The reflectivity of seven Nd2-xCexCuO4 single crystals has been measured at room temperature between 0.005 and 3 eV for 0 less-than-or-equal-to x less-than-or-equal-to 0.21. At x = 0, four transverse and longitudinal E(u) phonon modes have been determined. Two bands have been also identified at 1.6 eV and at 2.8 eV, which lose their intensity with doping. Such intensity is transferred to the well-known Drude and midinfrared contributions, and to a band at approximately 0.1 eV, which can be attributed to oxygen vacancies. At the insulator-to-metal transition, the Drude term abruptly increases, the 1.6-eV band vanishes. An overall strong similarity with the closing of the optical gap in highly doped semiconductors, is found. The reflectivity of a reduced sample with x = 0.07 suggests that the midinfrared band may not originate from oxygen vacancy states. Present results are compared with predictions of different theoretical models.
INFRARED OPTICAL CONDUCTIVITY OF THE ND-CE-CU-O SYSTEM / Lupi, Stefano; Calvani, Paolo; Capizzi, Mario; Maselli, Paola; W., Sadowski; E., Walker. - In: PHYSICAL REVIEW. B, CONDENSED MATTER. - ISSN 0163-1829. - STAMPA. - 45:21(1992), pp. 12470-12477. [10.1103/physrevb.45.12470]
INFRARED OPTICAL CONDUCTIVITY OF THE ND-CE-CU-O SYSTEM
LUPI, Stefano;CALVANI, Paolo;CAPIZZI, Mario;MASELLI, Paola;
1992
Abstract
The reflectivity of seven Nd2-xCexCuO4 single crystals has been measured at room temperature between 0.005 and 3 eV for 0 less-than-or-equal-to x less-than-or-equal-to 0.21. At x = 0, four transverse and longitudinal E(u) phonon modes have been determined. Two bands have been also identified at 1.6 eV and at 2.8 eV, which lose their intensity with doping. Such intensity is transferred to the well-known Drude and midinfrared contributions, and to a band at approximately 0.1 eV, which can be attributed to oxygen vacancies. At the insulator-to-metal transition, the Drude term abruptly increases, the 1.6-eV band vanishes. An overall strong similarity with the closing of the optical gap in highly doped semiconductors, is found. The reflectivity of a reduced sample with x = 0.07 suggests that the midinfrared band may not originate from oxygen vacancy states. Present results are compared with predictions of different theoretical models.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.