41 research outputs found
Superconductivity from Undressing. II. Single Particle Green's Function and Photoemission in Cuprates
Experimental evidence indicates that the superconducting transition in high
cuprates is an 'undressing' transition. Microscopic mechanisms giving
rise to this physics were discussed in the first paper of this series. Here we
discuss the calculation of the single particle Green's function and spectral
function for Hamiltonians describing undressing transitions in the normal and
superconducting states. A single parameter, , describes the strength
of the undressing process and drives the transition to superconductivity. In
the normal state, the spectral function evolves from predominantly incoherent
to partly coherent as the hole concentration increases. In the superconducting
state, the 'normal' Green's function acquires a contribution from the anomalous
Green's function when is non-zero; the resulting contribution to
the spectral function is for hole extraction and for hole
injection. It is proposed that these results explain the observation of sharp
quasiparticle states in the superconducting state of cuprates along the
direction and their absence along the direction.Comment: figures have been condensed in fewer pages for easier readin
Interplane Transport and Superfluid Density in Layered Superconductors
We report on generic trends in the behavior of the interlayer penetration
depth of several different classes of quasi two-dimensional
superconductors including cuprates, SrRuO, transition metal
dichalcogenides and organic materials of the -series. Analysis
of these trends reveals two distinct patterns in the scaling between the values
of and the magnitude of the DC conductivity: one realized in the
systems with a Fermi liquid (FL) ground state and the other seen in systems
with a marked deviation from the FL response. The latter pattern is found
primarily in under-doped cuprates and indicates a dramatic enhancement (factor
) of the energy scale associated with the formation of
the condensate compared to the data for the FL materials. We discuss
implications of these results for the understanding of pairing in high-
cuprates.Comment: 4 pages, 2 figure
Superconducting Fluctuation investigated by THz Conductivity of LaSrCuO Thin Films
Frequency-dependent terahertz conductivities of LaSrCuO thin
films with various carrier concentrations were investigated. The imaginary part
of the complex conductivity considerably increased from far above a
zero-resistance superconducting transition temperature,
, because of the existence of the fluctuating
superfluid density with a short lifetime. The onset temperature of the
superconducting fluctuation is at most for
underdoped samples, which is consistent with the previously reported analysis
of microwave conductivity. The superconducting fluctuation was not enhanced
under a 0.5 T magnetic field. We also found that the temperature dependence of
the superconducting fluctuation was sensitive to the carrier concentration of
LaSrCuO, which reflects the difference in the nature of the
critical dynamics near the superconducting transition temperature. Our results
suggest that the onset temperature of the Nernst signal is not related to the
superconducting fluctuation we argued in this paper.Comment: J. Phys. Soc. Jpn. in pres
3D Raman Imaging and Correlative Scanning Microscopy Techniques Workhsop
The workshop will give a detailed introduction to the operational principles and instrumental configurations relevant to confocal Raman Imaging and Scanning Microscopy (SEM, AFM, SNOM, Pulsed Force Mode). Our Speakers will cover several aspects of Raman and SPM imaging and their fields of applications. An extensive system demonstration gives the participants the opportunity to see this knowledge applied using an alpha300 RSA+ (combined AFM, SNOM & Confocal Raman Microscope)
Evidence of refractive index anisotropy in hybrid sol-gel slab waveguides deposited by spin-coating technique
Refractive index measurements of thin films using both Brewster and m-line technique: A combined experimental setup
High-energy angle resolved reflection spectroscopy on three-dimensional photonic crystals of self-organized polymeric nanospheres
We report on the optical characterization of three-dimensional opal-like photonic crystals made by self-organized nanospheres of poly[styrene-(co-2-hydroxyethyl methacrylate)] having a face centred cubic (fcc) structure oriented along the [111] direction. A detailed optical characterization of the samples is presented using angle resolved reflection spectroscopy in specular geometry. The investigated energies are between a/lambda= 0.5 and a/lambda= 1.5 (where a is the lattice parameter and lambda is the light wavelength), a region in which both first and second-order Bragg diffraction are expected. Some interesting features as branching of the Bragg peak dispersion and high energy reflection peaks are revealed. We compare the experimental data with theoretical calculations using both Bragg diffraction and band structure approach. A comparison with recent results reported in the literature is also presented. (c) 2008 Optical Society of America
Spectroscopic ellipsometry analyses of thin films in different environments: An innovative "reverse side" approach allowing multi angle measurements
An innovative ellipsometer sample holder has been designed and tested in order to measure thin films optical properties under different environments and so infer the porosity through effective medium approximation models. Compared to commercial cells that require a fixed angle of incidence or a cell with a cylindrical geometry, we present a simple cell in which the sample is mounted in "reverse side", allowing multiple angle analyses without the need for cell windows. Standard ellipsometry measurements are compared to the "reverse side" approach in order to confirm the feasibility of this new procedure, obtaining the same refractive index dispersion curves in both cases. Then different samples have been tested in "reverse side" under different environments to measure porosity. The multiangle approach has been found useful to improve the fitting of the experimental data by reducing both the fitting error and the correlation between parameters