Z. Schlesinger

Efficient Titanium Oxide/Conjugated Polymer Photovoltaics for Solar Energy Conversion

[19] Since the mixing ratio of the anions in the solution from which the crystals were grown was revealed to be almost identical to the stoichiometry determined by EPMA of the obtained crystal, the mixing ratio of the anions in the solution was adopted in the chemical formula of the crystal. The results of EPMA of k-(BETS)2FexGa1‐xBr1.0Cl3.0 are: for x = 0.50, Fe/Ga/Br/Cl = 0.51:0.49:1.13:2.85 (0.50:0.50:1.00:3.00); for x = 0.40, Fe/Ga/Br/Cl = 0.40:0.60:0.96:2.87 (0.40:0.60:1.00:3.00); for x = 0.30, Fe/Ga/Br/Cl = 0.32:0.68:1.11:3.07 (0.30:0.70:1.00:3.00); for x = 0.20, Fe/Ga/Br/Cl = 0.24:0.76:1.11:3.16 (0.20:0.80:1.00:3.00); for x = 0.10, Fe/Ga/Br/Cl = 0.12:0.88:1.04:3.22 (0.10:0.90:1.00:3.00). [20] Recent susceptibility measurements revealed that the angle between the easy axis of the antiferromagnetic structure and the c axis is about 35 in k-(BETS)2FeCl4 (E. Ojima, T. Sasaki, private communication). While the easy axis of k-(BETS)2FeBr0.6Cl3.4 is approximately parallel to the b* axis.

NON-FERMI-LIQUID BEHAVIOR OF SRRUO3 : EVIDENCE FROM INFRARED CONDUCTIVITY

The reflectivity of the itinerant ferromagnet SrRuO{sub 3} has been measured between 50 and 25thinsp000thinspthinspcm{sup {minus}1} at temperatures ranging from 40 to 300thinspthinspK, and used to obtain conductivity, scattering rate, and effective mass as a function of frequency and temperature. We find that at low temperatures the conductivity falls unusually slowly as a function of frequency (proportional to 1/{omega}{sup 1/2} ), and at high temperatures it even appears to increase as a function of frequency in the far-infrared limit. The data suggest that the charge dynamics of SrRuO{sub 3} are substantially different from those of Fermi-liquid metals. {copyright} {ital 1998} {ital The American Physical Society }

Ferromagnetism in the Mott Insulator Ba2NaOsO6

Results are presented of single crystal structural, thermodynamic, and reflectivity measurements of the double-perovskite Ba2NaOsO6. These characterize the material as a 5d1 ferromagnetic Mott insulator with an ordered moment of approximately 0.2microB per formula unit and TC=6.8(3) K. The magnetic entropy associated with this phase transition is close to Rln2, indicating that the quartet ground state anticipated from consideration of the crystal structure is split, consistent with a scenario in which the ferromagnetism is associated with orbital ordering.

Minimum fluence for laser blow‐off of thin gold films at 248 and 532 nm

The minimum 248 nm, 25 ns, and 532 nm, 15 ns laser fluences required to blow off thin gold films from optical quartz have been measured as a function of film thickness. The films apparently blow off when the gold‐quartz interface reaches the normal boiling point of gold. Even though the initial reflectivities at the two wavelengths are very different, the actual laser fluences required to blow off the films are very similar. While the reflectivities above the melting point appear to be very low, as expected, large decreases in the reflectivity at 532 nm may also occur prior to film melting.

Unusual low-energy phonon dynamics in the negative thermal expansion compound ZrW2O8.

An infrared study of the phonon spectra of ZrW2O8 as a function of temperature which includes the low-energy (2-10 meV) region relevant to negative thermal expansion is reported and discussed in the context of specific heat and neutron density of state results. The prevalence of infrared active phonons at low energy and their observed temperature dependence are highly unusual and indicative of exotic low-energy lattice dynamics. Eigenvector calculations indicate a mixing of librational and translational motion within each low-frequency IR mode. The role of the underconstrained structure in establishing the nature of these modes and the relationship between the IR spectra and the large negative thermal expansion in ZrW2O8 are discussed.

Kondo scaling in the optical response of YbIn1-xAgxCu4.

Theoretical work on Kondo systems predicts universality in the scaling of observable quantities with the Kondo temperature, T(K). Here we report infrared-frequency optical response measurements of the correlated system YbIn(1-x)AgxCu4. We observe that x-dependent variations in the frequency and strength of a low-energy excitation are related to the x-dependent Kondo temperature. Comparison of the inferred trends with existing theory and a model calculation provides a framework in which to view these experimental results as scaling phenomena arising from local-moment/conduction electron hybridization.

Optical study of the electronic phase transition of strongly correlated YbInCu 4

Infrared, visible, and near-UV reflectivity measurements are used to obtain conductivity as a function of temperature and frequency in YbInCu{sub 4}, which exhibits an isostructural phase-transition into a mixed-valent phase below T{sub v}{approx_equal}42 K. In addition to a gradual loss of spectral weight with decreasing temperature extending up to 1.5 eV, a sharp resonance appears at 0.25 eV in the mixed-valent phase. This feature can be described in terms of excitations into the Kondo (Abrikosov-Suhl) resonance, and, like the sudden reduction of resistivity, provides a direct reflection of the onset of coherence in this strongly correlated electron system. (c) 2000 The American Physical Society.

Electron cyclotron resonance in silicon/silicon germanium heterostructures

Far‐infrared measurements of the cyclotron resonance absorption of a two‐dimensional electron gas (2DEG) in a strained Si/SiGe heterostructure at low temperature (0.35–4 K) in the magnetic field range 2–14 T are reported. The effective mass was determined to be m*≂0.195±0.004 m0, and exhibited only a slight decrease (3%) at low carrier densities, in contrast to the large (40%) change observed in Si metal‐oxide‐semiconductor field effect transistors. In addition, the cyclotron absorption lines tend to be narrow (≲1 cm−1), and show a significant dependence on both field and carrier density that appears to be related to the filling of the quantized Landau and spin levels of the 2DEG.

Is FeSi a Kondo insulator

FeSi exhibits a Curie-like susceptibility accompanied by a moderate electronic conductivity at high temperature. At low temperature the magnetic susceptibility goes to zero, and a small charge gap appears. We discuss phenomenological and theoretical aspects of the relationship between FeSi and various rare-earth correlated systems often referred to as Kondo insulators.

Infrared properties of high Tc superconductors

Over the past several years a coherent phenomenology of the high {Tc} cuprate superconductors has begun to emerge. Infrared measurements have contributed several important ingredients to this picture including: (1) the inference of a scattering rate that is linear in frequency for {omega}>T, and of order {omega}, (2) a characteristic energy scale in the superconducting state of 500 cm{sup {minus}1} (60 meV), which can be interpreted as a superconducting pair excitation threshold or energy gap, and (3) evidence for very unusual temperature dependence in the vicinity of {Tc}. An attempt to describe these aspects of the data is presented here.