https://doi.org/10.1007/s10051-001-8697-y
(Sr/Ca)14Cu24O41 spin ladders studied by NMR under pressure
1
Laboratoire de Physique des Solides (UMR 8502) ,
Université Paris-Sud, 91405, Orsay, France
2
Département de Physique, Université de Sherbrooke,
Sherbrooke, Québec, J1K2R1, Canada
3
Laboratoire de Chimie des Solides (UMR 8648) , Université
Paris-Sud, 91405, Orsay, France
4
II. Physikalisches Institut, Universität zu Köln, Zülpicher
Str. 77, 50937 Köln, Germany
Corresponding author: a jerome@lps.u-psud.fr
Received:
8
March
2001
Revised:
27
July
2001
Published online: 15 December 2001
63Cu-NMR measurements have been performed on two-leg
hole-doped spin ladders SrCaxCu24O41 single crystals
at several pressures up to the pressure domain
where the stabilization of a superconducting ground state
can be achieved. The data reveal a marked decrease of the spin gap derived from
Knight shift measurements upon
Ca substitution and also under pressure and confirm the onset of low lying spin
excitations around Pc as previously reported. The spin gap in
is strongly reduced above 20 kbar. However, the
data of an experiment performed at P=36 kbar where superconductivity has been detected at 6.7 K by an
inductive technique have shown that a significant amount of spin excitations remains gapped at 80 K when superconductivity sets in. The standard relaxation model
with two and three-magnon modes explains fairly
well the activated relaxation data in the intermediate temperature regime corresponding
to gapped spin excitations using the spin gap data derived from Knight shift
experiments. The data of Gaussian relaxation rates of heavily doped samples support the limitation of the
coherence length at low temperature by the average distance between doped holes. We discuss the interplay
between superconductivity and the spin gap and suggest that these new results support the exciting prospect
of superconductivity induced by the interladder tunneling of preformed pairs as long as the pressure
remains lower than the pressure corresponding to the maximum of the superconducting critical temperature.
PACS: 74.25.Ha – Magnetic properties / 74.72.Jt – Other cuprates / 76.60.Cq – Chemical and Knight shifts
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2001