R. S. Tripathi

Role of interlayer interactions on transition temperature in high-Tc cuprate superconductors

Abstract The effect of interlayer interactions on transition temperature in high- T c layered superconductors has been studied using a one-band two-layer tight binding Hamiltonian with intra- and interlayer attractive interactions. The double-time Greens function technique is employed and higher-order Greens functions are linearized by using a mean field decoupling approximation. The expressions for the transition temperature ( T c ) and excitonic type interlayer correlation ( γ c ) are obtained. It is shown that interlayer interactions play an important role in the enhancement of T c in high- T c cuprates. We have also explained the relevance of our results in high- T c layered superconductors having two layers per unit cell under externally applied pressure.

Role of dipole-dipole interaction on the magnetic dynamics of anisotropic layered cuprate antiferromagnets

In the present paper, we report the role of dipole-dipole interaction on the magnetic dynamics of single layer antiferromagnets. For this, the model Hamiltonian includes the exchange Heisenberg Hamiltonian as well as dipole-dipole interactions. Within the linear spin-wave theory, we employ the double time Greens function technique to obtain expressions for the spin wave dispersion, sublattice magnetization and the magnetic contribution to specific heat as a function of various parameters of the model Hamiltonian. We observe through numerical calculations that in the absence of anisotropy in exchange couplings the dipole-dipole interaction works as an anisotropy and sustains the magnetization even in a pure 2D system.

Spin wave contribution to the thermal expansion of high-Tc cuprate superconductors

Abstract At low temperatures the spin wave excitations are of great importance. In the present paper, we represent the contribution of spin wave modes to the thermal expansion of high- T c cuprate systems in their normal state. The numerical results have been plotted for YBa 2 Cu 3 O 7 .

Superconducting properties of bilayer cuprates: role of CuO chains

In the present paper, we report the role of CuO chains on the superconducting properties of bilayer cuprate superconductors. The model Hamiltonian incorporates the intra-bilayer, inter-bilayer and bilayer-chain interactions. The expressions of the superconducting order parameter, transition temperature, density of states and electronic specific heat have been obtained using Greens function technique. The numerical calculations show that these properties are sensitive to the chain contributions. Our results are qualitatively in accord with the experimentally observed superconducting properties in bilayer cuprates.

Effect of interlayer interaction in high-Tc cuprate superconductors

We have studied the role of interlayer attractive interaction in a high-Tc system having two layers per unit cell. The single band two-layer tight binding model Hamiltonian is considered and the double time Greens function technique is applied within the mean field approximation. The expressions for the hole density, transition temperature, and intra- and interlayer order parameters are obtained which are found to be dependent on the interlayer interaction and other parameters appearing in the Hamiltonian. The numerical analysis shows that the coupling of the charge carriers (holes) between the layers provides better conditions for the stabilization of long-range order and high superconducting transition temperature in layered superconductors. It is also observed that superconductivity is confined to a narrow region of hole concentration and the single particle tunneling suppresses the transition temperature.

Role of Interlayer and Intersite Interactions in Superconducting State in High-Tc Layered Cuprates

We studied the role of interlayer and intersite interactions on transition temperature and specific heat of layered high-Tc cuprates. We used double-time Greens function technique in the spirit of mean field approximation in order to obtain the expressions for hole density, transition temperature, and specific heat. These expressions are found to be dependent on the carrier concentration and intersite and interlayer interactions. The numerical analysis shows that the effect of intersite interaction on transition temperature and specific heat is qualitatively similar to that of interlayer interactions and provides favorable conditions to establish long-range order in the superconducting state.

Pressure Dependence of Tc in High Temperature Superconductors: Role of Interlayer Interactions

We have studied the role of interlayer interactions (W) in the pressure dependence of Tc of layered superconductors. The expressions for dTc/dP are obtained by including the effects of layered structure within the framework of two different proposed models, namely the negative-U Hubbard model and the Hirsch model. We observe that the inclusion of interlayer interaction provides better explanation of pressure dependence of Tc. Our numerical results show that the systems having one CuO2 layer per unit cell may be well described by small values of W while the larger values of W accounts for the systems having two or more superconducting layers in a unit cell. The calculated values of dTc/dP vs. W are found to be in good agreement with those of experimental results obtained for various high Tc superconductors of cuprate family.

Effect of Interlayer Interaction on the Specific Heat of High-Tc Superconductors

The effect of interlayer interactions on the electronic specific heat of high-Tc layered superconductors has been studied within the framework of the Hirsch model. In the present paper we extend our previous work in order to evaluate the expression for specific heat. It is shown that the inclusion of interlayer interactions suppresses the height of the jump in the specific heat at Tc.