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Добавлено: Чт апр 20, 2006 12:52
High Energy Spin Excitations in Electron-Doped Superconducting Pr$_

Stephen D. Wilson,1 Shiliang Li,1 H. Woo,1 Pengcheng Dai,1, 2, ∗
H. A. Mook,2 C. D. Frost,3 Seiki Komiya,4 and Yoichi Ando4
1 Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996-1200, USA
2 Center for Neutron Scattering, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6393, USA
3 ISIS Facility, Rutherford Appleton Laboratory, Oxon OX11 0QX, UK
4 Central Research Institute of Electric Power Industry, Komae, Tokyo 201-8511, Japan
We use high-resolution inelastic neutron scattering to study the low-temperature magnetic ex-
citations of electron-doped superconducting Pr0.88LaCe0.12CuO4− (Tc = 21 ? 1 K) over a wide
energy range (4 meV ¯h! 330 meV). The eect of electron-doping is to cause a wave vector
(Q) broadening in the low-energy (¯h! 80 meV) commensurate spin fluctuations at (,) and to
suppress the intensity of spin-wave-like excitations at high energies (¯h! 100 meV). This leads to
a substantial redistribution in the spectrum of the local dynamical spin susceptibility ′′(!), and
reveals a new energy scale similar to that of the lightly hole-doped YB2Cu3O6.353 (Tc = 18 K).


Добавлено: Сб апр 22, 2006 16:57
Resonance Impurity Scattering in PrOs$_{4}$Sb$_{12}$

Authors: David Parker, Stephan Haas. Kazumi Maki
Subj-class: Superconductivity; Strongly Correlated Electrons

We study the effect of impurity scattering in the unitarity limit on the A and B phase superconductivity in PrOs4Sb12. We take the triplet superconducting order parameters and the impurity scattering is treated within the standard theory. We find the quasiparticle density of states and thermodynamics are very sensitive to the impurity scattering. The impurity scattering dependence of the superconducting transition temperature and the order parameter at T=0 are very similar to those in d-wave superconductors. Some of these characteristics will provide a sensitive test of the symmetry of the underlying order parameters.
Full-text: http://xxx.lanl.gov/pdf/cond-mat/0604493

Добавлено: Сб апр 22, 2006 17:19
On the Origin of the Tunneling Asymmetry in the Cuprate Superconductors: a variational perspective

Hong-Yu Yang1, Fan Yang2, Yong-Jin Jiang3 and Tao Li4
1Center for Advanced study, Tsinghua University ,Beijing 100084, P.R.China
2Department of Physics, Beijing Institute of Technology ,Beijing 100081, P.R.China
3Department of Physics, Zhejiang Normal University, Jinhua 321004, P.R.China
4Department of Physics, Renmin University of China, Beijing 100872, P.R.China
(Dated: April 21, 2006)
Through variational Monte Carlo calculation on Gutzwiller projected wave functions, we study
the quasiparticle(qp) weight for adding and removing an electron from a high temperature super-
conductor. We find the qp weight is particle-hole symmetric at suciently low energy. We propose
to use the tunneling asymmetry as a tool to study the mechanism of electron incoherence in high
temperature superconductors.


Добавлено: Чт май 04, 2006 11:41
Unadulterated spectral function of low energy quasiparticles: Bi-2212, nodal direction
D. V. Evtushinsky,1 A. A. Kordyuk,1, 2 S. V. Borisenko,2 V. B. Zabolotnyy,2 M. Knupfer,2 J. Fink,2 B. B¨uchner,2
A. V. Pan,3 A. Erb,4 C. T. Lin,5 and H. Berger6
1Institute of Metal Physics of National Academy of Sciences of Ukraine, 03142 Kyiv, Ukraine
2IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany
3ISEM, University of Wollongong, Wollongong, NSW 2522, Australia
4Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
5Max-Planck Institut f¨ur Festk¨orperforschung, 70569 Stuttgart, Germany
6Institut de Physique de la Mati´ere Complexe, EPFL, 1015 Lausanne, Switzerland
(Dated: May 1, 2005)
Fitting the momentum distribution photoemission spectra to the Voigt profile appears to be a
robust procedure to purify the interaction eects from the experimental resolution. In application
to Bi-2212 high-Tc cuprates, the procedure reveals the true scattering rate at low binding energies
and temperatures, and, consequently, the true value of the elastic scattering. Reaching the minimal
value 16 meV, the elastic scattering does not reveal a systematic dependence on doping level,
but is rather sensitive to impurity concentration, and can be explained by the forward scattering on
out-of-plane impurities. The inelastic scattering is found to form well-defined quasiparticles with the
scattering rate !2 and !3, above and below Tc, respectively. The observed ! − T asymmetry
of the scattering rate is also discussed.

