Interband-pairing Boosts Supercurrent Diode Effect in Multiband Superconductors, Achieving Efficiencies up to 70% and 50%

The pursuit of materials that conduct electricity without resistance, known as superconductivity, takes a significant step forward with new research into the behaviour of multiband superconductors. Jiong Mei, from the Beijing National Laboratory for Condensed Matter Physics, Shengshan Qin of the Beijing Institute of Technology, and Jiangping Hu demonstrate a mechanism that substantially boosts the supercurrent diode effect, a phenomenon where electrical current flows more easily in one direction than another, within these materials. Their work predicts that interactions between different energy bands within the superconductor, termed interband pairing, dramatically amplifies this effect, even with minimal external influence, while conventional approaches yield negligible results. By focusing on monolayer FeSe/STO, a promising material exhibiting this interband pairing, the team predicts efficiencies reaching levels suitable for high-temperature applications, and importantly, suggests that measuring this directional current flow offers a powerful new way to understand the fundamental nature of superconductivity in this material.

Josephson Diodes in Iron Superconductors

Scientists are investigating the Josephson diode effect, where electrical current flows preferentially in one direction through a superconducting junction, with a focus on iron-based superconductors, particularly monolayer FeSe. This effect, which breaks time-reversal symmetry, relies on asymmetry within the junction and is closely linked to the way electrons pair within the material. Researchers explore how different pairing states and symmetry breaking mechanisms contribute to this phenomenon. Key to understanding this effect are Josephson junctions, weak links between superconductors allowing Cooper pairs to tunnel.

Research focuses on monolayer FeSe/SrTiO3, where the interface between the two materials plays a crucial role. The substrate can induce strain and modify the electronic structure of the FeSe layer, influencing its superconducting properties. Scientists believe this system exhibits odd-parity superconductivity and the formation of pair density waves, creating an asymmetric Josephson junction and enabling a robust Josephson diode effect. Several mechanisms drive this effect, including asymmetry in the junction’s materials or geometry, the presence of odd-parity superconductivity, pair density waves, non-centrosymmetric superconductivity, strong electron-phonon coupling, and symmetry-protected states.

Multiband Superconductors Enable Strong Diode Effects

Scientists have demonstrated that multiband superconductors can significantly amplify the supercurrent diode effect, where electrical current flows preferentially in one direction. This research reveals that interband pairing, where Cooper pairs form between electrons in different energy bands, is crucial for achieving a substantial effect, even with weak spin-orbit coupling. The team focused on monolayer FeSe/STO, a material exhibiting signatures of interband pairing, to demonstrate a high-temperature platform for realizing this effect. Calculations predict diode efficiencies reaching up to 30% for d-wave pairing and 12% for η pairing in monolayer FeSe/STO, suggesting its potential as a platform for strong supercurrent diode effects. This theoretical framework provides a means to probe pairing symmetry within the material and offers critical insights into its superconducting state.

Interband Pairing Amplifies Supercurrent Diode Effect

Scientists have uncovered a mechanism enabling a robust supercurrent diode effect in Josephson junctions constructed from multiband superconductors. This work demonstrates that interband pairing significantly amplifies this effect, even with weak spin-orbit coupling, while intraband pairing alone would produce a negligible result. The research team focused on monolayer FeSe/STO, a material where recent experiments suggest the presence of interband pairing in either a nodeless d-wave or η pairing state. Using parameters derived from experimental observations, the team predicts that FeSe/STO can function as a high-temperature platform for realizing a substantial supercurrent diode effect.

Calculations reveal efficiencies reaching up to 30% for d-wave pairing and 12% for η pairing, demonstrating a strong connection between the pairing symmetry within the material and the magnitude of the supercurrent diode effect. The study establishes that measuring the supercurrent diode effect provides a powerful method for probing the pairing symmetry in monolayer FeSe/STO, offering critical insights into its superconducting state. Researchers found that the interband pairing component profoundly influences the Andreev bound states within the junction, leading to the enhanced diode efficiency. Calculations demonstrate that the interband pairing, combined with spin-orbit coupling and a Zeeman field, significantly alters the energy spectra of the system.

Interband Pairing Amplifies Supercurrent Diode Effect

This research demonstrates a mechanism for achieving a robust supercurrent diode effect in multiband superconductors, revealing that interband pairing significantly amplifies this effect even with weak spin-orbit coupling. The team predicts that materials like monolayer FeSe/STO, which exhibit both interband pairing and broken inversion symmetry, could serve as a high-temperature platform for realizing a substantial supercurrent diode effect, with efficiencies reaching up to 12% depending on the pairing state. These findings suggest that measuring the supercurrent diode effect provides a valuable method for probing the pairing symmetry within monolayer FeSe/STO, offering insights into its superconducting properties. The analysis indicates that similar effects could be observed in materials like CeRh2As2, particularly in high-field phases where odd-parity pairing and strong interband coupling are present. Future research directions include exploring the potential for a strong superconducting diode effect in monolayer FeSe/STO, building on the similarities between the supercurrent and superconducting diode effects. This work represents a significant advance in understanding and potentially harnessing non-reciprocal supercurrents in novel superconducting materials.