{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"3bde6b2f8054b22327825eddc4640fae4706281973a9aae87f5d946b0370a540","created":"2026-10-03T07:17:59Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"0598310eed192e46c81bc84dd6c5b761257c75311b1847c9085c2fd53412ea9d","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"cm.cuprates.twisted-trsb","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"Stacking two thin flakes of the cuprate Bi2Sr2CaCu2O8+x rotated by 45 degrees is predicted to create a superconducting state whose pairs circulate in one sense, breaking time-reversal symmetry; Josephson experiments by different groups disagree.","posed_since":"2021","precise":"For c-axis Josephson junctions between Bi2Sr2CaCu2O8+x flakes twisted by $\\theta$ near 45 degrees, pure $d_{(x^2-y^2)}$ pairing makes the first-order Josephson coupling vanish, and second-order coupling is predicted to stabilize a $d + i d$ state with spontaneous time-reversal breaking (Can et al., Nature Physics 2021). Determine whether the critical current $I_c(\\theta)$ is suppressed at 45 degrees as pure d-wave requires, and whether half-integer Shapiro steps, a Josephson diode effect and spontaneous magnetization near 45 degrees arise from time-reversal breaking rather than from interface disorder or an s-wave admixture. An answer is a reproducible $I_c(\\theta)$ on junctions with characterized interfaces plus a direct probe of time-reversal breaking at 45 degrees.","problem_ref":null,"references":"","settled_by":"Independent groups measuring $I_c(\\theta)$ on atomically sharp junctions, with local magnetometry or polar Kerr detection (or exclusion) of spontaneous time-reversal breaking at $\\theta = 45\\,\\mathrm{degrees}$.","status_note":"Zhao et al. (Science 2023) reported a Josephson diode effect and half-integer Shapiro steps near 45 degrees, while Zhu et al. (PRX 2021, PRB 2023) found Josephson tunneling persisting at 45 degrees across the doping dome and attributed it to s-wave pairing.","title":"Does 45-degree twisted $\\mathrm{Bi2Sr2CaCu2O8}+x$ break time-reversal 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