3,160 research outputs found
Orbital-selective Mass Enhancements in Multi-band CaSrRuO Systems Analyzed by the Extended Drude Model
We investigated optical spectra of quasi-two-dimensional multi-band CaSrRuO systems. The extended Drude model analysis on the
ab-plane optical conductivity spectra indicates that the effective mass should
be enhanced near . Based on the sum rule argument, we showed that the
orbital-selective Mott-gap opening for the bands, the widely
investigated picture, could not be the origin of the mass enhancement. We
exploited the multi-band effects in the extended Drude model analysis, and
demonstrated that the intriguing heavy mass state near should come from
the renormalization of the band.Comment: 4 figure
Finite-size scaling theory for explosive percolation transitions
The finite-size scaling (FSS) theory for continuous phase transitions has
been useful in determining the critical behavior from the size dependent
behaviors of thermodynamic quantities. When the phase transition is
discontinuous, however, FSS approach has not been well established yet. Here,
we develop a FSS theory for the explosive percolation transition arising in the
Erd\H{o}s and R\'enyi model under the Achlioptas process. A scaling function is
derived based on the observed fact that the derivative of the curve of the
order parameter at the critical point diverges with system size in a
power-law manner, which is different from the conventional one based on the
divergence of the correlation length at . We show that the susceptibility
is also described in the same scaling form. Numerical simulation data for
different system sizes are well collapsed on the respective scaling functions.Comment: 5 pages, 5 figure
Epitaxial growth and the magnetic properties of orthorhombic YTiO3 thin films
High-quality YTiO3 thin films were grown on LaAlO3 (110) substrates at low
oxygen pressures (<10-8 Torr) using pulsed laser deposition. The in-plane
asymmetric atomic arrangements at the substrate surface allowed us to grow
epitaxial YTiO3 thin films, which have an orthorhombic crystal structure with
quite different a- and b-axes lattice constants. The YTiO3 film exhibited a
clear ferromagnetic transition at 30 K with a saturation magnetization of about
0.7 uB/Ti. The magnetic easy axis was found to be along the [1-10] direction of
the substrate, which differs from the single crystal easy axis direction, i.e.,
[001].Comment: 14 pages, 4 figure
Observation of inhomogeneous domain nucleation in epitaxial Pb(Zr,Ti)O3 capacitors
We investigated domain nucleation process in epitaxial Pb(Zr,Ti)O3 capacitors
under a modified piezoresponse force microscope. We obtained domain evolution
images during polarization switching process and observed that domain
nucleation occurs at particular sites. This inhomogeneous nucleation process
should play an important role in an early stage of switching and under a high
electric field. We found that the number of nuclei is linearly proportional to
log(switching time), suggesting a broad distribution of activation energies for
nucleation. The nucleation sites for a positive bias differ from those for a
negative bias, indicating that most nucleation sites are located at
ferroelectric/electrode interfaces
Dielectric constants of Ir, Ru, Pt, and IrO2: Contributions from bound charges
We investigated the dielectric functions () of Ir, Ru, Pt,
and IrO, which are commonly used as electrodes in ferroelectric thin film
applications. In particular, we investigated the contributions from bound
charges (), since these are important scientifically as
well as technologically: the (0) of a metal electrode is one of
the major factors determining the depolarization field inside a ferroelectric
capacitor. To obtain (0), we measured reflectivity spectra of
sputtered Pt, Ir, Ru, and IrO2 films in a wide photon energy range between 3.7
meV and 20 eV. We used a Kramers-Kronig transformation to obtain real and
imaginary dielectric functions, and then used Drude-Lorentz oscillator fittings
to extract (0) values. Ir, Ru, Pt, and IrO produced
experimental (0) values of 4810, 8210, 5810, and
295, respectively, which are in good agreement with values obtained using
first-principles calculations. These values are much higher than those for
noble metals such as Cu, Ag, and Au because transition metals and IrO have
such strong d-d transitions below 2.0 eV. High (0) values will
reduce the depolarization field in ferroelectric capacitors, making these
materials good candidates for use as electrodes in ferroelectric applications.Comment: 26 pages, 6 figures, 2 table
In Situ deposition of YBCO high-T(sub c) superconducting thin films by MOCVD and PE-MOCVD
Metalorganic Chemical Vapor Deposition (MOCVD) offers the advantages of a high degree of compositional control, adaptability for large scale production, and the potential for low temperature fabrication. The capability of operating at high oxygen partial pressure is particularly suitable for in situ formation of high temperature superconducting (HTSC) films. Yttrium barium copper oxide (YBCO) thin films having a sharp zero-resistance transition with T( sub c) greater than 90 K and Jc approx. 10 to the 4th power A on YSZ have been prepared, in situ, at a substrate temperature of about 800 C. Moreover, the ability to form oxide films at low temperature is very desirable for device applications of HTSC materials. Such a process would permit the deposition of high quality HTSC films with a smooth surface on a variety of substrates. Highly c-axis oriented, dense, scratch resistant, superconducting YBCO thin films with mirror-like surfaces have been prepared, in situ, at a reduced substrate temperature as low as 570 C by a remote microwave-plasma enhanced metalorganic chemical vapor deposition (PE-MOCVD) process. Nitrous oxide was used as a reactant gas to generate active oxidizing species. This process, for the first time, allows the formation of YBCO thin films with the orthorhombic superconducting phase in the as-deposited state. The as-deposited films grown by PE-MOCVD show attainment of zero resistance at 72 K with a transition width of about 5 K. MOCVD was carried out in a commercial production scale reactor with the capability of uniform deposition over 100 sq cm per growth run. Preliminary results indicate that PE-MOCVD is a very attractive thin film deposition process for superconducting device technology
Spin-Orbit Coupling in Iridium-Based 5d Compounds Probed by X-ray Absorption Spectroscopy
We have performed x-ray absorption spectroscopy (XAS) measurements on a
series of Ir-based 5d transition metal compounds, including Ir, IrCl3, IrO2,
Na2IrO3, Sr2IrO4, and Y2Ir2O7. By comparing the intensity of the "white-line"
features observed at the Ir L2 and L3 absorption edges, it is possible to
extract valuable information about the strength of the spin-orbit coupling in
these systems. We observe remarkably large, non-statistical branching ratios in
all Ir compounds studied, with little or no dependence on chemical composition,
crystal structure, or electronic state. This result confirms the presence of
strong spin-orbit coupling effects in novel iridates such as Sr2IrO4, Na2IrO3,
and Y2Ir2O7, and suggests that even simple Ir-based compounds such as IrO2 and
IrCl3 may warrant further study. In contrast, XAS measurements on Re-based 5d
compounds, such as Re, ReO2, ReO3, and Ba2FeReO6, reveal statistical branching
ratios and negligible spin-orbit coupling effects.Comment: 9 pages, 4 figure
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