Добавлено: Пт май 12, 2006 11:16
Multifilament YBa2Cu3O6+x -coated conductors with minimized coupling losses
Authors: G. A. Levin, P. N. Barnes, J. W. Kell, N. Amemiya, Z. Jiang, K. Yoda, F. Kimura
Comments: Submitted to Appl. Phys. Lett. 10 pages, 3 figures
Subj-class: Superconductivity; Materials Science

We report an experimental approach to making multifilament coated conductors with low losses in applied time-varying magnetic field. Previously, the multifilament conductors obtained for that purpose by laser ablation suffered from high coupling losses. Here we report how this problem can be solved. When the substrate metal in the grooves segregating the filaments is exposed to oxygen, it forms high resistivity oxides that electrically insulate the stripes from each other and from the substrate. As the result, the coupling loss has become negligible over the entire range of tested parameters (magnetic field amplitudes B and frequencies f) available to us.

Добавлено: Пн май 15, 2006 10:26
Search for Cooper-pair Fluctuations in Severely Underdoped YBCO Films

Authors: Y. L. Zuev, I. Hetel, T. R. Lemberger
Comments: 3 pages, 2 figures
Subj-class: Superconductivity

The preformed-pairs theory of pseudogap physics in high-$T_C$ superconductors predicts a nonanalytic $T$-dependence for the $ab$-plane superfluid fraction, $\rho_S$, at low temperatures in underdoped cuprates. We report high-precision measurements of $\rho_S(T)$ on severely underdoped YBa$_2$Cu$_3$O$_{6+x}$ and Y$_{0.8}$Ca$_{0.2}$Ba$_2$Cu$_3$O$_{6+x}$ films. At low $T$, $\rho_S$ looks more like $1 - T^2$ than $1 - T^{3/2}$, in disagreement with theory.
Full-text: http://xxx.lanl.gov/PS_cache/cond-mat/p ... 605349.pdf

Добавлено: Чт май 18, 2006 10:50
Pressure Induced Changes in the Antiferromagnetic Superconductor YbPd2Sn

Authors: A-M. Cumberlidge (1), P.L. Alireza (1), A.F. Kusmartseva (1), E.E. Pearson (1), G.G. Lonzarich (1), N.R. Bernhoeft (2), B. Roessli (3) ((1) Cavendish Laboratory, University of Cambridge, UK, (2) Chinley, UK, (3) SINQ, PSI Villigen, Suisse)
Comments: 5 pages, 6 figures
Subj-class: Strongly Correlated Electrons; Superconductivity

Low temperature ac magnetic susceptibility measurements of the coexistent antiferromagnetic superconductor YbPd2Sn have been made in hydrostatic pressures < 74 kbar in moissanite anvil cells. The superconducting transition temperature is forced to T(SC) = 0 K at a pressure of 58 kbar. The initial suppression of the superconducting transition temperature is corroborated by lower hydrostatic pressure (p < 16 kbar) four point resisitivity measurements, made in a piston cylinder pressure cell. At ambient pressure, in a modest magnetic field of ~ 500 G, this compound displays reentrant superconducting behaviour. This reentrant superconductivity is suppressed to lower temperature and lower magnetic field as pressure is increased. The antiferromagnetic ordering temperature, which was measured at T(N) = 0.12 K at ambient pressure is enhanced, to reach T(N) = 0.58 K at p = 74 kbar. The reasons for the coexistence of superconductivity and antiferromagnetism is discussed in the light of these and previous findings. Also considered is why superconductivity on the border of long range magnetic order is so much rarer in Yb compounds than in Ce compounds. The presence of a new transition visible by ac magnetic susceptibility under pressure and in magnetic fields greater than 1.5 kG is suggested.
Full-text: http://xxx.lanl.gov/PS_cache/cond-mat/p ... 605429.pdf

Добавлено: Ср май 24, 2006 17:47
From Fermi Arcs to the Nodal Metal: Scaling of the
Pseudogap with Doping and Temperature

