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.

Infrared reflection measurements of the half-filled two-dimensional organic conductors κ-(BEDT-TTF)2Cu[N(CN)2]BrxCl1−x were performed as a function of temperature (5 K < T < 300 K) and Br-substitution (x = 0%, 40%, 73%, 85%, and 90%) in order to study the metal-insulator transition. We can distinguish absorption processes due to itinerant and localized charge carriers. The broad mid-infrared absorption has two contributions: transitions between the two Hubbard bands and intradimer excitations from the charges localized on the (BEDT-TTF)2 dimer. Since the latter couple to intramolecular vibrations of BEDT-TTF, the analysis of both electronic and vibrational features provides a tool to disentangle these contributions and to follow their temperature and electronic-correlations dependence. Calculations based on the cluster model support our interpretation.

temperature. In contrast to the selenium analogs TMTSF which are one-dimensional metals, the sulfur salts are semiconductors with localized spins on the TMTTF dimers. Taking into account the thermal expansion of the crystals at high temperature (TϾ20 K) the ESR intensity of all sulfur compounds can be described as a spin-1/2 antiferromagnetic Heisenberg chain with exchange constants 420рJ р500 K. Although the TMTSF compounds are one-dimensional organic metals down to 10 K, the temperature dependence of the spin susceptibility can also be described within the framework of the Hubbard model in the limit of strong Coulomb repulsion with JϷ1400 K. By modeling (TMTTF) 2 ClO 4 as an alternating spin chain, the change of the alternation parameter at the first-order phase transition (T AO ϭ72.5 K) indicates a tetramerization of the chain. (TMTTF) 2 PF 6 undergoes a spin-Peierls transition at T SP ϭ19 K which can be well described by Bulaevskii's model with a singlet-triplet gap ⌬ (0)ϭ32.3 K. We find evidence of antiferromagnetic fluctuations at temperatures well above the magnetic ordering in (TMTTF) 2 Br, (TMTSF) 2 PF 6 , and (TMTSF) 2 AsF 6 which follow the critical behavior expected for three-dimensional ordering. (TMTTF) 2 PF 6 and (TMTTF) 2 Br show one-dimensional lattice fluctuations.

Charge ordering in the (TMTTF) 2 X salts with centrosymmetric anions (X = PF − 6 , AsF − 6 , SbF − 6 ) leads to a ferroelectric state around 100 K. For the first time and in great completeness, the intra-and intermolecular vibrational modes of (TMTTF) 2 X have been investigated by infrared and Raman spectroscopy as a function of temperature and pressure for different polarizations. In this original paper, we explore the development and amount of charge disproportionation and the coupling of the electronic degrees of freedom to the counterions and the underlying lattice. The methyl groups undergo changes with temperature that are crucial for the anion cage formed by them. We find that the coupling of the TMTTF molecules to the hexafluorine anions changes upon cooling and especially at the charge-order transition, indicating a distortion of the anion. Additional features are identified that are caused by the anharmonic potential. The spin-Peierls transition entails additional modifications in the charge distribution. To complete the discussion, we also add the vibrational frequencies and eigenvectors based on ab-initio quantum-chemical calculations.