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 parallel ...
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 mec ...
exhibiting a
superconducting diode effect (SDE). It is an example of a
quantum material 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

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 me ...
; 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/Nb
3Br
8/NbSe
2 - a Josephson diode. This heterostructure is a quantum material Josephson junction, where the weak link (Nb
3Br
8) is a quantum material, that is predicted to be an
obstructed atomic insulator / 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 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 definit ...
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 observ ...
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 Coope ...
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