arXiv subjects

S. Mazumdar

Publications and source records attributed to S. Mazumdar.

61 records · Page 4Linked to original sources

arXiv2000

Re-integerization of fractional charges in the correlated quarter-filled band

Previous work has demonstrated the existence of soliton defect states with charges +/- e/2 in the limits of zero and of infinite on-site Coulomb interactions in the one-dimensional (1D) quarter-filled band. For large but finite on-site Coulomb interaction, the low temperature 2k_F bond distortion that occurs within the 4k_F bond-distorted phase is accompanied by charge-ordering on the sites. We show that a ``re-integerization'' of the defect charge occurs in this bond-charge density wave (BCDW) state due to a ``binding'' of the fractional charges. We indicate briefly possible implications of this result for mechanisms of organic superconductivity.

cond-mat.str-el↗

arXiv2000

Ultrafast optical nonlinearity in quasi-one-dimensional Mott-insulator ${\rm Sr_2CuO_3}$

We report strong instantaneous photoinduced absorption (PA) in the quasi-one-dimensional Mott insulator ${\rm Sr_2CuO_3}$ in the IR spectral region. The observed PA is to an even-parity two-photon state that occurs immediately above the absorption edge. Theoretical calculations based on a two-band extended Hubbard model explains the experimental features and indicates that the strong two-photon absorption is due to a very large dipole-coupling between nearly degenerate one- and two-photon states. Room temperature picosecond recovery of the optical transparency suggests the strong potential of ${\rm Sr_2CuO_3}$ for all-optical switching.

cond-mat.str-el↗

arXiv1999

Novel coexisting density wave ground state in strongly correlated, two-dimensional electronic materials

Two-dimensional (2D) strongly correlated electron systems underlie many of the most important phenomena in contemporary condensed matter physics, including the Quantum Hall Effect (QHE), ``high T_c'' superconductivity, and possible exotic conducting states in silicon MOSFETs. We demonstrate the existence of yet another exotic ground state in strongly correlated, 2D electronic materials: a novel, insulating bond-order/charge density wave state (BCDW) in the commensurate 1/4-filled band that persists for all anisotropies within the 2D lattice, in contradiction to the non-interacting electron prediction of the vanishing of density waves in 2D for non-1/2-filled bands. The persistence of the BCDW in the 2D lattice is a consequence of strong electron-electron (e-e) interaction and the resultant ``confinement,'' a concept recently widely debated. Our results have implications for experiments in the organic charge transfer solids (CTS), where they explain the observation of a ``mysterious'' coexistence of density waves, clarify the optical conductivity of the ``metallic'', and suggest an approach to the observed organic superconductivity.

cond-mat.str-el↗

arXiv1998

Theory of Coexisting Charge and Spin-Density Waves in (TMTTF)_2Br, (TMTSF)_2PF_6 and alpha-(BEDT-TTF)_2MHg(SCN)_4

Recent experiments indicate that the spin-density waves (SDWs) in (TMTTF)_2Br, (TMTSF)_2PF_6 and alpha-(BEDT-TTF)_2MHg(SCN)_4 are highly unconventional and coexist with charge-density waves (CDWs). We present a microscopic theory of this unusual CDW-SDW coexistence. A complete understanding requires the explicit inclusion of strong Coulomb interactions, lattice discreteness, the anisotropic two-dimensional nature of the lattice, and the correct bandfilling within the starting Hamiltonian.

cond-mat.str-el↗

arXiv1994

Metal-insulator and insulator-insulator transitions in the quarter-filled band organic conductors

The theory of the 2k_F and 4k_F instabilities in quarter-filled band organic conductors is revisited. The phase angles of the 2k_F bond and charge density waves are shown to change as electron correlation is turned on, and this switching of the phase angle is critical for understanding the bond distortion patterns in the real materials. Intersite Coulomb interactions in the real materials must be nonzero but less than a critical value. Both intersite and intrasite charge density waves are destabilized in the quasi-two-dimensional regime for realistic parameters, thus explaining the weakening of these phases in the superconducting materials.

cond-mat↗

arXiv1993

Pairing on Small Clusters in the Peierls-Hubbard Model: Implications for C$_{60}$

We study the pairing within the Peierls-Hubbard Model for electron- and hole-doped analogs of C$_{60}$ accessible to exact diagonalization techniques (cube, truncated tetrahedron, {\it etc.}). We discuss how inclusion of electron-phonon interactions can substantially modify the conclusions about pairing obtained when this coupling is neglected. We also discuss potential pitfalls in the extrapolation from these small system calculations to C$_{60}$, and stress the necessity of having the correct intuitive picture.

cond-mat↗

arXiv1993

Infinite Volume Extrapolations of Finite Cluster Calculations, ---How Correct are These?

Extrapolations of numerical data obtained from finite cluster calculations to the infinite volume limit can often give incorrect results. We discuss four separate cases: (a) the intensity of the lowest two-photon absorption in the infinite polyene, (b) bond alternation in the infinite polyene, (c) Cooper type pairing in the simple Hubbard model, and (d) pairing within the extended Hubbard model.

cond-mat↗