Electron-Lattice Interaction on α−Ga(010)

We have investigated the (010) surface of α−Ga by angle-resolved photoemission and low energy electron diffraction. We find a surface state around the ¯C point of the surface Brillouin zone. The electron-phonon coupling at this surface is very strong with an electron-phonon mass enhancement parameter of λ=1.4±0.10. Our spectra show high background intensity in a projected bulk band gap which cannot be accounted for by defect scattering and is therefore interpreted as indicating a nonquasiparticle behavior. Upon cooling the sample below 220 K we observe a phase transition accompanied by spectral changes near the Fermi level

"Cold Melting" of Invar Alloys

An anomalously strong volume magnetostriction in Invars may lead to a situation when at low temperatures the dislocation free energy becomes negative and a multiple generation of dislocations becomes possible. This generation induces a first order phase transition from the FCC crystalline to an amorphous state, and may be called "cold melting". The possibility of the cold melting in Invars is connected with the fact that the exchange energy contribution into the dislocation self energy in Invars is strongly enhanced, as compared to conventional ferromagnetics, due to anomalously strong volume magnetostriction. The possible candidate, where this effect can be observed, is a FePt disordered Invar alloy in which the volume magnetostriction is especially large

Morphology of structures in diffusional growth in three dimensions

In our experiments, we investigate in situ three-dimensional crystals during free growth into pure undercooled liquid xenon. The undercooling $\Delta T$ is in the range of $80 \mathrm{mK} \leq \Delta T \leq 168 \mathrm{mK}$. We initiated morphological transitions of the growing crystal from dendrite to seaweed by a cooling step. The fact that such a transition is possible indicates that a similar morphology diagram, as it is proposed by other authors for two-dimensional growth, is also valid in three dimensions, at least for transient patterns. During the transition from dendrite to seaweed the growth velocity of the crystal decreases and the tip radius increases. For a doublon it is found that the two fingers can be characterized by the tip radius of an unperturbed dendrite at the same nominal undercooling in our experiments, where transient patterns are observed

Three-dimensional reconstruction of xenon dendrites

Pattern formation in self-organizing systems is ubiquitous in nature. Theoretical predictions and model simulations have to be compared with data of experimentally grown structures to improve the understanding of pattern formation processes. Our measuremens of the thickness of dendritic fins support the validity of the analytical predictions (Brener E. Phys. Rev. Lett. 71 (1993) 3653). An image processing technique to be applied to transparent objects has been developed and three-dimensional shapes of xenon dendrites have been reconstructed from experimental data. Using the reconstructed dendrite it can be proved that 3D phase field simulations are in qualitative agreement with our experimentally grown dendrites