125,679 research outputs found
Spectral features of a many-body localized system weakly coupled to a heat bath
We study many-body-localized (MBL) systems that are weakly coupled to
thermalizing environments, focusing on the spectral functions of local
operators. We argue that these spectral functions carry signatures of
localization even away from the limit of perfectly isolated systems. We find
that, in the limit of vanishing coupling to a bath, MBL systems come in two
varieties, with either discrete or continuous local spectra. Both varieties of
MBL systems exhibit a "soft gap" at zero frequency in the spatially-averaged
spectral functions of local operators, which serves as a diagnostic for
localization. We estimate the degree to which coupling to a bath broadens these
spectral features, and find that characteristics of incipient localization
survive as long as the system-bath coupling is much weaker than the
characteristic energy scales of the system. Since perfect isolation is
impossible, we expect the ideas discussed in this paper to be relevant for all
experiments on many-body localization.Comment: Expanded discussion of multiple lengthscales and of properties as a
quantum memor
A Unified Description of Cuprate and Iron Arsenide Superconductors
We propose a unified description of cuprate and iron-based superconductivity.
Consistency with magnetic structure inferred from neutron scattering implies
significant constraints on the symmetry of the pairing gap for the iron-based
superconductors. We find that this unification requires the orbital pairing
formfactors for the iron arsenides to differ fundamentally from those for
cuprates at the microscopic level.Comment: 12 pages, 10 figures, 2 table
SU(4) Model of High-Temperature Superconductivity: Manifestation of Dynamical Symmetry in Cuprates
The mechanism that leads to high-temperature superconductivity in cuprates
remains an open question despite intense study for nearly two decades. Here, we
introduce an SU(4) model for cuprate systems having many similarities to
dynamical symmetries known to play an important role in nuclear structure
physics and in elementary particle physics. Analytical solutions in three
dynamical symmetry limits of this model are found: an SO(4) limit associated
with antiferromagnetic order; an SU(2) limit that may be interpreted as a
d-wave pairing condensate; and an SO(5) limit that may be interpreted as a
doorway state between the antiferromagnetic order and the superconducting
order. It is demonstrated that with a slightly broken SO(5) but under
constraint of the parent SU(4) symmetry, the model is capable of describing the
rich physics that is crucial in explaining why cuprate systems that are
antiferromagnetic Mott insulators at half filling become superconductors
through hole doping.Comment: 16 pages, 4 figures, proceedings of "Nuclei and Mesoscopic Physics"
to be published by AI
Pairing in the Framework of the Unitary Correlation Operator Method (UCOM): Hartree-Fock-Bogoliubov Calculations
In this first in a series of articles, we apply effective interactions
derived by the Unitary Correlation Operator Method (UCOM) to the description of
open-shell nuclei, using a self-consistent Hartree-Fock-Bogoliubov framework to
account for pairing correlations. To disentangle the particle-hole and
particle-particle channels and assess the pairing properties of \VUCOM, we
consider hybrid calculations using the phenomenological Gogny D1S interaction
to derive the particle-hole mean field. In the main part of this article, we
perform calculations of the tin isotopic chain using \VUCOM in both the
particle-hole and particle-particle channels. We study the interplay of both
channels, and discuss the impact of non-central and non-local terms in
realistic interactions as well as the frequently used restriction of pairing
interactions to the partial wave. The treatment of the center-of-mass
motion and its effect on theoretical pairing gaps is assessed independently of
the used interactions.Comment: 14 pages, 10 figures, to appear in Phys. Rev. C, title modified
accordingl
Dispersive regime of the Jaynes-Cummings and Rabi lattice
Photon-based strongly-correlated lattice models like the Jaynes-Cummings and
Rabi lattices differ from their more conventional relatives like the
Bose-Hubbard model by the presence of an additional tunable parameter: the
frequency detuning between the pseudo-spin degree of freedom and the harmonic
mode frequency on each site. Whenever this detuning is large compared to
relevant coupling strengths, the system is said to be in the dispersive regime.
The physics of this regime is well-understood at the level of a single
Jaynes-Cummings or Rabi site. Here, we extend the theoretical description of
the dispersive regime to lattices with many sites, for both strong and
ultra-strong coupling. We discuss the nature and spatial range of the resulting
qubit-qubit and photon-photon coupling, demonstrate the emergence of photon-
pairing and squeezing, and illustrate our results by exact diagonalization of
the Rabi dimer.Comment: 22 pages, 7 figures, 1 table, Published by NJP, Focus Issues "Focus
on Quantum Microwave Field Effects in Superconducting Circuits
- …