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We discuss how to decompose the Fock space of a many-fermion system embedded in two-dimensional square lattice. Wefirst notice that the symmetry group inherent in the system is one of the two-dimensional space groups. We shortly review thecorresponding irreducible representations of the group. We then find the characters of the reducible representation of the many-fermion Fock space. Using the characters, we obtain the multiplicity of each irreducible representation contained in the Fock space of a fixed number of fermions. We present specific examples, where we calculate the multiplicities which are the dimensions of the decomposed spaces. 相似文献
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P. Nozières F. Pistolesi 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):649-662
We consider a two-dimensional semiconductor with a local attraction among the carriers. We study the ground state of this
system as a function of the semiconductor gap. We find a direct transition from a superconducting to an insulating phase for
no doping at a critical value, the single particle excitations being always gapped. For finite doping we find a smooth crossover.
We calculate the critical temperature due to both the particle excitations and the Berezinkii-Kosterlitz-Thouless transition.
Received 8 December 1998 相似文献
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L. Y. Xie J. G. Wang R. K. Janev Y. Z. Qu C. Z. Dong 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2012,66(5):1-11
In this paper, we use the Green function method to determine the linear quantum mechanical susceptibilities of a single two-level atom and two two-level atoms located inside a coupled-resonator optical waveguide (CROW). We first calculate the susceptibility of a single atom in a CROW which has the same form as that of a single atom in free space, except for the modification of the atomic decay rate and the frequency shift. Then, we consider two non-identical, non-interacting two-level atoms inside two separate cavities of the CROW. We find that the susceptibility of this system contains not only the contributions of the two individual atoms, but also the contribution arising from the atom-atom correlation due to the CROW field. This additional contribution leads to an electromagnetically induced transparency-like (EIT-like) phenomenon. Furthermore, we find that the optical response of the atomic systems under consideration can be controlled by tuning the atomic transition frequency. Finally, we study the effects of the dissipation processes, i.e., the spontaneous emission of the atoms and the photon leakage from the CROW, on the optical susceptibility. 相似文献
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We study the asymptotic dynamics of a driven spin-boson system
where the environment is formed by a broadened localized mode.
Upon exploiting an exact mapping, an equivalent formulation of the
problem in terms of a quantum two-state system (qubit) coupled to
a harmonic oscillator which is itself Ohmically damped, is found.
We calculate the asymptotic population difference of the two
states in two complementary parameter regimes. For weak damping
and low temperature, a perturbative Floquet-Born-Markovian master
equation for the qubit-oscillator system can be solved. We find
multi-photon resonances corresponding to transitions in the
coupled quantum system and calculate their line-shape
analytically. In the complementary parameter regime of strong
damping and/or high temperatures, non-perturbative real-time path
integral techniques yield analytic results for the resonance line
shape. In both regimes, we find very good agreement with exact
results obtained from a numerical real-time path-integral
approach. Finally, we show for the case of strong detuning between
qubit and oscillator that the width of the n-photon resonance
scales with the nth Bessel function of the driving strength in
the weak-damping regime. 相似文献
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Xue-Jing Feng Jin-Xin Li Lu Qin Ying-Ying Zhang ShiQiang Xia Lu Zhou ChunJie Yang ZunLue Zhu Wu-Ming Liu Xing-Dong Zhao 《Frontiers of Physics》2023,18(5):52303
We investigate the itinerant ferromagnetism in a dipolar Fermi atomic system with the anisotropic spin−orbit coupling (SOC), which is traditionally explored with isotropic contact interaction. We first study the ferromagnetism transition boundaries and the properties of the ground states through the density and spin-flip distribution in momentum space, and we find that both the anisotropy and the magnitude of the SOC play an important role in this process. We propose a helpful scheme and a quantum control method which can be applied to conquering the difficulties of previous experimental observation of itinerant ferromagnetism. Our further study reveals that exotic Fermi surfaces and an abnormal phase region can exist in this system by controlling the anisotropy of SOC, which can provide constructive suggestions for the research and the application of a dipolar Fermi gas. Furthermore, we also calculate the ferromagnetism transition temperature and novel distributions in momentum space at finite temperature beyond the ground states from the perspective of experiment. 相似文献
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B. Kim M.-H. Chung 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(1):67-73
We consider the symmetry group inherent in
two-dimensional triangle and honeycomb lattice systems. We find
analytically and numerically the character of the reducible
representation for the corresponding Fock space. Using the
irreducible characters and the reducible character of the
representation, we decompose the Fock space explicitly. For example,
we calculate the multiplicity of each irreducible representation
contained in the Fock space. 相似文献
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Effect of interatomic electron correlation has been studied in narrow band solids using one-particle Green function method.
We follow Hubbard in drawing an analogy with an alloy and find a self-consistent solution which predicts a finite lifetime
for pseudoparticles. A specific case of a (non-magnetic) model system with half-filled parabolic band has been considered
to calculate the pseudoparticle density of states function. Unlike the result in the presence of intra-atomic correlations
alone, we find that this particular system is never an insulator, however large intra-atomic correlations may be. 相似文献
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M. Frank K. Huitu T. Rüppell 《The European Physical Journal C - Particles and Fields》2007,52(2):413-423
We construct an extension of the supersymmetric standard model where both CP symmetry and R-parity are spontaneously broken.
