28,290 research outputs found
Spin/Orbital Pattern-Dependent Polaron Absorption in Nd(1-x)Sr(x)MnO3
We investigated optical properties of Nd(1-x)Sr(x)MnO3 (x= 0.40, 0.50, 0.55,
and 0.65) single crystals. In the spin/orbital disordered state, their
conductivity spectra look quite similar, and the strength of the mid-infrared
absorption peak is proportional to x(1-x) consistent with the polaron picture.
As temperature lowers, the Nd(1-x)Sr(x)MnO3 samples enter into various
spin/orbital ordered states, whose optical responses are quite different. These
optical responses can be explained by the spin/orbital ordering
pattern-dependent polaron hopping.Comment: 3 figures (gzipped
Recent Progress in Droplet-Based Manufacturing Research
This article reports the recent progress of re-search made in the Droplet-Based Manufacturing Laboratory at MIT. The study has been focused on obtaining a fundamental understanding of microdroplet deposition and applying the technology to various practical applications. Specific scientific contributions include the development of an analytical model for droplet splashing/recoiling, an in situ droplet size control methodology, and a study of microstructure design for spray forming. The research per-formed in the lab provides both fundamental knowledge base and practical process developments for a range of manufacturing applications, including electronics packaging, spray forming and freeform fabrication.Singapore-MIT Alliance (SMA
Melting of Charge/Orbital Ordered States in NdSrMnO: Temperature and Magnetic Field Dependent Optical Studies
We investigated the temperature ( 15 290 K) and the magnetic
field ( 0 17 T) dependent optical conductivity spectra of a
charge/orbital ordered manganite, NdSrMnO. With variation
of and , large spectral weight changes were observed up to 4.0 eV. These
spectral weight changes could be explained using the polaron picture.
Interestingly, our results suggested that some local ordered state might remain
above the charge ordering temperature, and that the charge/orbital melted state
at a high magnetic field (i.e. at 17 T and 4.2 K) should be a three
dimensional ferromagnetic metal. We also investigated the first order phase
transition from the charge/orbital ordered state to ferromagnetic metallic
state using the - and % -dependent dielectric constants . In
the charge/orbital ordered insulating state, was positive and
. With increasing and , was
increased up to the insulator-metal phase boundaries. And then,
abruptly changed into negative and , which was
consistent with typical responses of a metal. Through the analysis of using an effective medium approximation, we found that the melting
of charge/orbital ordered states should occur through the percolation of
ferromagnetic metal domains.Comment: submitted to Phys. Rev.
Nearly Massless Electrons in the Silicon Interface with a Metal Film
We demonstrate the realization of nearly massless electrons in the most
widely used device material, silicon, at the interface with a metal film. Using
angle-resolved photoemission, we found that the surface band of a monolayer
lead film drives a hole band of the Si inversion layer formed at the interface
with the film to have nearly linear dispersion with an effective mass about 20
times lighter than bulk Si and comparable to graphene. The reduction of mass
can be accounted for by repulsive interaction between neighboring bands of the
metal film and Si substrate. Our result suggests a promising way to take
advantage of massless carriers in silicon-based thin-film devices, which can
also be applied for various other semiconductor devices.Comment: 4 pages, 4 figures, accepted for publication in Physical Review
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High-Performance, Wearable Thermoelectric Generator Based on a Highly Aligned Carbon Nanotube Sheet
A high-performance, wearable thermoelectric generator (TEG) was fabricated with a highly aligned carbon nanotube (CNT) sheet. The aligned CNT sheet exhibits extraordinary electrical conductivity compared to disordered CNT sheets and also can be directly fabricated as a continuous TEG without metal electrode interconnects. This provides a significant reduction in contact resistance between TE legs and electrodes compared to traditional TEGs, resulting in higher power output. In addition, the continuity of the module without any disconnected parts provides high degrees of mechanical stability and durability. This robust and scalable approach to flexible TEG fabrication paves the way for CNT applications in lightweight, flexible, and wearable electronics
A Scaling Behavior of Spectral Weight Changes in Perovskite Manganites La_{0.7-y}Pr_{y}Ca_{0.3}MnO_3
Optical conductivity spectra of La_{0.7-y}Pr_{y}Ca_{0.3}MnO_3 were
systematically investigated. For metallic samples, the spectral weight below
0.5 eV, whose magnitude can be represented by the effective carrier number
N_{eff}(0.5 eV), increases as temperature becomes lower. Regardless of the Pr
doping, all the measured values of N_{eff}(0.5 eV)/T_C fall into one scaling
curve. This scaling behavior could be explained by the theoretical model by
Roeder et al. [Phys. Rev. Lett. 76, 1356 (1996)], which includes spin double
exchange and Jahn-Teller lattice coupling to holes. With the Pr doping,
far-infrared conductivities were found to be suppressed, probably due to the
Anderson localization.Comment: Latex 2e, 8 pages including 4 postscript figures, submitted at Apr 2
Prompt photon hadroproduction at high energies in off-shell gluon-gluon fusion
The amplitude for production of a single photon associated with quark pair in
the fusion of two off-shell gluons is calculated. The matrix element found is
applied to the inclusive prompt photon hadroproduction at high energies in the
framework of kt-factorization QCD approach. The total and differential cross
sections are calculated in both central and forward pseudo-rapidity regions.
The conservative error analisys is performed. We used the unintegrated gluon
distributions in a proton which were obtained from the full CCFM evolution
equation as well as from the Kimber-Martin-Ryskin prescription. Theoretical
results were compared with recent experimental data taken by the D0 and CDF
collaborations at Fermilab Tevatron. Theoretical predictions for the LHC
energies are given.Comment: 32 pages, 18 figure
Optical Investigations of Charge Gap in Orbital Ordered La1/2Sr3/2MnO4
Temperature and polarization dependent electronic structure of La1/2Sr3/2MnO4
were investigated by optical conductivity analyses. With decreasing
temperature, for E//ab, a broad mid-infrared (MIR) peak of La1/2Sr3/2MnO4
becomes narrower and moves to the higher frequency, while that of
Nd1/2Sr3/2MnO4 nearly temperature independent. We showed that the MIR peak in
La1/2Sr3/2MnO4 originates from orbital ordering associated with CE-type
magnetic ordering and that the Jahn-Teller distortion has a significant
influence on the width and the position of the MIR peak.Comment: 10 pages, 4 figure
Non-Markovian stochastic Liouville equation and anomalous relaxation kinetics
The kinetics of phase and population relaxation in quantum systems induced by
noise with anomalously slowly decaying correlation function P (t) ~ (wt)^{-
alpha}, where 0 < alpha < 1 is analyzed within continuous time random walk
approach. The relaxation kinetics is shown to be anomalously slow. Moreover for
alpha < 1 in the limit of short characteristic time of fluctuations w^{-1} the
kinetics is independent of w. As alpha \to 1 the relaxation regime changes from
the static limit to fluctuation narrowing. Simple analytical expressions are
obtained describing the specific features of the kinetics.Comment: 7 pages, 2 figure
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