Advances in testing the effect of acceleration on time dilation using a synchrotron Mössbauer source

New results, additional techniques and know‐how acquired, developed and employed in a recent HC‐1898 experiment at the Nuclear Resonance Beamline ID18 of ESRF are presented, in the quest to explore the acceleration effect on time dilation. Using the specially modified Synchrotron Mössbauer Source and KB‐optics together with a rotating single‐line semicircular Mössbauer absorber on the rim of a specially designed rotating disk, the aim was to measure the relative spectral shift between the spectra of two states when the acceleration of the absorber is anti‐parallel and parallel to the source. A control system was used for the first time and a method to quantify the effects of non‐random vibrations on the spectral shift was developed. For several runs where the effect of these vibrations was negligible, a stable statistically significant non‐zero relative shift was observed. This suggests the influence of acceleration on time.     

Spectral splitting method for nonlinear Schrödinger equations with singular potential

We consider the time-dependent one-dimensional nonlinear Schrödinger equation with pointwise singular potential. By means of spectral splitting methods we prove that the evolution operator is approximated by the Lie evolution operator, where the kernel of the Lie evolution operator is explicitly written. This result yields a numerical procedure which is much less computationally expensive than multi-grid methods previously used. Furthermore, we apply the Lie approximation in order to make some numerical experiments concerning the splitting of a soliton, interaction among solitons and blow-up phenomenon.     

Nuclear resonance reflectivity from a [57Fe/Cr]30 multilayer with the Synchrotron Mössbauer Source

Mössbauer reflectivity spectra and nuclear resonance reflectivity (NRR) curves have been measured using the Synchrotron Mössbauer Source (SMS) for a [⁵⁷Fe/Cr]₃₀ periodic multilayer, characterized by the antiferromagnetic interlayer coupling between adjacent ⁵⁷Fe layers. Specific features of the Mössbauer reflectivity spectra measured with π‐polarized radiation of the SMS near the critical angle and at the `magnetic' maximum on the NRR curve are analyzed. The variation of the ratio of lines in the Mössbauer reflectivity spectra and the change of the intensity of the `magnetic' maximum under an applied external field has been used to reveal the transformation of the magnetic alignment in the investigated multilayer.     

The relationship between magnetic behaviour and local structure around Fe ions in Fe-doped TiO2 rutile

The magnetic and structural characterization of Ti_1−xFe_xO₂ (x=0.025, 0.05, 0.07, 0.125, and 0.15) samples prepared by mechano-synthesis using TiO₂ and Fe₂O₃ as starting materials are reported. XANES measurements performed at the Fe K-edge show that Fe ions are in 3+ oxidation state in the 7 at% Fe-doped sample and in a mixture of 2+ and 3+ oxidation states in the other samples. EXAFS results show the incorporation of Fe ions substituting Ti ones in the rutile TiO₂ structure. They also reveal a strong correlation between the number of oxygen nearest neighbours and the Fe²⁺ fraction, i.e the number of oxygen near neighbours decreases when the Fe²⁺ fraction increases. All samples present ferromagnetic-like behaviour at room temperature. We found a clear dependence between saturation magnetization and coercivity with the fraction of Fe²⁺ and/or the number of Fe near neighbour oxygen vacancies.     

Emergence of order in nanocrystalline SmFe9

Three samples consistent with 1 : 12, 2 : 17 and 1 : 7 stoichiometry, ball-milled and subsequently annealed at temperature T_a between 600 and 1200°C were studied by Rietveld analysis, coupled to Curie temperature T_c measurements and Mössbauer spectroscopy. For all samples, at 600°CT_a<900°C, the detected out-of-equilibrium phase is the hexagonal P6/mmm structure derived from TbCu₇ with the composition SmFe₉. At T_a900°C the ordered phase of Th₂Zn₁₇-type is observed. With increasing T_a the unit cell parameter small variation of the parent SmFe₉ induces a decrease of T_c and H_hf. For T_a=600°C SmFe₉ is defined by a=0.4919 nm, c=0.4162 nm, T_c=207°C and H_hf=232 kOe. The resulting ordered Sm₂Fe₁₇ is characterized by nm, c=3×0.4147 nm, T_c=144°C and H_hf=219 kOe. For T_a=750°C the SmFe₉ T_c is 171°C associated to H_hf=222 kOe.     

Enhanced Fröhlich interaction of semiconductor cuprous oxide films determined by temperature‐dependent Raman scattering and spectral transmittance

Anomalous low temperature behaviors in cuprous oxide (Cu₂O) film grown on quartz substrate have been investigated by temperature‐dependent Raman and transmittance spectra. The longitudinal optical components of two Γ₁₅‐ phonon modes become sharper and more intense at a low temperature. It can be found that the highest‐order electronic transition located at 6.4 eV exhibits a minimum transmittance near 200 K. Correspondingly, the variations from phonon intensity ratios reveal obvious anomalies with the decreasing temperature, indicating the existence of strong electron–phonon coupling mediated by Fröhlich interaction in the Cu₂O films below the temperature of 200 K. Copyright © 2012 John Wiley & Sons, Ltd.     

A generalized G‐function for the Quantum Rabi Model

The analytical solution of the quantum Rabi model is based on a transcendental function , the zeros of which determine the eigenenergies. is generalized here to a function , which allows a much better numerical control of the high‐energy part of the spectrum by an appropriate choice of the complex parameter z. Additionally, it is shown that all zeros of correspond to eigenvalues of the Hamiltonian as well as the zeros of for imaginary z.     

Mössbauer spectroscopy evidence of intrinsic non‐stoichiometry in iron telluride single crystals

The FeTe parent compound for iron‐superconductor chalcogenides was studied applying Mössbauer spectroscopy accompanied by ab initio calculations of electric field gradients at the iron nuclei. Room‐temperature (RT) Mössbauer spectra of single crystals have shown asymmetric doublet structure commonly ascribed to contributions of over‐stoichiometric iron or impurity phases. Low‐temperature Mössbauer spectra of the magnetically ordered compound could be well described by four hyperfine‐split sextets, although no other foreign phases different from Fe_1.05Te were detected by XRD and microanalysis within the sensitivity limits of the equipment. Density functional ab initio calculations have shown that over‐stoichiometric iron atoms significantly affect electron charge and spin density up to the second coordination sphere of the iron sub‐lattice, and, as a result, four non‐equivalent groups of iron atoms are formed by their local environment. The resulting four‐group model consistently describes the angular dependence of the single crystals Mössbauer spectra as well as intensity asymmetry of the doublet absorption lines in powdered samples at RT. We suppose that our approach could be extended to the entire class of FeSeTe_x compounds, which contain excess iron atoms.