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Publication Metadata only D=3 anisotropic and d=2 tj models: phase diagrams, thermodynamic properties, and chemical potential shift(Springer, 2006) Hinczewski, M.; Department of Physics; Berker, Ahmet Nihat; Faculty Member; Department of Physics; College of Sciences; 179795The anisotropic d=3 tJ model is studied by renormalization-group theory, yielding the evolution of the system as interplane coupling is varied from the isotropic three-dimensional to quasi-two-dimensional regimes. Finite-temperature phase diagrams, chemical potential shifts, and in-plane and interplane kinetic energies and antiferromagnetic correlations are calculated for the entire range of electron densities. We find that the novel tau phase, seen in earlier studies of the isotropic d=3 tJ model, persists even for strong anisotropy. While the tau phase appears at low temperatures at 30-35% hole doping away from [n(i)]=1, at smaller hole dopings we see a complex lamellar structure of antiferromagnetic and disordered regions, with a suppressed chemical potential shift, a possible marker of incommensurate ordering in the form of microscopic stripes. An investigation of the renormalization-group flows for the isotropic two-dimensional tJ model also shows a clear pre-signature of the tau phase, which in fact appears with finite transition temperatures upon addition of the smallest interplane coupling.Publication Metadata only İnelastic neutron scattering peak in Zn substituted YBa2Cu3O7(Elsevier Science Bv, 2000) Department of Physics; Bulut, Nejat; Faculty Member; Department of Physics; College of Sciences; N/AThe effects of nonmagnetic impurities on the Q = (pi, pi) spin-fluctuation spectral weight are studied in the normal state using the framework of the Hubbard model. It is shown that the impurity scattering of the spin fluctuations with momentum transfers near 2k(F) could lead to a peak in Im chi (Q, omega) at omega = 2\mu\, where mu is the chemical potential. the results on the single-layer and the bilayer CuO2 models are compared with the neutron scattering data on Zn substituted YBa2Cu3O7.Publication Metadata only The effect of nanoparticles on the surface hydrophobicity of polystyrene(Springer, 2008) N/A; Department of Chemistry; Yüce, Mehdi Yavuz; Demirel, Adem Levent; PhD Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 6568The surface hydrophobicity of polystyrene-nanoparticle nanocomposites has been investigated as a function of the nanoparticle content. The addition of hydrophobically coated nanoparticles in polystyrene increased the contact angle θ of a water drop with respect to that on polystyrene surface due to change of surface composition and/or surface roughness. When the nanoparticles dispersed well in the polymer, cos θ decreased linearly with increasing amount of nanoparticles indicating a composite surface consisting of smooth polystyrene regions and rough nanoparticle regions. In case of formation of nanoparticle aggregates in polystyrene, cos θ decreased sharply at a critical concentration of nanoparticles. The observed behaviour was modeled in terms of a transition from Wenzel regime to Cassie-Baxter regime at a critical roughness length scale below which the Laplace pressure prevented the penetration of the water drop into the surface undulations. We argue that multiple length scales are needed below the critical roughness length scale to increase the contact angle further by decreasing the fraction of surface area of solid material (increasing the fraction of surface area of air) underlying the water drop.Publication Metadata only The weak Li-2-He interaction revisited: a combined ab-initio and empirical modelling.(Springer, 2005) Bodo, Enrico; Gianturco, Franco A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129The potential energy surface (PES) for the interaction between Li-2((1)Sigma(g)(+)) and He-4 has been computed earlier by using an accurate, post-Hartree-Fock quantum calculation for its ground electronic state and was presented in previous papers(1,2). Here we report a revised version of the same interaction that we have generated using instead an empirical approach that replaces the two-body contributions in the ab-initio potential with external estimates. We have repeated Diffusion Monte Carlo calculations to obtain the quantum ground states for the Li2Hen clusters already discussed in our previous paper(1) and we compare the two sets of findings.Publication Metadata only Two superconducting phases in the d=3 hubbard model - phase diagram and specific heat from renormalization-group calculations.(Springer, 2005) Hinczewski, M.; Department of Physics; Berker, Ahmet Nihat; Faculty Member; Department of Physics; College of Sciences; 179795The phase diagram of the d=3 Hubbard model is calculated as a function of temperature and electron density < n(i)>, in the full range of densities between 0 and 2 electrons per site, using renormalization-group theory. An antiferromagnetic phase occurs at lower temperatures, at and near the half-filling density of < n(i)> = 1. The antiferromagnetic phase is unstable to hole or electron doping of at most 15%, yielding to two distinct"tau" phases: for large coupling U/t, one such phase occurs between 30-35% hole or electron doping, and for small to intermediate coupling U/t another such phase occurs between 10-18% doping. Both tau phases are distinguished by non-zero hole or electron hopping expectation values at all length scales. Under further doping, the tau phases yield to hole- or electron-rich disordered phases. We have calculated the specific heat over the entire phase diagram. The low-temperature specific heat of the weak-coupling tau phase shows an exponential decay, indicating a gap in the excitation spectrum, and a CUSP singularity at the phase boundary. The strong-coupling tau phase, on the other hand, has a critical exponent alpha approximate to-1, and an additional peak in the specific heat above the transition temperature possibly indicating pair formation. In the limit of large Coulomb repulsion, the phase diagram of the tJ model is recovered.