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

Electron correlations amplify quantum fluctuations and, as such, are recognized as the origin of many quantum phases. However, whether strong correlations can lead to gapless topological states is an outstanding question, in part because many of the ideas in topological condensed-matter physics rely on the analysis of an effectively non-interacting band structure. Therefore, a framework that allows the identification of strongly correlated topological materials is needed. Here we suggest a general approach in which strong correlations cooperate with crystalline symmetry to drive gapless topological states. We test this materials design principle by exploring Kondo lattice models and materials whose space-group symmetries promote different kinds of electronic degeneracies. This approach allows us to identify Weyl–Kondo nodal-line semimetals with nodes pinned to the Fermi energy, demonstrating that it can be applied to discover strongly correlated topological semimetals. We identify three heavy-fermion compounds as material candidates, provide direct experimental evidence for our prediction in Ce2Au3In5 and discuss how our approach may lead to many more. Our findings illustrate the potential of this materials design principle to guide the search for new topological metals in a broad range of strongly correlated systems. Strongly correlated topological materials are hard to identify. Now a design principle suggests a method for producing many topological metals where strong electron–electron interactions are a driving force. 

Topological semimetal driven by strong correlations and crystalline symmetry

There is considerable interest in the intersection of correlations and topology, especially in metallic systems. Among the outstanding questions are how strong correlations drive novel topological states and whether such states can be readily controlled. Here we study the effect of a Zeeman coupling on a Weyl-Kondo semimetal in a nonsymmorphic and noncentrosymmetric Kondo-lattice model. A sequence of distinct and topologically nontrivial semimetal regimes are found, each containing Kondo-driven and Fermi-energy-bound Weyl nodes. The nodes annihilate at a magnetic field that is smaller than what it takes to suppress the Kondo effect. As such, we demonstrate an extreme topological tunability that is isolated from the tuning of the strong correlations per se. Our results are important for experiments in strongly correlated systems, and set the stage for mapping out a global phase diagram for strongly correlated topology.

Extreme topological tunability of Weyl-Kondo semimetal to Zeeman coupling

The compound Ce4Pt12Sn25 has a rather complex cubic crystal structure in which the Ce atoms are encapsulated in cages of Pt and Sn resulting in a large Ce-Ce distance. Recently, specific heat and magnetic susceptibility measurements revealed a phase transition from a paramagnetic to an antiferromagnetic (AFM) ground state with a low Neel temperature of TN = 0.19K. Application of a magnetic field was shown to weaken the AFM phase and ultimately suppress it at a critical field of 0.7 T. Here we investigate the observed antiferromagnetic phase transition by electrical resistivity measurements in applied magnetic fields in the vicinity of this field-tuned quantum critical point.

https://iopscience.iop.org/article/10.1088/1742-6596/391/1/012036/pdf

Low-temperature electrical resistivity of antiferromagnetic Ce4Pt12Sn25

Crystalline solids are generally known as excellent heat conductors, amorphous materials or glasses as thermal insulators. It has thus come as a surprise that certain crystal structures defy this paradigm. A prominent example are type-I clathrates and other materials with guest-host structures. They sustain low-energy Einstein-like modes in their phonon spectra, but are also prone to various types of disorder and phonon-electron scattering and thus the mechanism responsible for their ultralow thermal conductivities has remained elusive. While recent ab initio lattice dynamics simulations show that the Einstein-like modes enhance phonon-phonon Umklapp scattering, they reproduce experimental data only at low temperatures. Here we show that a new effect, an "all phononic Kondo effect", can resolve this discrepancy. This is evidenced by our thermodynamic and transport measurements on various clathrate single crystal series and their comparison with ab initio simulations. Our new understanding devises design strategies to further suppress the thermal conductivity of clathrates and other related materials classes, with relevance for the field of thermoelectric waste heat recovery but also more generally for phononic applications. More fundamentally, it may trigger theoretical work on strong correlation effects in phonon systems.

/pdf/kondo-like-phonon-scattering-in-thermoelectric-clathrates-4mm49ncdmc.pdf

Kondo-like phonon scattering in thermoelectric clathrates

Shot noise measures out-of-equilibrium current ﬂuctuations and is a powerful tool to probe the nature of current-carrying excitations in quantum systems. Recent shot noise measurements in the heavy fermion strange metal YbRh 2 Si 2 exhibit a strong suppression of the Fano factor ( F ) – the ratio of the current noise to the average current in the DC limit. This system is representative of metals in which electron correlations are extremely strong. Here we carry out the ﬁrst theoretical study on the shot noise of diﬀusive metals in the regime of strong correlations. A Boltzmann-Langevin equation formulation is constructed in a quasiparticle description in the presence of strong correlations. We ﬁnd that F = √ 3 / 4 in such a correlation regime. Hence, the Fano factor suppression observed in experiments on YbRh 2 Si 2 necessitates a loss of the quasiparticles. Our work opens the door to systematic theoretical studies of shot noise as a means of characterizing strongly correlated metallic phases and materials.

Silke Paschen

Papers

Topological semimetal driven by strong correlations and crystalline symmetry

Extreme topological tunability of Weyl-Kondo semimetal to Zeeman coupling

Low-temperature electrical resistivity of antiferromagnetic Ce4Pt12Sn25

Kondo-like phonon scattering in thermoelectric clathrates

Shot noise as a characterization of strongly correlated metals