Optical studies of weak-ferromagnetic superconductors RuSr2RCu2O8 (R = Gd, Eu, Sm, and Nd)

• Main Author: 郭俐吟
• Other Authors: 劉祥麟
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/6z6g95

碩士 === 國立臺灣師範大學 === 物理學系 === 96 === We study the optical properties of weak-ferromagnetic superconductor system RuSr2RCu2O8 (R = Gd, Eu, Sm, and Nd). The room-temperature Raman spectrum of RuSr2GdCu2O8 is similar to the reported results [Physica C 341, 2209 (2000)]. When replaced with larger rare earth ions (R = Eu, Sm, and Nd) on Gd, the frequencies of A1g(5) and A1g(6) Raman-active phonons show a shift of the peak position to lower frequencies and their linewidths are broadening, which is mainly due to the expansion effects of the unit cell volume. The optical reflectance spectra of RuSr2RCu2O8 (R = Gd, Eu, Sm, and Nd) were measured between 10 and 340 K. At room temperature, the spectra of RuSr2RCu2O8 (R = Gd, Eu, and Sm) show the characteristics of metallic behavior at low frequencies with Drude response. With decreasing temperature, the phonon modes at about 638 cm-1 in RuSr2GdCu2O8 and 656 cm-1 in RuSr2EuCu2O8 harden and become narrowing. On the contrary, the frequencies of infrared-active phonon modes at about 346, 583, and 648 cm-1 in RuSr2NdCu2O8 shift toward lower frequency, which may be attributed to a strong spin-phonon interaction or a local lattice distortion. In the superconducting state, a partial sum-rule evaluation of the effective number of carriers from the optical conductivity indicates that the values of London penetration depth (λL) of RuSr2GdCu2O8 and RuSr2EuCu2O8 are about 9410 and 23805 Å, respectively.