共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
R.E. Mott 《Nuclear Physics B》1975,84(1):260-268
We investigate models where the SU (4) × SU (4) symmetry breaking Hamiltonian, SB, belongs to the (15, 15) and representations, and show how they are equivalent to models of SU (3) × SU (3) breaking where SB belongs to a mixture of different representations. The results for the ππ scattering lengths in the (15, 15) model are outside the experimental limits, but the model yields solutions with a wide range of values for the scattering lengths within the experimental bounds. 相似文献
3.
4.
We investigate the nonmagnetic phase of the spin-half frustrated Heisenberg antiferromagnet on the square lattice using exact diagonalization (up to 36 sites) and quantum Monte Carlo techniques (up to 144 sites). The spin gap and the susceptibilities for the most important crystal symmetry breaking operators are computed. A genuine and somehow unexpected "plaquette resonating valence bond," with spontaneously broken translation symmetry and no broken rotation symmetry, comes out from our numerical simulations as the most plausible ground state for J(2)/J(1) approximately 0.5. 相似文献
5.
A simple and rather general way to break SU(4) is to assume that the mass operator consists of a term which transforms as a scalar in the subgroup SU(3)c (which operates on u, d, and s quarks) and a term which transforms as a scalar in SU(3)s (which operates on u, d, and c). It is shown that this leads to a number of parallelogram laws between the masses. The generalized Okubo assumption falls within this framework and leads directly to Gell-Mann-Okubo relations between multiplets in the two subgroups. The specific SU(4) assumption of Okubo and others is a still further restriction. This group theoretic approach is compared with the results of the quark model. 相似文献
6.
Motivated by experiments in nanoscopic systems, we study a generalized Anderson, which consist of two spin degenerate doublets hybridized to a singlet by the promotion of an electron to two conduction bands, as a function of the energy separation δ between both doublets. For δ=0 or very large, the model is equivalent to a one-level SU(N) Anderson model, with N=4 and 2 respectively. We study the evolution of the spectral density for both doublets (ρ1σ(ω) and ρ2σ(ω)) and their width in the Kondo limit as δ is varied, using the non-crossing approximation (NCA). As δ increases, the peak at the Fermi energy in the spectral density (Kondo peak) splits and the density of the doublet of higher energy ρ2σ(ω) shifts above the Ferrmi energy. The Kondo temperature TK (determined by the half-width at half maximum of the Kondo peak in density of the doublet of lower energy ρ1σ(ω)) decreases dramatically. The variation of TK with δ is reproduced by a simple variational calculation. 相似文献
7.
8.
T.C. Yang 《Nuclear Physics B》1978,138(2):345-364
We suggest SUL(4) ? U(1) as the gauge symmetry of weak and electromagnetic interactions for quartets of quarks and leptons. We analyze how the (additional) SUL(4) weak currents (besides the SUL(2) subgroup) could affect the weak interactions of ordinary particles, the atomic parity violation, the neutral-current neutrino reactions and the decays of the τ heavy lepton and the charmed mesons. The suppression of neutral-current parity violation in atomic experiments can be naturally incorporated in this model while at the same time the success of the Weinberg-Salam model with respect to the inclusive neutral current data is kept. The model has limited freedom and therefore many definite predictions. 相似文献
9.
A.A. Zvyagin D.M. Apal'kov 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):565-569
We present a Bethe Ansatz based investigation of a one-dimensional (1D) Heisenberg spin chain in a real 3D crystal lattice.
We have shown that due to an influence of the lattice distortion on a crystalline field of ligands of magnetic ions, a Heisenberg
antiferromagnetic spin chain is unstable under the appearance of a magnetic anisotropy of the “easy-plane” type. The effects of an external magnetic
field and nonzero temperature onto such a phase transition are studied.
Received: 19 January 1998 / Revised: 16 March 1998 / Accepted: 17 March 1998 相似文献
10.
O.K. Kalashnikov 《Physics letters. [Part B]》1977,72(1):65-69
An asymptotically free SU(2) × SU(2) × SU(4) model of unified interaction is constructed. The gauge coupling constants are taken equal (in the order of magnitude) to the electromagnetic one. The strong interaction and the quark confinement is provided for by a gluonic mechanism. Some physical consequence of the model are briefly discussed. 相似文献
11.
Yoshihiro Nishiyama 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(2):295-299
Chiral order of the Josephson-junction ladder with half a flux quantum per plaquette is studied by means of the exact diagonalization
method. We consider an extreme quantum limit where each superconductor grain (order parameter) is represented by S=1/2 spin. So far, the semi-classical case, where each spin reduces to a plane rotator, has been considered extensively. We found that in the case of S=1/2, owing to the strong quantum fluctuations, the chiral (vortex lattice) order becomes dissolved except in a region, where
attractive intrachain and, to our surprise, repulsive interchain interactions both exist. On the contrary, for considerably
wide range of parameters, the superconductor (XY) order is kept critical. The present results are regarded as a demonstration of the critical phase accompanying chiral-symmetry
breaking predicted for frustrated XXZ chain field-theoretically.
