9,038 research outputs found
A conjecture on the relationship between critical residual entropy and finite temperature pseudo-transitions of one-dimensional models
Recently pseudo-critical temperature clues were observed in one-dimensional
spin models, such as the Ising-Heisenberg spin models, among others. Here we
report a relationship between the zero-temperature phase boundary residual
entropy (critical residual entropy) and pseudo-transition. Usually, the
residual entropy increases in the phase boundary, which means the system
becomes more degenerate at the phase boundary compared to its adjacent states.
However, this is not always the case; at zero temperature, there are some phase
boundaries where the entropy holds the largest residual entropy of the adjacent
states. Therefore, we can propose the following conjecture: If residual entropy
at zero-temperature is a continuous function at least from the one-sided limit
at a critical point, then pseudo-transition evidence will appear at finite
temperature near the critical point. We expect that this argument would apply
to study more realistic models. Only by analyzing the residual entropy at zero
temperature, one could identify a priori whether the system will exhibit the
pseudo-transition at finite temperature. To strengthen our conjecture, we use
two examples of Ising-Heisenberg models, which exhibit pseudo-transition
behavior: one frustrated coupled tetrahedral chain and another unfrustrated
diamond chain.Comment: 12 pages and 10 figure
Using single top rapidity to measure V_td, V_ts, V_tb at hadron colliders
Single top production processes are usually regarded as the ones in which
V_tb can be directly measured at hadron colliders. We show that the analysis of
the single top rapidity distribution in t-channel and tW production can also
set direct limits on V_td. At LHC with 10 fb^-1 at 14 TeV the combined limits
on V_td may be reduced by almost a factor of two when the top rapidity
distribution is used. This also implies that the limits on V_tb can also be
reduced by 15%, since both parameters as well as V_ts must be simultaneously
obtained from a global fit to data. At Tevatron the explotation of this
distribution would require very high statistics.Comment: LaTeX 19 pages, 48 PS figures. A section added with estimations of
systematics, LO/NLO comparison and a fast detector simulation. Final version
to appear in PR
Magnetization non-rational quasi-plateau and spatially modulated spin order in the model of the single-chain magnet, [{(CuL)_2 Dy}{Mo(CN)_8}] 2CH_3CN H_2O
Using the exact solution in terms of the generalized classical transfer
matrix method we presented a detailed analysis of the magnetic properties and
ground state structure of the simplified model of the single-chain magnet,
trimetallic coordination polymer compound, [{(CuL)_2 Dy}{Mo(CN)_8}] 2CH_3CN
H_2O is N,N'-propylenebis(3-methoxysalicylideneiminato). Due to appearance of
highly anisotropic Dy3+ ion this material is an unique example of the
one-dimensional magnets with Ising and Heisenberg bonds, allowing exact
statistical-mechanical treatment. We found two zero-temperature ground states
corresponding to different part of the magnetization curve of the material. The
zero-filed ground state is shown to be an antiferromagnetic configuration with
spatial modulation of the local Dy3+(which is proven to posses well defined
Ising like properties due two large anisotropy of g-factors) and composite
S=1/2 spin of the quantum spin trimer Cu-Mo-Cu in the form
"up"-"down"-"down"-"up". Another important feature of this compound is the
appearance of the quasi-plateau at non rational value of magnetization due to
difference of the g-factors of the Cu- and Mo-ion in quantum spin trimers. The
quasi-plateau is an almost horizontal part of the magnetization curve where the
corresponding zero-temperature ground state of the chain demonstrate slow but
monotonous dependence of the magnetization on the external magnetic field,
while the -projection of the total spin is constant
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