J. J. McGuire

Gap in the infrared response of HgBa 2 Ca 2 Cu 3 O 8 + δ

The ab-plane optical spectra of one underdoped and one nearly optimally doped single crystal of HgBa_2Ca_2Cu_3O_{8+delta} were investigated in the frequency range from 40 to 40,000 cm^-1. The frequency dependent scattering rate was obtained by Kramers Kronig analysis of the reflectance. Both crystals have a scattering rate gap of about 1000 cm^-1 which is much larger than the 700 cm^-1 gap seen in optical studies of several cuprates with maximum Tc around 93 K. There appears to be a universal scaling between scattering rate gap and maximum Tc for the cuprate superconductors.

Infrared and optical properties of pure and cobalt-doped LuNi 2 B 2 C

We present optical conductivity data for Lu(Ni 1 - x Co x ) 2 B 2 C over a wide range of frequencies and temperatures for x = 0 and 0.09. Both materials show evidence of being good Drude metals with the infrared data in reasonable agreement with dc resistivity measurements at low frequencies. An absorption threshold is seen at approximately 700 cm - 1 . In the cobalt-doped material, we see a superconducting gap in the conductivity spectrum with an absorption onset at 24′2 cm - 1 = 3.9′0.4k B T, suggestive of weak to moderately strong coupling. The pure material is in the clean limit and no gap can be seen. We discuss the data in terms of the electron-phonon interaction and find that it can be fit below 600 cm - 1 with a plasma frequency of 3.3 eV and an electron-phoon coupling constant λ t r = 0.33 using an α 2 F(ω) spectrum fit to the resistivity.

Incoherent interplane conductivity ofκ−(BEDT−TTF)2Cu[N(CN)2]Br

The interplane optical spectrum of the organic superconductor kappa-(BEDT-TTF)2Cu[N(CN)2]Br was investigated in the frequency range from 40 to 40,000 cm-1. The optical conductivity was obtained by Kramers-Kronig analysis of the reflectance. The absence of a Drude peak at low frequency is consistent with incoherent conductivity but in apparent contradiction to the metallic temperature dependence of the DC resistivity. We set an upper limit to the interplane transfer integral of tb = 0.1 meV. A model of defect-assisted interplane transport can account for this discrepancy. We also assign the phonon lines in the conductivity to the asymmetric modes of the ET molecule.

Incoherent interplane conductivity of {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br

The interplane optical spectrum of the organic superconductor kappa-(BEDT-TTF)2Cu[N(CN)2]Br was investigated in the frequency range from 40 to 40,000 cm-1. The optical conductivity was obtained by Kramers-Kronig analysis of the reflectance. The absence of a Drude peak at low frequency is consistent with incoherent conductivity but in apparent contradiction to the metallic temperature dependence of the DC resistivity. We set an upper limit to the interplane transfer integral of tb = 0.1 meV. A model of defect-assisted interplane transport can account for this discrepancy. We also assign the phonon lines in the conductivity to the asymmetric modes of the ET molecule.

Incoherent Interplane Conductivity of kappa-(BEDT-TTF)2Cu[N(CN)2]Br

The interplane optical spectrum of the organic superconductor kappa-(BEDT-TTF)2Cu[N(CN)2]Br was investigated in the frequency range from 40 to 40,000 cm-1. The optical conductivity was obtained by Kramers-Kronig analysis of the reflectance. The absence of a Drude peak at low frequency is consistent with incoherent conductivity but in apparent contradiction to the metallic temperature dependence of the DC resistivity. We set an upper limit to the interplane transfer integral of tb = 0.1 meV. A model of defect-assisted interplane transport can account for this discrepancy. We also assign the phonon lines in the conductivity to the asymmetric modes of the ET molecule.