4,065 research outputs found
Electronic states and magnetic excitations in LiV2O4: Exact diagonalization study
Motivated by recent inelastic neutron scattering experiment we examine
magnetic properties of LiV2O4. We consider a model which describes the
half-filled localized A1g spins interacting via frustrated antiferromagnetic
Heisenberg exchange and coupled by local Hund's interaction with the 1/8-filled
itinerant Eg band, and study it within an exact diagonalization scheme. In the
present study we limited the analysis to the case of the cluster of two
isolated tetrahedrons. We obtained that both the ground state structure and
low-lying excitations depend strongly on the value of the Hund's coupling which
favors the triplet states. With increasing temperature the triplet states
become more and more populated which results in the formation of non-zero
residual magnetic moment. We present the temperature dependence of calculated
magnetic moment and of the spin-spin correlation functions at different values
of Hund's coupling and compare them with the experimental results.Comment: 7 pages. 6 eps figure
The efficiency of the pumping of the lasers based on self-terminating atomic transitions operating in the energy input cut-off mode
The analysis of the electro-physical processes in the discharge circuit of the lasers based on the self-terminating transitions of metal atoms (LSTM) and the electrodes placed in the cold buffer zones of the gas discharge tube (GDT) is occurred. That design of the GDT can provide the efficient lasing at the reduction of the current flowing through the switch to zero after the charging of the capacitive components of the circuit from the storage capacitor. Under the circumstances the pumping of the active medium is determined by the energy input from the peaking capacitor and, consequently, the efficiency of the pumping can be increased by an order of magnitude, if (using a managed switch) the energy input into the active medium from the storage capacitor is “cut-off” after charging the capacitive components of the circuit. It was shown that the efficiency values of ∼ 9-11 % and of ∼ 5-6 % for the copper and gold vapor, lasers could be achieved
Coherence scale of the Kondo lattice
It is shown that the large-N approach yields two energy scales for the Kondo
lattice model. The single-impurity Kondo temperature, , signals the onset
of local singlet formation, while Fermi liquid coherence sets in only below a
lower scale, . At low conduction electron density
("exhaustion" limit), the ratio is much smaller than unity, and
is shown to depend only on and not on the Kondo coupling. The physical
meaning of these two scales is demonstrated by computing several quantities as
a function of and temperature.Comment: 4 pages, 4 eps figures. Minor changes. To appear in Phys. Rev. Let
Heavy-fermion and spin-liquid behavior in a Kondo lattice with magnetic frustration
We study the competition between the Kondo effect and frustrating exchange
interactions in a Kondo-lattice model within a large- dynamical
mean-field theory. We find a T=0 phase transition between a heavy Fermi-liquid
and a spin-liquid for a critical value of the exchange , the
single-impurity Kondo temperature. Close to the critical point, the Fermi
liquid coherence scale is strongly reduced and the effective mass
strongly enhanced. The regime is characterized by spin-liquid
magnetic correlations and non-Fermi-liquid properties. It is suggested that
magnetic frustration is a general mechanism which is essential to explain the
large effective mass of some metallic compounds such as LiVO.Comment: 7 pages, 1 figure. Late
Dynamics and scaling in the periodic Anderson model
The periodic Anderson model (PAM) captures the essential physics of heavy
fermion materials. Yet even for the paramagnetic metallic phase, a practicable
many-body theory that can simultaneously handle all energy scales while
respecting the dictates of Fermi liquid theory at low energies, and all
interaction strengths from the strongly correlated Kondo lattice through to
weak coupling, has remained quite elusive. Aspects of this problem are
considered in the present paper where a non-perturbative local moment approach
(LMA) to single-particle dynamics of the asymmetric PAM is developed within the
general framework of dynamical mean-field theory. All interaction strengths and
energy scales are encompassed, although our natural focus is the Kondo lattice
regime of essentially localized -spins but general conduction band filling,
characterised by an exponentially small lattice coherence scale .
Particular emphasis is given to the resultant universal scaling behaviour of
dynamics in the Kondo lattice regime as an entire function of , including its dependence on conduction band filling,
-level asymmetry and lattice type.A rich description arises, encompassing
both coherent Fermi liquid behaviour at low- and the crossover
to effective single-impurity scaling physics at higher energies -- but still in
the -scaling regime, and as such incompatible with the
presence of two-scale `exhaustion' physics, which is likewise discussed.Comment: 22 pages in EPJB format, 14 figures; accepted for publication in
EPJB; (small change in the comments section, no change in manuscript
Study of the , , Decays with an SND Detector on a VEPP-2M Collider
The process was studied in the energy range
MeV with an SND detector on a VEPP-2M collider. The
decay branching ratios , , and
were measured.Comment: 5 pages, 4 figure
Study of isobar electroproduction at VEPP-2M collider
Results from the Spherical Nonmagnetic Detector (SND) on
isobar electroproduction in the collisions of beam electrons (positrons) and
residual gas nuclei in the VEPP-2M collider are presented. On the
basis of the obtained data the expected counting rate of this process in future
high luminosity colliders (~-, -- and -factories)
was estimated.Comment: 7 pages LATEX and 3 figure
Effect of Disorder on Fermi surface in Heavy Electron Systems
The Kondo lattice model with substitutional disorder is studied with
attention to the size of the Fermi surface and the associated Dingle
temperature. The model serves for understanding heavy-fermion Ce compounds
alloyed with La according to substitution Ce{x}La{1-x}. The Fermi surface is
identified from the steepest change of the momentum distribution of conduction
electrons, and is derived at low enough temperature by the dynamical mean-field
theory (DMFT) combined with the coherent potential approximation (CPA). The
Fermi surface without magnetic field increases in size with decreasing x from
x=1 (Ce end), and disappears at such x that gives the same number of localized
spins as that of conduction electrons. From the opposite limit of x=0 (La end),
the Fermi surface broadens quickly as x increases, but stays at the same
position as that of the La end. With increasing magnetic field, a metamagnetic
transition occurs, and the Fermi surface above the critical field changes
continuously across the whole range of x. The Dingle temperature takes a
maximum around x=0.5. Implication of the results to experimental observation is
discussed.Comment: 5 pages, 5 figure
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