A. Kanigel1,2, M. R. Norman2, M. Randeria3, U. Chatterjee1,2, S. Suoma1, A. Kaminski4,
H.M. Fretwell4, S. Rosenkranz2 , M. Shi1, T. Sato5, T. Takahashi5, Z. Z. Li6, H. Raffy6, K.
Kadowaki7, D. Hinks2, L. Ozyuzer2, and J.C. Campuzano1,2
1Department of Physics, University of Illinois at Chicago, Chicago IL 60607, USA,
2Materials Science Division, Argonne National Laboratory, Argonne IL 60439, USA,
3Department of Physics, Ohio State University, Columbus, OH 43210, USA,
4Ames Laboratory and Department of Physics and Astronomy, Iowa State University,
Ames, IA 50011, USA,
5Department of Physics, Tohoku University, 980-8578 Sendai, Japan,
6Laboratorie de Physique des Solides, Universite Paris-Sud, 91405 Orsay Cedex, France,
7Institute of Materials Science, University of Tsukuba, Ibaraki 305-3573, Japan
The pseudogap phase in the cuprates is a most unusual state of matter1-4: it is a metal,
but its Fermi surface is broken up into disconnected segments known as Fermi arcs5.
Using angle resolved photoemission spectroscopy, we show that the anisotropy of the
pseudogap in momentum space and the resulting arcs depend only on the ratio
T/T*(x), where T*(x) is the temperature below which the pseudogap first develops at a
given hole doping x. In particular, the arcs collapse linearly with T/T* and extrapolate
to zero extent as T
" 0. This suggests that the T = 0 pseudogap state is a nodal liquid,
a strange metallic state whose gapless excitations are located only at points in
momentum space, just as in a d-wave superconductor.

http://xxx.lanl.gov/ftp/cond-mat/papers ... 605499.pdf

Добавлено: Ср май 31, 2006 12:13
Пожелание модаратору: ОЧЕНЬ хотелось что б высказывания идиотов не засоряли форум..

Negative Hall coefficients of heavily overdoped La2-xSrxCuO4

Authors: I. Tsukada, S. Ono
Comments: 4 pages including 4 color figures (eps files)
Subj-class: Superconductivity

The Hall coefficients (R_H) are investigated along the in-plane direction for carefully prepared La_2-xSrxCuO_4 thin films from x=0.08 to x=0.40. It is found that room-temperature value of R_H smoothly changes its sign from positive for x =< 0.28 to negative for x >= 0.32 showing contrasting behavior to previously reported results. This result indicates that a Fermi surface smoothly change from hole-like to electron-like in its shape by hole doping. According to the sign change of R_H, superconductivity disappears for x >= 0.32 films, which suggests that the positive R_H is one of the necessary conditions for superconductivity in p-type cuprates.
Full-text: http://xxx.lanl.gov/abs/cond-mat/0605720

Добавлено: Вс июн 04, 2006 17:14
The ?crab? bipolaron as a possible route to room temperature superconductivity

J.P. Hague,1 P.E. Kornilovitch,2 J.H. Samson,1 and A.S. Alexandrov1
1Department of Physics, Loughborough University, Loughborough, LE11 3TU, United Kingdom
2Hewlett-Packard Company, 1000 NE Circle Blvd, Corvallis, Oregon 97330, USA
(Dated: June 1, 2006)
We study a lattice bipolaron on a staggered triangular ladder and triangular and hexagonal
lattices with both long-range electron-phonon interaction and strong Coulomb repulsion using a
continuous-time quantum Monte-Carlo (CTQMC) technique. We describe a significant extension of
the CTQMC algorithm to the Coulomb-Fr¨ohlich model with two particles. The algorithm is preceded
by an exact integration over phonon degrees of freedom, and as such is extremely ecient. The
bipolaron eective mass and bipolaron radius are computed. Lattice bipolarons on such lattices are
small but very light in a wide range of parameters, which leads to a high Bose-Einstein condensation
http://xxx.lanl.gov/PS_cache/cond-mat/p ... 606036.pdf

Добавлено: Пн июн 05, 2006 14:39
Importance of the Electron-Phonon Interaction with the Forward Scattering Peak for Superconducting Pairing in Cuprates

Authors: Miodrag L. Kulic
Comments: 32 pages, 12 figures
Subj-class: Superconductivity

Basic experimental facts related to ARPES, tunnelling, optics ad neutron scattering measurements are discussed. They give evidence for the relevance of the electron-phonon interaction (EPI) in pairing mechanism of HTSC cuprates. A controllable theory for strong correlations and their effects on EPI is discussed which is based on the 1/N expansion method in the t-J model. Strong correlations renormalize EPI and other charge-fluctuation properties (by including nonmagnetic impurity scattering) and the forward scattering peak (FSP) appears in the effective interactions. Pronounced FSP in EPI of HTSC cuprates reconciles many puzzling results. The theory of EPI with FSP gives that the couplings in the s- and d-wave pairing channel are of the same magnitude near and below the optimal hole doping. FSP in the nonmagnetic impurity scattering potential is responsible for robustness of d-wave pairing in cuprates. The ARPES kink and the isotope effect in the nodal and anti-nodal points and the collapse of the elastic impurity scattering in the superconducting state, are explained by this theory. It also explains why the nodal kink is not-shifted in the superconducting state while the anti-nodal kink is shifted by the maximal superconducting gap. In systems with FSP in EPI besides the classical phase fluctuations there are also internal fluctuations of Cooper pairs giving rise to an additional contribution to the pseudogap.

