Masayuki Ochi

Temperature-Induced Lifshitz Transition in WTe2.

We use ultrahigh resolution, tunable, vacuum ultraviolet laser-based, angle-resolved photoemission spectroscopy (ARPES), temperature- and field-dependent resistivity, and thermoelectric power (TEP) measurements to study the electronic properties of WTe2, a compound that manifests exceptionally large, temperature-dependent magnetoresistance. The Fermi surface consists of two pairs of electron and two pairs of hole pockets along the X-Γ-X direction. Using detailed ARPES temperature scans, we find a rare example of a temperature-induced Lifshitz transition at T≃160  K, associated with the complete disappearance of the hole pockets. Our electronic structure calculations show a clear and substantial shift of the chemical potential μ(T) due to the semimetal nature of this material driven by modest changes in temperature. This change of Fermi surface topology is also corroborated by the temperature dependence of the TEP that shows a change of slope at T≈175  K and a breakdown of Kohlers rule in the 70-140 K range. Our results and the mechanisms driving the Lifshitz transition and transport anomalies are relevant to other systems, such as pnictides, 3D Dirac semimetals, and Weyl semimetals.

Evidence for magnetic Weyl fermions in a correlated metal

Weyl fermions have been observed as three-dimensional, gapless topological excitations in weakly correlated, inversion-symmetry-breaking semimetals. However, their realization in spontaneously time-reversal-symmetry-breaking phases of strongly correlated materials has so far remained hypothetical. Here, we report experimental evidence for magnetic Weyl fermions in Mn3Sn, a non-collinear antiferromagnet that exhibits a large anomalous Hall effect, even at room temperature. Detailed comparison between angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory (DFT) calculations reveals significant bandwidth renormalization and damping effects due to the strong correlation among Mn 3d electrons. Magnetotransport measurements provide strong evidence for the chiral anomaly of Weyl fermions-namely, the emergence of positive magnetoconductance only in the presence of parallel electric and magnetic fields. Since weak magnetic fields (approximately 10 mT) are adequate to control the distribution of Weyl points and the large fictitious fields (equivalent to approximately a few hundred T) produced by them in momentum space, our discovery lays the foundation for a new field of science and technology involving the magnetic Weyl excitations of strongly correlated electron systems such as Mn3Sn.

Acoustic radiation force on a solid elastic sphere in a spherical wave field

The acoustic radiation force on a homogeneous solid sphere placed freely in a spherical sound field in an inviscid fluid is calculated; the effect of the elasticity of the sphere material is studied. Calculated results are presented for a variety of solid spheres in water. Quite distinctive resonance departures from the rigid sphere solution are found.

Cluster multipole theory for anomalous Hall effect in antiferromagnets

Here, the authors discover a missing link between antiferromagnetism and the Hall effect by introducing a theoretical framework based on a novel concept, cluster multipole (CMP), to characterize macroscopic magnetization of antiferromagnets. Whereas the anomalous Hall effect (AHE) is usually observed in ferromagnets and explained as an outcome of the macroscopic dipole magnetization, CMP theory reveals that a certain type of antiferromagnetic (AFM) structure induces the AHE despite no net magnetization. The new order parameters enable us to characterize the AHE in the AFM states and explain the AHE in the AFM states of Mn

High antiferromagnetic transition temperature of a honeycomb compound SrRu2O6

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Temperature- and doping-dependent roles of valleys in the thermoelectric performance of SnSe: A first-principles study

Ir and Mn

Efficient algorithm of the transcorrelated method for periodic systems

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Acoustic radiation pressure on a rigid sphere in a spherical wave field

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Optimization of the Jastrow factor using the random-phase approximation and a similarity-transformed Hamiltonian: Application to band-structure calculation for some semiconductors and insulators

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Strain-induced topological transition in SrRu2O6 and CaOs2O6

= Sn, Ge), for which the large AHE has recently been studied. Furthermore, the theory can deal with the AHE in antiferromagnets on an equal footing with that in simple ferromagnets. The authors compare the AHE in antiferromagnetic Mn