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Lecture A. Rusydi


29 March 2006 FWN-Building 5118.-152, Nijenborgh 4, 9747 AG, Groningen
Speaker: Dr. A. Rusydi
Affiliation: University of Hamburg
Title: Experimental evidence of paired hole states in model high-Tc compounds
Date: Wed Mar 29, 2006
Start: 11.00
Location: FWN-Building 5118.-152
Host: T.T.M. Palstra
Telephone: +31 50 363 4419


The "spin ladder" is a reduced-dimensional analogue of the high temperature superconductors that was predicted to exhibit both superconductivity and an electronic charge density wave or "hole crystal" (HC). Superconductivity with Tc ~ 12 K indeed has been observed under hydrostatic pressure > 3 GPa. Recently, with resonant soft x-ray scattering (RSXS) we have found the HC in the ladders of the doped spin ladder system Sr14-xCaxCu24O41 (SCCO). The HC forms only with the commensurate wave vectors LL = 1/5 and LL = 1/3 (Not at 1/4!!) and exhibits a simple temperature scaling |1/3/ |1/5 = 5/3. For incommensurate values the HC "melts". The distribution of holes is revisited with semi-emperical reanalysis of the polarization-dependence x-ray absorption (XAS) data. A new interpretation of the XAS data leads to much larger ladder hole densities than previously suggested. These new hole densities lead to a simple interpretation of the HC which is paired holes in the rung of the ladders. With resonant inelastic (Raman) scattering, we have recently found a new excitation with an energy of about 200 meV that is comparable to twice the electronic binding energy, J. This excitation only occurs when the energy of incoming photon above the threshold of O2p _ Cu 3d excitation and does not observe for La6Ca8Cu24O41 (LCCO) which is a system without hole doped. This can be interpreted as a signature of short-range hole pairing which strongly supports our RSXS and XAS results.
Last modified:22 October 2012 2.30 p.m.