Electrons quasiparticles

An important prediction of LL theory is that the low-energy elementary excitations of a one-dimensional metal are not electronic quasiparticles, as... 

Additionally to the vibronic quasiparticle approximation, the electronic quasiparticle approximation can be used when the coupling to the leads is weak. In this case the lesser function can be parameterized through the number of electrons Fv in the eigenstates of the noninteracting molecular Hamiltonian H(0)... 

In the SC state the excess current Iexc (1), which is due to the Andreev reflection of electron quasiparticles from the N — S boundary inaW-c — S contact (c stands for constriction ), can be written as... 

The nonlinear term in the excess current (4) in its turn can be separated into two parts, which depend in a different way on the elastic scattering of electron quasiparticles ... 

Nesbet, R.K. (1986). Nonperturbative theory of exchange and correlation in one-electron quasiparticle states, Phys. Rev. B 34, 1526-1538. 

An interesting feature of Eq. (16.17) is worth mentioning. It is seen that two fermion operators are collected in this equation to form a pair of zero resulting spin. Such pairs are called Cooper pairs in the theory of superconductivity. Equation (16.17) can also be considered as a quasiparticle transformation which is, however, very different from the single-particle transformations we have seen previously. Two-electron quasiparticle transformations will be introduced in the next section in a somewhat different context. 

More advanced teclmiques take into account quasiparticle corrections to the DFT-LDA eigenvalues. Quasiparticles are a way of conceptualizing the elementary excitations in electronic systems. They can be detennined in band stmcture calculations that properly include the effects of exchange and correlation. In the... 

Straightforward analytical models, however, receive particular attention in the present book, as they are of unique significance in the comprehension of physical phenomena and, moreover, provide the very language to describe them. To exemplify, recall the effect caused on the phase transition theory by the exactly soluble two-dimensional Ising model. Nor can one overestimate the role of the quasiparticle concept in the theory of electronic and vibrational excitations in crystals. As new experimental evidence becomes available, a simplistic physical picture gets complicated until a novel organizing concept is created which covers the facts known from the unified standpoint (thus underlying the aesthetic appeal of science). 

Silicon is a model for the fundamental electronic and mechanical properties of Group IV crystals and the basic material for electronic device technology. Coherent optical phonons in Si revealed the ultrafast formation of renormalized quasiparticles in time-frequency space [47]. The anisotropic transient reflectivity of n-doped Si(001) featured the coherent optical phonon oscillation with a frequency of 15.3 THz, when the [110] crystalline axis was parallel to the pump polarization (Fig. 2.11). Rotation of the sample by 45° led to disappearance of the coherent oscillation, which confirmed the ISRS generation,... 

Here in eq. (38) "EpqfpQN a.pag is new Hartree-Fock operator for a new fermions (25), (26), operator Y,pQRsy>pQR a Oq 0s%] is a new fermion correlation operator and Escf is a new fermion Hartree-Fock energy. Our new basis set is obtained by diagonalizing the operator / from eq. (36). The new Fermi vacuum is renormalized Fermi vacuum and new fermions are renormalized electrons. The diagonalization of/ operator (36) leads Jo coupled perturbed Hartree-Fock (CPHF) equations [ 18-20]. Similarly operators br bt) corresponds to renormalized phonons. Using the quasiparticle canonical transformations (25-28) and the Wick theorem the V-E Hamiltonian takes the form... 

The finite rotations in the space of occupation numbers for the one-electron state define the transition to the quasiparticle wave functions... 

But this phase factor can be selected so that the signs of the CFP for almost filled shells are the same as in the quasispin method. It is worth recalling here that finite transformations generated by quasispin operators define the passage to quasiparticles. In much the same way, in the quasispin space of a shell of equivalent electrons the unitary transformations... 

A iV-electron vacancy (hole) in a shell may be denoted as nl N = ni4l+2-N (see aiso Chapters 9, 13 and 16). As we have seen in the second-quantization representation, symmetry between electrons and vacancies has deep meaning. Indeed, the electron annihilation operator at the same time is the vacancy creation operator and vice versa instead of particle representation hole (quasiparticle) representation may be used, etc. It is interesting to notice that the shift of energy of an electron A due to creation of a vacancy B l is approximately (usually with the accuracy of a few per cent) equal to the shift of the energy of an electron B due to creation of a vacancy A l, i.e. 

Usually, the electronic thermal conductance re can be calculated from the Wiedemann - Franz law, re TG/e2. However, as shown in Ref. [8, 9] for the ballistic limit f > d, this law gives a wrong result for Andreev wires if one uses an expression for G obtained for a wire surrounded by an insulator. Andreev processes strongly suppress the single electron transport for all quasiparticle trajectories except for those which have momenta almost parallel to the wire thus avoiding Andreev reflection at the walls. The resulting expression for the thermal conductance... 

The interband interaction constant IT > 0 corresponds to repulsion with possible electronic and electron-phonon contributions. The quasiparticle... 

MICROSCOPIC PHASE SEPARATION AND TWO TYPE OF QUASIPARTICLES IN LIGHTLY DOPED La2-xSrxCu04 OBSERVED BY ELECTRON PARAMAGNETIC RESONANCE... 

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