The effective mass of the quasiparticles in a d-wave superconducting system has been calculated via magnetization measurements done by SQUID by using the advanced derivative method used in our previous works. Phenomenological analogy between the double helix quantum wave, which does exist within the primitive cell of the d-wave superconductor, and the human DNA was previously made. In this work, the numerical proof of the analogy mentioned has been realized by determining the magnitude of the attractive force of d-wave structure and comparing with the magnitude of the force that holds the double strand of human DNA that are both of the same order of 10^{-10} N. Moreover, the wavelength of the double helix quantum wave of the superconducting system corresponds to ultraviolet region of the electromagnetic spectrum that exactly coincides with the wavelength which is used for exciting the states in human DNA.
Electrical resistivity and low temperature magnetoresistivity measurements made on a single crystal of UCu_2Si_2 are reported. By using as a phonon reference the temperature dependence of the electrical resistivity of ThCu_2Si_2 we could establish that UCu_2Si_2 has both a ferromagnetic and a Kondo behaviour. Such a phenomenon can be described by the underscreened Kondo lattice model. The magnetoresistivity revealed the presence of magnetic fluctuations within the ferromagnetic order as it was reported previously for UGe_2. Also one of the calculated Fermi surface sheets exhibits nesting properties, being in perfect agreement with the previous neutron diffraction data, supporting the possibility of a presence of the spin density wave phase. In this ternary silicide, where the strong ferromagnetic behaviour exists, this phase is signalised by magnetic fluctuations.
ARPES integrals are related to the momentum distribution n_{k}. In case of a metal, points k_{F} on the Fermi surface were identified by: (i) a change of sign in the temperature variation of the ARPES integrals or (ii) maximum slope in its angular variation. These criteria are based on the assumption of particle-hole symmetry in the vicinity of the Fermi edge. Here, we check (i) and (ii) on the level of the momentum distribution, for an electronic structure with most of its incoherent weight below the Fermi edge. Evaluating n_{k}(T) up to T ≈ Δ*, a Fermi liquid coherence energy, we find: criterion (i) remains stable, while (ii) deviates from k_{F} ∝ m*T/k_{F}. Published data on the hole doped t-J model are examined in this light.
We demonstrate which kind of information on the electronic structure one can get from one-dimensional profiles, interpreted in terms of two-dimensional reconstructed densities. The conversion from one-dimensional to two-dimensional is applied to one-dimensional angular correlation of annihilation radiation profiles of divalent hexagonal close packed metals Mg and Cd. On the example of Mg we show that one should be very careful while studying the Fermi surface from electron-positron (e-p) densities folded into the first Brillouin zone.
The most effective and popular algorithms to reconstruct the three-dimensional electron-positron momentum density from the measurements of the two-dimensional angular correlation of annihilation radiation are based on the Fourier transform or polynomial expansion. We compare the efficacy of different methods in reconstructing the momentum density of the rare-earth based compounds ErGa_3, CeIn_3 and model profiles, presenting also our new filtering algorithm.
Measurement of the two-dimensional angular correlation of the electron-positron annihilation radiation complemented with ab initio calculations can provide decisive information about the character of the f-electrons in rare earth compounds. We provide examples of f-electron localized and f-electron itinerant systems, respectively. (i) In the case of the antiferromagnetic heavy fermion and superconductor CeIn_3 the multisheet Fermi surface, reconstructed from our measurements in the paramagnetic phase, agrees closely with the predictions of band structure calculations regarding the Ce 4f electrons as fully localized. (ii) On the other hand, our studies of the antiferromagnet actinide based UGa_3 in the paramagnetic phase, compared with calculations which include the effects due to the non-uniform positron density and the electron-positron correlations, produce a substantial evidence that an unconstrained 5f-electron itinerant description applies.
We present mathematical methods of computerized tomography, based on an analytical inversion of the Radon transform either in terms of the Fourier transforms or series of orthogonal polynomials. These techniques, so-called transform methods, are discussed for reconstructing electronic densities from both line and plane projections measured either in the two-dimensional angular correlations of annihilation radiation or in one-dimensional angular correlations of annihilation radiation and the Compton scattering experiments. This paper is devoted to review all of the papers where such techniques were applied for studying electronic momentum densities and the Fermi surface of solids by angular correlations of annihilation radiation and the Compton scattering experiments.
