We report the observation of highly anisotropic Dirac fermions in a Bi square net of SrMnBi(2), based on a first-principles calculation, angle-resolved photoemission spectroscopy, and quantum oscillations for high-quality single crystals. We found that the Dirac dispersion is generally induced in the (SrBi)(+) layer containing a double-sized Bi square net. In contrast to the commonly observed isotropic Dirac cone, the Dirac cone in SrMnBi(2) is highly anisotropic with a large momentum-dependent disparity of Fermi velocities of ~8. These findings demonstrate that a Bi square net, a common building block of various layered pnictides, provides a new platform that hosts highly anisotropic Dirac fermions.

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Finding alternatives for Bi 2 Te 3 , the only thermoelectric material for near-room-temperature (RT) applications, is of great importance in thermoelectrics. Here, we report a very promising near-RT thermoelectric figure of merit (ZT max = 0.9 at 390 K, ZT ave = 0.68 between RT and 390 K) for Cu-excess α-Cu 2+x Se, comprising low-cost, abundant, and nontoxic elements. Although α-Cu 2+x Se has a propensity to form a large number of Cu vacancies to stabilize its structure by diminishing Cu−Cu interactions, excess Cu leads to a decrease in hole concentration by suppressing the formation of Cu vacancies, resulting in a power factor optimization in Cuexcess compounds. These effects of Cu addition were also elucidated by density functional theory calculations and the Boltzmann transport equation. Furthermore, we directly measured the Lorentz number (2.12 × 10 −8 V 2 K −2 at RT) of α-Cu 2 Se for the first time and determined the origin of its very low lattice thermal conductivity (0.27 W m −1 K −1 at RT). On the basis of phonon calculations, it is suggested that this ultralow lattice thermal conductivity is associated with the structural instability of α-Cu 2 Se, as evidenced by the existence of negative phonon frequency in its phonon dispersion. On the basis of our findings, we propose a new way to control the thermoelectric transport properties of α-Cu 2+x Se through overstoichiometric Cu addition, and we also suggest that Cu-excess α-Cu 2 Se is a very promising thermoelectric material to replace Bi 2 Te 3 for near-RT applications.

The temperature-dependent evolution of the Kondo lattice is a long-standing topic of theoretical and experimental investigation and yet it lacks a truly microscopic description of the relation of the basic f-c hybridization processes to the fundamental temperature scales of Kondo screening and Fermi-liquid lattice coherence. Here, the temperature dependence of f-c hybridized band dispersions and Fermi-energy f spectral weight in the Kondo lattice system CeCoIn5 is investigated using f-resonant angle-resolved photoemission spectroscopy (ARPES) with sufficient detail to allow direct comparison to first-principles dynamical mean-field theory (DMFT) calculations containing full realism of crystalline electric-field states. The ARPES results, for two orthogonal (001) and (100) cleaved surfaces and three different f-c hybridization configurations, with additional microscopic insight provided by DMFT, reveal f participation in the Fermi surface at temperatures much higher than the lattice coherence temperature, T*≈45 K, commonly believed to be the onset for such behavior. The DMFT results show the role of crystalline electric-field (CEF) splittings in this behavior and a T-dependent CEF degeneracy crossover below T* is specifically highlighted. A recent ARPES report of low T Luttinger theorem failure for CeCoIn5 is shown to be unjustified by current ARPES data and is not found in the theory.

This letter reports the utility of using the sol-gel process for exploring the library of multicomponent ZnO-based oxides as an active layer of thin film transistors. We chose InGaZnO as a starting material and modulated the Ga content to examine the potential of this material. Increasing the Ga ratio from 0.1 to 1 brought about a dynamic shift in the electrical behavior from conductor to semiconductor. This exploratory work critically helped us fabricate a device with robust device performance (a mobility of 1∼2 cm2 V−1 s−1 for the 400 °C-sintered samples and 0.2 cm2 V−1 s−1 for the 300 °C-sintered samples).

Optical second-harmonic generation (SHG) is a nonlinear parametric process that doubles the frequency of incoming light. Only allowed in non-centrosymmetric materials 1 , it has been widely used in frequency modulation of lasers 2 , surface scientific investigation 3 , and label-free imaging in biological and medical sciences 4 . Two-dimensional crystals are ideal SHG-materials not only for their strong light-matter interaction 5 and atomic thickness defying the phase-matching requirement but also for their stackability into customized hetero-crystals with high angular precision and material diversity 6 . Here we directly show that SHG in hetero-bilayers of transition metal dichalcogenides (TMDs) is governed by optical interference between two coherent SH fields with material-dependent phase delays using spectral phase interferometry. We also quantify the frequencydependent phase difference between MoS2 and WS2, which also agrees with polarizationresolved data and first-principles calculations on complex susceptibility. The secondharmonic analogue of Young's double-slit interference shown in this work demonstrates the potential of custom-designed parametric generation by atom-thick nonlinear optical materials.Two-dimensional (2D) materials have emerged as promising platforms for various photonic applications such as ultrafast photodetectors of gapless graphene 7 , valleytronics of