Spectroscopic views of high-<i>T</i><sub>c</sub>superconductors

Wendin, Göran

doi:10.1088/0031-8949/1989/t27/005

Cited by 28 publications

(4 citation statements)

References 201 publications

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“…Some of the cohesion is due to distortion. As Wendin (1989) points out, a spin polaron could produce important lattice distortion. Rice and Wang (1988) maintain that in a strictly two-dimensional system any attractive force will produce pairing.…”

Section: Mechanism Of Pairin# Of Spin Polaronsmentioning

confidence: 99%

The spin-polaron theory of high-T_csuperconductivity

Mott

1990

Advances in Physics

127

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An outline is given of the model for some high-temperature superconductors which assumes that the carriers are holes in the (hybridized) oxygen 2p band and form 'spin polarons' with the moments on the copper atoms. A comparison is made with observations of spin polarons in Gda-xvxS4 and with the properties of Lal_xSr~VOa in relation to those of La2_xSrxCuO4. It is assumed, following several authors, that in the superconductors the polarons form bipolarons, which are bosons, and a comparison is made with some other treatments of this hypothesis. It is proposed that in many such superconductors the boson, essentially a pair of these holes, moves in an impurity band, and that normally all the polarons (fermions) form bipolarons; the fermions repel each other on the same site (positive Hubbard U) but attract when on adjacent sites; the critical temperature T~ is then that at which the Bose gas becomes non-degenerate. In such materials a nondegenerate gas of bosons would carry the current above T~ as first suggested by Alexandrov et al. (1986). The linear increase in the resistivity above T~ is explained on this hypothesis. The effective mass of the bipolaron is, we believe, large (~20-30me). The copper 3d 9 moments in the superconducting range resonate between their two orientations as a consequence of the motion of the carriers, as they do in the description by Brinkman and Rice (1970) of highly correlated metals. Spin polarons, we believe, form only when this is so, but not in the antiferromagnetic range of x. A discussion is given of the resistivity above T~, thermopower above T~, and of the nature of the superconducting gap as shown by tunnelling. We confine our discussion to the materials containing copper, excluding for instance cubic Bal_xKxBiO3, and possibly any superconductor containing bismuth, where the bosons may be Bi 3+. Contents PAGE

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Section: Mechanism Of Pairin# Of Spin Polaronsmentioning

confidence: 99%

The spin-polaron theory of high-T_csuperconductivity

Mott

1990

Advances in Physics

127

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“…Several previous photoemission studies have focused on the geometrical and electronic structure of the interface between the superconductor and a metallic overlayer, thereby treating questions of importance for 0953-8984/96/091307+14$19.50 c 1996 IOP Publishing Ltd the utilization of HTS in different applications. See, for instance, [1,2,3]. However, by applying a perturbation on the superconductor, i.e.…”

Section: Introductionmentioning

confidence: 99%

A photoelectron spectroscopy and x-ray absorption study of single crystal with adsorbed Cs: on the origin of the states affected by electron doping and evidence for spatially resolved electron doping

Söderholm

Qvarford

Bernhoff

et al. 1996

J. Phys.: Condens. Matter

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The influence of electron doping, via deposition of small amounts of Cs, on the electronic structure of Bi 2 Sr 2 CaCu 2 O 8 has been studied by high-resolution photoelectron spectroscopy (PES) and x-ray absorption spectroscopy (XAS), utilizing synchrotron radiation. The changes in the electronic structure were monitored by PES of the valence band and of the O 1s, Bi 4f, Bi 5d, Ca 2p and Sr 3d core levels, and by XAS at the O 1s, Cu 2p and Ca 2p edges.The experimental data suggest that the loss of the Fermi edge and the loss of spectral intensity down to about 2 eV below the Fermi level, and the substantial loss of spectral intensity of the pre-edge structure in the O 1s XAS spectrum are mainly due to annihilation of states with O 2p character in the Cu-O layer. It is evident from bulk-and surface-sensitive XAS spectra that the electron doping by Cs affects the electronic structure more strongly close to the surface. This implies that the doping occurs locally and that the charge transfer between the different layers in the unit cell is not uniform. Thus it seems possible to alter the electronic properties of Bi 2 Sr 2 CaCu 2 O 8 locally through spatially resolved electron doping.When larger amounts of Cs are deposited, a chemical reaction occurs which causes a disruption of the Bi-O layer. This deposition regime is characterized by the presence of caesium oxide and reduced (metallic) Bi.

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“…Several other lattice modes have been identified in later work and attributed to defects, impurities, and nonstoichiometry, and somewhat varying positions of the major lattice mode are given in the literature, which also include several Raman studies [9][10][11]. The recent discovery of high-temperature supercon ductors in which a key role seems to be played by the copper oxide in the formation of Cooper pairs has renewed the interest in the infrared properties of the copper oxides [12].Considerably less has been reported about the black cupric oxide CuO. It is also a semiconductor, obviously with a smaller optical band gap than the red oxide.…”

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confidence: 99%

Copper Oxides (Cu2O, CuO)

Ribbing

Roos

1998

Handbook of Optical Constants of Solids

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Spectroscopic views of high-T_csuperconductors

Cited by 28 publications

References 201 publications

The spin-polaron theory of high-T_csuperconductivity

The spin-polaron theory of high-T_csuperconductivity

A photoelectron spectroscopy and x-ray absorption study of single crystal with adsorbed Cs: on the origin of the states affected by electron doping and evidence for spatially resolved electron doping

Copper Oxides (Cu2O, CuO)

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Spectroscopic views of high-Tcsuperconductors

Cited by 28 publications

References 201 publications

The spin-polaron theory of high-Tcsuperconductivity

The spin-polaron theory of high-Tcsuperconductivity

A photoelectron spectroscopy and x-ray absorption study of single crystal with adsorbed Cs: on the origin of the states affected by electron doping and evidence for spatially resolved electron doping

Copper Oxides (Cu2O, CuO)

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Spectroscopic views of high-T_csuperconductors

The spin-polaron theory of high-T_csuperconductivity

The spin-polaron theory of high-T_csuperconductivity