Excitation spectra of the negative-{ital U} Hubbard model: A small-cluster study

Journal Article · Fri Dec 01 04:00:00 EST 1995 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.52.15617· OSTI ID:132875

Ohta, Y; Nakauchi, A; Eder, R; Tsutsui, K; Maekawa, S ^[1]

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1. Department of Applied Physics, Nagoya University, Nagoya 464-01 (Japan)

An exact-diagonalization technique on small clusters is used to study low-lying excitations and superconductivity in the two-dimensional negative-{ital U} Hubbard model. We first calculate the Bogoliubov-quasiparticle spectrum, condensation amplitude, and coherence length as functions of the coupling strength {ital U}/{ital t}, thereby working out how the picture of Bogoliubov quasiparticles in the BCS superconductors is affected by increasing the attraction. We then define the Cooper-pair operator as a spatially extended composite boson and make a variational evaluation of its internal structure. We thereby calculate the single-particle spectral function of the Cooper pair and obtain the dispersion relation for its translational motion. The dynamical density correlation function of the pairs is also calculated. We thus demonstrate the applicability of our numerical method for gaining insight into low-lying excitations of models for the intermediate coupling superconductivity relevant to cuprate materials.

• OSTI ID: 132875
• Journal Information: Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 21 Vol. 52; ISSN 0163-1829; ISSN PRBMDO
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
CLUSTER MODEL
COHERENCE LENGTH
COOPER PAIRS
DISPERSION RELATIONS
ENERGY SPECTRA
EXCITED STATES
HUBBARD MODEL
NUMERICAL SOLUTION
QUASI PARTICLES
SPECTRAL FUNCTIONS
SUPERCONDUCTIVITY
TWO-DIMENSIONAL CALCULATIONS