共查询到20条相似文献,搜索用时 171 毫秒
1.
Anil Khurana 《Zeitschrift für Physik B Condensed Matter》1994,95(3):287-289
The Hubbard solution to the Hubbard model showed a non-trivial metal-insulator transition. The value of the one-particle density of states at the Fermi energy in that solution decreased continuously with increasing value of the Hubbard interaction and vanished at a critical value of the interaction. Such a solution is derived from a planar model, as an approximation to the exact construction of the model's one-particle Green function. 相似文献
2.
We investigate the Mott transition in the kagomé lattice Hubbard model using a cluster extension of dynamical mean field theory. The calculation of the double occupancy, the density of states, and the static and dynamical spin correlation functions demonstrates that the system undergoes the first-order Mott transition at the Hubbard interaction U/W approximately 1.4 (W:bandwidth). In the metallic phase close to the Mott transition, we find the strong renormalization of three distinct bands, giving rise to the formation of heavy quasiparticles with strong frustrated interactions. It is elucidated that the quasiparticle states exhibit anomalous behavior in the temperature-dependent spin correlation functions. 相似文献
3.
ABSTRACTSite-occupation embedding theory (SOET) is a density functional theory (DFT)-based method which aims at modelling strongly correlated electrons. It is in principle exact and applicable to model and quantum chemical Hamiltonians. The theory is presented here for the Hubbard Hamiltonian. In contrast to conventional DFT approaches, the site (or orbital) occupations are deduced in SOET from a partially interacting system consisting of one (or more) impurity site(s) and non-interacting bath sites. The correlation energy of the bath is then treated implicitly by means of a site-occupation functional. In this work, we propose a simple impurity-occupation functional approximation based on the two-level (2L) Hubbard model which is referred to as two-level impurity local density approximation (2L-ILDA). Results obtained on a prototypical uniform eight-site Hubbard ring are promising. The extension of the method to larger systems and more sophisticated model Hamiltonians is currently in progress. 相似文献
4.
A strong coupling expansion for a two‐band Hubbard model on two sites with nearly degenerate states is considered. A comparative analysis is performed for different schemes of perturbation theory which are applicable to systems with nearly degenerate states. A fourth order approach which builds on a four‐dimensional low‐energy subspace with nearly degenerate states captures accurately the transition from an antiferromagnetic to a ferromagnetic ground state at large on‐site Coulomb interaction. 相似文献
5.
A new kind of phase transition is proposed for lattice fermion systems with simplified f 2 configurations at each site. The free energy of the model is computed in the mean-field approximation for both the itinerant state with the Kondo screening, and a localized state with the crystalline electric field (CEF) singlet at each site. The presence of a first-order phase transition is demonstrated in which the itinerant state changes into the localized state toward lower temperatures. In the half-filled case, the insulating state at high temperatures changes into a metallic state, in marked contrast with the Mott transition in the Hubbard model. For comparison, corresponding states are discussed for the twoimpurity Kondo system with f 1 configuration at each site. 相似文献
6.
The Mott-Hubbard metal-insulator transition is one of the most important problems in correlated-electron systems. In the past decade, much progress has been made in examining a particle-hole symmetric form of the transition in the Hubbard model with dynamical mean field theory, where it was found that the electronic self-energy develops a pole at the transition. We examine the particle-hole asymmetric metal-insulator transition in the Falicov-Kimball model and find that a number of features change when the noninteracting density of states has a finite bandwidth. 相似文献
7.
Green’s function in the paramagnetic phase of the Hubbard model with strong electron correlations is calculated by the many-electron operators method. The density of states pattern is considered in the case of half-filling (metal-insulator transition) and in the doped case. The effect of the low-temperature Kondo scattering on the energy spectrum is analyzed, and the results are compared with the results of the dynamical mean-field theory (DMFT). 相似文献
8.
A simplified periodic Anderson model, without spin and Hubbard correlation, coupled to a branch of optical phonons is presented and discussed in connection with Rare Earth compounds exhibiting a transition to a mixed valence state. The phonon self energy is approximately calculated by diagrammatic techniques and used for a study of boson modes originating from the interplay of phonons withf-electrons mixed into band states. It is shown that weakly damped low lying or even soft modes may exist in connection with the transition. The relevance of these results to real systems, possible shortcomings of the model and the relations to other work in this field is described. 相似文献
9.
