Harvard University unveils innovative approach to high-temperature superconductors

The manufacturing method can facilitate material detection.

• Harvard team led by Philip Kim creates high-temperature superconductors using copper.
• Developed the world’s first advanced superconducting diode Quantitative statistics.
• Demonstrate directional supercurrent and control of quantum states at BSCCO.

Superconductors have intrigued physicists for decades. But these materials, which allow the flow of electrons to flow perfectly and without loss, usually exhibit this peculiarity of quantum mechanics only at very low temperatures – a few degrees higher Absolute zero – To make it impractical.

A research team led by Harvard professor of physics and applied physics Philip Kim has demonstrated a new strategy for making and manipulating a widely studied class of high-temperature superconductors, called cuprates, paving the way for engineering new and unusual forms of superconductivity in places never before. It was not possible to achieve it before. Material.

Using a unique method to fabricate low-temperature devices, Kim and his team wrote their report in the journal Sciences A promising candidate for the world’s first high-temperature superconducting diode – essentially a switch that makes current flow in one direction – is made of thin copper crystals. In theory, such a device could fuel emerging industries such as quantum computing, which relies on transient mechanical phenomena that are difficult to maintain.

Graphical representation of a twisted and stacked copper superconductor, with accompanying background data. Photography: Lucy Yip, Yoshi Saito, Alex Cui, Frank Chow

“High-temperature superconducting diodes are actually possible, without the application of magnetic fields, and open new doors of research in studying exotic materials,” Kim said.

Cuprates are oxides of copper that turned the world of physics upside down decades ago by showing that they become superconducting at temperatures much higher than theorists had thought, and “higher” is a relative term (the current record for a copper superconductor is -225). F). But manipulating these materials without destroying their superconducting phases is very complex due to their complex electronic and structural properties.

The SY team’s experiments were led by Frank Zhao, a former student in the Griffin Graduate School of Arts and Sciences and now a postdoctoral researcher at Griffin. Massachusetts Institute of Technology. Using an airless cryogenic crystal processing method in high-purity argon, Zhao designed a clean interface between two extremely thin layers of copper, calcium, bismuth and strontium oxide, nicknamed BSCCO (“bisco”). BSCCO is considered a “high-temperature” superconductor because it starts superconducting at about 288 degrees Fahrenheit — very cold by practical standards, but surprisingly high among superconductors, which typically must be cooled to about -400 degrees Fahrenheit.

Zhao first divided the BSCCO into two layers, each one-thousandth the width of a human hair. Then, at -130 degrees, he stacked the two layers at a 45-degree angle, like an ice cream sandwich with the chips misaligned, while retaining the superconductivity at the brittle interface.

The team discovered that the maximum supercurrent that can pass without resistance across the interface varies with the direction of the current. Crucially, the team also demonstrated electronic control of the interfacial quantum state by reversing this polarity. It was this control that actually allowed them to make a high-temperature switchable superconducting diode, a demonstration of fundamental physics that could one day be incorporated into a piece of computing technology, such as a quantum bit.

“This is a starting point in studying topological phases, which are characterized by quantum states protected from defects,” Zhao said.

Reference: “Time Reversal Symmetry Breaking Superconductivity Between Twisted Copper Superconductors” by SY Frank Zhao, Xiaomeng Cui, Pavel A. Volkov, Hyobin Yoo, Sangmin Lee, Jules A. Gardener, Austin J. Akey, Rebecca Engelke, Yuval Ronen , Ruidan Chung, Jinda Guo, Stefan Plug, Taron Tomorrow, Myung Kim, Marcel Franz, Jedediah H. Pixley, Nicola Buccia and Philip Kim, December 7, 2023, Sciences.
doi: 10.1126/science.abl8371

The Harvard team worked with colleagues Marcel Franz of the University of British Columbia and Jed Pixley of Rutgers University, whose team had previously performed rigorous theoretical calculations. And he expected Behavior of the copper superconductor in A Wide range From torsion angles. Reconciling experimental observations also requires new theoretical developments, undertaken by Pavel A. Volkov of the University of Connecticut.

The research was supported in part by the National Science Foundation, the Department of Defense, and the Department of Energy.