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Register a new userIntriguing examples of inhomogeneous broadening
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Three problems are considered in which inhomogeneous broadening can yield unusual consequences. One problem involves the energy levels of atoms moving within nanopores of nearly cylindrical cross section. A second involves atomic or molecular motion in a quasi-one dimensional interstitial channel within a bundle of carbon nanotubes. The third problem involves motion within a groove between two nanotubes at the surface of such a bundle. In each case, the density of states at low energy is qualitatively different from that occurring in the perfectly homogeneous case.
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We demonstrate that intersubband (ISB) polaritons are robust to inhomogeneous effects originating from the presence of multiple quantum wells (MQWs). In a series of samples that exhibit mid-infrared ISB absorption transitions with broadenings varying by a factor of 5 (from 4 meV to 20meV), we have observed polariton linewidths always lying in the 4 - 7 meV range only. We have experimentally verified the dominantly inhomogeneous origin of the broadening of the ISB transition, and that the linewidth reduction effect of the polariton modes persists up to room-temperature. This immunity to inhomogeneous broadening is a direct consequence of the coupling of the large number of ISB oscillators to a single photonic mode. It is a precious tool to gauge the natural linewidth of the ISB plasmon , that is otherwise masked in such MQWs system , and is also beneficial in view of perspective applications such as intersubband polariton lasers.
A new procedure aiming at disentangling the instrumental profile broadening and the relevant X-ray powder diffraction (XRPD) profile shape is presented. The technique consists of three steps: denoising by means of wavelet transforms, background suppression by morphological functions and deblurring by a Lucy--Richardson damped deconvolution algorithm. Real XRPD intensity profiles of ceria samples are used to test the performances. Results show the robustness of the method and its capability of efficiently disentangling the instrumental broadening affecting the measurement of the intrinsic physical line profile. These features make the whole procedure an interesting and user-friendly tool for the pre-processing of XRPD data.
Using first-principles calculations, we demonstrate that an Fe monolayer can assume very different magnetic phases on hexagonal hcp (0001) and fcc (111) surfaces of 4d- and 5d-transition metals. Due to the substrates d-band filling, the nearest-neighbor exchange coupling of Fe changes gradually from antiferromagnetic (AFM) for Fe films on Tc, Re, Ru and Os to ferromagnetic on Rh, Ir, Pd, and Pt. In combination with the topological frustration on the triangular lattice of these surfaces the AFM coupling results in a 120-degree Neel structure for Fe on Re and Ru and an unexpected double-row-wise AFM structure on Rh, which is a superposition of a left- and right-rotating 90-degree spin spiral.
Ni$_{0.8}$Fe$_{0.2}$ (Py) and Py alloyed with Cu exhibit intriguing ultrafast demagnetization behavior, where the Ni magnetic moment shows a delayed response relative to the Fe, an effect which is strongly enhanced by Cu alloying. We have studied a broad range of Cu concentrations to elucidate the effects of Cu alloying in Py. The orbital/spin magnetic moment ratios are largely unaffected by Cu alloying, signifying that Cu-induced changes in the ultrafast demagnetization are not related to spin-orbit interactions. We show that magnon diffusion can explain the delayed Ni response, which we attribute to an enhanced magnon generation rate in the Fe sublattice relative to the Ni sublattice. Furthermore, Py exhibits prominent RKKY-like exchange interactions, which are strongly enhanced between Fe atoms and diminished between Ni atoms by Cu alloying. An increased Fe magnon scattering rate is expected to occur concurrently with this increased Fe-Fe exchange interaction, supporting the results obtained from the magnon diffusion model.
We study the dependence of the surface tension of a fluid interface on the density profile of a third suspended phase. By means of an approximated model for the binary mixture and of a perturbative approach we derive close formulas for the free energy of the system and for the surface tension of the interface. Our results show a remarkable non-monotonous dependence of the surface tension on the peak of the density of the suspended phase. Our results also predict the local value of the surface tension in the case in which the density of the suspended phase is not homogeneous along the interface.
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