M. O. Rahman

Temperature dependent polarized XANES spectra for Zn-doped LSCO system

Abstract The cuprates seem to exhibit statistics, dimensionality and phase transitions in novel ways. The nature of excitations (i.e. quasiparticle or collective), spin-charge separation, stripes (static and dynamics), inhomogeneities, pseudogap, effect of impurity dopings (e.g. Zn, Ni) and any other phenomenon in these materials must be consistently understood. Zn-doped LSCO single crystal, were grown by travelling solvent floating zone technique. Temperature dependent polarized XANES (near edge local structure) spectra were measured at the BL13-B1 (Photon Factory) in the fluorescence mode from 10 to 300 K. Since both stripes and nonmagnetic Zn impurities substituted for Cu give rise to inhomogeneous charge and spin distribution it is interesting to understand the interplay of Zn impurities and stripes. To understand these points we have used Zn-doping and some of the results obtained are as follows: The spectra show a strong dependence with respect to the polarization angle, θ , as is evident at any temperature by comparing the spectra where the electric field vector is parallel to the ab -plane to the one where it is parallel to the c -axis. By using the XANES (temperature) difference spectra we have determined T * (experimentally we find, T * ≈ 160–170 K) for this sample. The XANES difference spectra shows that the changes in XANES features are larger in the ab -plane than the c -axis, this trend is expected since zinc is doped in the ab -plane at the copper site. Our study also complements the results in literature namely that zinc doping does not affect the c -axis transport.

Quantum Group Based Theory for Antiferromagnetism and Superconductivity: Proof and Further Evidence

Abstract Previously one of us presented a conjecture to model antiferromagnetism and high temperature superconductivity and their ‘unification’ by quantum group symmetry rather than the corresponding classical symmetry in view of the critique by Baskaran and Anderson of Zhang’s classical SO(5) model. This conjecture was further sharpened, experimental evidence and the important role of 1-d systems (stripes) was emphasized and moreover the relationship between quantum groups and strings via WZWN models were given in an earlier paper. In this brief note we give and discuss mathematical proof of this conjecture, which completes an important part of this idea, since previously an explicit simple mathematical proof was lacking. It is important to note that in terms of physics that the arbitrariness (freedom) of the d-wave factor g2(k) is tied to quantum group symmetry whereas in order to recover classical SO(5) one must set it to unity in an adhoc manner. We comment on the possible connection between this freedom and the pseudogap behaviour in the cuprates.

SET-based experiments for HTSC materials

Cuprates seem to exhibit statistics, dimensionality and phase transitions in novel ways. The nature of excitations (i.e. quasiparticle or collective), spin-charge separation, stripes (static and dynamics), inhomogeneities, pseudogap, effect of impurity dopings (e.g. Zn, Ni) and any other phenomenon in these materials must be consistently understood. In this paper we further discuss our original suggestion of using single electron tunnelling transistor (SET)-based experiments to understand the role of charge dynamics in these systems. Assuming that SET operates as an efficient charge detection system, we can expect to understand the underlying physics of charge transport and charge fluctuations in these materials for a range of doping. Experiments such as these can be classified in a general sense as mesoscopic and nano characterization of cuprates and related materials. In principle such experiments can show whether an electron is fractionalized in cuprates as indicated by angle-resolved photoemission spectroscopy data. In contrast to flux trapping experiments, SET-based experiments are more direct in providing evidence about spin-charge separation. In addition a detailed picture of nano charge dynamics in cuprates may be obtained.