Raman Scattering in CLBLCO an analogue to the Isotope effect

1. Abstract Meni Shay1, Gil Drachuck2, Galina Bazalitski2, Amit Keren2, Dirk Wulferding3, Peter Lemmens3,Zaher Salman4 1 Physics Department, Ort Braude College, Karmiel. 2 Physics Depatment, Technion, Haifa. 3 Technical University Braunschweig, Germany 4 Paul Scherrer Institute, Switzerland . Raman scattering is used to shed light on the yet-unsolved problem of the pairing mechanism in High-Temperature superconductivity. The acquisition of the Raman spectra was made possible after a successful growth of high quality single crystals of (CaLa)1(BaLa)2Cu3Oy. In this YBCO-like system, the Ca to Ba ratio designate a specific family. Each family has its own phase diagram, with variation of optimally doped transition temperature, , of about 30%. The Raman scattering peak from magnons is used for the determination of the superexchange coupling strength, J, in the antiferromagnetic phase. The Raman peak was measured for several samples from different families. It is found that is proportional to the Raman shift, as measured from different underdoped families having the same number of holes. It is also found that TN is proportional to the Raman shift of the fully underdoped samples. Research question Results Raman Scattering in CLBLCO an analogue to the Isotope effect Background The isotope effect ( ) found in metallic superconductors is considered to be a corner stone in their understanding. A similar effect, in High Temperature Superconductors, based on the system (CLBLCO for short), is presented in this work. This formula describes several different HTSC’s, where x, the amount of Calcium, determines a specific one. The phase diagrams1 are shown in the figure. The different superconductors differ in while many other properties remains the same. CLBLCO may serve as a compound having different “isotopes” 2 Magnon peak is found in the Raman spectra: Having typical temperature and Polarization dependence: Question: What is the relation between and ? Tc of optimally doped samples determined using magnetization measurement Indirect μSR determination of J suggests that [Ref 2] TN determination using μSR Raman Scattering 2 Magnon Raman scattering is a method for measuring J. Theory shows3 that Conclusions Spin wave expansion4 Experimental setup 6 broken bonds= 12 changes= 3J The Samples References Fully oriented, high quality, single crystal, freshly cleaved. With a specific oxygen content [1] A. Kanigel et. Al. Phys. Rev. Lett.88, 137003 (2002). R. Ofer A. Keren, Phys. Rev. B 74, 220508R (2006). [2] R. Ofer A. Keren, Phys. Rev. B 78, 140508 (2008). [3] Weber and Ford, Phys. Rev. B 40 6890 (1989). [4] C. Kittel, Quantum Theory of Solids, Ch. 4 (1987). • Samples differ in Calcium content and in Oxygen content • And are color coded in the following way •  x=0.1 y=6.4 n<0 •  x=0.1 y=6.6 n=0 •  x=0.4 y=6.4 n=0 B1g phonon intensity is used for in-plane orientation