Lanthanum cuprate

The biggest explosion in materials chemistry and physics occurred in late 1986 when high-temperature superconductivity was discovered in a lanthanum cuprate, a material which was a ceramic and on which a few chemists had worked earlier. As stated in a report of the US National Academy of Sciences, this discovery changed the role of chemistry in the study of materials, and materials chemistry became a more significant part of materials science. It is around this time that even chemists started to consider solid state chemistry as an integral and important part of main-stream chemistry. 

HTSC high-temperature superconductor SLC substituted lanthanum cuprate... 

Berenov, A., Wei, J., Wood, H., Rudkin, R., and Atkinson, A. 2007. Effect of aliovalent doping on the transport properties of lanthanum cuprates. Journal of Solid State Electrochemistry 11, 482-489. 

Localisation of electron den ty over a small region in a crystal lattice occupied by 02 leads to the increased importance of electron correlation which cannot be tackled by traditional one-electron or HF theories[61]. Here we build upon our previous studies in which we used ab initio, semi-empirical and semi-classical approaches to study 0) ionic crystalline peroxides (e.g. Si and Ba02 [70,71]), (ii) point defects in the bulk and on the sui % of ionic and semi-ionic materials (e.g. corundum, silica and aluminium silicates [72,73]), and (iii) bipolaron formation in lanthanum cuprate (a superconducting material [74]). 

In Table 2.6 we give general information about three tetragonal structures two modifications (rutile and anatase) of titanium dioxide Ti02 and lanthanum cuprate La2Cu04. 

The lanthanum cuprate structure (Fig. 2.13) belongs to the symmorphic space group I4/mmm with the body-centered tetragonal lattice and contains 7 atoms in the primitive unit cell. 

Magnetic Incommensurability and Fluctuating Charge Density Waves in Lanthanum Cuprates... 

The erystal La2-xBaiCu04 was the first high-temperature superconductor which was discovered in 1986 [1], Since then a whole series of imusual magnetic and transport properties was foimd in lanthanum cuprate perovskites and related compounds. In particular, one of the most interesting features of the inelastic neutron scattering in these crystals is that for hole concentrations x > 0.04, low temperatures and small energy transfers the scattering is peaked at incommensurate momenta (, -5 + ), in the reciprocal lattice units... 

Neutron scattering experiments also detected static charge stripes in the low-temperature tetragonal (LTT) phase of lanthanum cuprates Lai 6-. rNdo 4Ba tCu04 and La2- BajrCu04 [16-19]. One of the manifestations of the stripe formation is the anomalous suppression of superconductivity near the hole concentration x = in the latter crystal. A weaker... 

In this section we use the results obtained in the framework of the t-J and Hubbard models for the interpretation of the incommensurate magnetic response observed in lanthanum cuprate perovskites. Let us start from the t-J model. In the self-consistent calculations [55] of its magnetic properties the set of parameters t = -0.5 eV, J = O.leV was used. These parameters correspond to hole-doped cuprates [64,65]. Results of these self-consistent calculations will be used below. 

In antiferromagnetically ordered crystals which lanthanum cuprates belong to the dynamic structure factor peaks for momenta near the antiferromagnetic ordering vector Q. Therefore the major part of experimental data belongs to this region. As follows from Eq. (7), the spin excitation dispersion near this momentum can be approximated as... 

A typical Fermi surface derived from photoemission in moderately doped lanthanum cuprate perovskites [69] is shown in Figure 4. As follows from Eq. (7), for low temperatures, low frequencies and k = Q, hole states which make the main contribution to the spin-excitation damping are located near the hot spots - the intersection points of the Fermi surface and the boimdary of the magnetic Brillouin zone. 

Figure 4. The Fermi surface of a moderately doped lanthanum cuprate perovskite (solid lines) [69]. Dashed lines show the boundary of the magnetic Brillouin zone, gray circles are the hot spots, the dotted arrow is the antiferromagnetic momentum Q.

The above results were obtained in the normal state. The opening of the c -wave superconducting gap of the order of a few millielectronvolts, as observed in lanthanum cuprates [71], leads only to small changes in the above-discussed dependencies. 

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