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 Behnam Farid Physics , 1999, Abstract: We comment on the work by Moler, et al., [Science 279, 1193 (1998)] concerning determination of the c-axis penetration depth in the single-layer compound Tl-2201 through measuring the magnetic flux due to isolated interlayer Josephson vortices.
 Physics , 2013, DOI: 10.1103/PhysRevB.87.140509 Abstract: Inelastic neutron scattering measurements demonstrate that the magnetic interactions in antiferromagnetic LaFeAsO are two-dimensional. Spin wave velocities within the Fe layer and the magnitude of the spin gap are similar to the \textit{A}Fe$_2$As$_2$ based materials. However, the ratio of interlayer and intralayer exchange is found to be less than $\sim 10^{-4}$ in LaFeAsO, very similar to the cuprates, and $\sim$ 100 times smaller than that found in \textit{A}Fe$_2$As$_2$ compounds. The results suggest that the effective dimensionality of the magnetic system is highly variable in the parent compounds of the iron arsenides and weak 3-D interactions may limit the maximum attainable superconducting $T_{c}$.
 Physics , 1998, DOI: 10.1016/S0375-9601(98)00484-8 Abstract: A modified version of the interlayer tunneling model, including interlayer single particle hopping (ISPH), is considered as a phenomenological model to describe cuprate superconductors. The effective ISPH (t_\perp^{eff}) is taken along with a probability factor P, that involves the normal state pseudogap (E_g). This makes t_\perp^{eff} to mimic experimental observations that, ISPH is small in the underdoped regime and increases towards overdoping. Within the modified model, we establish the absence of bilayer splitting as observed in case of layered cuprates. Transition temperature (T_c) and the superconducting gap are calculated. A match, to the T-dependent superconducting gap data from experiment, is obtained and high values of the ratio of the superconducting gap to T_c are recovered. Depending on the values of E_g, T_c as a function of interlayer coupling shows mixed behaviour. This is a prediction and can be checked further.
 Physics , 1999, DOI: 10.1142/S0217979299001600 Abstract: We consider the interlayer pair-tunneling model for layered cuprates, including an effective single particle hopping along the c-axis. A phenomenological suppression of the c-axis hopping matrix element, by the pseudogap in cuprate superconductors, is incorporated. At optimal doping, quantities characteristic to the superconducting state, such as the transition temperature and the superconducting gap are calculated. Results from our calculations are consistent with the experimental observations with the noteworthy point that, the superconducting gap as a function of temperature shows excellent match to the experimental data. Predictions within the model, regarding T_c variation with interlayer coupling, are natural outcomes which could be tested further.
 Physics , 2012, DOI: 10.1209/0295-5075/98/57005 Abstract: A more extended low density region of coexisting uniform antiferromagnetism and d-wave superconductivity has been reported in multilayer cuprates, when compared to single or bilayer cuprates. This coexistence could be due to the enhanced screening of random potential modulations in inner layers or to the interlayer Heisenberg and Josephson couplings. A theoretical analysis using a renormalized mean field theory, favors the former explanation. The potential for an improved determination of the antiferromagnetic and superconducting order parameters in an ideal single layer from zero field NMR and infrared Josephson plasma resonances in multilayer cuprates is discussed.
 Physics , 2014, Abstract: The highest superconducting transition temperatures in the cuprates are achieved in bilayer and trilayer systems, highlighting the importance of intralayer interactions for high Tc. It has been argued that interlayer hybridization vanishes along the nodal directions by way of a specific pattern of orbital overlap. Recent quantum oscillation measurements in bilayer cuprates have provided evidence for a residual bilayer-splitting at the nodes that is sufficiently small to enable magnetic breakdown tunneling at the nodes. Here we show that several key features of the experimental data can be understood in terms weak spin-orbit interactions naturally present in bilayer systems, whose primary effect is to cause the magnetic breakdown to be accompanied by a spin flip. These features can now be understood include the equidistant set of three quantum oscillation frequencies, the asymmetry of the quantum oscillation amplitudes in c-axis transport compared to ab-plane transport, and the anomalous magnetic field angle dependence of the amplitude of side frequencies suggestive of small effective g-factors. We suggest that spin-orbit interactions in bilayer systems can further affect the structure of the nodal quasiparticle spectrum in the superconducting phase.
 Physics , 2000, DOI: 10.1103/PhysRevLett.86.4668 Abstract: We study the effects of quasiparticle interactions on disorder-induced localization of Dirac-like nodal excitations in superconducting high-$T_c$ cuprates. As suggested by the experimental ARPES and terahertz conductivity data in $Bi_2Sr_2CaCu_2O_{8+\delta}$, we focus on the interactions mediated by the order parameter fluctuations near an incipient second pairing transition $d\to d+is$. We find interaction corrections to the density of states, specific heat, and conductivity as well as phase and energy relaxation rates and assess the applicability of the recent localization scenarios for non-interacting random Dirac fermions to the cuprates.
 Physics , 2014, Abstract: For the moment, there is no exact description of van der Waals (vdW) interactions. ACFD-RPA \cite{Gould1} is expected to better describe vdW bonding, but it is not exact. The PBE/DFT-D2 method is less satisfactory, however, its results are in good agreement with experimental data. Although our fitting technique may weaken (not neglect) the vdW interactions and produce interlayer potentials with weakened vdW, the obtained interlayer potentials reproduce energetics of graphite near the equilibrium interlayer distance very well, as shown in Ref. \cite{Chen}. If having inputs which fully include vdW interactions and having better fitting functions, we believe that interlayer potentials can also fully include vdW interactions in graphite system.
 Physics , 2001, DOI: 10.1088/0953-8984/14/25/325 Abstract: Recent experiments indicate that the excitation spectrum of the cuprates is characterised, in the superconducting state, by two energy scales: the coherence energy'' \Delta_c and the pseudogap'' \Delta_p. Here we consider a simple generalisation of the BCS model that yields exotic pairing and can describe, phenomenologically, the generic trends in the critical temperature T_c of cuprate superconductors. We use the model to predict the gap in the single-particle spectrum arising from the superconductivity and we find evidence that it corresponds to the lower of the two energy scales, \Delta_c, seen in the experiments. This supports the view that the origin of the pseudogap is not superconducting fluctuations.
 Physics , 2014, DOI: 10.1103/PhysRevB.90.125108 Abstract: Motivated by recent observations of charge order in the pseudogap regime of hole-doped cuprates, we show that {\it crisscrossed} stripe order can be stabilized by coherent, momentum-dependent interlayer tunneling, which is known to be present in several cuprate materials. We further describe how subtle variations in the couplings between layers can lead to a variety of stripe ordering arrangements, and discuss the implications of our results for recent experiments in underdoped cuprates.
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