The application of the spin-polarized version of multiple scattering theory for obtaining electron charge and spin densities in both real and momentum spaces of concentrated, multi-atom disordered alloys is presented. This method is based on the Korringa-Kohn-Rostoker (KKR) band structure approach and coherent potential approximation (CPA) method. The effective one-electron potential is constructed within local spin density approximation. The magnetic neutron form factors are in real space of our main interest. With the recent developments of new synchrotron photon sources, the Compton profile becomes the most interesting target in momentum space. In the most of examples, spin momentum density and its specific structure due to Fermi surface will be shown. To get accurate enough description in momentum space and quantity like Compton profile, the determination of the Fermi surface must be done with high precision. In this context we show how to apply generalized Lloyd formula for accurate determination of the Fermi level. Also we show how to use efficiently complex energy integration method for the computation of matrix elements, G(r,r) or G(p,p), of the KKR-CPA Green function. Results for the iron-silicon ferromagnetic binary alloys and half-metallic ferromagnetic Heusler alloys are presented.
Single crystals of ErPdBi were grown from Bi-flux. The crystal structure of MgAgAs-type was confirmed using X-ray diffraction. Magnetization, magnetic susceptibility, electrical resistance and heat capacity measurements revealed an antiferromagnetic phase transition at T_{N} = 1.2 K. At high temperatures, the electrical resistance has a semiconducting-like character (dR/dT < 0 ). The resistance starts decreasing with decreasing T below 15 K and shows a very sharp drop below T_{N} but remains finite down to 0.4 K. Hence, no obvious evidence of superconductivity was found in the electrical transport data. On the other hand, the real part of AC magnetic susceptibility is negative below T_{C} = 1.6 K and its imaginary component has a clear maximum at this temperature that might be associated with the onset of superconducting state. The electrical resistance revealed Shubnikov-de Haas oscillations in magnetic fields 8-33 T. Their amplitude decreases with increasing T and disappears above 10 K. Cyclotron mass determined from this dependence is 0.21 m_{e}.
It is shown that if one takes into account the effective mass of the electron, which in real structures is actually different than the free electron mass, the electron and positron self-energy effects may result in flatter and smaller enhancement of the electron-positron momentum distribution. Thus, the many-body effects mentioned above, among other reasons like e.g. influence of lattice potential on electron and positron wave functions, can be responsible for decreasing of the discontinuity on the Fermi momentum and a greater smearing of the Fermi surface seen in several angular correlation of positron annihilation radiation experiments.
Electron-positron (e-p) momentum densities in Mg are studied using three different sets of angular correlation of annihilation radiation (ACAR) and Compton scattering experimental data. ACAR data, measured with almost identical resolution, give both a similar anisotropy of the Fermi surface and a similar e-p enhancement factor inside this surface. However, as concerns a contribution of Umklapp components of valence-electron densities there are essential differences depending on experimental data. Due to a strong dependence of such densities on different theoretical approaches describing e-p correlations, it is suggested to perform additional, high statistics and resolution ACAR measurements for Mg and analyze them as suggested in the paper.
Angular magnetoresistance of the filled skutterudite compound CeOs₄Sb₁₂ has been investigated along the [110] direction. Distinct differences between the angular magnetoresistance data at T = 0.55 K and 4.2 K coincide with a developing of spin-density waves at T ≈ 1.7 K in B = 5 T. Magnetoresistance experiments have been performed on a self-made assembly utilizing a commercial piezoelectric rotator.
We report the results of scalar and fully relativistic electronic structure calculations for nonsuperconducting Th₇Ru₃, using the full-potential linearized-muffin-thin-orbital and full-potential linearized augmented-plane wave methods. The obtained data, including electronic band structures, density of states, Fermi surfaces and electron localization function, reveal the presence of anisotropic spin-orbit coupling but its strength, exposed by splitting energies of the order of 10-40 meV, is much weaker as compared to those of Th₇Fe₃ or Th₇Co₃ superconductors. Moreover, the lack of Van Hove singularity near the Fermi level underscores a key point of the non-occurrence of superconductivity in the studied compound.
Cholestanone (C_{27}H_{46}O) single crystals were irradiated with ^{60}Co-γ rays at room temperature. The spectra were recorded for different orientations of the crystal in the magnetic field at 120 K using the EPR technique. Radiation damage center was attributed to ĊHCH_2 CH_2 radical. The principal values of the hyperfine coupling tensor of the unpaired electron with the protons and the principal values of the g tensor were determined. The results were found to be in good agreement with the existing literature.
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