Pressure effect onTcfor the rare-earth seriesRBa2

Abstract

The pressure dependence of the superconducting transition temperature T c in RBa 2 Cu 3 O 7Ϫ␦ (RϭY and rare earths͒ series has been investigated systematically on the basis of the t-tЈ-tЉ-J model with d-wave pairing by taking into account the variations of the hole concentration in the CuO 2 planes and the effective interaction with pressure. It is shown that the pressure-induced change of hole concentration increases with the trivalent rare-earth ion radius. The calculated T c and its pressure derivative dT c /dP are found to be the increasing functions of the radius of the R 3ϩ ions for the fully oxygenated RBa 2 Cu 3 O 7 . Good agreement with experiments suggests that the rare-earth ion size effect on dT c /dP in RBa 2 Cu 3 O 7 mainly originates from the pressure-induced charge transfer from the charge reservoir CuO chain to the conducting CuO 2 planes. The change of dT c /dP with hole concentration and the pressure dependence of T c in the recently discovered superconducting PrBa 2 Cu 3 O y are well reproduced in this simple model. We have arrived at the conclusion that the unusually large T c enhancement in PrBa 2 Cu 3 O y under pressure results from its underdoped nature. Further experiments are proposed to enhance T c at ambient pressure in PrBa 2 Cu 3 O y .

Electronic structure of PrBa2Cu3O7 after high-pressure compression from first principles

“…Our calculations are consistent with the theoretically predicted T c (P) for P ffi 9 GPa of the optimally doped superconductor PrBa 2 Cu 3 O y with the initial T c = 95 K [13]. Table 4 Partial charges corresponding to valence states inside atomic spheres in PrBa 2 Cu 3 O 7 system after the high-pressure compression.…”

“…The pressure dependence of critical temperature T c (P) in the discovered superconducting Pr123 crystals is quite well reproduced by the t-t 00 -J model [13] arriving at the conclusion that the unusually large T c enhancement in this compound results from its underdoped nature. The T c in PrBa 2 Cu 3 O x compound, with assumed T c = 85 K (underdoped system) in ambient pressure, as a function of pressure P in the range of 0 6 P 6 20 GPa was calculated giving as a result a parabolic-shaped curve with the maximum of 105.6 K at 9.7 GPa in very good agreement with the experiment [12].…”

“…As described above, two main situations for Pr123 in the range 9 6 P 6 10 GPa could potentially take place, namely, (i) the maximal increase of the initial T c for the underdoped system and (ii) the significant decrease of the initial T c for the optimally doped system [13]. The aim of this work is to study the electronic structure, charge distribution and magnetic moments obtained from the first principles calculations of fully oxygenated, ideally stoichiometric PrBa 2 Cu 3 O 7 system to find out if the negative pressure effect is plausible in this compound under the high-pressure compression of P ffi 9 GPa.…”

Direct correlation betweenTcandCuO2bilayer spacing inVarela1, Arias2, Sefrioui3 et al. 2002Phys. Rev. B

“…1, 15 An increase of the rare earth ionic radius from 0.99 Å for Yb to 1.08 for Nd is known to increase the distance between planes and also T c from 88 to 95 K. 16 Despite the extensive work, the results of some of the experiments are contradictory, 13,14 and a clear picture has not emerged yet. Changes in the distance between planes or modifications in the intracell distances due to cationic substitution may have, in addition, a direct influence in the charge transfer and thus on the carrier concentration.…”

“…1,15 An increase of the rare earth ionic radius from 0.99 Å for Yb to 1.08 for Nd is known to increase the distance between planes and also T c from 88 to 95 K.…”