62,578 research outputs found
Aging dynamics of ferromagnetic and reentrant spin glass phases in stage-2 CuCCl graphite intercalation compound
Aging dynamics of a reentrant ferromagnet stage-2
CuCoCl graphite intercalation compound has been studied
using DC magnetic susceptibility. This compound undergoes successive
transitions at the transition temperatures ( K) and
( K). The relaxation rate exhibits a
characteristic peak at below . The peak time as a
function of temperature shows a local maximum around 5.5 K, reflecting a
frustrated nature of the ferromagnetic phase. It drastically increases with
decreasing temperature below . The spin configuration imprinted at the
stop and wait process at a stop temperature () during the
field-cooled aging protocol, becomes frozen on further cooling. On reheating,
the memory of the aging at is retrieved as an anomaly of the
thermoremnant magnetization at . These results indicate the occurrence
of the aging phenomena in the ferromagnetic phase () as well
as in the reentrant spin glass phase ().Comment: 9 pages, 9 figures; submitted to Physical Review
Magnetic phase diagram of three-dimensional diluted Ising antiferromagnet NiMg(OH)
- diagram of 3D diluted Ising antiferromagnet
NiMg(OH) with = 0.8 has been determined from
measurements of SQUID DC magnetization and AC magnetic susceptibility. At =
0, this compound undergoes two magnetic phase transitions: an antiferromagnetic
(AF) transition at the N\'{e}el temperature (= 20.7 K) and a reentrant
spin glass (RSG) transition at ( 6 K). The - diagram
consists of the RSG, spin glass (SG), and AF phases. These phases meet a
multicritical point ( = 42 kOe, = 5.6 K). The
irreversibility of susceptibility defined by (= ) shows a negative local minimum for 10 35 kOe,
suggesting the existence of possible glassy phase in the AF phase. A broad peak
in and at 20 kOe for (= 26.4 K) suggests the existence of the Griffiths
phase.Comment: 11 pages, 14 figures; J. Phys. Soc. Jpn. 73 (2004) No. 1 issue, in
pres
Quantum phase transitions in the sub-ohmic spin-boson model: Failure of the quantum-classical mapping
The effective theories for many quantum phase transitions can be mapped onto
those of classical transitions. Here we show that such a mapping fails for the
sub-ohmic spin-boson model which describes a two-level system coupled to a
bosonic bath with power-law spectral density, J(omega) ~ omega^s. Using an
epsilon expansion we prove that this model has a quantum transition controlled
by an interacting fixed point at small s, and support this by numerical
calculations. In contrast, the corresponding classical long-range Ising model
is known to have an upper-critical dimension at s = 1/2, with mean-field
transition behavior controlled by a non-interacting fixed point for 0 < s <
1/2. The failure of the quantum-classical mapping is argued to arise from the
long-ranged interaction in imaginary time in the quantum model.Comment: 4 pages, 3 figs; (v2) discussion extended; (v3) marginal changes,
final version as published; (v4) added erratum pointing out that main
conclusions were incorrect due to subtle failures of the NR
On the perfect lattice actions of abelian-projected SU(2) QCD
We study the perfect lattice actions of abelian-projected SU(2) gluodynamics.
Using the BKT and duality transformations on the lattice, an effective string
model is derived from the direction-dependent quadratic monopole action,
obtained numerically from SU(2) gluodynamics in maximally abelian gauge. The
string tension and the restoration of continuum rotational invariance are
investigated using strong coupling expansion of lattice string model
analytically. We also found that the block spin transformation can be performed
analytically for the quadratic monopole action.Comment: 3 pages, Latex, 1 figures; talk presented at LATTICE9
String tension and glueball masses of SU(2) QCD from perfect action for monopoles and strings
We study the perfect monopole action as an infrared effective theory of SU(2)
QCD. It is transformed exactly into a lattice string model. Since the monopole
interactions are weak in the infrared SU(2) QCD, the string interactions become
strong. The strong coupling expansion of string model shows the quantum
fluctuation is small. The classical string tension is estimated analytically,
and we see it is very close to the quantum one in the SU(2) QCD. We also
discuss how to calculate the glueball mass in our model.Comment: LATTICE99(Confinement), 3 pages and 1 EPS figure
The unitary-model-operator approach to nuclear many-body problems
Microscopic nuclear structure calculations have been performed within the
framework of the unitary-model-operator approach. Ground-state and
single-particle energies are calculated for nuclei around ^{14}C, ^{16}O and
^{40}Ca with modern nucleon-nucleon interactions.Comment: 6 pages, 4 figures, Talk presented at the International Symposium on
Correlation Dynamics in Nuclei (CDN05), Jan. 1 - Feb. 4, 2005, Tokyo, Japa
The unitary-model-operator approach to nuclear many-body problems
Microscopic nuclear structure calculations have been performed within the
framework of the unitary-model-operator approach. Ground-state and
single-particle energies are calculated for nuclei around ^{14}C, ^{16}O and
^{40}Ca with modern nucleon-nucleon interactions.Comment: 6 pages, 4 figures, Talk presented at the International Symposium on
Correlation Dynamics in Nuclei (CDN05), Jan. 1 - Feb. 4, 2005, Tokyo, Japa
The unitary-model-operator approach to nuclear many-body problems
Microscopic nuclear structure calculations have been performed within the
framework of the unitary-model-operator approach. Ground-state and
single-particle energies are calculated for nuclei around ^{14}C, ^{16}O and
^{40}Ca with modern nucleon-nucleon interactions.Comment: 6 pages, 4 figures, Talk presented at the International Symposium on
Correlation Dynamics in Nuclei (CDN05), Jan. 1 - Feb. 4, 2005, Tokyo, Japa
A generalization of heterochromatic graphs
In 2006, Suzuki, and Akbari & Alipour independently presented a necessary and
sufficient condition for edge-colored graphs to have a heterochromatic spanning
tree, where a heterochromatic spanning tree is a spanning tree whose edges have
distinct colors. In this paper, we propose -chromatic graphs as a
generalization of heterochromatic graphs. An edge-colored graph is
-chromatic if each color appears on at most edges. We also
present a necessary and sufficient condition for edge-colored graphs to have an
-chromatic spanning forest with exactly components. Moreover, using this
criterion, we show that a -chromatic graph of order with
has an -chromatic spanning forest with exactly
() components if for any
color .Comment: 14 pages, 4 figure
Dynamics of the superfluid to Mott insulator transition in one dimension
We numerically study the superfluid to Mott insulator transition for bosonic
atoms in a one dimensional lattice by exploiting a recently developed
simulation method for strongly correlated systems. We demonstrate this methods
accuracy and applicability to Bose-Hubbard model calculations by comparison
with exact results for small systems. By utilizing the efficient scaling of
this algorithm we then concentrate on systems of comparable size to those
studied in experiments and in the presence of a magnetic trap. We investigate
spatial correlations and fluctuations of the ground state as well as the nature
and speed at which the superfluid component is built up when dynamically
melting a Mott insulating state by ramping down the lattice potential. This is
performed for slow ramping, where we find that the superfluid builds up on a
time scale consistent with single-atom hopping and for rapid ramping where the
buildup is much faster than can be explained by this simple mechanism. Our
calculations are in remarkable agreement with the experimental results obtained
by Greiner et al. [Nature (London) 415, 39 (2002)].Comment: 14 pages, 11 figures, RevTex 4. Replaced with published versio
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