36,397 research outputs found
Relativity Damps OPEP in Nuclear Matter
Using a relativistic Dirac-Brueckner analysis the OPEP contribution to the
ground state energy of nuclear matter is studied. In the study the pion is
derivative-coupled. We find that the role of the tensor force in the saturation
mechanism is substantially reduced compared to its dominant role in a usual
nonrelativistic treatment. We show that the damping of derivative-coupled OPEP
is actually due to the decrease of with increasing density. We point
out that if derivative-coupled OPEP is the preferred form of nuclear effective
lagrangian nonrelativistic treatment of nuclear matter is in trouble. Lacking
the notion of it cannot replicate the damping. We suggest an examination
of the feasibility of using pseudoscalar coupled N interaction before
reaching a final conclusion about nonrelativistic treatment of nuclear matter.Comment: 9 pages, 3 figures, in honor of Joseph Speth's 60th birthda
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
Coexisting tuneable fractions of glassy and equilibrium long-range-order phases in manganites
Antiferromagnetic-insulating(AF-I) and the ferromagnetic-metallic(FM-M)
phases coexist in various half-doped manganites over a range of temperature and
magnetic field, and this is often believed to be an essential ingredient to
their colossal magnetoresistence. We present magnetization and resistivity
measurements on Pr(0.5)Ca(0.5)Mn(0.975)Al(0.025)O(3) and Pr(0.5)Sr(0.5)MnO(3)
showing that the fraction of the two coexisting phases at low-temperature in
any specified measuring field H, can be continuously controlled by following
designed protocols traversing field-temperature space; for both materials the
FM-M fraction rises under similar cooling paths. Constant-field temperature
variations however show that the former sample undergoes a 1st order transition
from AF-I to FM-M with decreasing T, while the latter undergoes the reverse
transition. We suggest that the observed path-dependent phase-separated states
result from the low-T equilibrium phase coexisting with supercooled glass-like
high temperature phase, where the low-T equilibrium phases are actually
homogeneous FM-M and AF-I phases respectively for the two materials
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