Systematic NMR studies of high- T c and two-leg spin-ladder systems

• Published in: Journal of magnetism and magnetic materials Vol. 177; pp. 487 - 492
• Main Authors: Kitaoka, Y., Magishi, K., Matsumoto, S., Ishida, K., Ohsugi, S., Asayama, K., Uehara, M., Nagata, T., Akimitsu, J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1998
• Subjects: High- T c cuprates; NMR; Quantum fluctuation; Spin gap; Spin ladder; Superconductivity; High- T c cuprates; Spin ladder; NMR; Spin gap; Superconductivity; Quantum fluctuation
• ISSN: 0304-8853
• DOI: 10.1016/S0304-8853(97)00613-6

We review systematic NMR studies on underdoped high-
T
c
cuprates and two-leg spin-ladder systems, focusing on their spin gap and dynamics. The pressure-induced superconductivity was discovered in Sr
14−
x
Ca
x
Cu
24O
41 comprising the quasi-one-dimensional
S = ½ two-leg spin-ladder Cu
2O
3 planes. Remarkably, the new parent cuprate is the Mott insulator with the
spin gap in contrast to the antiferromagnetic (AF) insulator for the high-
T
c
cuprates. From the Cu-NMR results in the ladder Cu
2O
3 plane on single crystals Sr
14−
x
Ca
x
Cu
24O
41 with
x = 9 (hereafter denoted as Ca9) and
x = 11.5 (Ca11.5), it is shown that the spin gap,
Δ = 510K in the Sr14 is significantly reduced upon isovalent Ca substitution, but its magnitude remains nearly constant with
Δ = 270 and 280K for the Ca9 and Ca11.5, respectively. In
T range of
T ⩾ Δ, the spin dynamics in carrier-doped two-leg spin-ladder systems are characterized by the behaviour similar to the
S = ½ 1D Heisenberg system. By contrast, the transport property shares a common feature, i.e, due to the spin-gap opening the charge transport is confined in the 2D CuO
2 plane for underdoped high-
T
c
, cuprates and in the quasi-1 D ladder for spin-ladder compounds.