Exciton condensation in quantum Hall bilayers at total filling nu(T)=5

摘要

We study the coupled quantum Hall bilayers each at half-filled first excited Landau levels by varying the layer distance. Based on numerical exact diagonalization on a torus, we identify two distinct phases separated by a critical layer distance d(c). From d(c) to an infinite layer distance, the topological phase is smoothly connected to a direct tensor product of two Moore-Read states, while interlayer coherence emerges at d < d(c) characterized by xy easy-plane ferromagnetic energy spectra, gapless pseudospin excitations, long-range current-current correlations, and finite exciton superfluid stiffness, corresponding to the exciton superfluid state. More interestingly, the results of the ground-state fidelity, the evolution of the energy spectra, and the superfluid stiffness indicate a possible continuous transition. Theoretically, it can be interpreted as a topological phase transition which simultaneously changes the topology of the ground state and breaks symmetry, providing an interesting example of transitions beyond the Landau paradigm.