35,994 research outputs found
Conversion of glassy antiferromagnetic-insulating phase to equilibrium ferromagnetic-metallic phase by devitrification and recrystallization in Al substituted PrCaMnO
We show that PrCaMnO with 2.5% Al substitution and
LaCaMnO (LCMO) exhibit qualitatively similar and
visibly anomalous M-H curves at low temperature. Magnetic field causes a broad
first-order but irreversible antiferromagnetic (AF)-insulating (I) to
ferromagnetic (FM)-metallic (M) transition in both and gives rise to soft FM
state. However, the low temperature equilibrium state of
PrCaMnAlO (PCMAO) is FM-M whereas that
of LCMO is AF-I. In both the systems the respective equilibrium phase coexists
with the other phase with contrasting order, which is not in equilibrium, and
the cooling field can tune the fractions of the coexisting phases. It is shown
earlier that the coexisting FM-M phase behaves like `magnetic glass' in LCMO.
Here we show from specially designed measurement protocols that the AF-I phase
of PCMAO has all the characteristics of magnetic glassy states. It devitrifies
on heating and also recrystallizes to equilibrium FM-M phase after annealing.
This glass-like AF-I phase also shows similar intriguing feature observed in
FM-M magnetic glassy state of LCMO that when the starting coexisting fraction
of glass is larger, successive annealing results in larger fraction of
equilibrium phase. This similarity between two manganite systems with
contrasting magnetic orders of respective glassy and equilibrium phases points
toward a possible universality.Comment: Highlights potential of CHUF (Cooling and Heating in Unequal Fields),
a new measurement protoco
Large-Signal Simulation of 94 GHz Pulsed Silicon DDR IMPATTs Including the Temperature Transient Effect
In this paper large-signal modeling and simulation has been carried to study the frequency chirping due to temperature transients and the large-signal power and efficiency of pulsed silicon Double-Drift Region (DDR) Impact Avalanche Transit Time (IMPATT) device operating at 94 GHz. A large-signal simulation method based on non-sinusoidal voltage excitation incorporating the transient thermal effect has been developed by the authors. Results show that the device is capable of delivering a peak pulsed power output of 17.5 W with 12.8% efficiency when the voltage modulation is 60%. The maximum junction temperature rise is 350.2 K for a peak pulsed bias current of 6.79 A with 100 ns pulsewidth and 0.5 percent duty cycle; whereas the chirp bandwidth is 8.3 GHz
Is there still a strong CP problem?
The role of a chiral U(1) phase in the quark mass in QCD is analysed from
first principles. In operator formulation, there is a parity symmetry and the
phase can be removed by a change in the representation of the Dirac gamma
matrices. Moreover, these properties are also realized in a Pauli-Villars
regularized version of the theory. In the functional integral scenario,
attempts to remove the chiral phase by a chiral transformation are thought to
be obstructed by a nontrivial Jacobian arising from the fermion measure and the
chiral phase may therefore seem to break parity. But if one starts from the
regularized action with the chiral phase also present in the regulator mass
term, the Jacobian for a combined chiral rotation of quarks and regulators is
seen to be trivial and the phase can be removed by a combined chiral rotation.
This amounts to a taming of the strong CP problem.Comment: 6 pages, REVTeX; brief discussion available at
http://theory.saha.ernet.in/~mitra/scp.htm
Some Comments on the Spin of the Chern - Simons Vortices
We compute the spin of both the topological and nontopological solitons of
the Chern - Simons - Higgs model by using our approach based on constrained
analysis. We also propose an extension of our method to the non - relativistic
Chern - Simons models. The spin formula for both the relativistic and
nonrelativistic theories turn out to be structurally identical. This form
invariance manifests the topological origin of the Chern - Simons term
responsible for inducing fractional spin. Also, some comparisons with the
existing results are done.Comment: 12 pages, Late
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