title: Soft Modes, Localization, and Two-Level Systems in Spin Glasses.
abstract: In the three-dimensional Heisenberg spin glass in a random field, we study the properties of the inherent structures that are obtained by an instantaneous cooling from infinite temperature. For a not too large field the density of states g(ω) develops localized soft plastic modes and reaches zero as ω(4) (for large fields a gap appears). When we perturb the system adding a force along the softest mode, one reaches very similar minima of the energy, separated by small barriers, that appear to be good candidates for classical two-level systems.
authors.affiliation: Departamento de Física Teórica I, Universidad Complutense, 28040 Madrid, Spain, Dipartimento di Fisica, La Sapienza Università di Roma, 00185 Roma, Italy, and Instituto de Biocomputación y Física de Sistemas Complejos (BIFI), 50009 Zaragoza, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Baity-Jesi
authors.affiliation: Departamento de Física Teórica I, Universidad Complutense, 28040 Madrid, Spain, and Instituto de Biocomputación y Física de Sistemas Complejos (BIFI), 50009 Zaragoza, Spain.
authors.forename: V
authors.initials: V
authors.lastname: Martín-Mayor
authors.affiliation: Dipartimento di Fisica, NANOTEC-CNR, Soft and Living Matter Laboratory and INFN, La Sapienza Università di Roma, 00185 Roma, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Parisi
authors.affiliation: Centro Universitario de la Defensa, Carretera de Huesca s/n, 50090 Zaragoza, Spain, and Instituto de Biocomputación y Física de Sistemas Complejos (BIFI), 50009 Zaragoza, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Perez-Gaviro
mesh_terms: D005898:Glass / Q000737:chemistry*; D008956:Models, Chemical