High-temperature superconductivity

Abstract

The widely held notion that high-temperature superconductivity originates in the cuprate-planes is proven to be faulty. In the cuprates such as YBa2Cu3O7, we argue that the superconductivity resides in the BaO layers. This superconductivity is s-wave, not d-wave, in the bulk. The trio of ruthenate compounds, doped Sr 2 YRuO 6 , GdSr2Cu2RuO8, and Gd2−zCezSr2Cu2RuO10 all superconduct in their SrO layers, which is why they have almost the same ∼49 K onset temperatures for superconductivity. Faulty evidence for cuprate-plane superconductivityTwo of the most-cited papers in contemporary physics claim to show that the cuprate-planes of YBa 2 Cu 3 O x superconduct [1,2]. However, there are problems with both papers that have not been well-recognized: (i) the evidence of superconductivity in the cuprate-planes comes from a jump in charge which was evident in the work of Cava et al., but not in the work of Jorgensen et al.; and (ii) the studies of Jorgensen et al. claim to confirm the data of Cava et al., but actually do not in the most important way: Jorgensen does not have the Cava jump. In fact, a closer examination of the data reveals that only one datum is responsible for the jump in charge that is purportedly evidence for cuprate-plane superconductivity, and this datum was not reproduced in the data of Jorgensen et al. or (to our knowledge) elsewhere. This startling fact has been missed by many people because a continuous line was drawn through rather sparse data and conveyed the impression that the data are much denser than they are. In other words, the concept of cuprate-plane superconductivity has not been confirmed and rests on only one unreproduced datum. (See Fig. 1.) This is important to realize because the superconducting layers in most (and perhaps all) high-temperature superconductors are not the cuprate-planes, as was implied by the now-infamous fictitious jump in cuprate-plane Cu charge [3].Perhaps an independent confirmation of the problem with cuprate-plane superconductivity comes from the scanning tunneling microscopy data on Bi 2 Sr 2 CaCu 2 O 8 of the Illinois group [4,5]. (See Fig. 2). The surface layer of this compound, when it is cleaved, is the BiO layer. Underneath that is the SrO layer, and then a CuO 2 plane; after that comes a Ca layer and a second CuO 2 plane. Apparently the Illinois workers have imaged the BiO surface layer, and then a CuO 2 layer that is exposed by a step protruding from the side of the sample, apparently the second CuO 2 layer beneath the surface. An examination of their data reveals that their BiO layer looks like most others, with a U-shaped feature that is indicative of a layer nearby a superconducting layer. But their protruding CuO 2 plane does not look at all like a superconductor, and instead of a U-shaped feature, seems to have a band-gap with no density of states in the gap. The Illinois workers have interpreted their observations as evidence of dwave superconductivity in the cuprate-planes, but this interpretation is based primarily on the facts that (i) the...

Theory of high-TCsuperconductivity: transition temperature

“…Since their discovery, the list of high-T C superconductor families has grown to include (i) the (well-known) layered cuprate perovskites (e.g. YBa 2 Cu 3 O 7-δ ), (ii) ruthenocuprates such as GdSr 2 Cu 2 RuO 8 [114], and certain Cu-doped layered ruthenates [82,115] ). Since the latter five families (iii)-(vii) of compounds in addition to the ruthenates do not contain cuprate planes, it is manifestly clear that CuO 2 planes are not specifically required for high-T C superconductivity.…”

Magnetic properties of the double perovskite compound Sr2YRuO6

“…[3] Specific heat and magnetic susceptibility measurements reveal two phase transitions at ∼ 30 K and ∼ 26 K respectively, [1] while the physical state of Sr 2 YRuO 6 between these two transition temperatures continues to be elucidated. Additional interest in this material is originated from the occurrence of superconductivity when Ru is partially (up to 15%) replaced by Cu in both powders [3][4][5][6][7] and single crystals, [8][9][10] with superconducting volume fractions still under 10%. A broad knowledge of the magnetic state of Sr 2 YRuO 6 is fundamental to understand how the superconducting and ferromagnetic order parameters can adjust themselves in the crystal lattice.…”