Josephson effects in twisted cuprate bilayers
Bibliographic record
Abstract
Twisted bilayers of high-${T}_{c}$ cuprate superconductors have been argued to form topological phases with spontaneously broken time reversal symmetry $\mathcal{T}$ for certain twist angles. A key outstanding challenge is to identify unambiguous signatures of these topological phases in experiments. With this goal in mind we theoretically investigate a suite of Josephson phenomena between twisted cuprate layers. At intermediate twist angles we find an unusual nonmonotonic temperature dependence of the critical current, which we attribute to the unconventional sign structure of the $d$-wave order parameter. The onset of the $\mathcal{T}$-broken phase near the ${45}^{\ensuremath{\circ}}$ twist is marked by a crossover from the conventional $2\ensuremath{\pi}$-periodic Josephson relation $J(\ensuremath{\varphi})\ensuremath{\simeq}{J}_{c}sin\ensuremath{\varphi}$ to a $\ensuremath{\pi}$-periodic function as the single-pair tunneling becomes dominated by a second-order cotunneling process. Despite this fundamental change, the critical current remains a smooth function of the twist angle $\ensuremath{\theta}$ and temperature $T$ implying that a measurement of ${J}_{c}$ alone will not be a litmus test for the $\mathcal{T}$-broken phase. We show that clear signatures of the $\mathcal{T}$-broken phase appear when ${J}_{c}$ is measured in the presence of an applied magnetic field or radiofrequency drive: The resulting Fraunhofer oscillations acquire additional nodes and fractional Shapiro steps become visible. We discuss these results in light of recent experiments on twisted bilayers of the high-${T}_{c}$ cuprate superconductor ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".