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1.
G. Misguich P. Sindzingre 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(3):305-309
We compute the magnetic susceptibility and specific heat of the
spin-
Heisenberg model on the kagome lattice with
high-temperature expansions and exact diagonalizations. We compare
the results with the experimental data on ZnCu3(OH)6Cl2 obtained by Helton
et al. [Phys. Rev. Lett. 98, 107204 (2007)]. Down to
kBT/J≃0.2, our calculations reproduce accurately the
experimental susceptibility, with an exchange interaction
J≃190 K and a contribution of 3.7% of weakly interacting
impurity spins. The comparison between our calculations of the
specific heat and the experiments indicate that the low-temperature
entropy (below ~20 K) is smaller in ZnCu3(OH)6Cl2 than in the kagome
Heisenberg model, a likely signature of other interactions in the
system. 相似文献
2.
A. Avella F. Mancini E. Plekhanov 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(3):295-299
By means of the Density Matrix Renormalization Group technique, we have studied the region where XXZ-like behavior is most
likely to emerge within the phase diagram of the F-AF anisotropic extended (J-J’) Heisenberg chain. We have analyzed, in great
detail, the equal-time two-spin correlation functions, both in- and out-of- plane, as functions of the distance (and momentum).
Then, we have extracted, through an accurate fitting procedure, the exponents of the asymptotic power-law decay of the spatial
correlations. We have used the exact solution of XXZ model (J’ = 0) to benchmark our results, which clearly show the expected
agreement. A critical value of J’ has been found where the relevant power-law decay exponent is independent of the in-plane
nearest-neighbor coupling. 相似文献
3.
G. I. Japaridze S. Mahdavifar 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(1):59-66
The ground-state magnetic phase diagram of a spin S=1/2 two-leg ladder with alternating rung exchange J⊥(n)=J⊥[1 + (-1)n δ] is studied using the analytical and numerical approaches. In the limit where the rung exchange is dominant, we have mapped
the model onto the effective quantum sine-Gordon model with topological term and identified two quantum phase transitions
at magnetization equal to the half of saturation value from a gapped to the gapless regime. These quantum transitions belong
to the universality class of the commensurate-incommensurate phase transition. We have also shown that the magnetization curve
of the system exhibits a plateau at magnetization equal to the half of the saturation value. We also present a detailed numerical
analysis of the low energy excitation spectrum and the ground state magnetic phase diagram of the ladder with rung-exchange
alternation using Lanczos method of numerical diagonalizations for ladders with number of sites up to N = 28. We have calculated
numerically the magnetic field dependence of the low-energy excitation spectrum, magnetization and the on-rung spin-spin correlation
function. We have also calculated the width of the magnetization plateau and show that it scales as δν, where critical exponent varies from ν = 0.87±0.01 in the case of a ladder with isotropic antiferromagnetic legs to ν = 1.82±0.01
in the case of ladder with ferromagnetic legs. Obtained numerical results are in an complete agreement with estimations made
within the continuum-limit approach. 相似文献
4.
S. Mahdavifar 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(3):285-289
We have studied the behavior of the energy gap of the 1D AF
spin-
XXZ model in a transverse magnetic field (h)
using the exact diagonalization technique. The ground state phase
diagram consists of two spin-flop and paramagnetic phases. Using a
modified finite-size scaling approach, we have computed the
critical exponent of the energy gap in the vicinity of the
critical transverse field hc(Δ). Our numerical results
confirm that the continuous phase transition from the spin-flop
phase to the paramagnetic one is in the universality class of the
Ising model in the transverse field (ITF). By applying conformal
estimates of a small perturbation (h≪1), we have also
justified our numerical results. 相似文献
5.
G. -F. Zhang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(1):123-128
We construct an entangled quantum heat engine (EQHE) based on two two-spin systems with Dzyaloshinski-Moriya (DM) anisotropic
antisymmetric interaction. By applying the explanations of heat transferred and work performed at the quantum level in Kieu’s
work [Phys. Rev. Lett. 93, 140403 (2004)], the basic thermodynamic quantities, i.e., heat transferred, net work done in a cycle and efficiency of EQHE
are investigated in terms of DM interaction and concurrence. The validity of the second law of thermodynamics is confirmed
in the entangled system. It is found that there is a same efficiency for both antiferromagnetic and ferromagnetic cases, and
the efficiency can be controlled in two manners: (1) only by spin-spin interaction J and DM interaction D; (2) only by the temperature T and concurrence C. In order to obtain a positive net work, we need not entangle all qubits in two two-spin systems and we
only require the entanglement between qubits in a two-spin system not be zero. As the ratio of entanglement between qubits
in two two-spin systems increases, the efficiency will approach infinitely the classical Carnot one. An interesting phenomenon
is an abrupt transition of the efficiency when the entanglements between qubits in two two-spin systems are equal. 相似文献
6.
