8,705 research outputs found
External losses in photoemission from strongly correlated quasi two-dimensional solids
New expressions are derived for photoemission, which allow experimental
electron energy loss data to be used for estimating losses in photoemission.
The derivation builds on new results for dielectric response and mean free
paths of strongly correlated systems of two dimensional layers. Numerical
evaluations are made for (Bi2212) by using a
parametrized loss function. The mean free path for Bi2212 is calculated and
found to be substantially larger than obtained by Norman et al in a recent
paper. The photocurrent is expressed as the convolution of the intrinsic
approximation for the current from a specific 2D layer with an effective loss
function. The observed current is the sum of such currents from the first few
layers. The photo electron from a specific layer is found to excite low
energy acoustic plasmon modes due to the coupling between the layers.
These modes give rise to an asymmetric power law broadening of the photo
current an isolated two dimensional layer would have given. We define an
asymmetry index where a contribution from a Luttinger lineshape is additive to
the contribution from our broadening function. Already the loss effect
considered here gives broadening comparable to what is observed experimentally.
A superconductor with a gapped loss function is predicted to have a
peak-dip-hump lineshape similar to what has been observed, and with the same
qualitative behavior as predicted in the recent work by Campuzano et al.Comment: 17 pages, 10 figure
GW band structure of InAs and GaAs in the wurtzite phase
We report the first quasiparticle calculations of the newly observed wurtzite
polymorph of InAs and GaAs. The calculations are performed in the GW
approximation using plane waves and pseudopotentials. For comparison we also
report the study of the zinc-blende phase within the same approximations. In
the InAs compound the In 4d electrons play a very important role: whether they
are frozen in the core or not, leads either to a correct or a wrong band
ordering (negative gap) within the Local Density Appproximation (LDA). We have
calculated the GW band structure in both cases. In the first approach, we have
estimated the correction to the pd repulsion calculated within the LDA and
included this effect in the calculation of the GW corrections to the LDA
spectrum. In the second case, we circumvent the negative gap problem by first
using the screened exchange approximation and then calculating the GW
corrections starting from the so obtained eigenvalues and eigenfunctions. This
approach leads to a more realistic band-structure and was also used for GaAs.
For both InAs and GaAs in the wurtzite phase we predict an increase of the
quasiparticle gap with respect to the zinc-blende polytype.Comment: 9 pages, 6 figures, 3 table
Density dependent spin susceptibility and effective mass in interacting quasi-two dimensional electron systems
Motivated by recent experimental reports, we carry out a Fermi liquid
many-body calculation of the interaction induced renormalization of the spin
susceptibility and effective mass in realistic two dimensional (2D) electron
systems as a function of carrier density using the leading-order
`ladder-bubble' expansion in the dynamically screened Coulomb interaction.
Using realistic material parameters for various semiconductor-based 2D systems,
we find reasonable quantitative agreement with recent experimental
susceptibility and effective mass measurements. We point out a number of open
questions regarding quantitative aspects of the comparison between theory and
experiment in low-density 2D electron systems
Dependence of electronic polarization on octahedral rotations in TbMnO3 from first principles
The electronic contribution to the magnetically induced polarization in
orthorhombic TbMnO3 is studied from first principles. We compare the cases in
which the spin cycloid, which induces the electric polarization via the
spin-orbit interaction, is in either the b-c or a-b plane. We find that the
electronic contribution is negligible in the first case, but much larger, and
comparable to the lattice-mediated contribution, in the second case. However,
we how that this behavior is an artifact of the particular pattern of
octahedral rotations characterizing the structurally relaxed Pbnm crystal
structure. To do so, we explore how the electronic contribution varies for a
structural model of rigidly rotated MnO6 octahedra, and demonstrate that it can
vary over a wide range, comparable with the lattice-mediated contribution, for
both b-c and a-b spirals. We introduce a phenomenological model that is capable
of describing this behavior in terms of sums of symmetry-constrained
contributions arising from the displacements of oxygen atoms from the centers
of the Mn-Mn bonds.Comment: 8 pages, 5 figures, 3 table
Spin-dependent Hedin's equations
Hedin's equations for the electron self-energy and the vertex were originally
derived for a many-electron system with Coulomb interaction. In recent years it
has been increasingly recognized that spin interactions can play a major role
in determining physical properties of systems such as nanoscale magnets or of
interfaces and surfaces. We derive a generalized set of Hedin's equations for
quantum many-body systems containing spin interactions, e.g. spin-orbit and
spin-spin interactions. The corresponding spin-dependent GW approximation is
constructed.Comment: 5 pages, 1 figur
Improved Determination of the Width of the Top Quark
We present an improved determination of the total width of the top quark, Γt, using 5.4 fb-1 of
integrated luminosity collected by the D0 Collaboration at the Tevatron pp- Collider.
