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21.
M. Cini G. Stefanucci A. Balzarotti 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):293-304
The Cu-O plane and the clusters that possess the same C4v symmetry around a Cu ion have 2-hole eigenstates of the kinetic energy with vanishing on-site repulsion (W=0 pairs). Cluster calculations by exact diagonalisation show that these are the quasiparticles that lead to a paired ground
state, and have superconducting flux-quantisation properties. Here, we extend the theory to the full plane, and show that
the W=0 quasiparticles are again the natural explanation of superconducting flux-quantisation. Moreover, by a new approach which
is exact in principle, we calculate the effective interaction between two holes added to the ground state of the repulsive three-band Hubbard model. To explain how a noninteracting electron
gas becomes a superconductor when switching the local Coulomb interaction, we obtain a closed-form analytic expression including
the effects of all virtual transitions to 4-body intermediate states (exchange of an electron-hole pair). Our scheme is ready
to include other interactions which are not considered in the Hubbard model but may be important. In the plane, the W=0 pairs have 1
B
2
and 1
A
2
symmetry. The effective interaction in these channels is attractive and leads to a Cooper-like instability of the Fermi liquid,
while it is repulsive for triplet pairs. From , we derive an integral equation for the pair eigenfunction; the binding energy of the pairs is in the range of tens of meV. However, our symmetry-based method is far more general than the model.
Received 18 December 1998 相似文献
22.
We demonstrate the remnant presence of initial correlations in the steady-state electrical current jS flowing between low-dimensional interacting leads. The leads are described as Luttinger liquids and electrons can tunnel via a quantum point contact. We derive an analytic result for the time-dependent current and show that ground-state correlations have a large impact on the relaxation and long-time behavior. In particular, the I-V characteristic is not reproduced by quenching the interaction in time. We further present a universal formula of jS for an arbitrary sequence of interaction quenches and it is established that jS is history dependent for nonsmooth switching process. 相似文献
23.
E. Perfetto G. Stefanucci M. Cini 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):139-142
We show that different non-conventional superconductors have one fundamental feature in common: pair eigenstates of the Hamiltonian
are repulsion-free, the W = 0 pairs. In extended Hubbard models, pairing can occur for reasonable parameter values. For (N, N) nanotubes the binding energy of the pair depends strongly on the filling and decreases towards a reduced but nonzero value
for the graphite sheet N → ∞.
Received 13 July 2002 Published online 29 November 2002 相似文献
24.
M. Cini A. Balzarotti G. Stefanucci 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):269-280
We study the Cu5O4 cluster by exact diagonalization of a three-band Hubbard model and show that bound electron or hole pairs are obtained at
appropriate fillings, and produce superconducting flux quantization. The results extend earlier cluster studies and illustrate
a canonical transformation approach to pairing that we have developed recently for the full plane. The quasiparticles that
in the many-body problem behave like Cooper pairs are W
=0 pairs, that is, two-hole eigenstates of the Hubbard Hamiltonian with vanishing on-site repulsion. The cluster allows W
=0 pairs of d symmetry, due to a spin fluctuation, and ssymmetry, due to a charge fluctuation. Flux quantization is shown to be a manifestation of symmetry properties that hold for
clusters of arbitrary size.
Received 23 July 1999 相似文献
25.
An ab initio quantum-classical mixed scheme for the time evolution of electrode-device-electrode systems is introduced to study nuclear dynamics in quantum transport. Two model systems are discussed to illustrate the method. Our results provide the first example of current-induced molecular desorption as obtained from a full time-dependent approach and suggest the use of ac biases as a way to tailor electromigration. They also show the importance of nonadiabatic effects for ultrafast phenomena in nanodevices. 相似文献