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Films of Pb(111) with thickness ranging from 1 to 16 monolayers (ML) were grown on Ge(111) and examined by angle-resolved photoemission spectroscopy. The measured thickness dependences of the work function and surface energy from the same set of samples were both well described by damped sinusoidal oscillatory functions with the same period, but the oscillation phases differ by 1/4 period between the two quantities, as judged by the node positions. This difference agrees with the prediction of a generic quantum-well model. The varied node positions of damped oscillations of the work function and surface energy were examined in terms of the details of Pb subband dispersions, indicating the different roles of the density of states at the Fermi level to both thin-film properties. The surface dipoles of Pb films were found to have no relevant effects on the phase shift of thickness-dependent work functions except for the amplitudes of oscillations. The total boundary phase shifts of the quantum well states, extracted from the energy positions of the quantum-well states for both Pb/Ge(111) and freestanding Pb films, are compared and related to the thickness-dependent work function and surface energy. [ABSTRACT FROM AUTHOR]

The dependence on thickness of electronic and lattice structures of Pb films deposited on Ge(100) substrate was investigated with angle-resolved photoemission spectroscopy and low-energy electron diffraction. Pb films grew in the (111) surface direction with two (1 x 1) domains rotated 90 º relative to each other despite a square lattice of Ge(100); correspondingly, the heavy-hole band edge of Ge does not interact with quantum-well-state bands of Pb films. Symmetry arguments in terms of orbitals of Pb quantum-well states and Ge band edges correlate the consonant diminution of lattice and electronic coupling between the film and the substrate. [ABSTRACT FROM AUTHOR]

Longitudinal and Hall resistivities, scaling behavior, and magnetizations are examined to study the effect of flux pinning in Ba(Fe1-xCox)2As2 (BFCA) single crystals with x?=?0.08 and 0.01. Larger values of activation energy, critical current density, and pinning force are obtained in BFCA with x?=?0.10, indicating relatively strong pinning. The sign reversal of Hall resistivities is clearly observed in BFCA with x?=?0.10. The correlation between longitudinal and Hall resistivities shows the scaling behavior of ρxy∞(ρxx)β with exponents β?=?3.0-3.4 and 2.0?α?0.2 for BFCA crystals with x?=?0.08 and 0.10, respectively. Furthermore, the normal-state Hall angle is also observed to follow cot θH=ΛT2 + C in BFCA crystals, and is explained by the Anderson theory. The relatively large c/Λ value for BFCA with x?=?0.10 also implies a larger contribution of impurity scattering due to more Co atoms, which may cause stronger pinning of flux lines. The results are analyzed and coincide with theory, including the pinning-induced backflow effect and plastic flow mechanism in vortex dynamics. [ABSTRACT FROM AUTHOR]