- Letter
Off-diagonal long-range order implies vanishing charge gap
Phys. Rev. B 104, L180501 – Published 8 November, 2021
DOI: https://doi.org/10.1103/PhysRevB.104.L180501
Abstract
For a large class of quantum many-body systems with U(1) symmetry, we prove a general inequality that relates the (off-diagonal) long-range order with the charge gap. For a system of bosons or fermions on a lattice or in the continuum, the inequality implies that a ground state with off-diagonal long-range order inevitably has a vanishing charge gap, and hence is characterized by nonzero charge susceptibility. For a quantum spin system, the inequality implies that a ground state within a magnetization plateau cannot have transverse long-range order.
