17,028 research outputs found
Powerlaw optical conductivity with a constant phase angle in high Tc superconductors
In certain materials with strong electron correlations a quantum phase
transition (QPT) at zero temperature can occur, in the proximity of which a
quantum critical state of matter has been anticipated. This possibility has
recently attracted much attention because the response of such a state of
matter is expected to follow universal patterns defined by the quantum
mechanical nature of the fluctuations. Forementioned universality manifests
itself through power-law behaviours of the response functions. Candidates are
found both in heavy fermion systems and in the cuprate high Tc superconductors.
Although there are indications for quantum criticality in the cuprate
superconductors, the reality and the physical nature of such a QPT are still
under debate. Here we identify a universal behaviour of the phase angle of the
frequency dependent conductivity that is characteristic of the quantum critical
region. We demonstrate that the experimentally measured phase angle agrees
precisely with the exponent of the optical conductivity. This points towards a
QPT in the cuprates close to optimal doping, although of an unconventional
kind.Comment: pdf format, 9 pages, 4 color figures include
Proceedings of the Thirteenth International Conference on Time-Resolved Vibrational Spectroscopy
The thirteenth meeting in a long-standing series of “Time-Resolved Vibrational Spectroscopy” (TRVS) conferences was held May 19th to 25th at the Kardinal Döpfner Haus in Freising, Germany, organized by the two Munich Universities - Ludwig-Maximilians-Universität and Technische Universität München. This international conference continues the illustrious tradition of the original in 1982, which took place in Lake Placid, NY. The series of meetings was initiated by leading, world-renowned experts in the field of ultrafast laser spectroscopy, and is still guided by its founder, Prof. George Atkinson (University of Arizona and Science and Technology Advisor to the Secretary of State). In its current format, the conference contributes to traditional areas of time resolved vibrational spectroscopies including infrared, Raman and related laser methods. It combines them with the most recent developments to gain new information for research and novel technical applications. The scientific program addressed basic science, applied research and advancing novel commercial applications.
The thirteenth conference on Time Resolved Vibrational Spectroscopy promoted science in the areas of physics, chemistry and biology with a strong focus on biochemistry and material science. Vibrational spectra are molecule- and bond-specific. Thus, time-resolved vibrational studies provide detailed structural and kinetic information about primary dynamical processes on the picometer length scale. From this perspective, the goal of achieving a complete understanding of complex chemical and physical processes on the molecular level is well pursued by the recent progress in experimental and theoretical vibrational studies.
These proceedings collect research papers presented at the TRVS XIII in Freising, German
Integrated collinear refractive index sensor with Ge PIN photodiodes
Refractive index sensing is a highly sensitive and label-free detection
method for molecular binding events. Commercial implementations of biosensing
concepts based on plasmon resonances typically require significant external
instrumentation such as microscopes and spectrometers. Few concepts exist that
are based on direct integration of plasmonic nanostructures with optoelectronic
devices for on-chip integration. Here, we present a CMOS-compatible refractive
index sensor consisting of a Ge heterostructure PIN diode in combination with a
plasmonic nanohole array structured directly into the diode Al contact
metallization. In our devices, the photocurrent can be used to detect surface
refractive index changes under simple top illumination and without the aid of
signal amplification circuitry. Our devices exhibit large sensitivities > 1000
nm per refractive index unit in bulk refractive index sensing and could serve
as prototypes to leverage the cost-effectiveness of the CMOS platform for
ultra-compact, low-cost biosensors.Comment: 21 pages, 6 figures, supporting information with 11 pages and 11
figures attache
Properties of material in the submillimeter wave region (instrumentation and measurement of index of refraction)
The Properties of Materials in the Submillimeter Wave Region study was initiated to instrument a system and to make measurements of the complex index of refraction in the wavelength region between 0.1 to 1.0 millimeters. While refractive index data is available for a number of solids and liquids there still exists a need for an additional systematic study of dielectric properties to add to the existing data, to consider the accuracy of the existing data, and to extend measurements in this wavelength region for other selected mateials. The materials chosen for consideration would be those with useful thermal, mechanical, and electrical characteristics. The data is necessary for development of optical components which, for example, include beamsplitters, attenuators, lenses, grids, all useful for development of instrumentation in this relatively unexploited portion of the spectrum
Optical data of meteoritic nano-diamonds from far-ultraviolet to far-infrared wavelengths
We have used different spectroscopic techniques to obtain a consistent
quantitative absorption spectrum of a sample of meteoritic nano-diamonds in the
wavelength range from the vacuum ultraviolet (0.12 m) to the far infrared
(100 m). The nano-diamonds have been isolated by a chemical treatment from
the Allende meteorite (Braatz et al.2000). Electron energy loss spectroscopy
(EELS) extends the optical measurements to higher energies and allows the
derivation of the optical constants (n & k) by Kramers-Kronig analysis. The
results can be used to restrain observations and to improve current models of
the environment where the nano-diamonds are expected to have formed. We also
show that the amount of nano-diamond which can be present in space is higher
than previously estimated by Lewis et al. (1989).Comment: 11 pages, 7 figure
Far-infrared absorption and dispersion studies on methyl iodide solutions
A far-infrared dispersive liquid cell has been developed in collaboration with the National Physical Laboratory. This New Liquid Cell enables both the absorption coefficient and refractive index of a liquid to be accurately determined over the complete far-infrared frequency range. The New Liquid Cell has been used to make dispersive measurements of methyl iodide liquid and methyl iodide in a range of non-polar solvents. These were: carbon disulphide; carbon tetrachloride; n-heptane; n-decane; n-hexadecane and Santotrac 40 (an industrial traction fluid). This data has been combined with microwave measurements, enabling the total orientational correlation functions and the band moments to be determined. Results have also been obtained on the rates of reorientation and static angular correlations of methyl iodide molecules. This information on the liquid dynamics of methyl iodide has been used to elucidate the molecular environment of the solvents using methyl iodide as a probe molecule, which has given evidence for the presence of discrete solute 'pools' within the solvent environment for the longer chain length n-alkanes. Two theoretical models for molecular reorientation have been fitted to the experimental data. The first, a second order truncation of the Mori formalism though giving a good fit to the experimental far-infrared absorption coefficient and refractive index spectra, gave values for the molecular torques that did not agree with measured values. The second, a physically more meaningful model is based on the motion of a molecule which is described by a gaussian distribution of librational frequencies within a molecular cage, gives molecular torque values that agree well with experimental results
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