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The stopping cross sections S (E) of silicon for protons and alpha particles have been measured over the velocity range 0.3-1.2 MeV/u from a SIMOX target using the Rutherford Backscattering Spectrometry (RBS) with special emphasis put on experimental aspects. A detection geometry coupling simultaneously two solid-state Si detectors placed at 165 degrees and 150 degrees relative to each side of the incident beam direction was used to measure the energies of the scattered ions and determine their energy losses within the stopping medium. In this way, the basic energy parameter, Ex, at the Si-SiO2 interface for a given incident energy E0 is the same for ions backscattered in the two directions off both the Si and O target elements, and systematic uncertainties in the S (E) data mainly originating from the target thickness are significantly minimized. A powerful computer code has been elaborated for extracting the relevant S (E) experimental data and the associated overall uncertainty that amounts to less than 3%. The measured S (E) data sets were found to be in fair agreement with H. Paul compilation and with values calculated by the SRIM 06 computer code. In the case of 4He+ ions, experimental data for the gamma-effective charge parameter have been deduced via scaling the measured stopping cross sections to those for protons crossing the same target at the same velocity and compared to the predictions of the SRIM 06 code. It is found that the gamma-parameter values generated by the latter code slightly deviate from experiment over the velocity region around the stopping cross section maximum where strong charge exchanges usually occur.

High critical temperature cuprate superconducting materials are composed of copper oxide layers and interlayer charge reservoirs. When not doped, these cuprates are antiferromagnetic insulators. We propose to design new materials by combining alternating layers of parents of hole-doped and electron-doped of these cuprates and modifications thereof. Our goal is to find undoped cuprates that can be either an antiferromagnetic insulator or a quantum metal. The term quantum metal means a metal characterized by long range antiferromagnetic order or only strong antiferromagnetic correlations, i.e., it is thus a stable ground state against any other perturbations. The new metallic states sought here could be precursors to new superconducting states in the absence or presence of doping. Using the density functional theory, we report on two compounds {La}{Pr}CuO4 and {La}{V}CuO4 that illustrate the different physics described above. The curly brackets mean that the preparation of these compounds shall be done by depositing a layer containing Pr, then one CuO2 layer, then finally the La layer in {La}{Pr}CuO4 for example. The configuration formed by the positions of the charge reservoir atoms with respect to the CuO2 layer is an important factor in the new procedure we propose here. This paper reports on the X-ray diffraction, electronic, optical, and magnetic properties of these hypothetical materials. We found that {La}{Pr}CuO4 is a Mott insulator, but {La}{V}CuO4 is an undoped correlated quantum metal with long-range order. Our calculations were performed using the linearized plane wave method (FP-LAPW) implemented within the Wien2k software., Comment: 27 pages, 19 figures

The effect of the orientation of the cation MA (i.e., CH3NH3) on the physical properties of MAPbI3 are investigated using the density functional theory. We report that the Fermi energy level exhibits a large variation with MA orientation, and it is this Fermi level variation that makes this material unique and so different from the non-organic perovskites. The Fermi level variation with orientation of MA is proposed to be responsible for the experimentally observed intrinsic open-circuit voltage V_OC, ambipolarity, and long lifetime of the excitons. Based on our results, ferroelectric domains in the low-temperature orthorhombic phase or clusters of MA molecules not rotating in unison (as a consequence of e.g. impurities and/or defects) in the higher-temperature tetragonal and cubic phases are proposed to be responsible for ambipolarity. This is because any given two adjacent domains or clusters with different MA s average orientations may have very different Fermi levels, causing them to behave as an effective diode. Also, the measured significant lifetime of excitons in MAPbI3 finds a natural explanation using this effective diode. Thus, our work provides a unified manner for explaining at least these three important properties in terms of the rotation-induced Fermi level variations. We used the density functional theory to get our results., Comment: 30 pages, 11 figures

We calculated the self-energy corrections beyond the mean-field solution of the rotating antiferromagnetism theory using the functional integral approach. The frequency dependence of the scattering rate ${1}/{\tau}$ is evaluated for different temperatures and doping levels, and is compared with other approaches and with experiment. The general trends we found are fairly consistent with the extended Drude analysis of the optical conductivity, and with the nearly antiferromagnetic Fermi liquid as far as the ${\bf k}$-anisotropy is concerned and some aspects of the Marginal-Fermi liquid behavior. The present approach provides the justification from the microscopic point of view for the phenomenology of the marginal Fermi liquid ansatz, which was used in the calculation of several physical properties of the high-$T_C$ cuprates within the rotating antiferromagnetism theory. In addition, the expression of self-energy we calculated takes into account the two hot issues of the high-$T_C$ cuprate superconductors, namely the Fermi surface reconstruction and the hidden symmetry, which we believe are related to the pseudogap., Comment: To be submitted to Physica C

