3,050 research outputs found
Single-electron transistor based on a silicon-on-insulator quantum wire fabricated by a side-wall patterning method
We propose and implement a promising fabrication technology for geometrically well-defined single-electron transistors based on a silicon-on-insulator quantum wire and side-wall depletion gates. The 30-nm-wide silicon quantum wire is defined by a combination of conventional photolithography and process technology, called a side-wall patterning method, and depletion gates for two tunnel junctions are formed by the doped polycrystalline silicon sidewall. The good uniformity of the wire suppresses unexpected potential barriers. The fabricated device shows clear single-electron tunneling phenomena by an electrostatically defined single island at liquid nitrogen temperature and insensitivity of the Coulomb oscillation period to gate bias conditions.open252
Decay Constants and Semileptonic Decays of Heavy Mesons in Relativistic Quark Model
We investigate the and mesons in the relativistic quark model by
applying the variational method with the Gaussian wave function. We calculate
the Fermi momentum parameter , and obtain
GeV, which is almost independent of the input parameters, , ,
and . We then calculate the ratio /, and obtain the
result which is larger, by the factor of about 1.3, than
given by the naive nonrelativistic analogy. This result is in a good agreement
with the recent Lattice calculations. We also calculate the ratio
/. In these calculations the wave function at
origin is essential. We also determine by comparing the
theoretical prediction of the ACCMM model with the lepton energy spectrum of from the recent ARGUS analysis, and find that
GeV, when we use GeV. However, this
experimentally determined value of is strongly dependent on the value
of input parameter .Comment: 15 pages (Latex) (uses epsfig.sty, 1 figure appended as a uuencoded
compressed ps-file
Selective Growth of Epitaxial Sr\u3csub\u3e2\u3c/sub\u3eIrO\u3csub\u3e4\u3c/sub\u3e by Controlling Plume Dimensions in Pulsed Laser Deposition
We report that epitaxial Sr2IrO4 thin-films can be selectively grown using pulsed laser deposition (PLD). Due to the competition between the Ruddlesden-Popper phases of strontium iridates (Srn+1IrnO3n+1), conventional PLD methods often result in mixed phases of Sr2IrO4 (n = 1), Sr3Ir2O7 (n = 2), and SrIrO3 (n = ∞). We have discovered that reduced PLD plume dimensions and slow deposition rates are the key for stabilizing pure Sr2IrO4 phase thin-films, identified by real-time in-situ monitoring of their optical spectra. The slow film deposition results in a thermodynamically stable TiO2\\SrO\IrO2\SrO\SrO configuration at an interface rather than TiO2\\SrO\SrO\IrO2\SrO between a TiO2-terminated SrTiO3 substrate and a Sr2IrO4 thin film, which is consistent with other layered oxides grown by molecular beam epitaxy. Our approach provides an effective method for using PLD to achieve pure phase thin-films of layered materials that are susceptible to several energetically competing phases
Suppression of ferromagnetic ordering in doped manganites: Effects of the superexchange interaction
From a Monte Carlo study of the ferromagnetic Kondo lattice model for doped
manganites, including the antiferromagnetic superexchange interaction
(), we found that the ferromagnetic ordering was suppressed as
increased. The ferromagnetic transition temperature , as obtained from a
mean field fit to the calculated susceptibilities, was found to decrease
monotonically with increasing . Further, the suppression in
scales with the bandwidth narrowing induced by the antiferromagnetic
frustration originating from . From these results, we propose that the
change in the superexchange interaction strength between the electrons
of the Mn ions is one of the mechanisms responsible for the suppression in
observed in manganites of the type
(LaPr)CaMnO.Comment: 5 pages, 6 figures. To appear in PR
Electronic and Optical Properties of La-Doped Sr\u3csub\u3e3\u3c/sub\u3eIr\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e7\u3c/sub\u3e Epitaxial Thin Films
We have investigated structural, transport, and optical properties of tensile strained (Sr1−xLax)3Ir2O7 (x = 0, 0.025, 0.05) epitaxial thin films. While high-Tc superconductivity is predicted theoretically in the system, we have observed that all of the samples remain insulating with finite optical gap energies and Mott variable-range hopping characteristics in transport. Cross-sectional scanning transmission electron microscopy indicates that structural defects such as stacking faults appear in this system. The insulating behavior of the La-doped Sr3Ir2O7 thin films is presumably due to disorder-induced localization and ineffective electron doping of La, which brings to light the intriguing difference between epitaxial thin films and bulk single crystals of the iridates
Dependence of on Fermi momentum in ACCMM model
The Gaussian width of Fermi momentum, , is the most important
parameter of the ACCMM model, and its value is essential in the determination
of because the experimental analysis is allowed only at the
end-point region of inclusive semileptonic -decay spectrum. We extract the
