Tuning Knob for a Superconducting Diode
Superconductivity is usually a two-way street, but certain devices superconduct in only one direction. This directionality, which goes by the name of the Josephson diode effect (JDE), can occur in several different device architectures, including some that combine topological insulators with superconducting materials. Cai-Zhen Li from the Beijing Institute of Technology and colleagues have demonstrated a topological system in which the JDE can be tuned by varying the input voltage [1]. This control could be useful in superconducting electronics and quantum circuits.
The traditional Josephson junction is a barrier between two superconductors. A zero-resistance supercurrent can flow through the junction, but only if that current is below a critical value. Above that value, the resistance becomes greater than zero. Most junctions have the same critical current in both directions, but researchers have built junctions with direction-dependent critical currents.
One way to generate a superconducting diode is to use a topological insulator (TI) as the barrier material. TI-based junctions have been investigated before, but the origin of the JDE has not been clearly determined. Li and colleagues built a junction using BiSbTeSe2, a TI that is strongly insulating in its bulk. In the presence of a 50-millitesla magnetic field, the researchers measured the critical current of their device to be around 3 microamperes (µA) in one direction and around 1.5 µA in the opposite direction. The way these critical values changed with temperature suggested that the diode effect mainly comes from surface rather than bulk states in the TI. Moreover, changing the gate voltage (which controls the carrier density within the junction) offered a way to increase the asymmetry by 10%.
–Michael Schirber
Michael Schirber is the Deputy Editor of Physics Magazine.
References
- S.-L. Wu et al., “Tunable Josephson diode effect mediated by topological surface states in BiSbTeSe2 Josephson junctions,” Phys. Rev. B 113, 155435 (2026).