Received 20 February 2000 相似文献
12.
S. K. Bose 《Fortschritte der Physik》1976,24(10):555-564
We study the pseudoscalar mesons in the framework of broken chiral SU(4) SU(4) symmetry when the symmetry-breaking Hamiltonian, HSB, is taken as –(u0 + cu8 + du15) and the symmetry of the Hamiltonian is realized in Goldstone-Nambu way. An interesting property of two chimeral SU(4) subgroups and the Goldstone nature of some of the pseudoscalar mesons in certain symmetry limits are exploited to obtain some mass relations and the ratio c/d. 相似文献
13.
A complete set of solutions of SU(4) invariant gauge fields with SO(4) spherical symmetry (euclidian metric in space time) is obtained. It is shown that the solutions fall into two non equivalent classes following a spinor or vector decomposition of the four dimensional representation of SU(4) in SO(4). The energy of the first case and hence the topological quantum number are twice those of the second case. 相似文献
14.
The problem of determining the representation matrices of SU(4) is investigated. A convenient set of parameters is first introduced by writing the general element of the group as a product of exponential functions of the generators, and the generators are expressed as differential operators involving these parameters. Special matrix elements of finite transformations with a SU(3) singlet as the initial state are then obtained by solving the eigenvalue equation of the quadratic Casimir operator of SU(4). The solution has the form of a product of elementary functions and threed
mm
j
functions of SU(2) and is free from summation over intermediate states. By expanding one of thed
mm
j
functions in an appropriate series a sum rule for the special matrix elements of the permutation operator 12343412 is obtained. The discussions are strictly confined to SU(4), but, some of the results given here can be extended to unitary groups of higher dimensions. 相似文献
15.
A lepton hadron analogy is considered based on the gauge group SU(4)L × SU(4)R × U(1), which is broken entirely spontaneously. The model satisfies the physical requirements of the V-A theory, muon-electron universality, no neutral strangeness changing currents, the Cabibbo structure for the SU(3) currents, and triangle anomalies can be avoided. The contribution of the existing neutral currents to various neutrino processes are calculated. 相似文献
16.
We consider the SU(4) Skyrme model with explicit chiral and flavour symmetry-breaking terms. Using the masses of the 15-plet
pseudoscalar mesons as the input, we calculate the masses of the 20-plet baryons. The baryon masses predicted by this model
agree with results based on quark model to about 15%. We find that the generalized Gell-Mann Okubo mass relation is very well
satisfied. 相似文献
17.
H. Flyvbjerg 《Nuclear Physics B》1980,176(2):379-396
The effective energy for a covariantly constant background field in a pure Yang-Mills theory is calculated to loop order one. For gauge group SU(3) [SU(4)] it is found that the “vacuum” configuration consists of two [three] constant color magnetic fields of equal non-zero magnitude orthogonal to each other in color as well as physical space. We conclude that the structure of the Copenhagen vacuum is more complex than previously expected. 相似文献
18.
In order to remove some of the unsatisfactory features of the GIM model, we consider15-admixture in SU(4). ΔC=±ΔS decays remain unaffected. Lee-Sugawara sum-rule is obtained.15-admixture is extended then to63-admixture in SU(8). The most general Hamiltonian (H
w∼63⊕720⊕1232) in SU(8) is found to give Lee-Sugawara relation and Σ+
+=0 forS-wave decays of uncharmed baryons. Decay amplitude relations for ΔC=−1, ΔS=0 mode are obtained. 相似文献
19.
Because of the spin and Dirac-valley degrees of freedom, graphene allows the observation of one-, two- or four-component fractional quantum Hall effects in different parameter regions. We address the stability of various states in the SU(2) and SU(4) limits. In the SU(4) limit, we predict that new low-energy Goldstone modes determine the stability of the fractional quantum Hall states at 2/5, 3/7, etc; SU(4) skyrmions are not found to be relevant for the low-energy physics. These results are discussed in light of experiments. 相似文献
20.
A supersymmetric version of the left right symmetric partial unification group SU
C
(4) × SU
L
(2) × SU
R
(2) is presented. The spontaneous breakdown of gauge symmetry in a favourable chain of descent has been studied in detail.
The mass spectra have been calculated. The method of O’Raifeartaigh has been used to break supersymmetry. The lifting of degeneracy
of mass levels between physical multiplets has been shown to occur due to radiative corrections. 相似文献