研究者たちが高温超伝導体を作る新しい方法を編み出す(Researchers Craft New Way to Make High-Temperature Superconductors – With a Twist)

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2024-01-30 ラトガース大学

◆ルトガース大学の科学者らが含まれる国際チームが、広く研究されている高温超伝導体のクラスを作り出し、操作する新しい方法を開発しました。この技術は、以前には得られなかった材料で異常な形態の超伝導を創造する道を開くもので、冷却されると臨界温度で超伝導体は抵抗やエネルギー損失なしに電気を伝導できます。
◆この研究は、理論的な計算から生まれた実験で、ペンシルベニア州立大学のJedediah Pixley准教授率いる研究チームによるもので、PixleyとPavel Volkovによる予測が確認されました。これにより、高温超伝導デバイスの設計において、異なる形態の超伝導が生じる可能性があり、将来的には効率的な電力グリッドやエネルギー効率の高いコンピュータチップ、さらには量子コンピュータが新しい種類の超伝導材料で駆動される世界を想像しています。

<関連情報>

ねじれた銅酸化物超伝導体の間で時間反転対称性を破る超伝導が起こる Time-reversal symmetry breaking superconductivity between twisted cuprate superconductors

S. Y. FRANK ZHAO , XIAOMENG CUI , PAVEL A. VOLKOV , HYOBIN YOO , […], AND PHILIP KIM
Science  Published:7 Dec 2023
DOI:https://doi.org/10.1126/science.abl8371

Editor’s summary

Twisted two-dimensional (2D) structures exhibit a wealth of interesting behaviors. Recently, the 2D materials used in such superlattices have largely been graphene and various transition metal dichalcogenides. However, cuprate superconductors can also be thought of as 2D materials, with the copper-oxide planes coupled to each other through Josephson coupling. Zhao et al. created high-quality twisted structures of a bismuth-based cuprate by cleaving a single exfoliated crystal and placing the two halves on top of each other at various angles. Near the twist angle of 45°, Josephson coupling was suppressed by the d-wave superconducting order parameter of the material. The researchers also observed a Josephson diode effect caused by the breaking of time reversal symmetry. —Jelena Stajic

Abstract

Twisted interfaces between stacked van der Waals (vdW) cuprate crystals present a platform for engineering superconducting order parameters by adjusting stacking angles. Using a cryogenic assembly technique, we construct twisted vdW Josephson junctions (JJs) at atomically sharp interfaces between Bi2Sr2CaCu2O8+x crystals, with quality approaching the limit set by intrinsic JJs. 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.

1700応用理学一般
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