value of as a function of . We also calculate the
parameter in the relativistic quark model using the variational
method, and obtain GeV which is much larger than the commonly
used value, GeV, in experimental analyses. When we use GeV instead of 0.3 GeV, the value of from ACCMM model is
increased by a factor 1.81, and can give a good agreement with Isgur {\it et
al.} model.Comment: 1. Section 2 has been revised by considering the fact that in the
real experimental situation the only measured quantity is the number of
events in the high region compared to the total semi- leptonic event
number. 2. The article by C. Greub and D. Wyler (Phys. Lett. B295 (1992) 293)
has been included in references, which reports a similar conclusion for the
value of (=566 MeV), even though they used the different
approach. 3. This article will be published in Z. Phys. C (1995
Magnetic Field Dependence of Macroscopic Quantum Tunneling and Coherence of Ferromagnetic Particle
We calculate the quantum tunneling rate of a ferromagnetic particle of diameter in a magnetic field of arbitrary angle. We consider the
magnetocrystalline anisotropy with the biaxial symmetry and that with the
tetragonal symmetry. Using the spin-coherent-state path integral, we obtain
approximate analytic formulas of the tunneling rates in the small -limit for the magnetic field normal to the easy axis (), for the field opposite to the initial easy axis (),
and for the field at an angle between these two orientations (). In addition, we obtain numerically the tunneling rates for
the biaxial symmetry in the full range of the angle of the magnetic
field (), for the values of \epsilon =0.01 and
0.001.Comment: 25 pages of text (RevTex) and 4 figures (PostScript files), to be
published in Phys. Rev.
Enhanced Metallic Properties of SrRuO\u3csub\u3e3\u3c/sub\u3e Thin Films via Kinetically Controlled Pulsed Laser Epitaxy
Metal electrodes are a universal element of all electronic devices. Conducting SrRuO3 (SRO) epitaxial thin films have been extensively used as electrodes in complex-oxide heterostructures due to good lattice mismatches with perovskite substrates. However, when compared to SRO single crystals, SRO thin films have shown reduced conductivity and Curie temperatures (TC), which can lead to higher Joule heating and energy loss in the devices. Here, we report that high-quality SRO thin films can be synthesized by controlling the plume dynamics and growth rate of pulsed laser epitaxy (PLE) with real-time optical spectroscopic monitoring. The SRO thin films grown under the kinetically controlled conditions, down to ca. 16 nm in thickness, exhibit both enhanced conductivity and TC as compared to bulk values, due to their improved stoichiometry and a strain-mediated increase of the bandwidth of Ru 4d electrons. This result provides a direction for enhancing the physical properties of PLE-grown thin films and paves a way to improved device applications
Enhanced Metallic Properties of SrRuO\u3csub\u3e3\u3c/sub\u3e Thin Films via Kinetically Controlled Pulsed Laser Epitaxy
Metal electrodes are a universal element of all electronic devices. Conducting SrRuO3 (SRO) epitaxial thin films have been extensively used as electrodes in complex-oxide heterostructures due to good lattice mismatches with perovskite substrates. However, when compared to SRO single crystals, SRO thin films have shown reduced conductivity and Curie temperatures (TC), which can lead to higher Joule heating and energy loss in the devices. Here, we report that high-quality SRO thin films can be synthesized by controlling the plume dynamics and growth rate of pulsed laser epitaxy (PLE) with real-time optical spectroscopic monitoring. The SRO thin films grown under the kinetically controlled conditions, down to ca. 16 nm in thickness, exhibit both enhanced conductivity and TC as compared to bulk values, due to their improved stoichiometry and a strain-mediated increase of the bandwidth of Ru 4d electrons. This result provides a direction for enhancing the physical properties of PLE-grown thin films and paves a way to improved device applications
Average Kinetic Energy of Heavy Quark in Semileptonic B Decay
Within the ACCMM model the average kinetic energy of heavy quark in a
heavy-light meson is calculated as , solely from the fact that the Gaussian momentum probability
distribution has been taken in the ACCMM model. Therefore, the Fermi momentum
parameter of the ACCMM model is not a truly free parameter, but is
closely related to the average kinetic energy of heavy quark, which is
theoretically calculable in principle. In this context, we determine
by comparing the theoretical prediction of the ACCMM model with the model
independent lepton energy spectrum of from the recent
CLEO analysis, and find that GeV. We also
calculate in the relativistic quark model by applying the quantum
mechanical variational method, and obtained GeV. We show
the correspondences between the relativistic quark model and the heavy quark
effective theory. We then clarify the importance of the value of in
the determination of .Comment: 23 pages(LaTeX), 2 Postscript figures, uses aps.st
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