다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

BoltzTraP. A code for calculating band-structure dependent quantities

日本物理学会誌及びJournal of the Physical Society of Japanの月刊について

Physical Review B

Herein we cover the key concepts in the field of thermoelectric materials research, present the current understanding, and show the latest developments. Current research is aimed at increasing the thermoelectric figure of merit (ZT) by maximizing the power factor and/or minimizing the thermal conductivity. Attempts at maximizing the power factor include the development of new materials, optimization of existing materials by doping, and the exploration of nanoscale materials. The minimization of the thermal conductivity can come through solid-solution alloying, use of materials with intrinsically low thermal conductivity, and nanostructuring. Herein we describe the most promising bulk materials with emphasis on results from the last decade. Single-phase bulk materials are discussed in terms of chemistry, crystal structure, physical properties, and optimization of thermoelectric performance. The new opportunities for enhanced performance bulk nanostructured composite materials are examined and a look into the not so distant future is attempted.

New and Old Concepts in Thermoelectric Materials

We show that LaFe4Sb12 is a ferromagnetic quantum critical point system and that CeFe4Sb12 is a moderate heavy fermion compound. This is supported by our thermoelectric and thermodynamic experiments under magnetic field on both compounds, and a comparison with other physical properties of these compounds. For LaFe4Sb12, the quenching of the ferromagnetic spin fluctuations explains both the negative magnetothermopower and the decrease in the electronic heat capacity under magnetic field. We propose that the negative magnetothermopower is a generic property of compounds with ferromagnetic spin fluctuations when the diffusion term by spin fluctuations dominates at low temperature. On the other hand these critical ferromagnetic fluctuations are smeared out in CeFe4Sb12 due to the antiferromagnetic coupling between the d electrons of Fe and the 4f electron of Ce. As a result, CeFe4Sb12 is a moderate heavy fermion compound with Kondo temperature TK of about 80 K, which is consistent with the fact that cerium is almost trivalent in this material, and the partially screened magnetic moment of the cerium ions at TTk is 0.3B. Finally, in both compounds, the power laws observed at low temperature in the lattice thermal conductivity l could be explained by electron-phonon scattering.

Thermoelectric properties of Ce(La)Fe4Sb12 skutterudites under a magnetic field

Strongly correlated electron systems are among the most active research topics in modern condensed matter physics. In strongly correlated materials the electron interaction energies dominate the electron kinetic energy which leads to unconventional properties. Heavy fermion compounds form one of the classes of such materials. In heavy fermion compounds the interaction of itinerant electrons with local magnetic moments generates quasiparticles with masses up to several 1000 electron masses. This may be accompanied by exciting properties, such as unconventional superconductivity in a magnetic environment, non-Fermi liquid behavior and quantum criticality. Strong electronic correlations are responsible for physical phenomena on a low energy scale. Consequently, these phenomena have to be studied at low temperatures. This, in turn, requires ultimate quality of single crystals to avoid that the low temperature intrinsic properties are covered by extrinsic effects due to off-stoichiometry, impurities or other crystal imperfections. The overwhelming majority of heavy fermion systems are cerium and ytterbium intermetallic compounds. In the present paper we discuss the crystal growth of three cerium compounds, Ce3Pd20Si6, CeRu4Sn6 and CeAuGe. Ce3Pd20Si6 undergoes an antiferromagnetic phase transition at low temperatures and shows a magnetic field induced quantum critical point [Takeda et al (1995), Strydom et al (2006)]. CeRu4Sn6 [Das & Sampathkumaran (1992)] appears to be a Kondo insulator [Aepli & Fisk (1992)] with a highly anisotropic energy gap. CeAuGe is one of a the few cerium compounds showing a ferromagnetic phase transition at low temperatures [Pottgen et al (1998), Mhlungu & Strydom (2008)]. This is of special interest in the context of quantum criticality, since the occurrence of quantum criticality on the verge of a ferromagnetic ground state is a subject of current debate. Much attention in this paper is paid to the problem of stoichiometry. Single crystals of intermetallic compounds are grown at high temperatures, which facilitates the formation of thermal defects realized often as deviation from the stoichiometric composition. Thermal instabilities of some intermetallic phases require the use of flux techniques, i.e., growth from off-stoichiometric melts, which is another source of non-stoichiometry. Sizeable non-stoichiometries can be detected by measuring the composition by chemical and physical analytical techniques, e.g. energy dispersive X-ray spectroscopy analysis (EDX). Tiny deviations from the stoichiometry, on the other hand, can be found only froman analysis of the physical properties of single crystals. Thus physical property measurements are not only the 11

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Crystal Growth and Stoichiometry of Strongly Correlated Intermetallic Cerium Compounds

In the heavy-fermion antiferromagnet YbRh 2 Si 2 pronounced non-Fermi-liquid behaviour is known to be related to the system being close to an antiferromagnetic quantum critical point (QCP). Using the magnetic field as a control parameter, YbRh 2 Si 2 may continuously be driven through a (field-induced) QCP. The evolution of the Fermi sea volume with field is of great interest since it may discriminate between different QCP scenarios. If Hall measurements are used to probe the Fermi sea volume, the anomalous Hall effect has to be separated from the normal one. In this contribution it is shown how this can be achieved for the initial Hall coefficient in YbRh 2 Si 2 .

Anomalous Hall effect in YbRh2Si2

Quantum criticality in cubic heavy fermion compounds remains much less explored than in quasi-two-dimensional systems. However, such materials are needed to broadly test the recently suggested global phase diagram for heavy fermion quantum criticality. Thus, to boost these activities, we review the field, with focus on Ce-based systems with temperature–magnetic field or temperature–pressure phase diagrams that may host a quantum critical point. To date, CeIn3 and Ce3Pd20Si6 are the only two among these compounds where quantum critical behavior has been systematically investigated. Interestingly, both show Fermi surface reconstructions as function of the magnetic field that may be understood in terms of Kondo destruction quantum criticality.

Ordered Phases and Quantum Criticality in Cubic Heavy Fermion Compounds

The ``failed Kondo insulator'' CeNiSn has long been suspected to be a nodal metal, with a node in the hybridization matrix elements. Here we carry out a series of Nernst effect experiments to delineate whether the severely anisotropic magnetotransport coefficients do indeed derive from a nodal metal or can simply be explained by a highly anisotropic Fermi surface. Our experiments reveal that despite an almost twentyfold anisotropy in the Hall conductivity, the large Nernst signal is isotropic. Taken in conjunction with the magnetotransport anisotropy, these results provide strong support for an isotropic Fermi surface with a large anisotropy in quasiparticle mass derived from a nodal hybridization.

Silke Paschen

Papers

Thermoelectric properties of Ce(La)Fe4Sb12 skutterudites under a magnetic field

Crystal Growth and Stoichiometry of Strongly Correlated Intermetallic Cerium Compounds

Anomalous Hall effect in YbRh2Si2

Ordered Phases and Quantum Criticality in Cubic Heavy Fermion Compounds

Giant Isotropic Nernst Effect in an Anisotropic Kondo Semimetal.