Hole redistribution inSr14−xCaxCu24O41

Abstract

We report the results of a 63 Cu and 17 O NMR study of the nuclear quadrupole interaction tensor, 17,63 Q,␣ , in the hole doped spin ladder system Sr 14−x Ca x Cu 24 O 41 ͑x = 0 and 12͒ performed under ambient and high pressures. NMR data show that the hole density in the Cu 2 O 3 ladder layer grows with temperature, Ca content, and an applied pressure. We have derived the hole occupation of Cu 3d and O 2p orbitals at the different ion sites in the Cu 2 O 3 ladders as a function of temperature, Ca substitution, and pressure. We also suggest that the most important role of high pressure for the stabilization of a superconducting ground state in Ca-rich two-leg ladders is an increase of the hole concentration in the conducting Cu 2 O 3 planes while Ca substitution increases the coupling between ladders in the planes. We have obtained an estimate of 0.10 hole per Cu1 in Ca12 under 32 kbar at low temperature when this compound undergoes a superconducting transition at 5 K. Such a value fits fairly well with the doping phase diagram of cuprate superconductors.

Pairing tendencies in a two-orbital Hubbard model in one dimension

“…However, the issue of pairing was more challenging due to severe size restrictions. In [31] it was assumed that high pressure causes doping of the two-leg ladders, a result supported by recent density functional theory calculations [33], and in agreement with the Cu-oxide two-leg ladders context where experiments showed [34] that indeed pressure transfers charge away from the ladders into chains effectively doping them. Under these assumptions an intriguing result was unveiled: using 2×8 clusters indications of binding of two holes were observed at intermediate values of the on-site Hubbard U repulsion, and for a realistic Hund coupling J H /U = 0.25.…”

Observation of momentum-resolved charge fluctuations proximate to the charge-order phase using resonant inelastic x-ray scattering

“…In other words, holes are localized below T CO , which is indicated by a kink in resistivity23. Alternatively, a nuclear magnetic resonance study suggests that the number of holes in the ladder itself changes with temperature due to charge transfer between the ladder and the chain24.…”

Pressure dependence of superconductivity in doped two-leg ladder cuprates

“…On the other hand, when Ca is doped upon the original Sr-based Ca-undoped phase, the interatomic distance ladder-chain was found to be reduced (then the coupling between the ladders and chains is enhanced) by Ca substitution, leading to a redistribution of holes originally present only on the chains [10][11][12]. These experimental results show that an increase of the pressure (then an increase of the coupling between the ladders and chains) may be corresponding to an increase in the number of charge carriers on the ladders [8][9][10][11][12]. In this case, the kinetic energy increases with increasing pressure (doping), but at the same time, the spin correlation is destroyed, therefore the pressure effect (doping) on the doped two-leg ladder cuprates can be considered as a competition between the kinetic energy and magnetic energy, and the magnetic energy decreases with increasing pressure (doping).…”