791 research outputs found
Order parameter symmetries for magnetic and superconducting instabilities: Bethe-Salpeter analysis of functional renormalization-group solutions
The Bethe-Salpeter equation is combined with the temperature-cutoff
functional renormalization group approach to analyze the order parameter
structure for the leading instabilities of the 2D t-t' Hubbard model. We find
significant deviations from pure s-, d-, or p-wave forms, which is due to the
frustration of antiferromagnetism at small and intermediate t'. With adding a
direct antiferromagnetic spin-exchange coupling the eigenfunctions in the
particle-hole channel have extended s-wave form, while in the particle-particle
singlet pairing channel a higher angular momentum component arises besides the
standard d-wave symmetry, which flattens the angular dependence of the gap. For
t' closer to 1/2 we find a delicate competition of ferromagnetism and triplet
pairing with a nontrivial pair-wavefunction.Comment: 4 pages, 4 figures, RevTe
Quasiparticle anisotropy and pseudogap formation from the weak-coupling renormalization group point of view
Using the one-loop functional renormalization group technique we evaluate the
self-energy in the weak-coupling regime of the 2D t-t' Hubbard model. At van
Hove (vH) band fillings and at low temperatures the quasiparticle weight along
the Fermi surface (FS) continuously vanishes on approaching the (pi,0) point
where the quasiparticle concept is invalid. Away from vH band fillings the
quasiparticle peak is formed inside an anisotropic pseudogap and the
self-energy has the conventional Fermi-liquid characteristics near the Fermi
level. The spectral weight of the quasiparticle features is reduced on parts of
the FS between the near vicinity of hot spots and the FS points closest to
(pi,0) and (0,pi).Comment: 4 pages, 4 figures, RevTe
Doping Evolution of Oxygen K-edge X-ray Absorption Spectra in Cuprate Superconductors
We study oxygen K-edge x-ray absorption spectroscopy (XAS) and investigate
the validity of the Zhang-Rice singlet (ZRS) picture in overdoped cuprate
superconductors. Using large-scale exact diagonalization of the three-orbital
Hubbard model, we observe the effect of strong correlations manifesting in a
dynamical spectral weight transfer from the upper Hubbard band to the ZRS band.
The quantitative agreement between theory and experiment highlights an
additional spectral weight reshuffling due to core-hole interaction. Our
results confirm the important correlated nature of the cuprates and elucidate
the changing orbital character of the low-energy quasi-particles, but also
demonstrate the continued relevance of the ZRS even in the overdoped region.Comment: Original: 5 pages, 4 figures. Replaced: 6 pages and 4 figures, with
updated title and conten
Flux Periodicities in Loops of Nodal Superconductors
Supercurrents in superconducting flux threaded loops are expected to
oscillate with the magnetic flux with a period of hc/2e. This is indeed true
for s-wave superconductors larger than the coherence length xi_0. Here we show
that for superconductors with gap nodes, there is no such strict condition for
the supercurrent to be hc/2e rather than hc/e periodic. For nodal
superconductors, the flux induced Doppler shift of the near nodal states leads
to a flux dependent occupation probability of quasi-particles circulating
clockwise and counter clockwise around the loop, which leads to an hc/e
periodic component of the supercurrent, even at zero temperature. We analyze
this phenomenon on a cylinder in an approximative analytic approach and also
numerically within the framework of the BCS theory. Specifically for d-wave
pairing, we show that the hc/e periodic current component decreases with the
inverse radius of the loop and investigate its temperature dependence
Zincalstibite-9R: the first nine-layer polytype with the layered double hydroxide structure-type
Zincalstibite-9R, a new polytype in the hydrotalcite supergroup is reported from the Monte Avanza mine, Italy. It occurs as pale blue curved disc-like tablets flattened on {001} intergrown to form rosettes typically less than 50 μm in diameter, with cyanophyllite and linarite in cavities in baryte. Zincalstibite-9R is uniaxial (−), with refractive indices ω = 1.647(2) and ε = 1.626(2) measured in white light. The empirical formula (based on 12 OH groups) is (Zn^(2+)_(1.09)Cu^(2+)_(0.87)Al_(0.04))_(Σ2.00)Al_(1.01) (Sb^(5+)_(0.97)Si_(0.02))Σ_(0.99)(OH)_(12), and the ideal formula is (Zn,Cu)_2Al(OH)_6[Sb(OH)_6]. Zincalstibite-9R crystallizes in space group R3İ, with ɑ = 5.340(2), c = 88.01(2) Å, V = 2173.70(15) Å^3 and Z = 9. The crystal structure was refined to R_1 = 0.0931 for 370 unique reflections [F_o > 4σ(F)] and R_1 = 0.0944 for all 381 unique reflections. It has the longest periodic layer stacking sequence for a layered double hydroxide compound reported to date
Predominantly Superconducting Origin of Large Energy Gaps in Underdoped Bi2Sr2CaCu2O8-d from Tunneling Spectroscopy
New tunneling data are reported in underdoped Bi2Sr2CaCu2O8-d using
superconductor-insulator-superconductor break junctions. Energy gaps, Delta, of
51+2, 54+2 and 57+3 meV are observed for three crystals with Tc=77, 74, and 70
K respectively. These energy gaps are nearly three times larger than for
overdoped crystals with similar Tc. Detailed examination of tunneling spectra
over a wide doping range from underdoped to overdoped, including the Josephson
IcRn product, indicate that these energy gaps are predominantly of
superconducting origin.Comment: 10 pages, 4 figures, 1 tabl
Initial Quantitative Proteomic Map of 28 Mouse Tissues Using the SILAC Mouse
Identifying the building blocks of mammalian tissues is a precondition for understanding their function. In particular, global and quantitative analysis of the proteome of mammalian tissues would point to tissue-specific mechanisms and place the function of each protein in a whole-organism perspective. We performed proteomic analyses of 28 mouse tissues using high-resolution mass spectrometry and used a mix of mouse tissues labeled via stable isotope labeling with amino acids in cell culture as a "spike-in" internal standard for accurate protein quantification across these tissues. We identified a total of 7,349 proteins and quantified 6,974 of them. Bioinformatic data analysis showed that physiologically related tissues clustered together and that highly expressed proteins represented the characteristic tissue functions. Tissue specialization was reflected prominently in the proteomic profiles and is apparent already in their hundred most abundant proteins. The proportion of strictly tissue-specific proteins appeared to be small. However, even proteins with household functions, such as those in ribosomes and spliceosomes, can have dramatic expression differences among tissues. We describe a computational framework with which to correlate proteome profiles with physiological functions of the tissue. Our data will be useful to the broad scientific community as an initial atlas of protein expression of a mammalian species
Validity of the rigid band picture for the t-J model
We present an exact diagonalization study of the doping dependence of the
single particle Green's function in 16, 18 and 20 site clusters of t-J model.
We find evidence for rigid-band behaviour starting from the half-filled case:
upon doping, the topmost states of the quasiparticle band observed in the
photoemisson spectrum at half-filling cross the chemical potential and reappear
as the lowermost states of the inverse photoemission spectrum. Features in the
inverse photoemission spectra which are inconsistent with rigid-band behaviour
are shown to originate from the nontrivial point group symmetry of the ground
state with two holes, which enforces different selection rules than at
half-filling. Deviations from rigid band behaviour which lead to the formation
of the `large Fermi surface' in the momentum distribution occur only at
energies far from the chemical potential. A Luttinger Fermi surface and a
nearest neighbor hopping band do not exist.Comment: Remarks: Revtex file + 7 figures attached as compressed postscript
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