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

Some of the highest-transition-temperature superconductors across various materials classes exhibit linear-in-temperature `strange metal' or `Planckian' electrical resistivities in their normal state. It is thus believed by many that this behavior holds the key to unlock the secrets of high-temperature superconductivity. However, these materials typically display complex phase diagrams governed by various competing energy scales, making an unambiguous identification of the physics at play difficult. Here we use electrical resistivity measurements into the micro-Kelvin regime to discover superconductivity condensing out of an extreme strange metal state -- with linear resistivity over 3.5 orders of magnitude in temperature. We propose that the Cooper pairing is mediated by the modes associated with a recently evidenced dynamical charge localization-delocalization transition, a mechanism that may well be pertinent also in other strange metal superconductors.

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Superconductivity in an extreme strange metal

Ni2+–Fe3+ cyanometallate structures covalently embedded in silica: Influence of the blocking ligand at Ni2+

Magnetically hidden order is a hypernym for electronic ordering phenomena that are visible to macroscopic thermodynamic probes but whose microscopic symmetry cannot be revealed with conventional neutron or x-ray diffraction. In a handful of f -electron systems, the ordering of odd-rank multipoles leads to order parameters with a vanishing neutron cross-section. Among them, Ce 3 Pd 20 Si 6 is known for its unique phase diagram exhibiting two distinct multipolar-ordered ground states (phases II and II (cid:48) ), separated by a ﬁeld-driven quantum phase transition associated with a putative change in the ordered quadrupolar moment from O 02 to O xy . Using torque magnetometry at subkelvin temperatures, here we ﬁnd another phase transition at higher ﬁelds above 12 T, which appears only for low-symmetry magnetic ﬁeld directions B (cid:107) (cid:104) 11 L (cid:105) with 1 < L ≤ 2. While the order parameter of this new phase II (cid:48)(cid:48) remains unknown, the discovery renders Ce 3 Pd 20 Si 6 a unique material with two ﬁeld-driven phase transitions between distinct multipolar phases. They are both clearly manifested in the magnetic-ﬁeld dependence of the ﬁeld-induced ( 111 ) Bragg intensities measured with neutron scattering for B (cid:107) [ 112 ] . We also ﬁnd from inelastic neutron scattering that the number of nondegenerate collective excitations induced by the magnetic ﬁeld correlates with the number of phases in the magnetic phase diagram for the same ﬁeld direction. Furthermore, the magnetic excitation spectrum suggests that the new phase II (cid:48)(cid:48) may have a different propagation vector, revealed by the minimum in the dispersion that may represent the Goldstone mode of this hidden-order phase.

Cascade of magnetic-field-driven quantum phase transitions in Ce3Pd20Si6

The newly‐discovered clathrates Ba6Ge25 and its relatives consist of a rigidG ermanium framework, in which Barium or other metallic atoms are trapped. These ‘guest’ atoms can ‘rattle’ freely in the oversized cages at high temperature. In Ba6Ge25, some of Ba atoms aref rozen into the split positions randomly below 200 K. This structural phase transition results in a two‐step resistivity jump from metallic behavior to semiconductor‐like behavior characterized by a mean free path of 3A. Surprisingly, a BCS‐like superconducting transition occursa t Tc ≈ 0.24 K in such a ‘bad metal’. By applying hydrostatic pressure, the structural phase transition is suppressed but Tc increases drastically. Tc reaches a maximum value of 3.85K at a critical pressure pc ≈ 2.8 GPa, where the structural distortion is completely suppressed and the system exhibits metallic behavior over the whole temperature range. Higher pressures lead to a slight decrease of Tc. On replacing 1/3 of the Ba atoms with Na, no structural phase transi...

The Novel Superconducting Clathrates: Ba6Ge25 and Na2Ba4Ge25

YbRh2Si2 is a model system for quantum criticality. Particularly, Hall effect measurements helped identify the unconventional nature of its quantum critical point. Here, we present a high-resolution study of the Hall effect and magnetoresistivity on samples of different quality. We find a robust crossover on top of a sample dependent linear background contribution. Our detailed analysis provides a complete characterization of the crossover in terms of its position, width, and height. Importantly, we find in the extrapolation to zero temperature a discontinuity of the Hall coefficient occurring at the quantum critical point for all samples. Particularly, the height of the jump in the Hall coefficient remains finite in the limit of zero temperature. Hence, our data solidify the conclusion of a collapsing Fermi surface. Finally, we contrast our results to the smooth Hall-effect evolution seen in Chromium, the prototype system for a spin-density-wave quantum critical point.

Silke Paschen

Papers

Superconductivity in an extreme strange metal

Ni2+–Fe3+ cyanometallate structures covalently embedded in silica: Influence of the blocking ligand at Ni2+

Cascade of magnetic-field-driven quantum phase transitions in Ce3Pd20Si6

The Novel Superconducting Clathrates: Ba6Ge25 and Na2Ba4Ge25

Discontinuous Hall coefficient at the quantum critical point in YbRh2Si2