Within the t-J model, we study the electronic properties of the doped antiferromagnet on the kagom´e lattice based on the framework of the self-consistent mean-field theory. At the half-filling, the spin-liquid ground-state energy per site of the kagome antiferromagnet is Eg/NsJ=−0.859, which is in very good agreement with the numerical estimates. Away from the half-filling, the electron photoemission spectroscopy and density of states are discussed, and the results indicate that there is a gap in the normal-state of the system.

Within the t-J model, the c-axis charge dynamics of the copper oxide materials in the underdopedand optimally doped regimes is studied by considering the incoherent interlayer hopping. It is shownthat the c-axis charge dynamics is mainly governed by the scattering from the in-plane fluctuations.In the optimally doped regime, the c-axis resistivity is a linear in temperatures, and shows themetallic-like behavior for all temperatures, while the c-axis resistivity in the underdoped regimeis characterized by a crossover from the high temperature metallic-like to the low temperaturesemiconducting-like behavior, which are consistent with experiments and numerical simulations.

The c-axis charge dynamics of copper oxide materials in the underdoped andoptimally doped regimes has been studied by considering the incoherent interlayerhopping. It is shown that the c-axis charge dynamics for the chaincopper oxide materials is mainly governed by the scattering from the in-planefluctuation, and the c-axis charge dynamics for the no-chain copper oxidematerials is dominated by the scattering from the in-plane fluctuation incorporatingwith the interlayer disorder, which would be suppressed when theholon pseudogap opens at low temperatures and lower doping levels, leadingto the crossovers to the semiconducting-like range in the c-axis resistivity andthe temperature linear to the nonlinear range in the in-plane resistivity.

Within the framework of the fermion-spin theory based on the charge-spin separation, the charge dynamicsof the doped antiferromagnet on a triangular lattice is studied. The holon part is treated by using the loopexpansion to the second order. It is shown that the charge dynamics is mainly caused by charged holonsmoving in the background of spinon excitations. The optical conductivity spectrum shows an unusual behaviorat low energies and an anomalous midinfrared band, while the resistivity exhibits a nonlinearity intemperatures.

The dynamical spin structure factor and the Raman response are calculated for structurallydimerized and spin-Peierls chains in a magnetic field, using exact diagonalization techniques. Inboth cases there is a spin liquid phase composed of interacting singlet dimers at small fields h<hc1,an incommensurate regime (hc1<h<hc2) in which the modulation of the triplet excitation spectraadapts to the applied field, and a fully spin polarized phase above an upper critical field hc2. Forstructurally dimerized chains, the spin gap closes in the incommensurate phase, whereas spin-Peierlschains remain gapped. In the spin liquid regimes, the dominant feature of the triplet spectra is aone-magnon bound state, separated from a continuum of states at higher energies. There are alsoindications of a singlet bound state above the one-magnon triplet.

The excitation spectrum of the one-dimensional spin-orbital model in a magneticfield is studied, using a recently developed dynamical density matrixrenormalization group technique. The method is employed on chains with upto 80 sites, and examined for test cases such as the spin-1/2 antiferromagneticHeisenberg chain, where the excitation spectrum is known exactly fromthe Bethe Ansatz. In the spin-orbital chain, the characteristic dynamical responsedepends strongly on the model parameters and the applied magneticfield. The coupling between the spin and orbital degrees of freedom is foundto influence the incommensuration at finite magnetizations. In the regionsof the phase diagram with only massive spin and orbital excitations, a finitefield is required to overcome the spin gap. An incommensurate orbital modeis found to become massless in this partially spin-polarized regime, indicatinga strong coupling between the two degrees of freedom. In the critical regionwith three elementary gapless excitations, a prominent particle-hole excitationis observed at higher energies, promoted by the biquadratic term in themodel Hamiltonian of the spin-orbital chain.

Prolonged storage (～2 years) or gentle heating (50-80℃) of crystalline 2,5-dibromo-3, 4-ethylenedioxythiophene (DBEDOT) affords a highly conducting, bromine-doped poly (3, 4-ethylenedioxythiophene)(PEDOT), as confirmed by solid-state NMR, FTIR, CV, and vis-NIR spectroscopies. The novelsolid-state polymerization (SSP) does not occur for 2,5-dichloro-3,4-ethylenedioxythiophene (DCEDOT), and requires a much higher temperature (>130℃) for 2,5-diiodo-3,4-ethylenedioxythiophene (DIEDOT). X-ray structural analysis of the above dihalothiophenes reveals short HalâââHal distances between adjacentmolecules in DBEDOT and DIEDOT, but not in DCEDOT. The polymerization may also occur in the meltbut is significantly slower and leads to poorly conductive material. Detailed studies of the reaction wereperformed using ESR, DSC, microscopy, and gravimetric analyses. SSP starts on crystal defect sites; it isexothermic by 14 kcal/mol and requires activation energy of 26 kcal/mol (for DBEDOT). The temperaturedependence of the conductivity of SSP-PEDOT (σrt) 20-80S/cm) reveals a slight thermal activation. Itcan be further increased by a factor of 2 by doping with iodine. Using this approach, thin films of PEDOTwith conductivity as high as 20S/cm were fabricated on insulating flexible plastic surfaces.

63Cu nuclear magnetic resonance (NMR) spin-echo decay rate (T−1/2) measurements are reportedfor the normal and superconducting states of a single crystal of Pr1.85Ce0.15CuO4−y (PCCO) in amagnetic field B0=9T over the temperature range 2K<T<200 K. The spin-echo decay rateis temperature-dependent for T<55 K, and has a substantial dependence on the radio frequency (rf) pulse parameters below T≈ 25K. This dependence indicates that T−1/2 is strongly effected bya local magnetic field distribution that can be modified by the rf pulses, including ones that are notat the nuclear Larmor frequency. The low-temperature results are consistent with the formation ofa static inhomogeneous electronic structure that couples to the rf fields of the pulses.

(TMTTF)2AsF6 and (TMTTF)2SbF6 are both known to undergo a charge ordering phasetransition, though their ground states are different. The ground state of the first is Spin-Peierls, and thesecond is an antiferromagnet. We study the effect of pressure on the ground states and the charge-orderingusing 13C NMR spectroscopy. The experiments demonstrate that the the CO and SP order parameters arerepulsive, and consequently the AF state is stabilized when the CO order parameter is large, as it is for(TMTTF)2SbF6. An extension of the well-known temperature/pressure phase diagram is proposed.

The pressure induced quantum phase transition of the weakly itinerant ferromagnet MnSi isstudied using zero-field 29Si NMR spectroscopy and relaxation. Below P*≈1.2GPa, the intensityof the signal and the nuclear spin-lattice relaxation is independent of pressure, even though theamplitude of the magnetization drops by 20% from the ambient pressure amplitude. For P>P*,the decreasing intensity within the experimentally detectable bandwidth signals the onset of aninhomogeneous phase that persists to the highest pressure measured, P≥1.75GPa, which is wellbeyond the known critical pressure Pc=1.46GPa. Implications for the non-Fermi Liquid behaviorobserved for P>Pc are discussed.