Doping cuprate superconductors

Figure 8.6 Schematic depiction of a cuprate superconductor. Doping into the charge reservoir layers results in the transfer of holes to the superconducting layers.

Muller KA (2005) Essential Heterogeneities in Hole-Doped Cuprate Superconductors 114 1-11... 

The important and widely studied copper-oxide-derived high-temperature superconductors, known as cuprate superconductors, are basically insulators. Doping converts these into metallic materials, many of which are superconductors over rather more restricted composition ranges. Several of these materials have already been discussed La2Cu04 and Sr2Cu02F2 (Section 4.3.3), La2 A.SrxCu04 (Section 8.5.1), and Nd2, Ce,Cu04 (Section 8.5.2). 

Essential Heterogeneities in Hole-Doped Cuprate Superconductors... 

Heat capacity measurements on superconducting cuprates have been widely undertaken and recently Loram etal [25] reported condensation energies for a cuprate superconductor as a function of doping. In our theory the heat capacity per localised orbital (Cv IN0 is given by... 

MEASUREMENTS OF THE DOPING EFFECTS ON THE IN-PLANE PARACONDUCTIVITY IN CUPRATE SUPERCONDUCTORS... 

In conclusion, it was shown that the condensation energy in cuprate superconductors is highly sensitive to the doping level and is greatly reduced in underdoped region. 

Measurements of the Doping Effects on the in-Plane Paraconductivity in Cuprate Superconductors 85... 

The workshop included high-quality presentations on state of the art works, yet a key issue, discussed by many, was how homogeneous the cuprates are. STM data, as well as other reports, showed that the cuprate superconductors (SC s) studied were inhomogeneous, especially in the underdoped regime while experiments, like ARPES and magnetoresistance have established the existence of a Fermi Surface (FS), at least above some doping level, in the cuprates. 

Electron—hole asymmetry is encountered in cuprate superconductors.3 In the cuprates, superconductivity occurs in the electron-doped regime, although not as prominently as in the hole-doped regime. The electron-... 

Cuprate superconductors exhibit complicated phase diagrams which are functions of the doping parameter, x which controls the amount of the electron-transfer into or out of the cuprate plane. See for example Fig. 8.2. 

Studies on other high-temperature superconductors Positron annihilation measurements across Tc, coupled with the calculations of PDD have been carried out in a variety of hole-doped superconductors that include YBa2Cu40g [48], Bi-Sr-Ca-Cu-0 [49], and Tl-Ba-Ca-Cu-0 [50, 51] systems. We will not labor with the details here, except to state that a variety of temperature dependencies are seen and these can be rationalized when the results are analysed in terms of positron density distribution and the electron-positron overlap function [39]. These calculations show that the positron s sensitivity to the superconducting transition arises primarily from the ability to probe the Cu-O network in the Cu-0 layer. The different temperature dependencies of lifetime, i.e., both the increase and decrease, can be understood in terms of a model of local electron transfer from the planar oxygen atom to the apical oxygen atom, after taking into account the correct positron density distribution within the unit cell of the cuprate superconductor. 

Pulsed laser ablation has been developed in many fields for the fabrication of thin films of oxide materials, in particular high Tc cuprate superconductors. In these materials, the increase of the carrier concentration can be obtained in many cases by chemical doping (cationic or anionic), in order to induce superconductivity. 

Meissner-efTect and microwave-absorption measurements on bulk samples show that Rb ,C6o is superconducting with a maximum transition temperature of 28 K. This is a 10-K (60%) increase over the K-doped material. Only Bao.6Ko.4Bi03 and the cuprate superconductors have higher transition temperatures. 

The observation of superconductivity at 18 K in Kj(C6o (Ref. 1) demonstrated the possibility of obtaining high superconducting transition temperatures in the doped fullerenes. In this paper we report the observation of superconductivity at 28 K on doping of Cso with rubidium. This transition temperature is dramatically higher than previously observed in any molecular, elemental, or in-termetallic superconductor, and is surpassed only by Bao.6Ko.4Bi03 and the cuprate superconductors. 

Figure 17. Typical behavior of a cuprate superconductor on doping. The break between metal and insulator above T,. is variable and indicated by a dashed line.

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