the spin-orbital couplings, variations in the electronic structure across the heterostructure can generally turn the ground state of the junction from 0- to a generic value of the Josephson phase, thus realizing the so-called φ-junction. Hallmarks of the resulting Josephson behavior, apart from non-standard current-phase relation, are provided by an unconventional temperature and magnetic field dependence of the critical current. These findings indicate the path for the design of superconducting orbitronics devices and account for several observed anomalies of the supercurrent in oxide interface superconductors.

High Orbital‐Moment Cooper Pairs by Crystalline Symmetry Breaking

“…[48] For acentric multiorbital superconductors with the spin-triplet pairing involving only different orbitals, an even-parity s-wave topological phase can be achieved [49] with an intrinsic tendency to yield 0-, 𝜋-, and 𝜙-Josephson phase couplings together with dominant high-harmonics in the current phase relation. [50][51][52] Motivated by these advances in the study of superconducting orbitronics effects, in this manuscript we demonstrate how in 2D supercondutors with low crystalline symmetries Cooper pairs with equal orbital moment can be formed. In particular, we show that Cooper pairs with net orbital component and maximal orbital polarization can possess a pairing amplitude texture in momentum space due to the nontrivial phase imprinted by the combination of pairing components with equal and different orbital character.…”

“…From a general point of view, a 𝜑-junction is achieved by: i) combination of 0-and 𝜋-Josephson couplings; [46,[68][69][70][71] ii) by employing suitable parameters range and junction geometries; [72][73][74][75] or iii) by means of higher harmonics. [52,68] The use of inversion symmetry breaking in topological superconductors or at the interface of conventional superconductors can also lead to 𝜋 or 𝜑-Josephson junctions. In other words, the generation of nontrivial Josephson phase couplings typically requires either an unconven-tional type of superconductor or the use of magnetism in superconducting heterostructures.…”

“…[ 48 ] For acentric multiorbital superconductors with the spin‐triplet pairing involving only different orbitals, an even‐parity s‐wave topological phase can be achieved [ 49 ] with an intrinsic tendency to yield 0‐, π‐, and ϕ‐ Josephson phase couplings together with dominant high‐harmonics in the current phase relation. [ 50–52 ]…”

Parity-spin superconducting qubit based on topological insulators

“…More recently, qubit architectures exploiting symmetry protection have been developed, including the parity-protected qubit [27][28][29][30][31][32] and fluxonium qubit [33][34][35], aiming to realize hardware with intrinsic robustness against noise. Moreover, progress in materials science offers additional degrees of freedom, such as spin [36][37][38][39][40][41][42] and edge states [43][44][45][46][47][48][49][50][51], for controlling Josephson junctions. These capabilities create new platforms, such as gatemon [52,53], to implement symmetry-protected qubits.…”

Orbitronics effects in spin-singlet superconductors

“…14 For acentric multiorbital superconductors with inter-orbital spin-triplet pairing, an s-wave topological phase can be obtained 15 with an intrinsic tendency to yield 0-, π-, and ϕ-Josephson phase couplings together with dominant high-harmonics in the current phase relation of superconducting heterostructures. [16][17][18] Motivated by the challenges posed by the search of superconducting orbitronics effects, in this manuscript, along the line of the work in ref., 19 we demonstrate how the superconducting phase pattern in momentum space depends on the orientation of the orbital moment of the Cooper pairs and on the amplitude of its projection. The dependence of their texture on the interactions that break mirror and rotation symetries is explicitly demonstrated.…”