Relevance of magnetism to cuprate superconductivity: Lanthanides versus charge-compensated cuprates

Abstract

We address what seemed to be a contradiction between the lanthanide series REBa2Cu3Oy (RE123) and the charge-compensated series (CaxLa1−x)(Ba1.75−xLa0.25+x)Cu3Oy (CLBLCO) regarding the superexchange (J) dependence of the maximum superconductivity (SC) critical temperature T max c (J); RE and x are implicit variables. This is done by measuring the Néel temperature and the temperature dependence of the magnetic order parameter for RE=Nd, Sm, Eu, Gd, Dy, Yb, Y, and for Y(BaSr)Cu3Oy, at various very light dopings. The doping is determined by thermopower, and the magnetic properties by muon spin rotation. We find that the normalized-temperature dependence of the order parameter is identical for all RE123 in the undoped limit (with the exception of Gd123) implying identical out-of-plane magnetic coupling. The extrapolation of TN to zero doping suggests that, despite the variations in ionic radii, J varies too weakly in this system to test the relation between SC and magnetism. This stands in contrast to CLBLCO where both T max c and T max N vary considerably in the undoped limit, and a positive correlation between the two quantities was observed.

Paramagnons and high-temperature superconductivity in a model family of cuprates

“…A positive correlation between T c and J inferred from T N has indeed been found previously 11 . Yet, spectroscopic determination of the associated energies suggested a weaker correspondence 13 , and historically different impressions were once obtained 12 , 14 – 16 . This is because major modifications of J are difficult to achieve, and they go along with structural modifications whose consequences are difficult to assess.…”

Paramagnons and high-temperature superconductivity in mercury-based cuprates

“…Even though a positive correlation between T c and parent compounds' antiferromagnetic ordering temperature has been found in some cases [20], spectroscopic determination of the associated energies suggests a much weaker correspondence [22], sometimes with controversial results [21,23,24]. This is because major modifications of the magnetic exchange interactions (J) are difficult to achieve [25], and they go along with structural modifications whose consequences are difficult to assess. In particular, most of the materials previously studied in this regard have relatively low T c , making it unclear whether the variation in T c is linked to the magnetic energy or some detrimental effects on T c , including chemical disorder [26] and competing states such as charge order [1], which may vary at the same time as the tuning takes place.…”

Strongly coupled charge, orbital and spin order in TbTe$_{3}$

“…In the presence of magnetic ions the CDW may influence and be influenced by the magnetic orders such as the appearance of stripe order−a collective, long-period modulation of spins and charge carriers within the CuO 2 planes observed in cuprate systems [3]. It is also closely associated with superconductivity which appears nearby in the phase diagram [4,5]. In many cases the superconductivity is unconventional and is possibly mediated via magnetism as proposed for layered transition-metal chalcogenides, pnictides and copper-oxide high-T c superconductors.…”