Spin modulations in detwinned OrthoII YBCO6.5 crystals
Subtitle: an NMR study.
Contributors: Statt, Bryan (supervisor)
Published: 2004
Language: eng
Number of pages: 333
Subjects: Physics Theses
Description: Copper nuclear magnetic resonance (NMR) has been used to investigate the properties of stoichiometric detwinned OrthoII YBa2Cu 3O6.5 (YBCO6.5) crystals grown in BaZrO3 crucibles. In particular the aim of this study was to investigate the pseudo-gap and other properties of CuO2 planes as well as to determine the nature of the ground state of CuO chains in this system. In our NMR study of OrthoII YBCO6.5, four well resolved resonances have been observed. Line assignments have been made to each of the four expected crystallographically inequivalent sites. Our NMR study confirms the high quality of these crystals and emphasizes the importance of oxygen disorder in determining properties of YBCO6+x material. These highly stoichiometric crystals exhibit interesting properties that were not observed before in previous generations of oxygen depleted YBCO6+x material.The presence of a pseudogap in CuO2 planes is confirmed below 250 K by Knight shift measurements. Moreover, we have found no evidence for static magnetic moments or pinning of stripes in these planes. Our study also indicates that although the chain-plane coupling in OrthoII YBCO6.5 is weaker than in YBCO7, it is still strong enough to induce some inhomogeneity in the CuO2 planes due to the presence of spin (charge) oscillations in the chains. Therefore, the effects chains might have on the electronic properties of CuO2 planes with regards to the presence of charge modulations and stripes in these planes should be taken into consideration.Based on a detailed NMR study of static and dynamic properties of the full chain Cu sites, it is shown that the ground state of the quasi-1D CuO chains in OrthoII YBCO6.5 cannot be described by a conventional CDW/SDW system. However, our study provides strong evidence for the presence of spin (charge) oscillations with varying amplitude (Friedel-like oscillations nucleated at the chain ends) along the chains in this system. As expected, increasing temperature tends to smear out the oscillations. Unexpectedly we have also observed a transition with decreasing applied field which collapses the oscillations. This is interpreted in terms of magnetically induced incoherent chain-plane hopping.
Notes: Thesis (Ph.D.), Dept. of Physics, University of Toronto.

Electronic version licensed for access by U. of T. users.

Source: Dissertation Abstracts International, Volume: 65-05, Section: B, page: 2461.