Special Emergent Phenomena Seminar 290S/QM Seminar Speaker Yizhuang You (UCSD) Wednesday, October 6 at 11:00 am

Time/Venue Wednesday,  October 6 at 11 am ONLY VIA ZOOM (not in person) Zoom: https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09 Meeting ID: 995 2349 9113 Passcode: 600704
Host Mike Zaletel
Title
Kohn-Luttinger Superconductivity and Inter-Valley Coherence in Rhombohedral Trilayer Graphene
Abstract Motivated by recent experiments on ABC-stacked rhombohedral trilayer graphene (RTG) which observed spin-valley symmetry-breaking and superconductivity, we study instabilities of the RTG metallic state to symmetry breaking orders. We find that interactions select the inter-valley coherent order (IVC) as the preferred ordering channel over a wide range, whose theoretically determined phase boundaries agree well with experiments on both the hole and electron doped sides. The Fermi surfaces near van Hove singularities admit partial nesting between valleys, which promotes both inter-valley superconductivity and IVC fluctuations. We investigate the interplay between these fluctuations and the Hunds (intervalley spin) interaction using a renormalization group approach. For antiferromagnetic Hund’s coupling, intervalley pairing appears in the spin-singlet channel with enhanced T_c, that scales with the dimensionless coupling g as T_c\sim\exp(-1/\sqrt{g}) , compared to the standard \exp(-1/g) scaling. In its simplest form, this scenario assumes a sign change in the Hund’s coupling on increasing hole doping. On the other hand, the calculation incorporates breaking of the independent spin rotations between valleys from the start, and strongly selects spin singlet over spin triplet pairing, and naturally occurs in proximity to the IVC, consistent with observations.



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