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A specific heat and magnetization study of highTc ceramic superconductors

Authors :: Rosenberg, M.
Mittag, M.
Job, R.
Chojetzki, W.
Wernhardt, R.
Sabrowsky, H.
Neubauer, R.
Source :: Zeitschrift für Physik B Condensed Matter; June 1987, Vol. 69 Issue: 2-3 p151-157, 7p
Publication Year :: 1987
Abstract: From the temperature dependence of the specific heat of the semiconductor La<subscript>2</subscript>CuO<subscript>4</subscript> and the high temperature superconductors La<subscript>1.8</subscript>Sr<subscript>0.2</subscript>CuO<subscript>4</subscript> (T<subscript>c</subscript>=37.2 K) and YBa<subscript>1.9</subscript>K<subscript>0.1</subscript>Cu<subscript>3</subscript>O<subscript>6.9</subscript> (T<subscript>c</subscript>=91.5 K) in the range 1.5–30 K, a strong similarity of the lowfrequency part of their phonon density of states with a peak around 10 meV could be inferred. In the case of La<subscript>1.8</subscript>Sr<subscript>0.2</subscript>CuO<subscript>4</subscript> the thermodynamical critical field belowT<subscript>c</subscript> has been determined and using the Rutger's formula and the BCS model, a Sommerfeld coefficient ?=9 mJ·mol<superscript>-1</superscript> K<superscript>-1</superscript> was obtained, which, taking into account recent results of band structure calculations leads to an electron-phonon enhancement factor ?=1.3, value compatible withT<subscript>c</subscript>=36 K when using McMillan's formula forT<subscript>c</subscript>. A systematic study of the magnetization offered evidence for strong flux trapping effects at higher fields and for Meissner shielding by superconducting Josephson currents in fields below 6 mT at 4.2 K.