W. Brzezicki A. M. Oleś 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(3):361-368
We introduce a spin ladder with Ising interactions along the legs and intrinsically frustrated Heisenberg-like ferromagnetic
interactions on the rungs. The model is solved exactly in the subspaces relevant for the ground state by mapping to the quantum
Ising model, and we show that a first order quantum phase transition separates the classical from quantum regime, with the
spin correlations on the rungs being either ferromagnetic or antiferromagnetic, and different spin excitations in both regimes.
The present case resembles the quantum phase transition found in the compass model in one and two dimensions. 相似文献
7.
S. Chen H. Büttner 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):15-18
We generalize the Shastry-Sutherland model to three dimensions. By representing the model as a sum of the semidefinite positive
projection operators, we exactly prove that the model has exact dimer ground state. Several schemes for constructing the three-dimensional
Shastry-Sutherland model are proposed.
Received 20 February 2002 / Received in final form 27 May 2002 Published online 17 September 2002 相似文献
8.
D.V. Dmitriev V.Ya. Krivnov A.A. Ovchinnikov 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):91-97
We study the spin ladder model with interactions between spins on neighboring rungs. The model Hamiltonian with the exact
singlet ground state degenerated with ferromagnetic state is obtained. The singlet ground state wave function has a special
recurrent form and depends on two parameters. Spin correlations in the singlet ground state show double-spiral structure with
period of spirals equals to the system size. For special values of parameters they have exponential decay. The spectrum of
the model is gapless and there are asymptotically degenerated excited states for special values of parameters in the thermodynamic
limit.
Received 7 May 1999 相似文献
9.
It is generally believed that the ground state of the ferromagnetic Heisenberg-Dirac-Van Vleck Hamiltonians acting ons=1/2 spins of a lattice withN sites has the maximum possible value of the total spinS=N/2 and isN+1 times degenerate. We present a rigorous proof of this statement, independent of the lattice dimension and topology.
A member of the Doppler Institute of Mathematical Physics, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical
University, Prague. 相似文献
10.
In this paper we study the quantum phase transition and low temperature behavior in a square lattice quantum two-dimensional XY model with single-ion anisotropy and spin S=1. Starting with the Villain representation, a Landau-Ginzburg expression is written. The large D phase is studied using the bond operator formalism. 相似文献
11.
We investigate the FIR magneto-optical transitions in doped self-assembled InAs quantum dots with an average filling ranging from 0.6 to 6 electrons per dot. Significant changes in the magnetic field dispersion, the line-width and the amplitude of the transitions are observed as the doping level is varied, in agreement with our theoretical calculations. We show that our technique is an effective tool to obtain informations regarding the dot size homogeneity and the electron filling uniformity.Received: 22 July 2003, Published online: 2 October 2003PACS:
73.21.La Quantum dots - 78.20.Ls Magnetooptical effects - 78.30.Fs III-V and II-VI semiconductors - 78.67.Hc Quantum dotsE. Deleporte: Present address: Laboratoire de Photonique Quantique et Moleculaire, École Normale Superieure de Cachan, 94235 Cachan Cedex, FranceJ.M. Gérard: Present address: CEA-Grenoble DRFMC/SP2M/PSC, Laboratoire de Physique des semiconducteurs, 38054 Grenoble, France 相似文献
12.
H. Niggemann J. Zittartz 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):731-738
We present a class of optimum ground states for quantum spin- models on the Cayley tree with coordination number 3. The interaction is restricted to nearest neighbours and contains 5
continuous parameters. For all values of these parameters the Hamiltonian has parity invariance, spin-flip invariance, and
rotational symmetry in the xy-plane of spin space. The global ground states are constructed in terms of a 1-parametric vertex state model, which is a direct generalization of the well-known matrix product ground state approach. By using recursion relations and the transfer matrix technique we derive exact analytical expressions for local
fluctuations and longitudinal and transversal two-point correlation functions.
Received 1 March 1999 相似文献
13.