We study the electroweak symmetry breaking sector of the model and find minima consistent with the experimental bounds on
Higgs boson masses. Neutrino masses and mixing angles are generated through both seesaw and bilinear R-parity violation. We
show that the hierarchical mass pattern is obtained, and mixings are consistent with measured values. Due to the spontaneous
CP and R-parity violation, the neutrino sector is CP violating, and we calculate the corresponding phase. We further restrict
the parameter space to agree with the limits on the electric dipole moment of the neutron. Finally, we study the CP violation
parameter εK in the kaon system and show that we obtain results consistent with the experimental value. 相似文献
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We present a qualitative study of the subdiffractive light beam propagation in photonic crystals, based on the theoretical analysis of full Maxwell equation system beyond the slowly varying envelope and paraxial approximations. We calculate the zero diffraction curve in the parameter space, we calculate the weak asymptotical broadening (spreading in transverse direction), and we also analyze the dependence of subdiffractive propagation on the polarization orientation (both for TM and TE polarization). 相似文献
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Enhanced localization of waves in one-dimensional random media due to nonlinearity: Fixed input case
Ba Phi NguyenKihong Kim Fabian RotermundHanjo Lim 《Physica B: Condensed Matter》2011,406(23):4535-4537
We study the influence of nonlinearity on wave localization in one-dimensional random media. Using a discrete nonlinear Schrödinger equation with a random on-site energy term, we calculate the localization length in a numerically exact manner. Unlike in many previous works, we fix the intensity of the incident wave and calculate quantities as a function of other parameters. We find that localization is enhanced due to nonlinearity for the focusing and defocusing nonlinearities. For small nonlinearity, the localization length is a decreasing function of nonlinearity. For sufficiently large nonlinearity, however, the localization length is found to approach a saturation value. 相似文献
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In this note we employ methods borrowed from spin glass theory to study the phase space structure of fields in an inflating universe. In particular, we compute the overlap distribution of a suitably coarse-grained, massless scalar on a (1+1)-dimensional (hence baby) de Sitter background, and find that (after an appropriate shift and rescaling) it is given by a Gumbel distribution. We also calculate the triple overlap distribution of this system, whose characteristic function turns out to be a product of two Gumbel factors. 相似文献
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We study the classical dynamics of the rare gas-dihalogen Ne?Br2 complex in its ground electronic state. By considering the dihalogen bond frozen at its equilibrium distance, the system has two degrees of freedom and its potential energy surface presents linear and T-shape isomers. We find the nonlinear normal modes of both isomers that determine the phase space structure of the system. By means of surfaces of section and applying the numerical continuation of families of periodic orbits, we detect and identify the different bifurcations suffered by the normal modes as a function of the system energy. Finally, using the Orthogonal Fast Lyapunov Indicator (OFLI), we study the evolution of the fraction of the phase space volume occupied by regular motions. 相似文献
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S. Gutiérrez-López A. Castellanos-Moreno A. Corella-Madueño R.A. Rosas J.A. Reyes 《Optics Communications》2012,285(9):2439-2444
We consider a model for a one-dimensional photonic crystal formed by a succession of nonlinear Kerr-type equidistant spaceless interfaces immersed in a linear medium. We calculate analytically the band structure of this system as a function of the incident wave intensity, and find two main tendencies: the appearance of prohibited bands, and the separation and narrowing of these bands. We consider as well a finite version of this photonic crystal for a limited number of alternating linear and non linear set of stacks for which we calculate reflectance as a function of the electromagnetic wave intensity, band index and number of periods. A system with these features can be constructed by alternating very thin slabs of a nonlinear soft matter material with thicker solid films, which can be used to design a device to control light propagation for specific wavelength intervals and light intensities of the same propagating signal. 相似文献
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First we calculate the Wigner phase-space distribution function for the Klein-Gordan Landau problem on a commmutative space. Then we study the modifications introduced by the coordinate-coordinate noncommuting and momentum-momentum noncommuting, namely, by using a generalized Bopp's shift method we construct the Wigner function for the Klein-Gordan Landau problem both on a noncommutative space (NCS) and a noncommutative phase space (NCPS). 相似文献
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We derive the bosonization rules for free fermions on a half-line with physically sensible boundary conditions for Luttinger fermions. We use path-integral methods to calculate the bosonized fermionic currents on the half-line and derive their commutation relations for a system with a boundary. We compute the fermion determinant of the fermionic fluctuations for a system with a boundary using Forman's approach. We find that the degrees of freedom induced at the boundary do not to modify the commutation relations of the bulk. We give an explicit derivation of the bosonization rules for the fermion operators for a system with boundaries. We derive a set of bosonization rules for the Fermi operators which include the explicit effect of the boundaries and of boundary degrees of freedom. As a byproduct, we calculate the one-particle Green function and determine the effects of the boundaries on its analytic structure. 相似文献
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We explore the quantum dynamical behavior of the Morse oscillator in the phase space using the Wigner function. For an initial wave packet excited with Gaussian probability distribution, we calculate the associated Wigner function and compute its time evolution. By calculating the marginal probabilities, we study the formation of quantum carpets both in the position space and in the momentum space. In addition, in view of these probabilities, we present the time evolution of the position and momentum expectation values. The structure of quantum carpets and the time-evolved expectation values mimic the emergence of quantum revivals and fractional revivals. 相似文献