Two-Dimensional Cobalt(II) Benzoquinone Frameworks for Putative Kitaev Quantum Spin Liquid Candidates.

The realization and discovery of quantum spin liquid (QSL) candidate materials are crucial for exploring exotic quantum phenomena and applications associated with QSLs. Most existing metal-organic two-dimensional (2D) quantum spin liquid candidates have structures with spins arranged on the triangular or kagome lattices, whereas honeycomb-structured metal-organic compounds with QSL characteristics are rare. Here, we report the use of 2,5-dihydroxy-1,4-benzoquinone (Xdhbq, X = Cl, Br, H) as the linkers to construct cobalt(II) honeycomb lattices (NEt)[Co(Xdhbq)] as promising Kitaev-type QSL candidate materials.

KMgBi: A Narrow Band Gap Semiconductor with a Channel Structure.

The creation of new families of intermetallic or Zintl-phase compounds with high-spin orbit elements has attracted a considerable amount of interest due to the presence of unique electronic, magnetic, and topological phenomena in these materials. Here, we establish the synthesis and structural and electronic characterization of KMgBi single crystals having a new structure type. KMgBi crystallizes in space group having unit cell parameters = 4.

Extraordinary Thermoelectric Properties of Topological Surface States in Quantum-Confined CdAs Thin Films.

Topological insulators and semimetals have been shown to possess intriguing thermoelectric properties promising for energy harvesting and cooling applications. However, thermoelectric transport associated with the Fermi arc topological surface states on topological Dirac semimetals remains less explored. This work systematically examines thermoelectric transport in a series of topological Dirac semimetal CdAs thin films grown by molecular beam epitaxy.

Synergizing a Large Ordinary Nernst Effect and Axis-Dependent Conduction Polarity in Flat Band KMgBi Crystals.

The exploration of quantum materials in which an applied thermo/electrical/magnetic field along one crystallographic direction produces an anisotropic response has led to unique functionalities. Along these lines, KMgBi is a layered, narrow gap semiconductor near a critical state between multiple Dirac phases due to the presence of a flat band near the Fermi level. The valence band is highly anisotropic with minimal cross-plane dispersion, which, in combination with an isotropic conduction band, enables axis-dependent conduction polarity.

Axis dependent conduction polarity in the air-stable semiconductor, PdSe.

Axis-dependent conduction polarity (ADCP) is a unique electronic phenomena in which the charge polarity of carrier conduction can differ from p-type to n-type depending on the direction of travel through the crystal. Most materials that exhibit ADCP are metals, and very few semiconducting materials exhibit this effect. Here, we establish that PdSe, a ∼0.

Electric field-dependent phonon spectrum and heat conduction in ferroelectrics.

This article shows experimentally that an external electric field affects the velocity of the longitudinal acoustic phonons (), thermal conductivity (κ), and diffusivity () in a bulk lead zirconium titanate-based ferroelectric. Phonon conduction dominates κ, and the observations are due to changes in the phonon dispersion, not in the phonon scattering. This gives insight into the nature of the thermal fluctuations in ferroelectrics, namely, phonons labeled ferrons that carry heat and polarization.

Large magnon-induced anomalous Nernst conductivity in single-crystal MnBi.

Thermoelectric modules are a promising approach to energy harvesting and efficient cooling. In addition to the longitudinal Seebeck effect, transverse devices utilizing the anomalous Nernst effect (ANE) have recently attracted interest. For high conversion efficiency, it is required that the material have a large ANE thermoelectric power and low electrical resistance, which lead to the conductivity of the ANE.

Giant anomalous Nernst signal in the antiferromagnet YbMnBi.

A large anomalous Nernst effect (ANE) is crucial for thermoelectric energy conversion applications because the associated unique transverse geometry facilitates module fabrication. Topological ferromagnets with large Berry curvatures show large ANEs; however, they face drawbacks such as strong magnetic disturbances and low mobility due to high magnetization. Herein, we demonstrate that YbMnBi, a canted antiferromagnet, has a large ANE conductivity of ~10 A m K that surpasses large values observed in other ferromagnets (3-5 A m K).

Thermal chiral anomaly in the magnetic-field-induced ideal Weyl phase of BiSb.

The chiral anomaly is the predicted breakdown of chiral symmetry in a Weyl semimetal with monopoles of opposite chirality when an electric field is applied parallel to a magnetic field. It occurs because of charge pumping between monopoles of opposite chirality. Experimental observation of this fundamental effect is plagued by concerns about the current pathways.

