C. C. Homes

First-principles study of the structure and lattice dielectric response of CaCu 3 Ti 4 O 12

Structural and electronic properties of

A UNIVERSAL SCALING RELATION IN HIGH-TEMPERATURE SUPERCONDUCTORS

{\mathrm{CaCu}}_{3}{\mathrm{Ti}}_{4}{\mathrm{O}}_{12}

Charge transfer in the high dielectric constant materials CaCu 3 Ti 4 O 12 and CdCu 3 Ti 4 O 12

are calculated using density-functional theory within the local spin-density approximation. After an analysis of structural stability, zone-center optical phonon frequencies are evaluated using the frozen-phonon method and mode effective charges are determined from computed Berry-phase polarizations. Excellent agreement between calculated and measured phonon frequencies is obtained. The calculated mode effective charges are in poorer agreement with experiment, although they are of the correct order of magnitude and the lattice contribution to the static dielectric constant is calculated to be

Charge density wave formation accompanying ferromagnetic ordering in quasi-one-dimensional BaIrO3

\ensuremath{\sim}40.

Silicon beam splitter for far-infrared and terahertz spectroscopy

On the basis of these results, various mechanisms are considered for the enormous dielectric response reported in recent experiments. No direct evidence is found for intrinsic lattice or electronic mechanisms, suggesting that increased attention should be given to extrinsic effects.

Sum rules and energy scales in the high-temperature superconductorYBa2Cu3O6+x

Since the discovery of superconductivity at elevated temperatures in the copper oxide materials there has been a considerable effort to find universal trends and correlations amongst physical quantities, as a clue to the origin of the superconductivity. One of the earliest patterns that emerged was the linear scaling of the superfluid density (ρs) with the superconducting transition temperature (Tc), which marks the onset of phase coherence. This is referred to as the Uemura relation, and it works reasonably well for the underdoped materials. It does not, however, describe optimally doped (where Tc is a maximum) or overdoped materials. Similarly, an attempt to scale the superfluid density with the d.c. conductivity (σdc) was only partially successful. Here we report a simple scaling relation (ρs∝σdcTc, with σdc measured at approximately Tc) that holds for all tested high-Tc materials. It holds regardless of doping level, nature of dopant (electrons versus holes), crystal structure and type of disorder, and direction (parallel or perpendicular to the copper–oxygen planes).

In-plane polarized collective modes in detwinned YBa2Cu3O6.95 observed by spectral ellipsometry

The cubic perovskite-related ceramic CaCu 3 Ti 4 O 1 2 has a very high static dielectric constant e 0 ≥10 000 at room temperature (RT), which drops to about 100 below ≃ 100 K. Substituting Cd for Ca reduces the RT value of e 0 by over an order of magnitude. The origin of the large e 0 is not fully understood, but may be due to an internal barrier layer capacitance (IBLC) effect. Infrared measurements on the Ca and Cd compounds show that low-frequency modes increase dramatically in strength at low temperature, suggesting a change in the effective charges and increasing electronic localization that may lead to a breakdown of the IBLC effect.

Electronic correlations and unusual superconducting response in the optical properties of the iron chalcogenide FeTe0.55Se0.45

The magnetic, transport, optical, and structural properties of quasi-one-dimensional BaIrO 3 show evidence for the simultaneous onset of electronic density wave formation and ferromagnetism at Tc3a 175 K: Two additional features in the chain direction dc conductivity show a sudden change to metallic behavior below Tc2a 80 K and then a Mott-like transition at Tc1a 26 K: Highly non-linear dc conductivity, optical gap formation at <9kBTc3, additional phonon modes, and emergent X-ray satellite structure support density wave formation. Even at very high (30 T) fields the saturation Ir moment is very small, <0.04mB/Ir. q 2000 Elsevier Science Ltd. All rights reserved.

Extracting the electron-boson spectral function a 2 FÑvÖ from infrared and photoemission data using inverse theory

Silicon beam splitters several millimeters thick offer numerous advantages over thin freestanding dielectric beam splitters. For routine spectroscopy for which resolutions of better than 1 cm(-1) are not required, a silicon beam splitter can replace several Mylar beam splitters to span the entire far-infrared region. In addition to superior long-wavelength performance that extends well into the terahertz region, the silicon beam splitter has the additional advantage that its efficiency displays little polarization dependence.

Scaling of the superfluid density in high-temperature superconductors

The Ferrell-Glover-Tinkham (FGT) sum rule has been applied to the temperature dependence of the in-plane optical conductivity of optimally doped