15,664 research outputs found
Signatures of a Noise-Induced Quantum Phase Transition in a Mesoscopic Metal Ring
We study a mesoscopic ring with an in-line quantum dot threaded by an
Aharonov-Bohm flux. Zero-point fluctuations of the electromagnetic environment
capacitively coupled to the ring, with spectral density, can
suppress tunneling through the dot, resulting in a quantum phase transition
from an unpolarized to a polarized phase. We show that robust signatures of
such a transition can be found in the response of the persistent current in the
ring to the external flux as well as to the bias between the dot and the arm.
Particular attention is paid to the experimentally relevant cases of ohmic
() and subohmic () noise.Comment: 4 pages, 4 figures, realistic parameters estimated, reference update
Magneto-structural coupling and harmonic lattice dynamics in CaFeAs probed by M\"ossbauer spectroscopy
In this paper we present detailed M\"ossbauer spectroscopy study of
structural and magnetic properties of the undoped parent compound
CaFeAs single crystal. By fitting the temperature dependence of the
hyperfine magnetic field we show that the magneto-structural phase transition
is clearly first-order in nature and we also deduced the compressibility of our
sample to be . Within the Landau's theory of phase
transition, we further argue that the observed phase transition may stem from
the strong magneto-structural coupling effect. Temperature dependence of the
Lamb-M\"ossbauer factor show that the paramagnetic phase and the
antiferromagnetic phase exhibit similar lattice dynamics in high frequency
modes with very close Debye temperatures, 270\,K.Comment: 6 pages,5 figures Accepted by J. Phys.: Condens. Matte
First-principles study of thin magnetic transition-metal silicide films on Si(001)
In order to combine silicon technology with the functionality of magnetic
systems, a number of ferromagnetic (FM) materials have been suggested for the
fabrication of metal/semiconductor heterojunctions. In this work, we present a
systematic study of several candidate materials in contact with the Si surface.
We employ density-functional theory calculations to address the thermodynamic
stability and magnetism of both pseudomorphic CsCl-like Si (=Mn, Fe, Co,
Ni) thin films and Heusler alloy MnSi (=Fe, Co, Ni) films on Si(001).
Our calculations show that Si-termination of the Si films is energetically
preferable during epitaxy since it minimizes the energetic cost of broken bonds
at the surface. Moreover, we can explain the calculated trends in thermodynamic
stability of the Si thin films in terms of the -Si bond-strength and the
3d orbital occupation. From our calculations, we predict that ultrathin
MnSi films are FM with sizable spin magnetic moments at the Mn atoms, while
FeSi and NiSi films are nonmagnetic. However, CoSi films display itinerant
ferromagnetism. For the MnSi films with Heusler-type structure, the MnSi
termination is found to have the highest thermodynamic stability. In the FM
ground state, the calculated strength of the effective coupling between the
magnetic moments of Mn atoms within the same layer approximately scales with
the measured Curie temperatures of the bulk MnSi compounds. In particular,
the CoMnSi/Si(001) thin film has a robust FM ground state as in the bulk,
and is found to be stable against a phase separation into CoSi/Si(001) and
MnSi/Si(001) films. Hence this material is of possible use in FM-Si
heterojunctions and deserves further experimental investigations.Comment: 13 pages, 8 figure
Spin alignments of vector mesons in deeply inelastic lepton-nucleon scattering
We extend the calculations of the spin alignments of vector mesons in
annihilation in a recent Rapid Communication to deeply inelastic
lepton-nucleon scatterings. We present the results for different mesons in the
current fragmentation regions of at high energies
and at both high and low energies. We also present
the predictions for at NOMAD energies in the
target fragmentation region using a valence quark model.Comment: 4 pages, 6 figures; to appear in Phys. Rev.
Constructions of the soluble potentials for the non-relativistic quantum system by means of the Heun functions
The Schr\"{o}dinger equation where
is rewritten as a more popular form of a second order
differential equation through taking a similarity transformation
with . The Schr\"{o}dinger invariant
can be calculated directly by the Schwarzian derivative and the
invariant of the differential equation . We
find an important relation for moving particle as and thus
explain the reason why the Schr\"{o}dinger invariant keeps constant.
As an illustration, we take the typical Heun differential equation as an object
to construct a class of soluble potentials and generalize the previous results
through choosing different as before. We get a more general
solution through integrating
directly and it includes all
possibilities for those parameters. Some particular cases are discussed in
detail.Comment: 11 page
Mechanism of pseudogap probed by a local impurity
The response to a local strong non-magnetic impurity in the pseudogap phase
is examined in two distinctly different scenarios: phase-fluctuation (PF) of
pairing field and d-density-wave (DDW) order. In the PF scenario, the resonance
state is generally double-peaked near the Fermi level, and is abruptly
broadened by vortex fluctuations slightly above the transition temperature. In
the DDW scenario, the resonance is single-peaked and remains sharp up to
gradual intrinsic thermal broadening, and the resonance energy is analytically
determined to be at minus of the chemical potential.Comment: 4 pages, 2 figure
Applying data visualization techniques for stock relationship analysis
© 2018, University of Nis. All rights reserved. Decision making in stock investment is often made based on current events in the market and the analysis of historical data on specific stocks. Besides, similar rates of price changing over a long-term period on different stocks may indicate potential connections between those listed corporations. The proposed methodology applies the force-directed algorithm and time-series chart to offer stakeholders capability to gain deeper insights initiative on potential relationships between stocks comes with less human interventions. Hence to assist in future decision making on stock investment via graph layouts
Perdeuterated cyanobiphenyl liquid crystals for infrared applications
Perdeuterated 4'-pentyl-4-cyanobiphenyl (D5CB) was synthesized and its physical properties evaluated and compared to those of 5CB. D5CB retains physical properties similar to those of 5CB, such as phase transition temperatures, dielectric constants, and refractive indices. An outstanding feature of D5CB is that it exhibits a much cleaner and reduced infrared absorption. Perdeuteration, therefore, extends the usable range of liquid crystals to the mid infrared by significantly reducing the absorption in the near infrared, which is essential for telecom applications
Two-photon interference with two independent pseudo-thermal sources
The nature of two-photon interference is a subject that has aroused renewed
interest in recent years and is still under debate. In this paper we report the
first observation of two-photon interference with independent pseudo-thermal
sources in which sub-wavelength interference is observed. The phenomenon may be
described in terms of the classical statistical distribution of the two sources
and their optical transfer functions.Comment: Phys. Rev. A 74, 053807 (2006
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