F. K?rmann J. Kienert S. Schwieger W. Nolting 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(4):499-504
Adding a non-magnetic Cu overlayer on Ni8/Cu(001) is known to induce the reorientation of the magnetic easy axis from in-plane to out-of-plane and to reduce the Curie
temperature. In this paper both effects are described on the same footing using an effective Heisenberg trilayer. The model
takes into account thermal fluctuations of the magnetization and allows to separate explicitly between two possible mechanisms
behind the experimental observations, namely between a reduction of the magnetic moment by hybridization and a lattice relaxation
at the Ni/Cu interface. Ferromagnetic resonance data for the reorientation and the decreased Curie temperature due to the
Cu cap layer are best reproduced by assuming a reduction of the magnetic moment at the interface by ≈1/3. 相似文献
14.
Z.-S. Liu 《Applied Physics A: Materials Science & Processing》2009,95(2):443-445
In a rare-earth antiferromagnet, two neighboring magnetic ions order spontaneously in opposite directions below the Néel temperature.
Especially when it is placed in an external magnetic field, the two magnetic ions react to the field in different ways, so
that they usually have different magnitudes and orientations below the magnetic transition temperature. Therefore, to describe
the magnetic structure of an antiferromagnet, the single-ion ferromagnetic-like model is inadequate. To solve this problem,
a two-ion model for rare-earth antiferromagnets is proposed and used in this work to investigate the magnetic properties of
DyNi2B2C. The magnetic susceptibility curves obtained with this model show good agreements with experimental data. 相似文献
15.
M. van den Bossche F.-C. Zhang F. Mila 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(3):367-370
In order to understand the properties of Mott insulators with strong ground state orbital fluctuations, we study the zero
temperature properties of the SU(4) spin-orbital model on a square lattice. Exact diagonalizations of finite clusters suggest that the ground state is disordered
with a singlet-multiplet gap and possibly low-lying SU(4) singlets in the gap. An interpretation in terms of plaquette SU(4) singlets is proposed. The implications for LiNiO2 are discussed.
Received 6 July 2000 相似文献
16.
G. Bannasch W. Selke 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(3):439-444
Classical Heisenberg antiferromagnets with uniaxial exchange anisotropy and a cubic anisotropy term in a field on simple cubic
lattices are studied with the help of ground state considerations and extensive Monte Carlo simulations. Especially, we analyze
the role of non-collinear structures of biconical type occurring in addition to the well-known antiferromagnetic and spin-flop
structures. Pertinent phase diagrams are determined, and compared to previous findings. 相似文献
17.
B. Bourahla A. Khater R. Tigrine 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(3):343-349
This paper describes a theoretical study, at a microscopic scale, of the
properties of a symmetric magnetic nanocontact. In particular, we study a
symmetric nanocontact separating two waveguide groups of semi-infinite spin
ordered ferromagnetic monatomic chains. The individual and total conductance
of bulk magnons of the chains, scattering coherently at the nanocontact, and
the localised density of spin states in the nanocontact domain, are
calculated and analysed. The inter-atomic magnetic exchange is varied on the
nanocontact to investigate the consequences of magnetic softening and
hardening for the calculated properties. Transmission and reflection
scattering cross sections are calculated from elements of a Landauer type
scattering matrix. The results highlight the localized spin states on the
nanocontact domain and their interactions with incident magnons. The results
demonstrate also the magnetic and symmetry properties of the nanocontact
domain. 相似文献
18.
19.
S. Chen L. Wang Y. P. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(3):265-270
We study the ground-state properties of frustrated Heisenberg ferrimagnetic
ladders with antiferromagnetic exchange interactions and two types of
alternating sublattice spins. In the limit of strong rung couplings, we show
that the mixed spin-1/2 and spin-1 ladders can be systematically mapped onto
a spin-1/2 Heisenberg model with additional next-nearest-neighbor exchanges.
The system is either in a ferrimagnetic state or in a critical spin-liquid
state depending on the competition between the spin exchanges along the legs
and the diagonal exchanges. 相似文献
20.
W. Hofstetter W. Zwerger 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):751-756
We present a field-theoretic renormalization group calculation in two loop order for classical O(N)-models with an inverse square interaction in the vicinity of their lower critical dimensionality one. The magnetic susceptibility
at low temperatures is shown to diverge like with a=(N-2)/(N-1) and . From a comparison with the exactly solvable Haldane-Shastry model we find that the same temperature dependence applies also
to ferromagnetic quantum spin chains.
Received: 20 February 1998 / Revised: 27 April 1998 / Accepted: 30 April 1998 相似文献