Researcher:
Bulut, Nejat

Profile Picture
ORCID

Job Title

Faculty Member

First Name

Nejat

Last Name

Bulut

Name

Name Variants

Bulut, Nejat

Email Address

Birth Date

Filters

2000 - 20037

Advanced Search

Filter by

Settings

Researcher Of Publications: search.filters.isAuthorOfPublication.e4f4638a-ded5-4422-ba16-fcf8d1ab9e29

Search Results

Now showing 1 - 7 of 7
  • Placeholder
    PublicationMetadata only
    Dx2-y2 superconductivity and the Hubbard model
    (Taylor & Francis, 2002) Department of Physics; Bulut, Nejat; Faculty Member; Department of Physics; College of Sciences; 4963
    The numerical studies of d(x2-y2)-wave pairing in the two-dimensional (2D) and the 2-leg Hubbard models are reviewed. For this purpose, the results obtained from the determinantal Quantum Monte Carlo and the Density-Matrix Renormalization-Group calculations are presented. These are calculations which were motivated by the discovery of the high-T-c cuprates. In this review, the emphasis is placed on the microscopic many-body processes which are responsible for the d(x2-y2)-wave pairing correlations observed in the 2D and the 2-leg Hubbard models. In order to gain insight into these processes, the results on the effective pairing interaction as well as the magnetic, density and the single-particle excitations will be reviewed. In addition, comparisons will be made with the other numerical approaches to the Hubbard model and the numerical results on the t-J model. The results reviewed here indicate that an effective pairing interaction which is repulsive at (pi,pi) momentum transfer, and enhanced single-particle spectral weight near the (pi,0) and (0,pi) points of the Brillouin zone, create optimum conditions for d(x2)-(y2)-wave pairing. These are two effects which act to enhance the d(x2-y2)-wave pairing correlations in the Hubbard model. Finding additional ways is an active research problem.
  • Placeholder
    PublicationMetadata only
    Comparison of the NMR and neutron scattering experiments on cuprates with nonmagnetic impurities
    (World Scientific Publ Co Pte Ltd, 2000) Department of Physics; Department of Physics; Bulut, Nejat; Yaz, Ümit; Faculty Member; Undergraduate Student; Department of Physics; College of Sciences; College of Sciences; 4963; N/A
    The NMR and neutron scattering experiments on YBa2Cu3O7 with U and Zn impurities are compared using a simple framework exhibiting short-range antiferomagnetic correlations. The model parameters are determined by fitting the NMR rate T-2(-1) of the pure system, and the effective impurity potential is approximated by a static extended form. The results of the calculations are compared with the experimental data, and their implications are discussed.
  • Placeholder
    PublicationMetadata only
    Analysis of the knight shift data on Li and Zn substituted YBa2Cu3O6+x
    (Elsevier, 2001) Department of Physics; Bulut, Nejat; Faculty Member; Department of Physics; College of Sciences; N/A
    The Knight shift data on Li and Zn substituted YBa2Cu3O6+x are analyzed using an itinerant model with short-range antiferromagnetic correlations. The model parameters, which are determined by fitting the experimental data on the transverse nuclear relaxation rate T-2(-1) of pure YBa2Cu3O6+x, are used to calculate the Knight shifts for various nuclei around a nonmagnetic impurity located in the CuO2 planes. The calculations are carried out for Li and Zn impurities substituted into optimally doped and underdoped YBa2Cu3O6+x. The results are compared with the Li-7 and Y-89 Knight shift measurements on these materials. (C) 2001 Elsevier Science B.V. All rights reserved.
  • Placeholder
    PublicationMetadata only
    Effects of dilute nonmagnetic impurities on the Q = (π,π) spin-fluctuation spectrum in YBa2Cu3O7
    (Elsevier, 2001) Department of Physics; Bulut, Nejat; Faculty Member; Department of Physics; College of Sciences; N/A
    The effects of nonmagnetic impurities on the Q = (pi, pi) spin-fluctuation spectral weight Im chi (Q, omega) are studied within the framework of the two-dimensional Hubbard model using the random phase approximation. In the first part of the paper, the effects of the nonmagnetic impurities on the magnetic susceptibility of the noninteracting (U = 0) system, chi (0)(q, omega), are calculated with the self-energy and the vertex corrections using various forms of the effective electron-impurity interaction. Here, the range and the strength of the impurity potential are varied as well as the concentration of the impurities. It Is shown that the main effect of dilute impurities on X,(Q, w) is to cause a weak smearing. In the second part, Im chi (Q, omega) is calculated for the interacting system. Here, the calculations are concentrated on the processes which involve the impurity scattering of the spin fluctuations with finite momentum transfers. Results are given for various values of the model parameters, and comparisons are made with the neutron scattering data on Zn substituted YBa2Cu3O7. (C) 2001 Elsevier Science B.V. All rights reserved.
  • Placeholder
    PublicationMetadata 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/A
    The 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.
  • Thumbnail Image
    PublicationOpen Access
    Effects of dilute Zn impurities on the uniform magnetic susceptibility of YBa2Cu3O7-δ
    (American Physical Society (APS), 2000) Department of Mathematics; Bulut, Nejat; Faculty Member; Department of Mathematics; College of Sciences
    The effects of dilute Zn impurities on the uniform magnetic susceptibility are calculated in the normal metallic state for a model of the spin fluctuations of the layered cuprates. It is shown that scatterings from extended impurity potentials can lead to a coupling of the q∼ (π, π) and the q∼0 components of the magnetic susceptibility χ(q). Within the presence of antiferromagnetic correlations, this coupling can enhance the uniform susceptibility. The implications of this result for the experimental data on Zn substituted YBa2Cu3O7-δ are discussed.
  • Thumbnail Image
    PublicationOpen Access
    Quantum Monte Carlo study of a nonmagnetic impurity in the two-dimensional Hubbard model
    (American Physical Society (APS), 2003) Department of Physics; Bulut, Nejat; Faculty Member; Department of Physics; College of Sciences
    In order to investigate the effects of nonmagnetic impurities in strongly correlated systems, quantum Monte Carlo (QMC) simulations have been carried out for the doped two-dimensional Hubbard model with one nonmagnetic impurity. Using a bare impurity potential which is onsite and attractive, magnetic and single-particle properties have been calculated. The QMC results show that giant oscillations develop in the Knight shift response around the impurity site due to the short-range antiferromagnetic correlations. These results are useful for interpreting the NMR data on Li- and Zn-substituted layered cuprates.