The electronic contribution to the specific heat of NdBa \(\mathsf{_2}\mathsf{Cu_3}\mathsf{O_{6 + x}}\)

Article

Abstract.

From measurements of the specific heat of \(\mathrm{NdBa_2Cu_3O_{6 + \mathnormal{x}}}\) in the temperature range between 20 K and 300 K the electronic contribution C e (T)/T has been derived. The results depend strongly on the assumptions made for the normal-state reference, especially the phonon contribution. Taking into account entropy conservation between the superconductor and a hypothetical normal-state reference, we found a temperature independent electronic contribution of this normal-state reference without any sign of a pseudogap for both optimum doped and underdoped samples. For oxygen concentrations between x = 0.79 and x = 0.89 a broad hump in C e (T)/T is observed around 120 K, which we ascribe to pair formation above T c . The dependence of the hole concentration n h in the copper oxide planes on the oxygen concentration x in the copper oxide chains was calculated by means of bond-valence sums. We found that the optimum doping of the copper oxide planes is n h,opt = 0.24 for \(\mathrm{\mathnormal{R}Ba_2Cu_3O_{6 + \mathnormal{x}}}\) (R = Nd, Y) irrespective of the element on the rare-earth site.

Keywords

Entropy Neural Network Complex System Oxygen Concentration Nonlinear Dynamics 

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Copyright information

© Springer-Verlag Berlin/Heidelberg 2004

Authors and Affiliations

  • U. Tutsch
    • 1
  • P. Schweiss
    • 2
  • H. Wühl
    • 1
    • 3
  • B. Obst
    • 1
  • Th Wolf
    • 2
  1. 1.Institut für Technische PhysikForschungszentrum KarlsruheKarlsruheGermany
  2. 2.Institut für FestkörperphysikForschungszentrum KarlsruheKarlsruheGermany
  3. 3.IEKPUniversität KarlsruheKarlsruheGermany

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