The Fermi surface calculated within the rotating antiferromagentism theory undergoes a topological change when doping changes from p-type to n-type, in qualitative agreement with experimental data for n-type cuprate Nd$_{2-x}$Ce$_x$CuO$_4$ and p-type La$_{2-x}$Sr$_x$CuO$_4$. Also, the reconstruction of the Fermi surface observed experimentally close to optimal doing in p-type cuprates, and slightly higher than optimal doping in the overdoped regime for this n-type high-$T_C$ cuprate is well accounted for in this theory, and is a consequence of quantum criticality caused by the disappearance of rotating antiferromagnetism. The present results are in qualitative agreement with the recently observed quantum oscillations in some high-$T_C$ cuprates regarding the change in the size of the Fermi surface as doping evolves and the location of its reconstruction. This paper presents new results about the application of the rotating antiferromagnetism theory to the study of electronic structure for n-type materials.

The phase of the rotating order parameter in rotating antiferromagnetism is calculated using a combination of mean-field theory and Heisenberg equation. This phase shows a linear time dependence, which allows us to interpret rotating antiferromagnetism as a synchronized Larmor-like precession of all the spins in the system or as an unusual ${\bf q}=(\pi,\pi)$ spin-wave around a zero local magnetization. We discuss implications for the pseudogap state of high-$T_C$ superconducting materials. Rotating antiferromagnetism has been proposed to model the pseudogap state in these materials.

We extend the definition of the Jordan-Wigner transformation to three dimensions using the generalization of ideas that were used in the two-dimensional case by one of the present authors. Under this transformation, the 3D XY Hamiltonian is transformed into a system of spinless fermions coupled to a gauge field with only two components. We calculate the flux per plaquette for the 3 elementary perpendicular plaquettes of a cubic lattice, and find that it is nonzero for only two of the plaquettes. We provide a simple interpretation for the average phase-per-plaquette being $\pi$ on the plaquettes where it is nonzero. Then we apply these findings to the investigation of the Heisenberg bilayer antiferromagnet.

The paramagnetic phase of the one-dimensional Kondo lattice model is investigated for electron densities below half-filling using a new mean-field approach. The physical parameters that govern this phase are identified to be the spin-flip processes of both the localized and itinerant spins. A nonmagnetic quantum state, where the local magnetization is a rotating vector with a nonzero average length, is proposed in order to describe this phase. This state does not break SU(2) symmetry in agreement with Mermin-Wagner theorem. The line boundary between this phase and the ferromagnetic phase is calculated in the coupling-density phase diagram. Also, expressions are calculated for the velocities of the conduction electrons excitations, and heat capacity and entropy versus temperature are analyzed. Good agreement with many of the available numerical data is achieved., Comment: PRB 62, 710 (2000)

Heisenberg ladders are investigated using the bond-mean-field theory [M.Azzouz, Phys. Rev. B 48, 6136 (1993)]. The zero inter-ladder coupling energy gap, the uniform spin susceptibility and the nuclear magnetic resonance spin-relaxation rate are calculated as a function of temperature and magnetic field. For weakly coupled ladders, the energy spectrum vanishes at incommensurate wavevectors giving rise to nodes. As a consequence, the spin susceptibility becomes linear at low temperature. Our results for the single ladder successfully compare to experiments on SrCu_2O_3 and (VO)_2P_2O_7 materials and new predictions concerning the coupling to the magnetic field are made., Comment: 4 revtex pages, 3 figures available upon request

The ground state energy and the singlet-triplet energy gap of the antiferromagnetic Heisenberg model on a ladder is investigated using a mean field theory and the density matrix renormalization group. Spin wave theory shows that the corrections to the local magnetization are infinite. This indicates that no long range order occurs in this system. A flux-phase state is used to calculate the energy gap as a function of the transverse coupling, $J_\perp$, in the ladder. It is found that the gap is linear in $J_\perp$ for $J_\perp\gg 1$ and goes to zero for $J_\perp\to 0$. The mean field theory agrees well with the numerical results., Comment: 11pages,6 figures (upon request) Revtex 3.0, Report#CRPS-94-04