15 research outputs found
On the possibility of superconductivity in PrBa2Cu3O7
Recent reports about observations of superconductivity in PrBa2Cu3O7 raise a
number of questions: (i) of various theories striving to explain the Tc
suppression in PrxY{1-x}Ba2Cu3O7, are there any compatible with possible
superconductivity in stoichiometric PrBa2Cu3O7? (ii) if this superconductivity
is not an experimental artifact, are the superconducting carriers (holes) of
the same character as in the other high-Tc cuprates, or do they represent
another electronic subsystem? (iii) is the underlying mechanism the same as in
other high-Tc superconductors? I present an answer to the first two questions,
while leaving the last one open.Comment: 4 pages 4 eps fig
Superconducting properties of RuSr2GdCu2O8 studied by SQUID magnetometry
For polycrystalline RuSr2GdCu2O8 (Ru-1212), distinct peaks have been reported
in d.c. magnetization in the superconducting state of the sample. Sr2GdRuO6
(Sr-2116), the precursor for the preparation of Ru-1212, shows similar peaks in
the same temperature regime. Based on measurements performed on both bulk and
powdered samples of Ru-1212 and Sr-2116, we exclude the possibility, that the
observed behavior of the magnetization of Ru-1212 is due to Sr-2116 impurities.
The effect is related to the superconductivity of Ru-1212, but it is not an
intrinsic property of this compound. We provide evidence that the observation
of magnetization peaks in the superconducting state of Ru-1212 is due to flux
motion generated by the movement of the sample in an inhomogeneous field,
during the measurement in the SQUID magnetometer. We propose several tests,
that help to decide, whether the features observed in a SQUID magnetization
measurement of Ru-1212 represent a property of the compound or not.Comment: 22 pages, 9 figure
From granules to bulk superconductors using Richardson-Gaudin equations
paper n° 164International audienceWe provide a compact expression of the ground-state energy of N-Cooper pairs valid from small to large sample volumes, as checked by numerically solving Richardson-Gaudin equations which give the exact eigenstates of BCS superconductors. This expression contains a contribution linear in the potential amplitude, dominant for small samples, and an exponential contribution dominant when the number of states available for pairing gets larger than a material-dependent threshold independent from sample size. These âavailable statesâ are the states feeling the BCS potential, reduced by the Pauli exclusion principle through a âmoth-eaten effectâ which comes from the composite boson nature of Cooper pairs. This work also presents an elegant derivation of the N-Cooper pair energy obtained recently, which makes use of the roots of the degree-N Hermite polynomial