Doping a moire Mott insulator: A t-J model study of twisted cuprates

We theoretically explore twisted cuprate multilayers, a moire material family where the individual layers are themselves strongly correlated. We study the twisted t-J model, using a slave-boson mean field treatment that is compatible with Mott physics at small doping. Furthermore, we incorporate the interlayer tunneling form-factor dictated by the symmetry of the Cu d(x2-y2) orbital. Including both these features leads to a phase diagram distinct from earlier weak-coupling treatments that predicted large gap spontaneous topological superconductors. Instead, we find that spontaneous time reversal (T) breaking occurs around twist angle of theta = 45 degrees, but only in a narrow window. Moreover, a nearly gapless superconductor is obtained, whose spectroscopic features parallels that in monolayer cuprates, despite the broken time reversal and reflection symmetries. At smaller theta however, driving an interlayer current can lead to a gapped topological phase. The energy-phase relation of the interlayer Josephson junction displays notable double-Cooper-pair tunneling which dominates around 45 degrees. The theta dependence of the Josephson critical current and the Shapiro steps are consistent with recent experiments. Utilizing the moire structure as a probe of correlation physics, e.g., the pair density wave state, is discussed.

Automated summary

In this study, we theoretically explored the properties of twisted cuprate multilayers, a moire material family where the individual layers are strongly correlated. We found that at a specific twist angle, spontaneous time reversal breaking occurs, leading to a nearly gapless superconductor with spectroscopic features similar to monolayer cuprates. At smaller twist angles, driving an interlayer current can result in a gapped topological phase. The energy-phase relation of the interlayer Josephson junction displayed notable double-Cooper-pair tunneling dominant at approximately 45 degrees. The results were consistent with recent experiments, and the use of the moire structure as a probe of correlation physics, such as the pair density wave state, was discussed.