S. Ejima F. Gebhard R. M. Noack 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(2):191-200
We use the Random Dispersion Approximation (RDA) to study the
Mott-Hubbard transition in the Hubbard model at half band filling.
The RDA becomes exact for the Hubbard model in infinite dimensions.
We implement the RDA on finite chains and employ the Lanczos exact
diagonalization method in real space to calculate the ground-state energy,
the average double occupancy, the charge gap, the momentum distribution,
and the quasi-particle weight. We find a satisfactory agreement with
perturbative results in the weak- and strong-coupling limits.
A straightforward extrapolation of the RDA data
for L ≤ 14 lattice results in a continuous Mott-Hubbard transition at
Uc≈W.
We discuss the significance of a possible signature
of a coexistence region between insulating and metallic
ground states in the RDA that would correspond to
the scenario of a discontinuous Mott-Hubbard transition
as found in numerical investigations
of the Dynamical Mean-Field Theory for the Hubbard model. 相似文献
10.
Reinert F Nicolay G Eltner B Ehm D Schmidt S Hufner S Probst U Bucher E 《Physical review letters》2000,85(18):3930-3933
We present high-resolution photoelectron spectra on the A15-type conventional superconductor V 3Si, where-for the first time-both singularities of the BCS density of states can be resolved by photoemission spectroscopy (PES). With a transition temperature of about T(c) approximately 17 K the gap Delta(gap) of this compound has a magnitude of approximately 5 meV. A measurement by PES on this small energy scale requires a very high energy resolution (DeltaE less, similar5 meV) and sample temperatures significantly below T(c). 相似文献
11.
S.-J. Gu J. Cao S. Chen Y. Liu H.-Q. Lin 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(4):477-481
The band effects on the conductivity of a one-dimensional
two-band Hubbard model is studied based on the ground state energy
analysis. It is found that the system with filling factor one is a
metal at zero temperature if the on-site interaction U is smaller
than a critical value Uc, and is an insulator if U is larger
than Uc. The value of metal-insulator transition point Uc is
obtained. This result is different from that of 1D single-band
Hubbard model where the quantum phase transition point Uc=0.
Therefore, the orbital degree of freedom plays an essential role in
the states of matter. 相似文献
12.
We formulate a U(1) gauge theory of the Hubbard model in the slave-rotor representation. From this formalism it is argued that spin liquid phases may exist near the Mott transition in the Hubbard model on triangular and honeycomb lattices at half filling. The organic compound kappa-(BEDT-TTF)2Cu2(CN)3 is a good candidate for the spin liquid state on a triangular lattice. We predict a highly unusual temperature dependence for the thermal conductivity of this material. 相似文献
13.
本文报道了氢化非晶碳薄膜在2.9-4.5eV光激发下的发光谱。它的光致发光谱是无结构的不对称宽带,半宽度约为0.8eV。在低于3.56eV的光激发下,谱带的峰值能量随激发能量的降低明显红移。在安德森带结构和指数分布的带尾态密度的基础上,考虑了尾态中粒子的两种跃迁过程,实验的PL谱就可得到解释。并用这个简单模型计算了这种材料的光致发光谱特征。 相似文献
14.
Opeil CP Mihaila B Schulze RK Mañosa L Planes A Hults WL Fisher RA Riseborough PS Littlewood PB Smith JL Lashley JC 《Physical review letters》2008,100(16):165703
Ultraviolet-photoemission (UPS) measurements and supporting specific-heat, thermal-expansion, resistivity, and magnetic-moment measurements are reported for the magnetic shape-memory alloy Ni2MnGa over the temperature range 100T(PM) is due to the Ni d minority-spin electrons. Below T(M) this peak disappears, resulting in an enhanced density of states at energies around 0.8 eV. This enhancement reflects Ni d and Mn d electronic contributions to the majority-spin density of states. 相似文献
15.
