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81.
The nearest-neighbor resonating-valence bond (NNRVB) state is studied using classical anticommuting (Grassmann) variables. The classical partition function corresponding to the self-overlap of the NNRVB wavefunction is generated from a local (bond) Hamiltonian expressed in terms of four anticommuting variables. It is shown that the one-particle-per-site constraint introduces an interaction term which is a local product of all four variables. Two approaches are applied to study this Hamiltonian: (i) a self-consistent field decoupling scheme and (ii) a systematic perturbation expansion around the unconstrained soluble point. Bounds on the norm of the wavefunction are derived. Extensions to the presence of holes, long-range valence bonds, and the introduction of phase fluctuations [which violate the Marshall sign rule and yield aU(1) gauge theory] are discussed. 相似文献
82.
With the miniaturization of devices, size and interface effects become increasingly important for the properties and performances
of nanomaterials. Here, we present a thermodynamic approach to the mechanism behind size-induced unusual behavior in the phase
stabilities of ferromagnetic (FM), antiferromagnetic (AFM), ferroelectric (FE), and superconductive (SC) nanocrystals, which
are different dramatically from their bulk counterparts. This method is based on the Lindemann criterion for melting, Mott’s
expression for the vibrational melting entropy, and the Shi model for the size-dependent melting temperature. Simple and unified
functions, without any adjustable parameter, are established for the size and interface dependences of thermal and phase stabilities
of FM, AFM, FE and SC nanocrystals. According to these analytic functions, as the size of nanocrystals is reduced, the thermal
and phase stabilities may strengthen or weaken, depending on the confluence of the surface/volume ratio of nanocrystals and
the FM(AFM, FE or SC)/substrate interface situations. The validity of this model is confirmed by a large number of experimental
results. This theory will be significant for the choice of materials and the design of devices for practical application.
相似文献
83.
The properties of the nonlinear TM waves on the interface between a dielectric and an antiferromagnet are studied. The relationship
between the field components of TM wave is discussed in detail, and the dispersion characteristics as well as the position
of the peak field are exposed. The theoretical analysis shows that for the nonlinear TM waves there exist passband(s) and
stopband(s) which can be switched into each other by varying the power. It is revealed that, in the case of
, the nonlinear TM waves on the interface are backward surface waves with the group and phase velocities opposite.
Project supported by the National Natural Science Foundation of China (Grant No. 69477020). 相似文献
84.
Physical properties of TmPtIn have been investigated by means of magnetic, electrical transport, calorimetric as well as neutron diffraction measurements. The compound crystallizes in the hexagonal ZrNiAl-type crystal structure. It orders antiferromagnetically below TN = 3.5 K with the Tm magnetic moments confined to the basal hexagonal plane. They form a non-collinear “triangular” magnetic structure that may be described by the propagation vector . At 1.6 K, the Tm magnetic moment is equal to 5.59(9)μB. The antiferromagnetic character of the electronic ground state is reflected in the low temperature behaviors of the magnetic susceptibility and the specific heat, which may be described by spin-wave theory of antiferromagnetic magnons with linear dispersion relation. The compound exhibits metallic character of electrical conduction. 相似文献