Large Josephson current in Weyl nodal loop semimetals due to odd-frequency superconductivity

Abstract

Weyl nodal loop semimetals (WNLs) host a closed nodal line loop Fermi surface in the bulk, protected zero-energy flat band, or drumhead, surface states, and strong spin-polarization. The large density of states of the drumhead states makes WNL semimetals exceedingly prone to electronic ordering. At the same time, the spin-polarization naively prevents conventional superconductivity due to its spin-singlet nature. Here we show the complete opposite: WNLs are extremely promising materials for superconducting Josephson junctions, entirely due to odd-frequency superconductivity. By sandwiching a WNL between two conventional superconductors we theoretically demonstrate the presence of very large Josephson currents, even up to orders of magnitude larger than for normal metals. The large currents are generated both by an efficient transformation of spin-singlet pairs into oddfrequency spin-triplet pairing by the Weyl dispersion and the drumhead states ensuring exceptionally proximity effect. As a result, WNL Josephson junctions offer unique possibilities for detecting and exploring odd-frequency superconductivity.

Thermoelectricity carried by proximity-induced odd-frequency pairing in ferromagnet/superconductor junctions

“…Later, other manifestations of odd-ω superconductivity have also been reported using scanning tunneling measurement [9] and the paramagnetic Meissner effect [23] following several theoretical predictions [24][25][26]. There also exist other proposals based on Josephson current [27,28] and Kerr effect [17] for the detection of odd-ω pairing in unconventional superconductors. In all the abovementioned work, the electron transport properties are used to identify and understand the role of odd-ω pairing.…”

Direct detection of odd-frequency superconductivity via time- and angle-resolved photoelectron fluctuation spectroscopy

“…We have further discussed the experimental feasibility of our proposal. Materials that have been suggested to host odd-frequency pairing and thus qualify as nat-ural candidates to test our proposal include doped topological insulators [26,27], Sr 2 RuO 4 [28], UPt 3 [29], superconducting Weyl semimetals [30,31], iron-pnictide superconductors [24], as well as Rashba wires on superconducting substrates [32,33].…”

Dia- and paramagnetic Meissner effect from odd-frequency pairing in multi-orbital superconductors

“…The condition to generate odd-frequency pairing in a multi-orbital superconductor [7,8] is in fact easily fulfilled as it only requires finite inter-orbital (single particle) hybridization and that the strength of the superconducting pairing is different in different orbitals, also known as a pairing asymmetry or orbital selectivity [19]. As such, many known multiband superconductors have recently been shown to host odd-frequency pairing, including doped topological insulators [9,14], Sr 2 RuO 4 [15], UPt 3 [16], and superconducting Weyl semimetals [17,24]. Based on these results, even the iron-based superconductors with orbital selective pairing [19] likely host odd-frequency pairing.…”

“…As odd-frequency pairing is intrinsically time dependent it has so far been hard to detect directly, becoming essentially a hidden dynamic order. However, for specific systems signatures of odd-frequency pairing have been found in experimentally accessible quantities, such as the existence of finite density of states at zero energy [21], Kerr effect [15,16], or Josephson current in junctions where even-frequency superconductivity becomes forbidden [17,18,22,23]. Most prominent of the odd-frequency signatures is probably however the prediction of a paramagnetic Meissner effect [25][26][27][28][29][30][31][32].…”