Kim, Harvard, and his fellow researchers have a promising candidate for the world’s first high-temperature, superconducting diode—essentially, a switch that makes current flow in one direction—made out of thin cuprate crystals. This would be the first superconducting switch made using higher temperature cuprate superconductors instead of lower temperature and more expensive superconductors.
The team’s experiments were led by S. Y. Frank Zhao, a former student at the Griffin Graduate School of Arts and Sciences and now a postdoctoral researcher at MIT. Using an air-free, cryogenic crystal manipulation method in ultrapure argon, Zhao engineered a clean interface between two extremely thin layers of the cuprate bismuth strontium calcium copper oxide, nicknamed BSCCO.
The team discovered that the maximum supercurrent that can pass without resistance through the interface is different depending on the current’s direction. Crucially, the team also demonstrated electronic control over the interfacial quantum state by reversing this polarity.
This control was what effectively allowed them to make a switchable, high-temperature superconducting diode—a demonstration of foundational physics that could one day be incorporated into a piece of computing technology, such as a quantum bit.
Journal Science – Twisted interfaces between stacked van der Waals (vdW) cuprate crystals present a platform for engineering superconducting order parameters by adjusting stacking angles. Employing a cryogenic assembly technique, we construct twisted vdW Josephson junctions (JJ) at atomically sharp interfaces between Bi2Sr2CaCu2O8+x crystals with quality approaching the limit set by intrinsic JJ. Near 45° twist angle, we observe fractional Shapiro steps and Fraunhofer patterns, consistent with the existence of two degenerate Josephson ground states related by time-reversal symmetry (TRS). By programming the JJ current bias sequence, we controllably break TRS to place the JJ into either of the two ground states, realizing reversible Josephson diodes without external magnetic fields. Our results open a path to engineering topological devices at higher temperatures.
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