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

The recent excitement about Dirac and Weyl fermion systems has renewed interest in magnetotransport properties of multicarrier systems. However, the complexity of their analysis, even in the simplest two-carrier case, has hampered a good understanding of the underlying phenomena. Here we propose a new analysis scheme for two independent conduction channels, that strongly reduces previous ambiguities and allows one to draw robust conclusions. This is demonstrated explicitly for the example of three-dimensional topological insulators. Their temperature and gate voltage-dependent Hall coefficient and transverse magnetoresistance behavior, including the phenomenon of huge linear transverse magnetoresistance, can be traced back to two conduction channels, with fully determined carrier concentrations and mobilities. We further derive an upper limit for the transverse magnetoresistance. Its violation implies field dependencies in the electronic band structure or scattering processes, or the presence of more than two effective carrier types. Remarkably, none of the three-dimensional topological insulators or semimetals with particularly large transverse magnetoresistance violates this limit.

Robust scheme for magnetotransport analysis in topological insulators

Intermetallic clathrates are promising materials for thermoelectric applications This is not only due to their low thermal and high electrical conductivities (“phonon glass – electron crystal”) but also due to the expectation that they are semiconductors and thus have large thermopower values Band structure calculations of the stoichiometric compound Eu8Ga16Ge30 indeed yield a semiconducting ground state However, with conventional synthesis methods the exact 8:16:30 stoichiometry could not be reached Herein we use the melt-spinning technique to obtain Eu8Ga16–xGe30+x samples with smaller x than previously realized The quenching procedure and the results of the characterization of the quenched phases by X-ray powder diffraction and electron microscopy are presented The electrical resistivity shows that, in contrast to conventional synthesis procedures, semiconducting compounds can be produced

Melt‐spun Eu8Ga16–xGe30+x Clathrates

Quantum criticality beyond the Landau paradigm represents a fundamental problem in condensed matter and statistical physics. Heavy fermion systems with multipolar degrees of freedom can play an important role in the search for its universal description. We consider a Kondo lattice model with both spin and quadrupole degrees of freedom, which we show to exhibit an antiferroquadrupolar phase. Using a field theoretical representation of the model, we find that Kondo couplings are exactly marginal in the renormalization group sense in this phase. This contrasts with the relevant nature of the Kondo couplings in the paramagnetic phase and, as such, it implies that a Kondo destruction and a concomitant small to large Fermi surface jump must occur as the system is tuned from the antiferroquadrupolar ordered to the paramagnetic phase. Implications of our results for multipolar heavy fermion physics in particular and metallic quantum criticality in general are discussed.

Kondo Destruction and Multipolar Order-- Implications for Heavy Fermion Quantum Criticality.

The thermal conductivityl of EuB6 has been measured in the temperature range between 0.4 and 50 K. In this temperature regime the thermal conductivity is mainly due to phonons. A broad maximum with a relatively large absolute value of about 50 W/Km is observed at 17 K. Below this temperature the thermal conductivity follows a T behavior, which may be attributed to phonon-electron scattering. At temperatures above 17 K a surprisingly weakT dependence of l is observed which we relate to the peculiar phonon dispersion relation of divalent hexaborides.

Thermal conductivity of EuB 6

We have performed 63Cu, 65Cu, and 137Ba NMR on Ba8Cu5SixGe41−x, a series of intermetallic clathrates known for their potential as thermoelectric materials, in order to investigate the electronic behavior of the samples. The spectra and spin–lattice relaxation times were measured at 77 K and 290 K for the entire composition range 0 ≤ x ≤ 41. Magnetic and quadrupole shifts and relaxation rates of the Cu NMR data were extracted, and thereby carrier-induced metallic contributions identified. The observed shifts change in a nonlinear way with increasing Si substitution: from x = 0 to about 20 the shifts are essentially constant, while approaching x = 41 they increase rapidly. At the same time, Ba NMR data indicate greater Ba-site participation in the conduction band in Ba8Cu5Si41 than in Ba8Cu5Ge41. The results indicate surprisingly little change in electronic features vs. Si content for most of the composition range, while Ba8Cu5Si41 exhibits enhanced hybridization and a more metallic framework than Ba8Cu5Ge41.

Silke Paschen

Papers

Robust scheme for magnetotransport analysis in topological insulators

Melt‐spun Eu8Ga16–xGe30+x Clathrates

Kondo Destruction and Multipolar Order-- Implications for Heavy Fermion Quantum Criticality.

Thermal conductivity of EuB 6

NMR study of Ba8Cu5Si(x)Ge(41-x) clathrate semiconductors.