The total width Γt is
extracted from the partial decay width Γ(t →Wb) and the branching fraction Β(t → Wb). Γ(t → Wb) is
obtained from the t-channel single top-quark production cross section and Β(t → Wb)
is measured in tt- events. For a top mass of 172.5 GeV, the resulting width is Γt = 2.00 +0:47 - 0:43 GeV. This translates to a top-quark
lifetime of Ï„t = (3.29 +0:90 -0.63) x 10-25s. We also extract an improved direct limit on the Cabibbo-
Kobayashi-Maskawa quark-mixing matrix element 0.81 < │Vtb│ ≤ 1 at 95% C.L. and a limit of │Vtb ‘│<
0.59 for a high-mass fourth-generation bottom quark assuming unitarity of the fourth-generation quark-mixing
matrix.We thank the staffs at Fermilab and collaborating
institutions, and acknowledge support from the DOE and
NSF (USA); CEA and CNRS/IN2P3 (France); FASI,
Rosatom, and RFBR (Russia); CNPq, FAPERJ, FAPESP,
and FUNDUNESP (Brazil); DAE and DST (India);
Colciencias (Colombia); CONACyT (Mexico); NRF
(Korea); CONICET and UBACyT (Argentina); FOM
(The Netherlands); STFC and the Royal Society (United
Kingdom); MSMT and GACR (Czech Republic); BMBF
and DFG (Germany); SFI (Ireland); The Swedish Research
Council (Sweden); and CAS and CNSF (China)
Combination of CDF and D0 Measurements of the W boson Helicity in Top Quark Decays
We report the combination of recent measurements of the helicity of the W boson from top quark decay by the CDF and D0 collaborations, based on data samples corresponding to integrated luminosities of the 2.7-5.4 fb-1 of pp- collisions collected during Run II of the Fermilab Tevatron collider. Combining measurements that simultaneously determine the fractions of the W bosons with longitudinal (f0) and right-handed (f+) helicities, we find f0= 0.722 ± 0.081[±0.062(stat) ± 0.052(syst)] and f+ = -0.033 ± 0.046[±0.034(stat) ± 0.031(syst)]. Combining measurements where one of the helicity fractions is fixed to the value expected in the standard model, we find f0 = 0.682 ± 0.057[±0.035(stat) ± 0.046(syst)] for fixed f+ and f+ = -0.015 ± 0.035[±0.018(stat) ± 0.030(syst)] for fixed f0. The results are consistent with standard model expectations.We thank the staffs at Fermilab and collaborating institutions,
and acknowledge support from the DOE and NSF
(USA); CEA and CNRS/IN2P3 (France); FASI, Rosatom
and RFBR (Russia); CNPq, FAPERJ, FAPESP, and
FUNDUNESP (Brazil); DAE and DST (India); INFN
(Italy); Ministry of Education, Culture, Sports, Science,
and Technology (Japan); Colciencias (Colombia);
CONACyT (Mexico); World Class University Program,
National Research Foundation, NRF (Korea); CONICET
and UBACyT (Argentina); Australian Research Council
(Australia); FOM (The Netherlands); STFC and the Royal
Society (United Kingdom); MSMT and GACR (Czech
Republic); CRC Program and NSERC (Canada);
Academy of Finland (Finland); BMBF and DFG
(Germany); SFI (Ireland); Slovak R&D Agency
(Slovakia); Programa Consolider-Ingenio 2010 (Spain);
Swedish Research Council (Sweden); Swiss National
Science Foundation (Switzerland); NSC (Republic of
China); CAS and CNSF (China); and the A. P. Sloan
Foundation (USA)
Combination of the Top Quark Mass Measurements from the Tevatron Collider
The top quark is the heaviest known elementary particle, with a mass about 40 times larger than the
mass of its isospin partner, the bottom quark. It decays almost 100% of the time to a W boson and a bottom
quark. Using top-antitop pairs at the Tevatron proton-antiproton collider, the CDF and D0 Collaborations
have measured the top quark’s mass in different final states for integrated luminosities of up to 5.8 fb-1.
This paper reports on a combination of these measurements that results in a more precise value of the mass
than any individual decay channel can provide. It describes the treatment of the systematic uncertainties
and their correlations. The mass value determined is 173.18 ± 0.56(stat) ± 0.75(syst) GeV or
173.18 ± 0.94 GeV, which has a precision of ±0.54%, making this the most precise determination of
the top-quark mass.We thank the Fermilab staff and technical staffs of the
participating institutions for their vital contributions and
acknowledge support from the DOE and NSF (USA), ARC
(Australia), CNPq, FAPERJ, FAPESP, and FUNDUNESP
(Brazil), NSERC (Canada), NSC, CAS, and CNSF
(China), Colciencias (Colombia), MSMT and GACR
(Czech Republic), the Academy of Finland, CEA, and
CNRS/IN2P3 (France), BMBF and DFG (Germany),
DAE and DST (India), SFI (Ireland), INFN (Italy),
MEXT (Japan), the Korean World Class University
Program and NRF (Korea), CONACyT (Mexico), FOM
(Netherlands), MON, NRC KI, and RFBR (Russia), the
Slovak R&D Agency, the Ministerio de Ciencia e
Innovacio´n, and Programa Consolider-Ingenio 2010
(Spain), The Swedish Research Council (Sweden), SNSF
(Switzerland), STFC and the Royal Society (United
Kingdom), and the A. P. Sloan Foundation (USA)
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