3,811 research outputs found
The History of Glatfelter Hall
A history of one of the oldest buildings on the Gettysburg College Campus, Glatfelter Hall. The paper covers the time period from the construction of the building in 1888 to after its first major renovation in 1929
Theory of magnetic phases of hexagonal rare earth manganites
The magnetic phases of hexagonal perovskites RMnO_3 (R=Ho, Er, Tm, Yb, Sc, Y)
are analysed using group theory and the Landau theory of phase transitions. The
competition between various magnetic order parameters is discussed in the
context of antiferromagnetic interactions. A phenomenological model based on
four one-dimensional magnetic order parameters is developed and studied
numerically. It is shown that coupling of the various order parameters leads to
a complex magnetic field-temperature phase diagram and the results are compared
to experiment.Comment: 11 pages, 14 figures. Manuscript with higher quality figures can be
obtained here: http://www.physics.mun.ca/~curnoe/papers/RMnO3.submit.pd
Parity Effect in a mesoscopic superconducting ring
We study a mesoscopic superconducting ring threaded by a magnetic flux when
the single particle level spacing is not negligible. It is shown that, for a
superconducting ring with even parity, the behavior of persistent current is
equivalent to what is expected in a bulk superconducting ring. On the other
hand, we find that a ring with odd parity shows anomalous behavior such as
fluxoid quantization at half-integral multiples of the flux quantum and
paramagnetic response at low temperature. We also discuss how the parity effect
in the persistent current disappears as the temperature is raised or as the
size of the ring increases.Comment: 8 pages, 2 figures, to appear in Europhys. Let
Pulsed high-power arc heater with improved cathode and triggering mechanism
System employs pulsed, constricted arc heater capable of multi-MW power, permitting quasi-stationary flow conditions during latter half of pulse of about 5 msec. System description is given
Delayed response of a fermion-pair condensate to a modulation of the interaction strength
The effect of a sinusoidal modulation of the interaction strength on a
fermion-pair condensate is analytically studied. The system is described by a
generalization of the coupled fermion-boson model that incorporates a
time-dependent intermode coupling induced via a magnetic Feshbach resonance.
Nontrivial effects are shown to emerge depending on the relative magnitude of
the modulation period and the relaxation time of the condensate. Specifically,
a nonadiabatic modulation drives the system out of thermal equilibrium: the
external field induces a variation of the quasiparticle energies, and, in turn,
a disequilibrium of the associated populations. The subsequent relaxation
process is studied and an analytical description of the gap dynamics is
obtained. Recent experimental findings are explained: the delay observed in the
response to the applied field is understood as a temperature effect linked to
the condensate relaxation time.Comment: 6 page
Long-Range Order of Vortex Lattices Pinned by Point Defects in Layered Superconductors
How the vortex lattice orders at long range in a layered superconductor with
weak point pinning centers is studied through a duality analysis of the
corresponding frustrated XY model. Vortex-glass order emerges out of the vortex
liquid across a macroscopic number of weakly coupled layers in perpendicular
magnetic field as the system cools down. Further, the naive magnetic-field
scale determined by the Josephson coupling between adjacent layers is found to
serve as an upperbound for the stability of any possible conventional vortex
lattice phase at low temperature in the extreme type-II limit.Comment: 13 pgs., 1 table, published versio
SU(2) gauge theory of the Hubbard model: Emergence of an anomalous metallic phase near the Mott critical point
We propose one possible mechanism for an anomalous metallic phase appearing
frequently in two spatial dimensions, that is, local pairing fluctuations.
Introducing a pair-rotor representation to decompose bare electrons into
collective pairing excitations and renormalized electrons, we derive an SU(2)
gauge theory of the Hubbard model as an extended version of its U(1) gauge
theory\cite{Florens,LeeLee} to allow only local density fluctuations. Since our
effective SU(2) gauge theory admits two kinds of collective bosons
corresponding to pair excitations and density fluctuations respectively, an
intermediate phase appears naturally between the spin liquid Mott insulator and
Fermi liquid metal of the U(1) gauge theory,\cite{Florens,LeeLee} characterized
by softening of density-fluctuation modes as the Fermi liquid, but gapping of
pair-excitation modes. We show that this intermediate phase is identified with
an anomalous metallic phase because there are no electron-like quasiparticles
although it is metallic
Determination of critical current density from arbitrary flux relaxation process
The current-carrying ability of a type-II superconductor is generally
represented by its critical current density. This can be determined by
measuring a flux relaxation process starting with a testing current density
that is greater than or equal to the critical value. Here we show that a flux
relaxation process starting with an intermediate current density can be
converted into a process starting with the critical current density by
introducing a virtual time interval. Therefore, one may calculate the critical
current density from the flux relaxation process starting with a current
density below the critical value. The exact solutions of the time dependence of
current density in the flux relaxation process were also discussed.Comment: 5 page
Quantum spin configurations in Tb2Ti2O7
Low energy collective angular momentum states of the Tb3+ ions in Tb2Ti2O7
are classified according to the irreducible representations of the octahedral
point group. Degeneracy lifting due to the exchange interaction is discussed.
Diffuse neutron scattering intensity patterns are calculated for each
collective angular momentum state and the ground state is inferred by comparing
to experiment.Comment: 5 pages, 1 colour figure. Slight corrections and additions to text
and figur
Spectrum of the Andreev Billiard and Giant Fluctuations of the Ehrenfest Time
The density of states in the semiclassical Andreev billiard is theoretically
studied and shown to be determined by the fluctuations of the classical
Lyapunov exponent . The rare trajectories with a small value of
give rise to an anomalous increase of the Ehrenfest time
and, consequently, to the appearance of
Andreev levels with small excitation energy. The gap in spectrum is obtained
and fluctuations of the value of the gap due to different positions of
superconducting lead are considered.Comment: 4 pages, 3 figure
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