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

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

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

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

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

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

beta(1)-Adrenoreceptor Autoantibodies in Heart Failure Physiology and Therapeutic Implications

Antibodies that activate the β1-AR (β1-adrenoreceptor) can induce heart failure in animal models. These antibodies are often found in patients with heart failure secondary to varying etiologies. Their binding to the β1 receptor leads to prolonged receptor activation with subsequent induction of cellular dysfunction, apoptosis, and arrhythmias. β-blocker therapy while highly effective for heart failure, may not be sufficient treatment for patients who have β1 receptor autoantibodies. Removal of these autoantibodies by immunoadsorption has been shown to improve heart failure in small studies. However, immunoadsorption is costly, time consuming, and carries potential risks. An alternative to immunoadsorption is neutralization of autoantibodies through the intravenous application of small soluble molecules, such as peptides or aptamers, which specifically target and neutralize β1-AR autoantibodies. Peptides may induce immunogenicity. Animal as well as early phase human studies with aptamers have not shown safety concerns to date and have demonstrated effectiveness in reducing autoantibody levels. Novel aptamers have the potential advantage of having a wide spectrum of action, neutralizing a variety of known circulating G-protein coupled receptor autoantibodies. These aptamers, therefore, have the potential to be novel therapeutic option for patients with heart failure who have positive for β1-AR autoantibodies. However, clinical outcomes trials are needed to assess the clinical utility of this novel approach to treat heart failure

Proceedings of the 1st WSEAS International Conference on "Environmental and Geological Science and Engineering (EG'08)"

This book contains the proceedings of the 1st WSEAS International Conference on Environmental and Geological Science and Engineering (EG'08) which was held in Malta, September 11-13, 2008. This conference aims to disseminate the latest research and applications in Renewable Energy, Mineral Resources, Natural Hazards and Risks, Environmental Impact Assessment, Urban and Regional Planning Issues, Remote Sensing and GIS, and other relevant topics and applications. The friendliness and openness of the WSEAS conferences, adds to their ability to grow by constantly attracting young researchers. The WSEAS Conferences attract a large number of well-established and leading researchers in various areas of Science and Engineering as you can see from http://www.wseas.org/reports. Your feedback encourages the society to go ahead as you can see in http://www.worldses.org/feedback.htm The contents of this Book are also published in the CD-ROM Proceedings of the Conference. Both will be sent to the WSEAS collaborating indices after the conference: www.worldses.org/indexes In addition, papers of this book are permanently available to all the scientific community via the WSEAS E-Library. Expanded and enhanced versions of papers published in this conference proceedings are also going to be considered for possible publication in one of the WSEAS journals that participate in the major International Scientific Indices (Elsevier, Scopus, EI, ACM, Compendex, INSPEC, CSA .... see: www.worldses.org/indexes) these papers must be of high-quality (break-through work) and a new round of a very strict review will follow. (No additional fee will be required for the publication of the extended version in a journal). WSEAS has also collaboration with several other international publishers and all these excellent papers of this volume could be further improved, could be extended and could be enhanced for possible additional evaluation in one of the editions of these international publishers. Finally, we cordially thank all the people of WSEAS for their efforts to maintain the high scientific level of conferences, proceedings and journals

The Nature of Heavy Quasiparticles in Magnetically Ordered Heavy Fermions

The optical conductivity of the heavy fermions UPd2Al3 and UPt3 has been measured in the frequency range from 10 GHz to 1.2 THz (0.04 meV to 5 meV) at temperatures 1 K < T < 300 K. In both compounds a well pronounced pseudogap of less than a meV develops in the optical response at low temperatures; we relate this to the antiferromagnetic ordering. From the energy dependence of the effective electronic mass and scattering rate we derive the energies essential for the heavy quasiparticle. We find that the enhancement of the mass mainly occurs below the energy which is related to magnetic correlations between the local magnetic moments and the itinerant electrons. This implies that the magnetic order in these compounds is the pre-requisite to the formation of the heavy quasiparticle and eventually of superconductivity.Comment: RevTeX, 4 pages, 3 figures, email: [email protected]

Pseudogap Formation and Heavy Carrier Dynamics in Intermediate Valence YbAl3

Infrared optical conductivity [$\sigma(\omega)$] of the intermediate valence compound YbAl$_3$ has been measured at temperatures 8 K $\leq T \leq$ 690 K to study its microscopic electronic structures. Despite the highly metallic characters of YbAl$_3$, $\sigma(\omega)$ exhibits a clear pseudogap (strong depletion of spectral weight) of about 60 meV below 40 K. It also shows a strong mid-infrared peak centered at $\sim$ 0.25 eV. Energy-dependent effective mass and scattering rate of the carriers obtained from the data indicate the formation of a heavy-mass Fermi liquid state. These characteristic results are discussed in terms of the hybridization states between the Yb 4$f$ and the conduction electrons. It is argued, in particular, that the pseudogap and the mid-infrared peak result from the indirect and the direct gaps, respectively, within the hybridization state. band.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jp