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Physics Seminar Date: 15th Feb, 2023 Venue: Lecture Hall 803 Time: 11 AM The Phase Puzzle of \nu = 0 Graphene and Beyond Ankur Das Weizmann Institute of Science, Israel. 15-02-23 Abstract The true ground state of ν = 0 (charge neutrality) monolayer graphene quantum Hall has long been debated. Famously the symmetry of the monolayer graphene at ν = 0 (charge neutrality) was analyzed by J. Alicea and P. A. Fisher (PRB 2006), and canted anti-ferromagnet (CAF) was predicted by I. F. Herbut (PRB 2007). However, the complete picture of the Hamiltonian was missing until the seminal paper by M. Kharitonov (PRB 2012), which predicts a phase transition from a vanilla insulator (CAF) to a topological insulator Ferromagnetic phase (F) as one changes the Zeeman energy keeping the cyclotron energy fixed. This was later confirmed in the experiment by A. F. Young et al. (Nature 2014). Motivated by recent experiments (L. He et al. PRB 2019; Ali Yazdani et al. Science 2022; B. Sacepe et al. Nature 2022), we revisit this phase diagram. We show that, generically, in the regime of interest, there is a region of coexistence between magnetic and bond orders in the phase diagram. We demonstrate this result both in continuum and lattice models and argue that the coexistence phase naturally provides an explanation for unreconciled experimental observations on the quantum Hall effect in graphene. We further extend this idea to the whole phase diagram. This opens up many questions about different possibilities and new ideas, and possible mesoscopic experimental consequences. Ref: Phys. Rev. Lett. 128, 106803, (2022); arXiv:2211.02531
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