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Abstract:
HEAVY-fermion superconductors (in which the charge carriers have an
effective mass approximately 100 times the free electron mass) have been
the subject of intense study during the past decade 1, in part because
of the suggestion that some of these materials may exhibit
non-conventional pairing mechanisms 2. Here we report a demonstration of
quantum coherence of the superconducting wavefunction between the
conventional superconductor niobium and the recently discovered 3
heavy-fermion superconductor UPd2Al3, which is a potential candidate for
a non-conventional pairing mechanism 4. The experimental method is
similar to our earlier work on high-T(c) materials 5,6: we use a small
pointed rod of UPd2Al3 to bridge the gap in an almost closed niobium
ring. We observe persistent currents in the composite ring, and trapped
flux, which is in discrete quantum states separated by the flux quantum
h/2e. Although the observation of phase coherence between UPd2Al3 and
niobium may not constrain the nature of the pairing in UPd2Al3, we also
observe Josephson-like current-voltage characteristics at the junction,
but with very small products of critical current and normal-state
resistance. If other possible causes can be eliminated, these small
I(c)R(n) values may point to a small tunnelling probability between the
two superconductors, and hence to unconventional pairing in UPd2Al3.
