Glassiness and superconductivity in strongly Pr-doped YBa2Cu3O7-δ single crystals

Doping Mott insulators with charge causes dramatic changes in their physics. Spectacular results of the doping are superconductivity in cuprates and colossal magnetoresistivity in manganites. In all cases, doping is accompanied by mesoscopic phase separation that signalises that the magnetic short-range forces start to be competed by the long-range Coulomb force. The long range order is, therefore, frustrated by the latter and, due to the spin-charge coupling, the system turn into a phase separated one [1] and displays a specific glassiness which is self generated [2, 3]. Glassy state is present in most of phase diagrams of cuprates, but its occurrence and the relation with the neighbouring phases is not universal [4]. In La-based cuprates, the glassy state emerges directly from the antiferromagnetic (AFM) state at a doping level lower than the critical one for the occurrence of superconductivity (SC) but survives at higher hole concentration [5-7]. The glassiness is still under debate in the case of the bilayered YBa2Cu3O6+x [8-13]. A singular case is Y1−xPrxBa2Cu3O7−δ where the doping level is controlled by both oxygen and praseodymium. The increase of oxygen content increases the hole concentration, whereas Pr generate a depletion of the Zhang-Rice conduction band [14]. For fully oxygenated system, δ ≅ 0, the glassy state coexists with superconductivity for x ≥ 0.4 but was not detected above xc ≤ 0.55, where SC state vanishes. Therefore there is no intermediate phase between AFM and SC states [15-17]. Actually, there are two subsystems susceptible to show magnetic interaction, specifically the Cu and Pr subsystems, and they equally display both AFM and glassy ordering at high Pr content. An attempt of phase diagram in a narrow concentration range around xc with a remarkable richness in phases is shown in Figure 1 [17, 18]. This equilibrium picture goes along with strong phase fluctuations of low symmetry phases due to the decreased dimensionality and charge density. The fluctuations are expected to alter the magnetic response of the paramagnetic high temperature phase. This communication present the results of the investigations of the magnetic response of Y1−xPrxBa2Cu3O7−δ in this rich-in-phase concentration range aiming to depict the role of the fluctuation in each phase. The main finding was that the paramagnetic phase is not completely reversible but is dressed with an important irreversibility extending up to 200 K.