International Journal of Modern Physics B

Sum frequency generation (SFG) vibrational spectroscopy has been employed to study a variety of interesting biological phenomena occurring at interfaces. This review summarizes recent SFG studies on proteins, lipid monolayers and bilayers, and other biological molecules. Molecular level details revealed by SFG in these studies show that SFG is a powerful technique for characterizing conformation, orientation and ordering of biological molecules at interfaces.

Some of the properties of nonlinear squeezed vacuum states associated with trapped ions are considered, especially the photon number distribution, the phase properties, the Husimi–Kano Q function and the Wigner–Moyal W function of these nonlinear squeezed vacuum states. The structure of these functions is shown to depend on the nonlinearity parameter, its functional dependence and the squeezing parameter. It is shown that increasing the nonlinearity parameter results in the photon number distribution being squeezed independent.

Electrons, when scattered by static random disorder, form standing waves that can be imaged using scanning tunneling microscopy. Such interference patterns, observable by the recently developed technique of Fourier transform scanning tunneling spectroscopy (FT-STS), are shown to carry unique fingerprints characteristic of the electronic order present in a material. We exploit this feature of the FT-STS technique to propose a test for the nature of the enigmatic pseudogap phase in the high-T_c cuprate superconductors. Through their sensitivity to the quasiparticle spectra and coherence factors, the FT-STS patterns, in principle, carry enough information to unambiguously determine the nature of the condensate responsible for the pseudogap phenomenon. In practice, the absence of a detailed understanding of the scattering mechanism, together with the experimental uncertainties, prevent such an unambiguous determination. We argue, however, that the next generation of FT-STS experiments, currently underway, should be able to distinguish between the pseudogap dominated by the remnants of superconducting order from the pseudogap dominated by some competing order in the particle-hole channel. Using general arguments and detailed numerical calculations, we point to certain fundamental differences between the two scenarios and discuss the prospects for future experiments.

We have derived an analytic expression for the contact value of the local density of binary hard-sphere systems under gravity. We have obtained the crossover conditions for the Brazil-nut type segregation of binary hard-sphere mixtures and binary hard-sphere chain mixtures from the segregation criterion, where the segregation occurs when the density (or the pressure) of the small spheres at the bottom is higher than that of the large spheres, or vice versa. For the binary hard-sphere chain mixtures, the crossover condition for the segregation depends on the number of monomers composed of hard-sphere chains as well as the mass and the diameter of each species. The fundamental-measure theories (FMTs) and local density approximation (LDA) are employed to examine the crossover condition for the segregation of the gravity-induced hard-sphere mixtures. The calculated results show that the LDA does not explain the density oscillation near the bottom, whereas the modified fundamental-measure theory (MFMT) compares with molecular dynamics simulations.

By strictly adhering to the microscopic theory of composite fermions (CFs) for the Landau-level filling fractions ν_e=p/(2p+1), we reproduce, with remarkable accuracy, the surface-acoustic-wave (SAW)-based experimental results by Willett and co-workers concerning two-dimensional electron systems with ν_e close to ½. Our results imply that the electron band mass m_b, as distinct from the CF mass m_⋆, must undergo a substantial increase under the conditions corresponding to ν_e ≈ ½. In view of the relatively low aerial electronic densities n_e to which the underlying SAW experiments correspond, our finding conforms with the experimental results by Shashkin et al. [Phys. Rev. B 66, 073303 (2002)], concerning two-dimensional electrons in silicon, that signal sharp increase in m_b for n_e decreasing below approximately 2×10¹¹cm^-2. We further establish that a finite mean-free path ℓ₀ is essential for the observed linearity of the longitudinal conductivity σ_xx(q) as deduced from the SAW velocity shifts.

This paper extends the two-local-spin-mediated interaction (TLSMI) for the superconductivity in the CuO₂ plane of the high-T_c cuprates to the Cu-O chain superconductivity in YBa₂Cu₃O_7-δ (Y123), and sets up a theory for the chain superconductivity in Y123. We explain the observed 60 K chain superconductivity and predicts that the pseudogap should exist in the Cu-O chain of Y123.

The influence of inversion layer thickness on the activation energy and turn-on characteristics of a polycrystalline silicon thin-film transistor (poly-Si TFT) have been investigated theoretically by developing an analytical model. It is observed that activation energy decreases as the gate bias increases and is larger for a larger poly-Si inversion layer thickness. It is also observed that effective carrier mobility and drain current increase rapidly with the increase in gate voltage for all values of inversion layer thickness and are larger for lower inversion layer thickness. The computed results are in reasonable agreement with the experimental observations.