title: Clustering of Nonergodic Eigenstates in Quantum Spin Glasses.
abstract: The two primary categories for eigenstate phases of matter at a finite temperature are many-body localization (MBL) and the eigenstate thermalization hypothesis (ETH). We show that, in the paradigmatic quantum p-spin models of the spin-glass theory, eigenstates violate the ETH yet are not MBL either. A mobility edge, which we locate using the forward-scattering approximation and replica techniques, separates the nonergodic phase at a small transverse field from an ergodic phase at a large transverse field. The nonergodic phase is also bounded from above in temperature, by a transition in configuration-space statistics reminiscent of the clustering transition in the spin-glass theory. We show that the nonergodic eigenstates are organized in clusters which exhibit distinct magnetization patterns, as characterized by an eigenstate variant of the Edwards-Anderson order parameter.
authors.affiliation: Department of Physics, Boston University, Boston, Massachusetts 02215, USA.|Department of Physics, University of Washington, Seattle, Washington 98195, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Baldwin
authors.affiliation: Department of Physics, Boston University, Boston, Massachusetts 02215, USA.
authors.forename: C R
authors.initials: CR
authors.lastname: Laumann
authors.affiliation: Rudolf Peierls Centre for Theoretical Physics, Oxford University, Oxford OX1 3NP, United Kingdom.
authors.forename: A
authors.initials: A
authors.lastname: Pal
authors.affiliation: Abdus Salam ICTP Trieste, Strada Costiera 11, 34151 Trieste, Italy.|INFN, Sezione di Trieste, Via Valerio 2, 34127 Trieste, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Scardicchio