4,072 research outputs found
Instability of many-body localized systems as a phase transition in a nonstandard thermodynamic limit
The many-body localization (MBL) phase transition is not a conventional
thermodynamic phase transition. Thus to define the phase transition one should
allow the possibility of taking the limit of an infinite system in a way that
is not the conventional thermodynamic limit. We explore this for the so-called
"avalanche" instability due to rare thermalizing regions in the MBL phase for
quenched-random systems in more than one spatial dimension, finding an
unconventional way of scaling the systems so that they do have a type of phase
transition. These arguments suggest that the MBL phase transition in systems
with short-range interactions in more than one dimension is a transition where
entanglement in the eigenstates begins to spread in to some typical regions:
the transition is set by when the avalanches start. Once this entanglement gets
started, the system does thermalize. From this point of view, the much-studied
case of one-dimensional MBL with short-range interactions is a special case
with a different, and in some ways more conventional, type of phase transition.Comment: 10 pages, 2 figure
Spin-catalyzed hopping conductivity in disordered strongly interacting quantum wires
In one-dimensional electronic systems with strong repulsive interactions,
charge excitations propagate much faster than spin excitations. Such systems
therefore have an intermediate temperature range [termed the "spin-incoherent
Luttinger liquid'" (SILL) regime] where charge excitations are "cold" (i.e.,
have low entropy) whereas spin excitations are "hot." We explore the effects of
charge-sector disorder in the SILL regime in the absence of external sources of
equilibration. We argue that the disorder localizes all charge-sector
excitations; however, spin excitations are protected against full localization,
and act as a heat bath facilitating charge and energy transport on
asymptotically long timescales. The charge, spin, and energy conductivities are
widely separated from one another. The dominant carriers of energy are neither
charge nor spin excitations, but neutral "phonon" modes, which undergo an
unconventional form of hopping transport that we discuss. We comment on the
applicability of these ideas to experiments and numerical simulations.Comment: 14 pages, 6 figure
Convergence rates of the DPG method with reduced test space degree
This paper presents a duality theorem of the Aubin-Nitsche type for
discontinuous Petrov Galerkin (DPG) methods. This explains the numerically
observed higher convergence rates in weaker norms. Considering the specific
example of the mild-weak (or primal) DPG method for the Laplace equation, two
further results are obtained. First, the DPG method continues to be solvable
even when the test space degree is reduced, provided it is odd. Second, a
non-conforming method of analysis is developed to explain the numerically
observed convergence rates for a test space of reduced degree
Evaluation of Waterhyacinth and Paddy Straw Waste for Culture of Oyster Mushrooms
Waterhyacinth (
Eichhornia crassipes
(Mart.) Solms.) was
evaluated at ratios of 25, 50 and 75% with paddy straw (
Oryza
sativa
L.) for oyster mushroom (
Pleurotus sajor-caju)
cultivation.
There was an increase in yield with decreasing ratio
waterhyacinth
Grain orientation in high Tc superconductors by molten salt powder synthesis
The molten salt or the flux method is used to fabricate a grain oriented YBa2Cu3O(7-x) (123) superconductor. Here we suggest a two-stage approach in using the 'green phase', Y2BaCuO5 (211), as seed crystals in the formation of YBa2Cu3O(7-x). The process uses Y2BaCuO5 formed by molten salt synthesis. The Y2BaCuO5 phase was observed to be stable in water and in most of the salt systems. Salt processing can form a small quantity of anisotropic particles of Y2BaCuO5. This material can form the 123 phase when tape cast and sintered in the presence of the required levels of Ba and Cu
Weak crystallization theory of metallic alloys
We extend the Weak Crystallization theory to the case of metallic alloys. The
additional ingredient -- itinerant electrons -- generates nontrivial dependence
of free energy on the angles between ordering wave vectors of ionic density.
That leads to stabilization of FCC, Rhombohedral, and icosahedral
quasicrystalline (iQC) phases, which are absent in the generic theory with only
local interactions. The condition for stability of iQC that we find, is
consistent with the Hume-Rothery rules known empirically for majority of stable
iQC; namely, the length of the primary Bragg peak wavevector is approximately
equal to the diameter of the Fermi surface.Comment: 10 pages, 5 figure
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
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