We report on the detailed analysis of the infrared (IR) conductivity of two prototypical high-Tc systems YBa2Cu3Oy and La2−xSrxCuO4 throughout the complex phase diagram of these compounds. Our focus in this work is to thoroughly document the electromagnetic response of the nodal metal state which is initiated with only few holes doped in parent antiferromagnetic systems and extends up to the pseudogap boundary in the phase diagram. The key signature of the nodal metal is the two-component conductivity: the Drude mode at low energies followed by a resonance in mid-IR. The Drude component can be attributed to the response of coherent quasiparticles residing on the Fermi arcs detected in photoemission experiments. The microscopic origin of the mid-IR band is yet to be understood. A combination of transport and IR data uncovers fingerprints of the Fermi liquid behavior in the response of the nodal metal. The comprehensive nature of the data sets presented in this work allows us to critically re-evaluate common approaches to the interpretation of the optical data. Specifically we re-examine the role of magnetic excitations in generating electronic self energy effects through the analysis of the IR data in high magnetic field.

We investigate the hole dynamics in two prototypical high temperature superconducting systems: La2−xSrxCuO4 and YBa2Cu3Oy using a combination of DC transport and infrared spectroscopy. By exploring the effective spectral weight obtained with optics in conjunction with DC Hall results we find that the transition to the Mott insulating state in these systems is of the "vanishing carrier number" type since we observe no substantial enhancement of the mass as one proceeds to undoped phases. Further, the effective mass remains constant across the entire underdoped regime of the phase diagram. We discuss the implications of these results for the understanding of both transport phenomena and pairing mechanism in high-Tc systems.PACS numbers: 74.25. Gz, 74.25.Kc, 74.72.Dn At zero temperature in a Mott-Hubbard (MH) insulator, carriers are localized due to strong electron-electron interactions. In some systems long range antiferromagnetic (AF) order is favored due to superexchange.

We investigate near-field infrared spectroscopy and superfluid polariton imaging experiments on conventional and unconventional superconductors. Our modeling shows that near-field spectroscopy can measure the magnitude of the superconducting energy gap in Bardeen-Cooper-Schrieffer-like superconductors with nanoscale spatial resolution. We demonstrate how the same technique can measure the c-axis plasma frequency, and thus the c-axis superfluid density, of layered unconventional superconductors with a similar spatial resolution. Our modeling also shows that near-field techniques can image superfluid surface mode interference patterns near physical and electronic boundaries. We describe how these images can be used to extract the collective mode dispersion of anisotropic superconductors with sub-diffractional spatial resolution.

We investigated the electronic structures of the two-dimensional layered perovskite Sr 2 MO 4 (M=4d Ru, 4d Rh, and 5d Ir) using optical spectroscopy and polarizationdependent O 1s x-ray absorption spectroscopy. While the ground states of the series of compounds are rather different, their optical conductivity spectra σ(ω) exhibit similar interband transitions, indicative of the common electronic structures of the 4d and 5d layered oxides. layered compounds because of the potential to discover novel phenomena. 4The electronic structures of 4d and 5d layered TMO should be quite different from those of 3d TMO. For a 3d TMO, the Hund coupling energy J H (~3 eV) is much larger than the crystal field splitting 10Dq (1-2 eV) between the t 2g and e g states. 5,6 For example, the electronic structure of LaSrMnO 4 (a 3d 4 system) with a high spin configuration is drawn schematically in Fig. 1(a). 5,6 The exchange splitting of the e g states is sufficiently large to place the e g ↑ band below the t 2g ↓ band. -y 2 ), and this value is typically about 1 eV. Since most interband transitions are very broad, this e g orbital splitting is barely observed in the optical conductivity spectra σ(ω).In contrast, for 4d and 5d TMO, the crystal field splitting should be larger than the 3 exchange splitting due to the extended nature of the 4d and 5d orbitals. Therefore, they are usually in the low spin configuration, in which all of the t 2g bands are lower than the e g bands. According to recent x-ray absorption spectroscopy (XAS) studies on the Ca 2- Fig. 1(b In this paper, we report the optical conductivity spectra σ(ω) and polarizationdependent O 1s XAS data for Sr 2 MO 4 (M=Ru, Rh, and Ir). The optical spectra showed three charge transfer transitions in the energy region between 0 and 8 eV with a systematic trend with M. By comparing σ(ω) with the XAS spectra, we could determine the electronic structures of Sr 2 MO 4 . In particular, we found that the splitting of the e g orbitals due to the elongation of the MO 6 octahedra along the c-axis is quite large, about 2 eV. We also discuss the low energy optical responses of Sr 2 MO 4 in relation to their ground states.