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International Journal of Modern Physics B

STABILITY OF PHOTOINDUCED SUPERCONDUCTING STATES IN STRONGLY CORRELATED TWO-DIMENSIONAL ELECTRON SYSTEMS

Hiroki Gomi, TOSHIHIRO UEDA, Akira Takahashi, Masaki Aihara

Published Jan 30, 2005• 4 citations
Publisher

Abstract

We theoretically investigate the properties of multiphoton excited states in strongly correlated two-dimensional electron systems at half-filling using the extended Hubbard model in the strong correlation case. We find that the photoinduced d-wave superconducting states are stable against the nearest neighbor Coulomb interaction within the realistic Coulomb parameters.

DOI
10.1142/s0217979205027846

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We theoretically investigate the properties of multiphoton excited states in strongly correlated two-dimensional electron systems at half-filling using the extended Hubbard model in the strong correlation case. We find that the photoinduced d-wave superconducting states are stable against the nearest neighbor Coulomb interaction within the realistic Coulomb parameters.
We theoretically investigate the properties of multiphoton excited states in strongly correlated two-dimensional electron systems. The effective Hamiltonian of the Hubbard model for the multiphoton excited states is derived assuming strong Coulomb repulsion. Diagonalizing the effective Hamiltonian exactly, the lowest energy state in two-photon excited manifold is calculated in the 20 site two-dimensional square lattice at half filling. Analysis of correlation functions suggests that the antiferromagnetic spin order characteristic of the half filled ground state is destroyed by two-photon excitation, and two different d-wave superconducting states and a spiral spin state are photogenerated.
We theoretically investigate the properties of multiphoton excited states in strongly correlated one-dimensional (1D) and two-dimensional (2D) electron systems at half filling using the extended Hubbard model. In the 2D case, we find the photoexcited states where two or more than two holons and doublons are strongly bound, and the cluster of bound holons and doublons coexists with the surrounding antiferromagnetic (AF) spin order, for the realistic Coulomb interaction parameters. The holon-doublon cluster (HDC) states have a unique charge aggregation mechanism originating from the spin-spin interaction in the AF spin background as well as from the direct Coulomb interaction. In the 1D case, the HDC states are destabilized by the spin-spin interaction in contrast to the 2D case. These charge aggregation mechanisms are the outcomes of exotic natures of holons and doublons, and the difference in the mechanism between the 1D and 2D cases is due to the difference in the coupling between spin and charge degrees of freedom. We also calculate the light-induced absorption that enables us to experimentally observe the predicted HDC states.
The effective Hamiltonian of the Hubbard model for multiphoton excited states is derived assuming a strong Coulomb repulsion. Diagonalizing the effective Hamiltonian exactly, the lowest energy one-photon excited state is calculated in the two-dimensional Hubbard model at half-filling, and its physical properties are investigated. For t/U< 0.0165,t/U<~0.0165,t/U< 0.0165, where t is the magnitude of the transfer integral between the nearest-neighbor sites and U is an on-site Coulomb repulsion energy, ferromagnetic spin order is photogenerated from the antiferromagnetic ground state, and, for t/U> 0.0166,t/U>~0.0166,t/U> 0.0166, antiferromagnetic spin order survives one-photon excitation. Photoinjected opposite charges are unbound because of strong electron correlation for t/U< 0.08,t/U<~0.08,t/U< 0.08, and bound for t/U> 0.08.t/U>~0.08.t/U> 0.08. The probability that the photoinjected opposite charges are on nearest-neighbor sites is strongly suppressed through all the correlation regions including this charge-bound region. We see a tendency toward spin-charge separation, but the coupling is not small in the one-photon excited state. The local spin structure around the bound positive and negative charges injected by photoexcitation is quite different from that induced by two-hole doping; this result suggests that multiphoton excitation will generate an electronic order which differs from that generated by doping.
The authors study a simple model for superconductivity based on an extended Hubbard model with on-site repulsive and inter-site attractive interaction for arbitrary electron density. The two-dimensional square lattice d-wave pairing is most stable for a nearly half-filled band. p-wave and then extended s-wave pairing become stable upon decreasing band filling. Competition between the various anisotropic pairings and antiferromagnetism as well as the effect of next-nearest-neighbour hopping is discussed. The authors relate the present model to high-T c superconducting oxides.
We investigate the influence of nonlocal interactions on superconducting correlations within the extended Hubbard model. In addition to the on-site Coulomb interaction and nearest-neighbor hopping, we include next-nearest-neighbor hopping together with several physically relevant nonlocal terms, namely nearest-neighbor Coulomb interaction, correlated hopping, exchange interaction, and pair hopping. Using Lanczos exact diagonalization on a 4×44\times44×4 cluster, supported by projector quantum Monte Carlo simulations for selected parameter regimes, we analyze pairing correlations in both the s- and d-wave channels. We demonstrate that nonlocal interactions exert a highly nontrivial and symmetry-dependent influence on superconducting correlations. While the on-site repulsion in cooperation with next-nearest-neighbor hopping enhances d-wave pairing tendencies, correlated hopping and nearest-neighbor Coulomb interaction strongly promote s-wave correlations, whereas exchange and pair-hopping interactions can efficiently suppress superconductivity beyond relatively small critical strengths. When all nonlocal interactions are considered simultaneously, the resulting phase diagrams reveal a complex interplay and competition between different pairing symmetries. Our results highlight the crucial role of extended interactions in shaping the pairing landscape of strongly correlated systems and demonstrate that a comprehensive treatment beyond the minimal Hubbard model is essential for a realistic description of unconventional superconductivity.