Parent compounds AFe2As2 (A = Ca, Ba, Eu) of the 122 family of the iron-based superconductors have been studied by Fe57 Mössbauer spectroscopy in the temperature range 4.2–∼300 K. Spin density waves (SDW) have ...
Parent compounds AFe2As2 (A = Ca, Ba, Eu) of the 122 family of the iron-based superconductors have been studied by Fe57 Mössbauer spectroscopy in the temperature range 4.2–∼300 K. Spin density waves (SDW) have been found with some confidence. They are either incommensurate with the lattice period or the ratio of the respective periods is far away from the ratio of small integers. SDW shape is very unconventional (i.e., differs from the sinusoidal shape). Magnetic order starts with lowered temperature as narrow sheets of the significant electron spin density separated by areas with very small spin density. Magnetic sheets are likely to be ordered in the alternate antiferromagnetic fashion as the material as a whole behaves similarly to the collinear antiferromagnet. A further lowering of temperature simply expands sheet thickness leading to the near triangular SDW. Finally, sheets fill the whole available space and the almost rectangular shape of the SDW is reached. The substantial maximum amplitude of SDW appears at the temperature just below the magnetic onset temperature, and this maximum amplitude increases slightly with lowering temperature. The square root from the mean squared hyperfine field behaves versus temperature according to the universality class (1,2) (i.e., with the electronic spin space having dimensionality equal to unity and the real space having dimensionality equal to 2). The more or less pronounced tail above transition temperature due to the development of incoherent SDW is seen.
In this paper we present the out-of-core solver algorithm for three dimensional (3D) multi-physics problems solved by the Finite Element Method (FEM). The solver is able to solve problems where 3D meshes contain finit...
详细信息
In this paper we present the out-of-core solver algorithm for three dimensional (3D) multi-physics problems solved by the Finite Element Method (FEM). The solver is able to solve problems where 3D meshes contain finite elements of different kind (tetrahedral, prism and pyramid elements) with the number of equations and polynomial orders of approximation varying locally on finite element edges, faces, and interiors. The solver works at the level of nodes, representing blocks of the global matrix associated with different vertices, edges, faces, and interiors of different elements. The solver minimizes the memory usage by dumping out all local systems from all nodes of the entire elimination tree during the elimination phase. The systems are going to be reutilized later during the backward substitution stage. The solver is tested on a challenging computational problem: acoustics of the human head. The memory usage of the solver is compared against that of the MUMPS solver.
The compound EuFe2−xCoxAs2 was investigated by means of 57Fe and 151Eu Mössbauer spectroscopy versus temperature (4.2–300 K) for x = 0 (parent), x = 0.34–0.39 (superconductor), and x = 0.58 (overdoped). It was ...
The compound EuFe2−xCoxAs2 was investigated by means of 57Fe and 151Eu Mössbauer spectroscopy versus temperature (4.2–300 K) for x = 0 (parent), x = 0.34–0.39 (superconductor), and x = 0.58 (overdoped). It was found that the spin density wave (SDW) is suppressed by Co substitution; however, it survives in the region of superconductivity, but iron spectra exhibit some nonmagnetic components in the superconducting region. Europium orders magnetically, regardless of the cobalt concentration, with the spin reorientation from the a-axis in the parent compound toward the c-axis with increasing replacement of iron by cobalt. The reorientation takes place close to the a-c plane. Some trivalent europium appears in EuFe2−xCoxAs2 versus substitution due to the chemical pressure induced by Co atoms, and it experiences some transferred hyperfine field from Eu2+. Iron experiences some transferred field due to the europium ordering for substituted samples in the SDW and nonmagnetic state both, while the transferred field is undetectable in the parent compound. Superconductivity coexists with the 4f-europium magnetic order within the same volume. It seems that superconductivity has some filamentary character in EuFe2−xCoxAs2, and it is confined to the nonmagnetic component seen by the iron Mössbauer spectroscopy.
An effective medium model using AMPS-1D (Analysis of Microelectronic and Photonic Structure) simulation program was shown to be applicable for bulk heterojunction polymer solar cell modeling. The model was successfull...
详细信息
ISBN:
(纸本)9781424499663
An effective medium model using AMPS-1D (Analysis of Microelectronic and Photonic Structure) simulation program was shown to be applicable for bulk heterojunction polymer solar cell modeling. The model was successfully applied to P3HT/PCBM bulk heterojunction solar cell;the simulation results show that in P3HT/PCBM with ohmic contacts the open circuit voltage is governed by the LUMO of the acceptor and the HOMO of donor with a total voltage loss of 0.37 V. The efficiency of the photovoltaic device was greatly enhanced by increasing the interface band gap E_(gi) which is the energy different between HOMO of the donor and LUMO of the acceptor. The results show that by increasing the interface band gap from 1.0 eV to 1.6 eV the efficiency increases from 3.58 % to 8.29 %. Decreasing the donor optical band gap results in a maximum efficiency of 7.32 % when the value of the optical band gap is 1.5 eV (the absorption window is 385 nm). By combining both effects the maximum efficiency was found to be 9.34 % for an optical band gap 1.63 eV. Further, the influence of the back contact potential barrier on the performance of the solar cell was studied. The result shows that for non-ohmic contact the open circuit voltage is highly correlated with the difference of work functions of the two electrodes.
We present a number of schemes that use quantum mechanics to preserve privacy, in particular, we show that entangled quantum states can be useful in maintaining privacy. We further develop our original proposal [see M...
详细信息
We present a number of schemes that use quantum mechanics to preserve privacy, in particular, we show that entangled quantum states can be useful in maintaining privacy. We further develop our original proposal [see M. Hillery, M. Ziman, V. Bužek, and M. Bieliková, Phys. Lett. A 349, 75 (2006)] for protecting privacy in voting, and examine its security under certain types of attacks, in particular dishonest voters and external eavesdroppers. A variation of these quantum-based schemes can be used for multiparty function evaluation. We consider functions corresponding to group multiplication of N group elements, with each element chosen by a different party. We show how quantum mechanics can be useful in maintaining the privacy of the choices group elements.
In the paper we present the design and test results of an integrated circuit combining the sample&hold and the analogue multiplexer, which is foreseen to be implemented in a multi-channel Application Specific Inte...
详细信息
The structure factor for an arbitrarily decorated Penrose tiling has been calculated in the average unit cell description. The obtained formula uses only the physical coordinates of the atoms decorating a structure. T...
详细信息
We address the question of real space pairing induced by exchange interaction, customarily associated with the presence of the broken-symmetry magnetism. For such mechanism of pairing, the appearance of superconductiv...
We address the question of real space pairing induced by exchange interaction, customarily associated with the presence of the broken-symmetry magnetism. For such mechanism of pairing, the appearance of superconductivity (or superfluidity) without magnetism presents itself still as a highly nontrivial problem and it seems, it can be practically realized only when the kinetic energy of individual-particle motion is comparable or even smaller than the magnitude of exchange interaction that takes place among strongly correlated fermions, where the kinetic exchange and/or the Hund's rule coupling can become relatively strong in the vicinity of the onset of the Mott insulating state. In that situation, the pairing arises from a coherent correlated pair motion rather than from a free motion of a tightly bound pair. We elaborate on this question in general terms, as well as provide selected results in the mean-field approximation in concrete situations.
A tuning fork-based noncontact atomic force microscopy was used to collect three-dimensional (3D) frequency shift data set over the cleaved KBr(001) surface at 5 K. The results suggest that significant tip relaxation ...
详细信息
暂无评论