We present the first systematic observation of scaling of thermal hysteresis with the temperature scanning rate around an abrupt thermodynamic transition in correlated electron systems. We show that the depth of supercooling and superheating in vanadium sesquioxide (V_{2}O_{3}) shifts with the temperature quench rates. The dynamic scaling exponent is close to the mean field prediction of 2/3. These observations, combined with the purely dissipative continuous ordering seen in "quench-and-hold" experiments, indicate departures from classical nucleation theory toward a barrier-free phase ordering associated with critical dynamics. Observation of critical-like features and scaling in a thermally induced abrupt phase transition suggests that the presence of a spinodal-like instability is not just an artifact of the mean field theories but can also exist in the transformation kinetics of real systems, surviving fluctuations.
The electronic structure of sodium tungsten bronzes, Na x WO 3 , for full range of x is investigated by highresolution angle-resolved photoemission spectroscopy ͑HR-ARPES͒. The experimentally determined valenceband structure has been compared with the results of ab initio band-structure calculation. The HR-ARPES spectra taken in both the insulating and metallic phase of Na x WO 3 reveal the origin of metal-insulator transition ͑MIT͒ in the sodium tungsten bronze system. In the insulating Na x WO 3 , the near-E F states are localized due to the strong disorder caused by the random distribution of Na + ions in WO 3 lattice. While the presence of an impurity band ͑level͒ induced by Na doping is often invoked to explain the insulating state found at low concentrations, there is no signature of impurity band ͑level͒ found from our results. Due to disorder and Anderson localization effect, there is a long-range Coulomb interaction of conduction electrons; as a result, the system is insulating. In the metallic regime, the states near E F are populated and the Fermi level shifts upward rigidly with increasing electron doping ͑x͒. The volume of electronlike Fermi surface ͑FS͒ at the ⌫͑X͒ point gradually increases with increasing Na concentration due to W 5dt 2g band filling. A rigid shift of E F is found to give a qualitatively good description of the FS evolution.
We have carried out high-resolution angle-resolved and resonant photoemission spectroscopy ͑RPES͒ on heavy-fermion superconductors Ce 2 CoIn 8 and Ce 2 RhIn 8 to study the electronic band structure and the nature of the Ce 4f electrons. We have experimentally determined the valence-band structure and compared them with the full-potential linear augmented plane-wave band calculations. We found that both compounds have quasitwo-dimensional cylindrical Fermi surfaces centered at the M͑A͒ point in the Brillouin zone, which may be an essential parameter for the development of the superconductivity. Comparison with the band calculations based on the itinerant and localized models suggests that the Ce 4f electrons are essentially localized in both compounds at a measured temperature of 40 K. RPES results have confirmed the localized character of the Ce 4f electrons in both compounds, with a relatively stronger localized nature in Ce 2 RhIn 8 than in Ce 2 CoIn 8 . This difference in the strength of localized character well explains the difference in the magnetic properties between the two compounds.
have been measured following excitation by 59.54 keV ␥ rays from a 200 mCi 241 Am point source. Comparison of the intensity ratios for Ni with the multiconfiguration Dirac-Fock calculations indicates decreasing 3d electron population with the increase of silicon concentration, a trend similar to the one predicted by the previous theoretical calculations ͓O. Bisi and C. Calandra, J. Phys. C 14, 5479 ͑1982͔͒. However, quantitatively our results for the Ni 3d electron population are different from the results reported there. The intensity ratios for Ni and Cu in disilicide compounds indicate enhancement of the K-to-K␣ ratio over the pure metal values, but for the other silicide compounds the Ni intensity ratios show opposite behavior than Cu, suggesting a difference in the nature of electron delocalization.
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