A Josephson diode is an electronic device that superconducts electrical current in one direction and is

resistive The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual parallels ...

in the other direction. The device is a

Josephson junction In physics, the Josephson effect is a phenomenon that occurs when two superconductors are placed in proximity, with some barrier or restriction between them. It is an example of a macroscopic quantum phenomenon, where the effects of quantum mech ...

exhibiting a superconducting diode effect (SDE). It is an example of a

quantum material Quantum materials is an umbrella term in condensed matter physics that encompasses all materials whose essential properties cannot be described in terms of semiclassical particles and low-level quantum mechanics. These are materials that present ...

Josephson junction (QMJJ), where the weak link in the junction is a quantum material. Josephson diodes can be subdivided into two categories, those requiring an external (magnetic) field and those not requiring an external magnetic field; the so-called “field-free” Josephson diodes. In 2021, the field-free Josephson diode was realized.

History

Schematic of Josephson diode using NbSe2 and Nb3Br8

The Josephson diode is named after British physicist

Brian David Josephson Brian David Josephson (born 4 January 1940) is a Welsh theoretical physicist and professor emeritus of physics at the University of Cambridge. Best known for his pioneering work on superconductivity and quantum tunnelling, he was awarded the Nob ...

, who predicted the

Josephson effect In physics, the Josephson effect is a phenomenon that occurs when two superconductors are placed in proximity, with some barrier or restriction between them. It is an example of a macroscopic quantum phenomenon, where the effects of quantum mech ...

; and the resistive diode, since it has a similar function. In 2007 a "Josephson diode" was proposed with a design that was similar to conventional p-n junctions in semiconductor, but utilizing hole and electron doped superconductors. This is different from the "Josephson fluxonic diode" that was introduced before the 2000s. It is also different from how the term is currently used, where a Josephson diode is a Josephson junction exhibiting a superconducting diode effect. In 2020, a superconducting diode effect was shown in an artificial b/V/Tasub>n superlattice. A field-free superconducting diode effect was realized in 2021, in a van der Waals heterostructure of NbSe₂/Nb₃Br₈/NbSe₂ - a Josephson diode. This heterostructure is a quantum material Josephson junction, where the weak link (Nb₃Br₈) is a quantum material, that is predicted to be an

obstructed atomic insulator Obstruction may refer to: Places * Obstruction Island, in Washington state * Obstruction Islands, east of New Guinea Medicine * Obstructive jaundice * Obstructive sleep apnea * Airway obstruction, a respiratory problem ** Recurrent airway obstr ...

/ Mott insulator. The conductor used in the 2020 demonstration was non-centrosymmetric which breaks spatial symmetry, meaning it distinguishes between electrons with positive and negative momentum. In addition, the 2021 system also broke temporal symmetry – allowing spin-up electrons with positive momentum to behave differently from spin-down electrons with negative momentum.

Superconducting diode effect

The superconducting diode effect is an example of nonreciprocal superconductivity, where a material is superconducting in one direction and resistive in the other. This leads to

half-wave rectification A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation (converting DC to AC) is performed by an Power ...

when a square wave AC-current is applied. In 2020, this effect was demonstrated in an artificial b/V/Tasub>n superlattice. The phenomenon in the Josephson diode is believed to originate from asymmetric Josephson tunneling.

Theories

Currently, the precise mechanism behind the Josephson diode effect is not fully understood. However, some theories have emerged that are now under theoretical investigation. There are two types of Josephson diodes, relating to which

symmetries Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definiti ...

are being broken. The

inversion Inversion or inversions may refer to: Arts * , a French gay magazine (1924/1925) * ''Inversion'' (artwork), a 2005 temporary sculpture in Houston, Texas * Inversion (music), a term with various meanings in music theory and musical set theory * ...

breaking Josephson diode and the inversion breaking plus time-reversal breaking Josephson diode. The minimal

symmetry breaking In physics, symmetry breaking is a phenomenon in which (infinitesimally) small fluctuations acting on a system crossing a critical point decide the system's fate, by determining which branch of a bifurcation is taken. To an outside observe ...

requirement for forming the Josephson diode is inversion symmetry breaking. The symmetry breaking is required to obtain nonreciprocal transport. Another proposed mechanism for short Josephson junctions, originates from finite momentum

Cooper pair In condensed matter physics, a Cooper pair or BCS pair (Bardeen–Cooper–Schrieffer pair) is a pair of electrons (or other fermions) bound together at low temperatures in a certain manner first described in 1956 by American physicist Leon Cooper ...

s. It may also be possible that the superconducting diode effect in the JD originates from self-field effects, but this still has to be rigorously studied.

References

{{reflist Diodes Josephson effect