[18p-Z31-1~19] 17.3 層状物質

[18p-Z31-17] イジング超伝導体/2次元磁性体ジョセフソン接合における異常ジョセフソン位相

〇井土 宏¹、Kim Philip² (1.東北大AIMR、2.ハーバード大物理)

キーワード：2次元物質、ジョセフソン効果、磁気トンネル接合

When two superconductors are connected across a ferromagnet, the spin configuration of the transferred Cooper pairs can be modulated due to magnetic exchange interaction. The resulting supercurrent can reverse its sign across the magnetic Josephson junction (JJ) . The recent rise of 2D ferromagnets (F) and superconductors (S) provides an opportunity to build JJ with an atomically thin magnetic weak link formed in all crytallined junction. Here we demonstrate Josephson phase modulation in vertically stacked S-F-S van der Waals (vdW) heterostructure, employing superconducting NbSe₂ and atomically thin magnetic insulator (MI) Cr₂Ge₂Te₆. We probe the phase of MI-JJ by constructing a SQUID based on MI JJs. We demonstrate a doubly degenerate non-trivial JJ phase, formed by momentum conserving tunneling of Ising Cooper pairs across magnetic domains in the Cr₂Ge₂Te₆ barrier. The doubly degenerate ground states in MI JJs provide a two-level quantum system that can be utilized as a new dissipationless component for superconducting quantum devices, including phase batteries, memories, and quantum Ratchets.