title: Entanglement entropy of random quantum critical points in one dimension.
abstract: For quantum critical spin chains without disorder, it is known that the entanglement of a segment of N>>1 spins with the remainder is logarithmic in N with a prefactor fixed by the central charge of the associated conformal field theory. We show that for a class of strongly random quantum spin chains, the same logarithmic scaling holds for mean entanglement at criticality and defines a critical entropy equivalent to central charge in the pure case. This effective central charge is obtained for Heisenberg, XX, and quantum Ising chains using an analytic real-space renormalization-group approach believed to be asymptotically exact. For these random chains, the effective universal central charge is characteristic of a universality class and is consistent with a c-theorem.
authors.affiliation: Kavli Institute of Theoretical Physics, Santa Barbara, California 93106, USA.
authors.forename: G
authors.initials: G
authors.lastname: Refael
authors.forename: J E
authors.initials: JE
authors.lastname: Moore