Добавлено: Чт июн 08, 2006 11:54
Pseudogap enhancement due to magnetic impurities in d-density waves

Bal´azs D´ora,1, Kazumi Maki,2 Attila Virosztek,1, 3 and Andr´as V´anyolos1
1Department of Physics, Budapest University of Technology and Economics, H-1521 Budapest, Hungary
2Department of Physics and Astronomy, University of Southern California, Los Angeles CA 90089-0484, USA
3Research Institute for Solid State Physics and Optics, P.O.Box 49, H-1525 Budapest, Hungary
(Dated: June 8, 2006)
We study the eect of quantum magnetic impurities on d-wave spin density waves (d-SDW).
The impurity spins are aligned coherently according to the spin space anisotropy of the condensate.
Both the order parameter and transition temperature increases due to the coherent interplay between
magnetic scatterers and d-SDW. This can explain the recent experimental data on the pseudogap
enhancement of Ni substituted NdBa2{Cu1−yNiy}O6.8 from Pimenov et al. (Phys. Rev. Lett. 94,
227003 (2005)).

Добавлено: Чт июн 22, 2006 4:01
Superconductivity in Cu_xTiSe_2

E. Morosan1*, H. W. Zandbergen2, B. S. Dennis3, J. W. G. Bos1,
Y. Onose4, T. Klimczuk1, A. P. Ramirez3, N. P. Ong4, and R. J. Cava1
1Department of Chemistry, Princeton University, Princeton, NJ 08540, USA
2National Centre for HREM, Department of Nanoscience,
Delft Institute of Technology, Al Delft, The Netherlands
3Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974, USA
4Department of Physics, Princeton University, Princeton, NJ 08540, USA
*e-mail: emorosan@princeton.edu.
Charge density waves (CDWs) are periodic modulations of the conduction
electron density in solids. They are collective states that arise from intrinsic
instabilities often present in low dimensional electronic systems. The layered
dichalcogenides are the most well-studied examples, with TiSe2 one of the first
CDW-bearing materials known. The competition between CDW and
superconducting collective electronic states at low temperatures has long been held
and explored, and yet no chemical system has been previously reported where finely
controlled chemical tuning allows this competition to be studied in detail. Here we
report how, upon controlled intercalation of TiSe2 with Cu to yield CuxTiSe2, the
CDW transition is continuously suppressed, and a new superconducting state
emerges near x = 0.04, with a maximum Tc of 4.15 K found at x = 0.08. CuxTiSe2
thus provides the first opportunity to study the CDW to Superconductivity
transition in detail through an easily-controllable chemical parameter, and will
provide new insights into the behavior of correlated electron systems.


Добавлено: Чт июн 22, 2006 4:31
Effect of the pseudogap on the uniform magnetic susceptibility of Y1-xCaxBa2Cu3O7-d

Authors: S. H. Naqib, J. R. Cooper
Comments: Submitted to Physica C (M2S-HTSC 2006 Proceedings)
Subj-class: Superconductivity

The effects of planar hole content, p, on the temperature-dependent uniform (q = 0) magnetic susceptibility, c(T), of polycrystalline Y1-xCaxBa2Cu3O7-d compounds with 0.0 </= x </= 0.20 were investigated over a wide range of oxygen deficiency (d). Systematic variations in c(T) were found with changing p. The characteristic pseudogap temperature scale, Eg(p)/kB, was extracted from the analysis of the c(T,p) data. We have found clear evidence that the pseudogap in the quasi-particle spectral weight appears abruptly at a planar hole content of p ~ 0.19, and that it grows rapidly with decreasing p.

Full-text: http://xxx.lanl.gov/abs/cond-mat/0606519

Добавлено: Пт июн 23, 2006 10:16
High-pressure synthesis and superconductivity of Ca2-xNaxCuO2Cl2

Nikolai D. Zhigadlo*, Janusz Karpinski
Laboratory for Solid StatePhysics, ETH Zurich, 8093 Zurich, Switzerland
Ca2-xNaxCuO2Cl2 is a structural analogue to the La2-xSrxCuO4 superconductor. By substituting Na+ for Ca2+ mobile holes are
introduced into the CuO2 planes. A series of experiments shows that the Na content x depends not only on the pressure
during synthesis but also on the synthesis temperature and time. Ca2-xNaxCuO2Cl2 crystals (x≈0.10 and Tc,on=13.5 K) up to
~1x1x0.05 mm3 have been grown by a flux method at 35 kbar and the temperature was slowly ramped from 1250ºC to
1050ºC within 8 h. Applying higher synthesis pressure (up to 55 kbar) and temperature (up to 1700ºC) results in
polycrystalline samples with highest Tc,on =28.0 K at x≈0.20.