Combining Spin-Seebeck and Nernst Effects in Aligned MnBi/Bi Composites.

The spin-Seebeck effect (SSE) is an advective transport process traditionally studied in bilayers composed of a ferromagnet (FM) and a non-magnetic metal (NM) with strong spin-orbit coupling. In a temperature gradient, the flux of magnons in the FM transfers spin-angular momentum to electrons in the NM, which by the inverse spin-Hall effect generates an SSE voltage. In contrast, the Nernst effect is a bulk transport phenomenon in homogeneous NMs or FMs.

The Chemical Design Principles for Axis-Dependent Conduction Polarity.

The recent discovery that specific materials can simultaneously exhibit n-type conduction and p-type conduction along different directions of the single crystal has the potential to impact a broad range of electronic and energy-harvesting technologies. Here, we establish the chemical design principles for creating materials with this behavior. First, we define the single-carrier and multicarrier mechanisms for axis-dependent conduction polarity and their identifying band structure fingerprints.

The Fermi surface geometrical origin of axis-dependent conduction polarity in layered materials.

Electronic materials generally exhibit a single isotropic majority carrier type, electrons or holes. Some superlattice and hexagonal materials exhibit opposite conduction polarities along in-plane and cross-plane directions due to multiple electron and hole bands. Here, we uncover a material genus with this behaviour that originates from the Fermi surface geometry of a single band.

Interface-Induced Phenomena in Magnetism.

This article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer.

Correction: Eu-Eu valence transition in double, Eu-, and Na-doped PbSe from transport, magnetic, and electronic structure studies.

Correction for 'Eu-Eu valence transition in double, Eu-, and Na-doped PbSe from transport, magnetic, and electronic structure studies' by Bartlomiej Wiendlocha et al., Phys. Chem.

Eu-Eu valence transition in double, Eu-, and Na-doped PbSe from transport, magnetic, and electronic structure studies.

The Eu atoms in PbEuSe have long been assumed to be divalent. We show that p-type doping of this magnetic semiconductor alloy with Na can modify the effective Eu valence: a mixed, Eu-Eu state appears in PbEuNaSe at particular values of y. Magnetization, carrier concentration, resistivity, and thermopower of PbEuNaSe are reported for a number of samples with different x and y.

Compromise and Synergy in High-Efficiency Thermoelectric Materials.

The past two decades have witnessed the rapid growth of thermoelectric (TE) research. Novel concepts and paradigms are described here that have emerged, targeting superior TE materials and higher TE performance. These superior aspects include band convergence, "phonon-glass electron-crystal", multiscale phonon scattering, resonant states, anharmonicity, etc.

Observation of spin Seebeck contribution to the transverse thermopower in Ni-Pt and MnBi-Au bulk nanocomposites.

Transverse thermoelectric devices produce electric fields perpendicular to an incident heat flux. Classically, this process is driven by the Nernst effect in bulk solids, wherein a magnetic field generates a Lorentz force on thermally excited electrons. The spin Seebeck effect also produces magnetization-dependent transverse electric fields.

Phonon-induced diamagnetic force and its effect on the lattice thermal conductivity.

Phonons are displacements of atoms around their rest positions in a crystalline solid. They carry sound and heat, but are not classically associated with magnetism. Here, we show that phonons are, in fact, sensitive to magnetic fields, even in diamagnetic materials.

High performance Na-doped PbTe-PbS thermoelectric materials: electronic density of states modification and shape-controlled nanostructures.

Thermoelectric heat-to-power generation is an attractive option for robust and environmentally friendly renewable energy production. Historically, the performance of thermoelectric materials has been limited by low efficiencies, related to the thermoelectric figure-of-merit ZT. Nanostructuring thermoelectric materials have shown to enhance ZT primarily via increasing phonon scattering, beneficially reducing lattice thermal conductivity.

Enhancement of thermoelectric efficiency in PbTe by distortion of the electronic density of states.

The efficiency of thermoelectric energy converters is limited by the material thermoelectric figure of merit (zT). The recent advances in zT based on nanostructures limiting the phonon heat conduction is nearing a fundamental limit: The thermal conductivity cannot be reduced below the amorphous limit. We explored enhancing the Seebeck coefficient through a distortion of the electronic density of states and report a successful implementation through the use of the thallium impurity levels in lead telluride (PbTe).