Heavy fermion fluid in high magnetic fields: an infrared study of CeRu4_4Sb12_{12}

We report a comprehensive infrared magneto-spectroscopy study of CeRu$_4$Sb$_{12}$ compound revealing quasiparticles with heavy effective mass m$^*$, with a detailed analysis of optical constants in fields up to 17 T. We find that the applied magnetic field strongly affects the low energy excitations in the system. In particular, the magnitude of m$^*$ $\simeq$ 70 m$_b$ (m$_b$ is the quasiparticle band mass) at 10 K is suppressed by as much as 25 % at 17 T. This effect is in quantitative agreement with the mean-field solution of the periodic Anderson model augmented with a Zeeman term

Electronic Structure and Charge Dynamics of Huesler Alloy Fe2TiSn Probed by Infrared and Optical Spectroscopy

We report on the electrodynamics of a Heusler alloy Fe2TiSn probed over four decades in energy: from the far infrared to the ultraviolet. Our results do not support the suggestion of Kondo-lattice behavior inferred from specific heat measurements. Instead, we find a conventional Drude-like response of free carriers, with two additional absorption bands centered at around 0.1 and 0.87 eV. The latter feature can be interpreted as excitations across a pseudogap, in accord with band structure calculations.Comment: 3 pages, 4 figure

Pressure-tuning of the c-f hybridization in Yb metal detected by infrared spectroscopy up to 18 GPa

It has been known that the elemental Yb, a divalent metal at mbient pressure, becomes a mixed-valent metal under external pressure, with its valence reaching ~2.6 at 30 GPa. In this work, infrared spectroscopy has been used to probe the evolution of microscopic electronic states associated with the valence crossover in Yb at external pressures up to 18 GPa. The measured infrared reflectivity spectrum R(w) of Yb has shown large variations with pressure. In particular, R(w) develops a deep minimum in the mid-infrared, which shifts to lower energy with increasing pressure. The dip is attributed to optical absorption due to a conduction c-f electron hybridization state, similarly to those previously observed for heavy fermion compounds. The red shift of the dip indicates that the $c$-$f$ hybridization decreases with pressure, which is consistent with the increase of valence.Comment: 2 pages, to appear in J. Phys. Soc. Jpn. Supp

Strong-coupling Effects in cuprate High-TcT_{c} Superconductors by magnetooptical studies

Signatures of strong coupling effects in cuprate high-$T_{c}$ superconductors have been authenticated through a variety of spectroscopic probes. However, the microscopic nature of relevant excitations has not been agreed upon. Here we report on magneto-optical studies of the CuO$_{2}$ plane carrier dynamics in a prototypical high-$T_{c}$ superconductor YBa$$Cu$_{3}$O$_{y}$ (YBCO). Infrared data are directly compared with earlier inelastic neutron scattering results by Dai \textit{et al}. [Nature (London) \textbf{406}, 965 (2000)] revealing a characteristic depression of the magnetic resonance in H $\parallel$ \textit{c} field less than 7 T. This analysis has allowed us to critically assess the role of magnetic degrees of freedom in producing strong coupling effects for YBCO system.Comment: 4 pages, two figure

The Missing Link: Magnetism and Superconductivity

The effect of magnetic moments on superconductivity has long been a controversial subject in condensed matter physics. While Matthias and collaborators experimentally demonstrated the destruction of superconductivity in La by the addition of magnetic moments (Gd), it has since been suggested that magnetic fluctuations are in fact responsible for the development of superconducting order in other systems. Currently this debate is focused on several families of unconventional superconductors including high-Tc cuprates, borocarbides as well as heavy fermion systems where magnetism and superconductivity are known to coexist. Here we report a novel aspect of competition and coexistence of these two competing orders in an interesting class of heavy fermion compounds, namely the 1-1-5 series: CeTIn5 where T=Co, Ir, or Rh. Our optical experiments indicate the existence of regions in momentum space where local moments remain unscreened. The extent of these regions in momentum space appears to control both the normal and superconducting state properties in the 1-1-5 family of heavy fermion (HF) superconductors.Comment: 6 pages, 2 figure

Infrared probe of the anomalous magnetotransport of highly oriented pyrolytic graphite in the extreme quantum limit

We present a systematic investigation of the magnetoreflectance of highly oriented pyrolytic graphite in magnetic field B up to 18 T . From these measurements, we report the determination of lifetimes tau associated with the lowest Landau levels in the quantum limit. We find a linear field dependence for inverse lifetime 1/tau(B) of the lowest Landau levels, which is consistent with the hypothesis of a three-dimensional (3D) to 1D crossover in an anisotropic 3D metal in the quantum limit. This enigmatic result uncovers the origin of the anomalous linear in-plane magnetoresistance observed both in bulk graphite and recently in mesoscopic graphite samples

Dysprosium-carboxylate nanomeshes with tunable cavity size and assembly motif through ionic interactions

We report the design of dysprosium directed metallo-supramolecular architectures on a pristine Cu(111) surface. By an appropriate selection of the ditopic molecular linkers equipped with terminal carboxylic groups (TPA, PDA and TDA species), we create reticular and mononuclear metal–organic nanomeshes of tunable internodal distance, which are stabilized by eight-fold Dy⋯O interactions. A thermal annealing treatment for the reticular Dy:TDA architecture gives rise to an unprecedented quasi-hexagonal nanostructure based on dinuclear Dy clusters, exhibiting a unique six-fold Dy⋯O bonding motif. All metallo-supramolecular architectures are stable at room temperature. Our results open new avenues for the engineering of supramolecular architectures on surfaces incorporating f-block elements forming thermally robust nanoarchitectures through ionic bonds

Calculation of Optical Conductivity, Resistivity and Thermopower of Filled Skutterudite CeRu4_4Sb12_{12} based on a Realistic Tight-binding Model with Strong Correlation

The filled-skutterudite compound CeRu$_4$Sb$_{12}$ shows a pseudo-gap structure in the optical conductivity spectra similar to the Kondo insulators, but metallic behavior below 80 K. The resistivity shows a large peak at 80 K, and the Seebeck coefficient is positive and also shows a large peak at nearly the same temperature. In order to explain all these features, a simplified tight-binding model, which captures the essential features of the band calculation, is proposed. Using this model and introducing the correlation effect within the framework of the dynamical mean field approximation and the iterative perturbation theory, the temperature dependences of the optical conductivity, resistivity and the Seebeck coefficient are calculated, which can explain the experiments.Comment: 4 pages, 6 figure

Optical and thermodynamic properties of the high-temperature superconductor HgBa_2CuO_4+delta

In- and out-of-plane optical spectra and specific heat measurements for the single layer cuprate superconductor Hg-1201 at optimal doping (Tc = 97 K) are presented. Both the in-plane and out-of-plane superfluid density agree well with a recently proposed scaling relation rho_{s}=sigma_{dc}T_{c}. It is shown that there is a superconductivity induced increase of the in-plane low frequency spectral weight which follows the trend found in underdoped and optimally doped Bi-2212 and optimally doped Bi-2223. We observe an increase of optical spectral weight which corresponds to a change in kinetic energy of approximately 0.5 meV/Cu which is more than enough to explain the condensation energy. The specific heat anomaly is 10 times smaller than in YBCO and 3 times smaller than in Bi-2212. The shape of the anomaly is similar to the one observed in YBCO showing that the superconducting transition is governed by thermal fluctuations.Comment: 11 pages, 13 figure