Strongly correlated electrons

Double pump experiments on an organic charge transfer complex TTF-CA by Iwai and coworkers demonstrated a new class of coherent control on a strongly correlated electron-lattice system [44]. While the amplitude of the coherent oscillation increased linearly with pump fluence for single pump experiments, the amplitude in the double pump experiments with a fixed pulse interval At = T exhibited a strongly super-linear fluence dependence (Fig. 3.16). The striking difference between the single- and double-pulse results indicated a cooperative nature of the photo-induced neutral-ionic transition. 

Geldart DJW, Rasolt M (1992) In M.P. Das and D. Neilson (eds) Strongly Correlated Electron Systems. Nova Science, New York, p 123... 

Keywords strongly correlated electrons nondynamic correlation density matrix renormalization group post Hartree-Fock methods many-body basis matrix product states complete active space self-consistent field electron correlation... 

Hallberg, K. Density matrix renormalization a review of the method and its applications. In Theoretical Methods for Strongly Correlated Electrons (eds D. Senechal, A.-M. Tremblay, and... 

Self-Interaction Error, Strongly Correlated Electron Systems, and DFT + U... 

The fact that self-interaction errors are canceled exactly in HF calculations suggests that a judicious combination of an HF-like approach for localized states with DFT for everything else may be a viable approach for strongly correlated electron materials. This idea is the motivation for a group of methods known as DFT+U. The usual application of this method introduces a correction to the DFT energy that corrects for electron self-interaction by introducing a single numerical parameter, U — J, where U and J involve different aspects of self-interaction. The numerical tools needed to use DFT+U are now fairly widely implemented in plane-wave DFT codes. 

S. Rettrup and B. J. Mogensen, Strongly Correlated Electron Systems in Chemistry (S. Ramasesha and D. D. Saxma eds.) Narosa Publ. House, New Delhi, India, 1996, 55. 

McKenzie RH (1998) A strongly correlated electron model for the layered organic superconductors tc-(BEDT-TTF)2X. Comments. Condens Matter Phys 18 309-337... 

Molecule contains strongly correlated electrons in the partially filled valence d-shell of the transition metal central atom ... 

It was found that because of the strong electron correlation the phonon-induced charge transfer depends on the spin. Consequently the phonon modifies the spin correlation and spin dynamics [12]. In the strongly correlated electron systems phonons interact not only with charge, but also with spins. 

Th. Mercouris, Y. Komninos, C.A. Nicolaides, Time-resolved hyperfast processes of strongly correlated electrons during the coherent excitation and decay of multiply excited and inner-hole excited states, Phys. Rev. A 76 (3) (2007) 033417. 

S.R. Julian, International Conference on Strongly Correlated Electron Systems, Program and Abstracts (2004) 1. 

Likewise the Hubbard model the periodic Anderson model (PAM) is a basic model in the theory of strongly correlated electron systems. It is destined for the description of the transition metals, lanthanides, actinides and their compositions including the heavy-fermion compounds. The model consists of two groups of electrons itinerant and localized ones (s and d electrons), the hybridization between them is admitted. The model is described by the following parameters the width of the s-electron band W, the energy of the atomic level e, the on-site Coulomb repulsion U of d-electrons with opposite spins, the parameter V of the... 

Physics described by the model with so many parameters is very rich and the model is able particularly to treat heavy fermion systems. To study the model many approaches were suggested (see reviews [2-5]). They are successful for particular regions of the parameter space but no one is totally universal. In this paper we apply to PAM the generating functional approach (GFA) developed first by Kadanoff and Baym [6] for conventional systems and generalized for strongly correlated electron systems [7-10]. In particular it has been applied to the Hubbard model with arbitrary U in the X-operators formalism [10]. The approach makes it possible to derive equations for the electron Green s function (GF) in terms of variational derivatives with respect to fluctuating fields. 

Strongly correlated electron systems including high-Tc superconductors were discussed in talks by S. Ovchinnikov (Theory for transition metal oxides), G. Petrakovskii (Magnetism of 2D spin systems),... 

Rudolf Haussmann, Self-Consistent Field Theory and Bosonization for Strongly Correlated Electron Systems, Springer, Berlin, 1999. 

D. Baeriswyl, D. K. Campbell and S. Mazumdar, in Conjugated Conducting Polymers, H. G. Kiess (Ed.), (Springer, Berlin 1992) Y. Anusooya, B. Srinivasan and S. Ramasesha, in Strongly Correlated Electron Systems in Chemistry, S. Ramasesha and D. D. Sarma (Eds.), (Naxosa Publishing House, New Delhi, 1996) p. 67. 

Spin permutation technique in the theory of strongly correlated electron systems... 

One of the simplest models describing a system of strongly correlated electrons on a crystal lattice is the Hubbard Hamiltonian [8] ... 

For strongly correlated electron systems with non half-filled bands there are electron hops between occupied and unoccupied lattice sites. In the general case these hops lift spin degeneracy in first PT order in ty. This leads to more... 

The purpose of these notes is to show how some strongly correlated electron models like the one-band Hubbard model with infinite electron repulsion on rectangular and triangular lattices can be described in terms of spinless fermions and the operators of cyclic spin permutations. We will consider in detail the... 

However, in the preceding two decades, there have been many experimental discoveries, beside high-Tc superconductivity, evidencing that we do not have yet the proper theoretical skills and tools to deal well with strongly correlated electron systems. For instance, heavy-fermions, fractional quantum Hall effect, ladder materials, and very specially high-Tc superconductivity seem not accessible from the weak coupling limit. 

In conclusion we note that the construction of considered models is based on the following property. Their Hamiltonians are the sums of the cell Hamiltonians that are local and non-commuting with each other. At the same time the ground-state wave function of the total Hamiltonian is the ground state for each cell Hamiltonian. It is clear that these models are rather special. Nevertheless, the study of them is useful for understanding properties of the real frustrated spin systems and strongly correlated electronic models. 

Dagotto, E. 2003 Nanoscalephase separation and colossal magnetoresistance. Berlin, Germany Springer. Dagotto, E. 2005 Complexity in strongly correlated electronic systems, Science 309, 257-362. (doi 10.1126/science. 1107559)... 

Interesting historical work on the RVB can be obtained in J. Woods Halley, ed., Theories of High Temperature Superconductivity, Addison-Wesley, Reading, Mass., 1988 Zi-Zhao Gan and Zhao-Bin Su, eds., Two-Dimensional Strongly Correlated Electronic Systems, Gordon and Breach, New York, 1988. 

Frustration Effect in Strongly Correlated Electron Systems with Orbital Degree of Freedom... 

We start from the model Hamiltonian to describe the strongly correlated electron system with the eg orbital degree of freedom. A system of the present interest is a Mott insulator where one electron occupies one of the doubly degenerate orbitals at each site in a simple cubic lattice. The doubly degenerate orbital degree of freedom is represented by the pseudo-spin operator with an amplitude of 1/2 defined by... 

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