Jian ZHONG 《理论物理通讯》1989,12(2):137-144
The CDW-SDW transition in the half-filled extended Hubbard model is investigated with the broken-symmetry Hartree theory formulated in terms of the Bogoliubov variational approach. The finite temperature phase-diagram in the weak coupling regime is derived analytically with a model density of states. The results show that there exist charge-order and antiferromagnetic order, but no mixed phase exists at any temperatures. 相似文献
16.
17.
V. V. Val’kov M. M. Korovushkin 《Journal of Experimental and Theoretical Physics》2011,112(1):108-120
The diagram technique for Hubbard operators is used to investigate the influence of intersite Coulomb interactions on the
energy structure and Cooper instability of strongly correlated fermions. Allowance for intersite correlations in doped Mott-Hubbard
insulators is shown to lead to a splitting of the lower subband of Hubbard fermions and to the formation of a band of fluctuation
states as soon as the intersite interaction energy becomes comparable to or exceeds the mean kinetic energy. The spectral
intensity of the splitoff band is proportional to the root-mean-square fluctuation of the occupation numbers and increases
with doping level. The predicted effect changes significantly the structure of the density of electronic states. This leads
to a renormalization of the pole of the scattering amplitude in the Cooper channel and manifests itself as a nonuniform (in
electron concentration) modification of the dependence of the critical superconducting transition temperature. 相似文献
18.
S. V. Nikolaev S. G. Ovchinnikov 《Journal of Experimental and Theoretical Physics》2010,111(4):635-644
The cluster perturbation theory is presented in the 2D Hubbard model constructed using X operators in the Hubbard-I approximation. The short-range magnetic order is taken into account by dividing the entire lattice
into individual 2 × 2 clusters and solving the eigenvalue problem in an individual cluster using exact diagonalization taking
into account all excited levels. The case of half-filling taking into account jumps between nearest neighbors is considered.
As a result of numerical solution, a shadow zone is discovered in the quasiparticle spectrum. It is also found that a gap
in the density of states in the quasiparticle spectrum at zero temperature exists for indefinitely small values of Coulomb
repulsion parameter U and increases with this parameter. It is found that the presence of this gap in the spectrum is due to the formation of a
short-range antiferromagnetic order. An analysis of the temperature evolution of the density of states shows that the metal-insulator
transition occurs continuously. The existence of two characteristic energy scales at finite temperatures is demonstrated,
the larger scale is associated with the formation of a pseudogap in the vicinity of the Fermi level, and the smaller scale
is associated with the metal-insulator transition temperature. A peak in the density of states at the Fermi level, which is
predicted in the dynamic mean field theory in the vicinity of the metal-insulator transition, is not observed. 相似文献
19.
Filling dependence of correlation exponents and metal-Mott insulator transition in strongly correlated electron systems
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Using a universal relation between electron filling factor and ground state energy,this paper studies the dependence of correlation exponents on the electron filling factor of one-dimensional extended Hubbard model in a strong coupling regime,and demonstrates that in contrast to the usual Hubbard model(gc = 1/2),the dimensionless coupling strength parameter g c heavily depends on the electron filling,and it has a "particle-hole" symmetry about electron quarter filling point.As increasing the nearest neighbouring repulsive interaction,the single particle spectral weight is transferred from low energy to high energy regimes.Moreover,at electron quarter filling,there is a metal-Mott insulator transition at the strong coupling point gc = 1/4,and this transition is a continuous phase transition. 相似文献
20.
We consider the Hubbard model at half filling, driven by an external, stationary laser field. This stationary, but periodic in time, electromagnetic field couples to the charge current, i.e. it induces an extra contribution to the hopping amplitude in the Hubbard Hamiltonian (photo‐induced hopping). We generalize the dynamical mean‐field theory (DMFT) for nonequilibrium with periodic‐in‐time external fields, using a Floquet mode representation and the Keldysh formalism. We calculate the non‐equilibrium electron distribution function, the density of states and the optical DC conductivity in the presence of the external laser field for laser frequencies above and below the Mott‐Hubbard gap. The results demonstrate that the system exhibits an insulator‐metal transition as the frequency of the external field is increased and exceeds the Mott‐Hubbard gap. This corresponds to photo‐induced excitations into the upper Hubbard band. 相似文献