Crystal growth and in-plane optical properties of Tl$_2$Ba$_2$Ca$_{n-1}$Cu$_n$O$_x$ (n=1,2,.pdf

a r X i v : c o n d - m a t / 0 5 0 3 2 5 0 v 2 [ c o n d - m a t .s u p r - c o n ] 1 8 A u g 2 0 0 5 Crystal growth and in-plane optical properties of Tl2Ba2Can?1CunOx (n=1,2,3) superconductors Y. C. Ma and N.L. Wang? Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People’s Republic of China (Dated: February 2, 2008) Single crystals of thallium-based cuprates with the general formula Tl2Ba2Can?1CunOx(n=1,2,3) have been grown by the flux method. The superconducting transition temperatures determined by the ac magnetic susceptibility are 92 K, 109 K, and 119 K for n=1,2,3 respectively. X-ray diffrac- tion measurements and EDX compositional analysis were described. We measured in-plane optical reflectance from room temperature down to 10 K, placing emphasis on Tl-2223. The reflectance roughly has a linear-frequency dependence above superconducting transition temperature, but dis- plays a pronounced knee structure together with a dip-like feature at higher frequency below Tc. Correspondingly, the ratio of the reflectances below and above Tc displays a maximum and a mini- mum near those feature frequencies. In particular, those features in Tl2223 appear at higher energy scale than Tl2212, and Tl2201. The optical data are analyzed in terms of spectral function. We discussed the physical consequences of the data in terms of both clean and dirty limit. PACS numbers: 74.25.Gz, 74.72.Jt I. INTRODUCTION Since the discovery of the high temperature supercon- ductors(HTSC) in the 1980’s, many experiments have been done to disclose the microscopic origin of high temperature superconductivity. For example, inelastic neutron scattering revealed a peculiar magnetic reso- nance mode at an energy of 41 meV in two-dimensional reciprocal lattice position (π,π) for optimally doped YBa2Cu3O6+x[1, 2]. The angle resolved photoemission spectroscopy (ARPES) has indicated a kink in the band dispersion as well