Split superconducting transitions in the specific heat and magnetic susceptibility of YBa2Cu3Ox versus oxygen content

On the origin of the double superconducting transition in overdoped YBa2Cu3Ox

“…In the latter case the onset of irreversibility was reported to be connected with the lower transition. A higher oxygenation of the grain surface was made responsible, preventing further oxygenation of the interior of the grains during the oxygenation process [3]. Due to the grain structure of the polycrystalline samples, the surface has a much larger contribution to the volume, thus explaining the sensitivity of bulk measurements to both transitions.…”

A survey of the Van Hove scenario for high-tc superconductivity with special emphasis on pseudogaps and striped phases

“…From combined specific heat and susceptibility measurements, Janod, et al [788] show that the two T c 's are split by ≈ 4K at YBCO 7 , and smoothly merge near the optimum T c , ∼YBCO 6.92 , and then another split peak arises in underdoped samples! (The conversion between annealing temperature, used in [788], and δ is discussed in [789]. ) Janod, et al [788,789] interpret the split transition in terms of limited oxygen diffusion: a thick shell near the grain surface is fully oxygenated, impeding diffusion into the grain interior.…”

“…(The conversion between annealing temperature, used in [788], and δ is discussed in [789]. ) Janod, et al [788,789] interpret the split transition in terms of limited oxygen diffusion: a thick shell near the grain surface is fully oxygenated, impeding diffusion into the grain interior. Conder, et al [790] have shown that this interpretation is unlikely, and that nanoscale phase separation is a more probable interpretation.…”

A Displacive Structural Transformation in theCuO2Planes ofYBa2Kaldis1, Röhler2, Liarokapis3 et al. 1997Phys. Rev. Lett.686460View full textAdd to dashboardCite

“…In the T-x phase diagram of the cuprate superconductors x opt indicates the phase separation line between the underdoped and overdoped regimes. While optimum doped YBa 2 Cu 3 O 6.92 exhibits a single superconducting transition various laboratories have reported from measurements of the magnetization [3][4][5][6][7], resistivity [8], and specific heat [7,8] of overdoped YBa 2 Cu 3 O x , x $ 6.95, two superconducting phases with critical temperatures split by about 2.5 K. Optimum doped YBa 2 Cu 3 O 6.92 has an intermediate oxygen concentration with respect to its insulating (antiferromagnetic) parent phase and the overdoped metallic phase. It is an important indication that only a very narrow compositional range is most favorable for the superconductivity.…”