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This article shows experimentally that an external electric field affects the velocity of the longitudinal acoustic phonons (v_LA), thermal conductivity (κ), and diffusivity (D) 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. It also opens the way for phonon-based electrically driven all-solid-state heat switches, an enabling technology for solid-state heat engines. A quantitative theoretical model combining piezoelectric strain and phonon anharmonicity explains the field dependence ofv_LA, κ, andDwithout any adjustable parameters, thus connecting thermodynamic equilibrium properties with transport properties. The effect is four times larger than previously reported effects, which were ascribed to field-dependent scattering of phonons. 

The thermal chiral anomaly is a new mechanism for thermal transport that occurs in Weyl semimetals (WSMs). It is attributed to the generation and annihilation of energy at Weyl points of opposite chirality. The effect was observed in the Bi1−xSbx alloy system, at x = 11% and 15%, which are topological insulators at zero field and driven into an ideal WSM phase by an external field. Given that the experimental uncertainty on x is of the order of 1%, any systematic study of the effect over a wider range of x requires precise knowledge of the transition composition xc at which the electronic bands at the L-point in these alloys have Dirac-like dispersions. At x > xc, the L-point bands are inverted and become topologically non-trivial. In the presence of a magnetic field along the trigonal direction, these alloys become WSMs. This paper describes how the temperature dependence of the frequency of the Shubnikov–de Haas oscillations F(x,T) at temperatures of the order of the cyclotron energy can be used to find xc and characterize the topology of the electronic Fermi surface. Semimetallic Bi1−xSbx alloys with topologically trivial bands have dF(x,T)/dT ≥ 0; those with Dirac/Weyl fermions display dF(x,T)/dT < 0. 

Vacuum field effect transistors have been envisioned to hold the promise of replacing solid-state electronics when the ballistic transport of electrons in a nanoscale vacuum can enable significantly high switching speed and stability. However, it remains challenging to obtain high-performance and reliable field-emitter materials. In this work, we report a systematic study on the field emission of novel two-dimensional tin selenide (SnSe) with rational design of its structures and surface morphologies. SnSe in the form of atomically smooth single crystals and nanostructures (nanoflowers) is chemically synthesized and studied as field emitters with varying channel lengths from 6 μm to 100 nm. Our study shows that devices based on SnSe nanoflowers significantly improve the performance and enable field emission at a reduced voltage due to a surface-enhanced local electrostatic field, and further lead to nonlinear dependent channel scaling when the channel length is shorter than 600 nm. We measured a record-high short-channel field-enhancement factor of 50 600 for a 100 nm device. Moreover, we investigated the emission stability and measured the fluctuations of the emission current which are smaller than 5% for more than 20 hours. Our results demonstrated a high-performance and highly reliable field emitter based on 2D SnSe nanostructures and we developed an important building block for nanoscale vacuum field effect transistors.