2,345 research outputs found
SET based experiments for HTSC materials: II
The cuprates seem to exhibit statistics, dimensionality and phase transitions
in novel ways. The nature of excitations
[i.e. quasiparticle or collective], spin-charge separation, stripes [static
and dynamics], inhomogeneities, psuedogap, effect of impurity dopings [e.g. Zn,
Ni] and any other phenomenon in these materials must be consistently
understood. In this note we further discuss our original suggestion of using
Single Electron Tunneling Transistor
[SET] based experiments to understand the role of charge dynamics in these
systems. Assuming that SET operates as an efficient charge detection system we
can expect to understand the underlying physics of charge transport and charge
fluctuations in these materials for a range of doping. Experiments such as
these can be classed in a general sense as mesoscopic and nano characterization
of cuprates and related materials. In principle such experiments can show if
electron is fractionalized in cuprates as indicated by ARPES data. In contrast
to flux trapping experiments SET based experiments are more direct in providing
evidence about spin-charge separation. In addition a detailed picture of nano
charge dynamics in cuprates may be obtained.Comment: 10 pages revtex plus four figures; ICMAT 2001 Conference Symposium P:
P10-0
Insulators for Pb(1-x)Sn(x)Te
Thin films of LaF3 were e-gun and thermally deposited on several substrates. The e-gun deposited films are fluorine deficient, have high ionic conductivities that persist to 77 K, and high effective dielectric constants. The thermally deposited material tends to be closer to stoichiometric, and have higher effective breakdown field strengths. Thermally deposited LaF3 films with resistivities in excess of 10 to the 12th power ohms - cm were deposited on metal coated glass substrates. The LaF3 films were shown to adhere well to PbSnTe, surviving repeated cycles between room temperature and 77 K. The LaF3 films on GaAs were also studied
Fermion and Anti-Fermion Effective Masses in High Temperature Gauge Theories in -Asymmetric Background
We calculate the splitting between fermion and anti-fermion effective masses
in high temperature gauge theories in the presence of a non-vanishing chemical
potential due to the -asymmetric fermionic background. In particular we
consider the case of left-handed leptons in the theory when
the temperature is above GeV and the gauge symmetry is restored.Comment: 13 pages, TIPAC-93001
Monopoles near the Planck Scale and Unification
Considering our (3+1)-dimensional space-time as, in some way, discrete or l
attice with a parameter , where is the Planck length,
we have investigated the additional contributions of lattice artifact monopoles
to beta-functions of the renormalisation group equations for the running fine
structure constants (i=1,2,3 correspond to the U(1), SU(2) and
SU(3) gauge groups of the Standard Model) in the Family Replicated Gauge Group
Model (FRGGM) which is an extension of the Standard Model at high energies. It
was shown that monopoles have times smaller magnetic charge in FRGGM
than in SM ( is the number of families in FRGGM). We have estimated al
so the enlargement of a number of fermions in FRGGM leading to the suppression
of the asymptotic freedom in the non-Abelian theory. We have shown that, in
contrast to the case of AntiGUT when the FRGGM undergoes the breakdown at
GeV, we have the possibility of unification if the
FRGGM-breakdown occurs at GeV. By numerical calculations we
obtained an example of the unification of all gauge interactions (including
gravity) at the scale GeV. We discussed the
possibility of or (SUSY or not SUSY) unifications.Comment: 49 pages, 7 figure
First-Principles Calculation of Born Effective Charges and Spontaneous Polarization of Ferroelectric Bismuth Titanate
In this study, we present the results of our first-principles calculations of
the band structure, density of states and the Born effective charge tensors for
the ferroelectric (ground state B1a1) and paraelectric (I4/mmm) phases of
bismuth titanate. The calculations are done using the generalized gradient
approximation (GGA) as well as the local density approximation (LDA) of the
density functional theory. In contrast to the literature, our calculations on
B1a1 structure using GGA and LDA yield smaller indirect band gaps as compared
to the direct band gaps, in agreement with the experimental data. The density
of states shows considerable hybridization among Ti 3d, Bi 6p and O 2p states
indicating covalent nature of the bonds leading to the ferroelectric
instability. The Born effective charge tensors of the constituent ions for the
ground state (B1a1) and paraelectric (I4/mmm) structures were calculated using
the Berry phase method. This is followed by the calculation of the spontaneous
polarization for the ferroelectric B1a1 phase using the Born effective charge
tensors of the individual ions. The calculated value for the spontaneous
polarization of ferroelectric bismuth titanate using different Born effective
charges was found to be in the range of 55+/-13 C/cm2 in comparison to the
reported experimental value of (50+/-10 C/cm2) for single crystals. The
origin of ferroelectricity is attributed to the relatively large displacements
of those oxygen ions in the TiO6 octahedra that lie along the a-axis of the
bismuth titanate crystal.Comment: 36 pages, 5 figure
An Improved upper limit on the decay K^+ -> pi^+ mu^+ e^-
Based on results of a search for the lepton-family-number-violating decay
with data collected by experiment E865 at the
Alternating Gradient Synchrotron of Brookhaven National Laboratory, we place an
upper limit on the branching ratio at (90% C.L.).
Combining the results with earlier E865 data and those of a previous
experiment, E777, an upper limit on the branching ratio of (90% C.L.) is obtained.Comment: v2: 13 pages, submitted to the Phys. Rev. D v3: 13 pages, resubmitted
to Phys. Rev. D (corrections include: a more detailed overview of the
combined analysis of the available experimntal data
New, high statistics measurement of the K+ -> pi0 e+ nu (Ke3) branching ratio
E865 at the Brookhaven National Laboratory AGS collected about 70,000 K+(e3)
events with the purpose of measuring the relative K+(e3) branching ratio. The
pi0 in all the decays was detected using the e+e- pair from pi0 -> e+e-gamma
decay and no photons were required. Using the Particle Data Group branching
ratios for the normalization decays we obtain
BR(K+(e3(gamma))=(5.13+/-0.02(stat)+/-0.09(sys)+/-0.04(norm))%, where
V_{us}$ element of the CKM matrix, and the matrix's
unitarity are discussed.Comment: 4 pages, 5 figures; final version accepted by PR
Search for Heavy Leptons at Hadron Colliders
Four models are considered which contain heavy leptons beyond the three
families of the standard model. Two are fourth-generation extensions of the
standard model in which the right-handed heavy leptons are either isosinglets
or in an isodoublet; the other two are motivated by the aspon model of CP
violation. In all these models, the heavy neutrino can either be heavier than,
or comparable in mass to, the charged lepton leading to the possibility that
the charged lepton is very long-lived. Production cross section and signatures
for the heavy leptons are computed for the SSC and LHC.Comment: 17 pages(8 figures are not included),TRI-PP-92-9
Neighboring-Pixel-Based Maximum Power Point Tracking Algorithm for Partially Shaded Photovoltaic (PV) Systems
In this paper, a neighboring-pixel-based virtual imaging (NPBVI) technique is developed to comprehensively detect the shading conditions on PV arrays. The proposed VI technique is then merged with a probabilistic mechanism of shaded module currents. Finally, a mathematical model is presented, which predicts the current voltage (I-V) region corresponding to the global maximum (GM) of the shaded PV array. The effectiveness of the proposed NPBVI MPPT is validated through numerous experiments that were carried out using a hardware prototype with a 150 W power rating. For the experiments, a PV array consisting of 3 × 2 (Np× Ns ) 20 W PV modules was utilized. The experiments showcase agreement that the proposed method successfully identified the GM region of a partially shaded PV array
- …