1,032,077 research outputs found
Excited state quantum phase transitions in many-body systems
Phenomena analogous to ground state quantum phase transitions have recently
been noted to occur among states throughout the excitation spectra of certain
many-body models. These excited state phase transitions are manifested as
simultaneous singularities in the eigenvalue spectrum (including the gap or
level density), order parameters, and wave function properties. In this
article, the characteristics of excited state quantum phase transitions are
investigated. The finite-size scaling behavior is determined at the mean field
level. It is found that excited state quantum phase transitions are universal
to two-level bosonic and fermionic models with pairing interactions.Comment: LaTeX (elsart), 37 pages; to be published in Ann. Phys. (N.Y.
Weakly disordered absorbing-state phase transitions
The effects of quenched disorder on nonequilibrium phase transitions in the
directed percolation universality class are revisited. Using a strong-disorder
energy-space renormalization group, it is shown that for any amount of disorder
the critical behavior is controlled by an infinite-randomness fixed point in
the universality class of the random transverse-field Ising models. The
experimental relevance of our results are discussed.Comment: 4 pages, 2 eps figures; (v2) references and discussion on experiments
added; (v3) published version, minor typos corrected, some side discussions
dropped due to size constrain
Submillimeter-Wave Measurements and Analysis of the Ground and ν2 = 1 States of Water
In order to facilitate further studies of water in the interstellar medium, the envelopes of late-type stars, jets, and shocked regions, the frequencies of 17 newly measured H_2 ^(16)O transitions between 0.841 and 1.575 THz are reported. A complete update of the available water line frequencies and a detailed calculation of unmeasured rotational transitions and transition intensities as a function of temperature are presented for the ground and ν_2 = 1 state levels below 3000 cm^(-1) of excitation energy. The new terahertz transitions were measured with a recently developed laser difference frequency spectrometer. Six of these transitions arise from the ν_2 = 1 state, and the other 11 are in the ground state; all have lower state energies from 700 to 1750 cm^(-1) and should be accessible to Stratospheric Observatory For Infrared Astronomy (SOFIA) through the atmosphere. The transitions near 0.850 THz are accessible from the ground with existing receivers. Observations of the newly measured ν_2 = 1 state transitions, which include the 1_(1, 1)-0_(0, 0) fundamental at 1.2057 THz and five other very low J transitions, should provide valuable insights into role played by the ν2 = 1 state in the cooling dynamics of jets, shocks, masers, and strongly infrared-pumped regions. The line list is presented to assist in the planning of observational campaigns with the Far-Infrared Space Telescope (FIRST) and other proposed space missions with which a full suite of water observations can be carried out
State transitions in Polish agriculture
Poland's imminent entry into the EU re-emphasises the long-standing need for the restructuring of the country's agricultural sector and the associated re-allocation of its bloated workforce. The transition matrix of net flows derived from an annual panel of micro-data taken from the LFS confirms the impression of the stagnation that is conveyed by gross movements that are computable from the published statistics. Multinomial logit estimation of the probabilities of exit from Polish farming lend weight to the conclusion that radical policy innovations are required if many of Europe's ambitions and targets are to remain credible in the years to come.
Non equilibrium phase transitions and Floquet Kibble-Zurek scaling
We study the slow crossing of non-equilibrium quantum phase transitions in
periodically-driven systems. We explicitly consider a spin chain with a uniform
time-dependent magnetic field and focus on the Floquet state that is
adiabatically connected to the ground state of the static model. We find that
this {\it Floquet ground state} undergoes a series of quantum phase transitions
characterized by a non-trivial topology. To dinamically probe these
transitions, we propose to start with a large driving frequency and slowly
decrease it as a function of time. Combining analytical and numerical methods,
we uncover a Kibble-Zurek scaling that persists in the presence of moderate
interactions. This scaling can be used to experimentally demonstrate
non-equilibrium transitions that cannot be otherwise observed.Comment: 7 pages, 3 figures, Supplemental Material. (In this last version, the
one published in EPL, we provide a better discussion of the Floquet adiabatic
theorem, the construction of the Floquet ground state as an adiabatic
continuation and the nature of the phase transitions.
Bifurcations in the theory of current transfer to cathodes of dc discharges and observations of transitions between different modes
General scenarios of transitions between different spot patterns on
electrodes of dc gas discharges and their relation to bifurcations of
steady-state solutions are analyzed. In the case of cathodes of arc discharges,
it is shown that any transition between different modes of current transfer is
related to a bifurcation of steady-state solutions. In particular, transitions
between diffuse and spot modes on axially symmetric cathodes, frequently
observed in the experiment, represent an indication of the presence of
pitchfork or fold bifurcations of steady-state solutions. Experimental
observations of transitions on cathodes of dc glow microdischarges are analyzed
and those potentially related to bifurcations of steady-state solutions are
identified. The relevant bifurcations are investigated numerically and the
computed patterns are found to conform to those observed in the course of the
corresponding transitions in the experiment
Ground state overlap and quantum phase transitions
We present a characterization of quantum phase transitions in terms of the
the overlap function between two ground states obtained for two different
values of external parameters. On the examples of the Dicke and XY models, we
show that the regions of criticality of a system are marked by the extremal
points of the overlap and functions closely related to it. Further, we discuss
the connections between this approach and the Anderson orthogonality
catastrophe as well as with the dynamical study of the Loschmidt echo for
critical systems.Comment: 5 pages. Version to be published, title change
- …