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Elemental tellurium is a strongly spin-orbit coupled Peierls-distorted semiconductor whose band structure features topologically protected Weyl nodes. Using time-dependent density functional theory calculations, we show that impulsive optical excitation can be used to transiently control the amplitude of the Peierls distortion, realizing a mechanism to switch tellurium between three states: Weyl semiconductor, Weyl metal and non-Weyl metal. Further, we present experimental evidence of this inverse-Peierls distortion using time-resolved optical second harmonic generation measurements. These results provide a pathway to multifunctional ultrafast Weyl devices and introduce Peierls systems as viable hosts of light-induced topological transitions., 7 pages main text, 4 figures, 11 pages supplementary information

Ultrafast lasers are an increasingly important tool to control and stabilize emergent phases in quantum materials. Among a variety of possible excitation protocols, a particularly intriguing route is the direct light-engineering of microscopic electronic parameters, such as the electron hopping and the local Coulomb repulsion (Hubbard $U$). In this work, we use time-resolved x-ray absorption spectroscopy to demonstrate the light-induced renormalization of the Hubbard $U$ in a cuprate superconductor, La$_{1.905}$Ba$_{0.095}$CuO$_4$. We show that intense femtosecond laser pulses induce a substantial redshift of the upper Hubbard band, while leaving the Zhang-Rice singlet energy unaffected. By comparing the experimental data to time-dependent spectra of single- and three-band Hubbard models, we assign this effect to a $\sim140$ meV reduction of the onsite Coulomb repulsion on the copper sites. Our demonstration of a dynamical Hubbard $U$ renormalization in a copper oxide paves the way to a novel strategy for the manipulation of superconductivity, magnetism, as well as to the realization of other long-range-ordered phases in light-driven quantum materials., 13 pages, 7 figures

Hybrid organic/inorganic thermoelectric materials based on conducting polymers and inorganic nanostructures have been demonstrated to combine both the inherently low thermal conductivity of the polymer and the superior charge transport properties (high power factors) of the inorganic component. While their performance today still lags behind that of conventional inorganic thermoelectric materials, solution-processable hybrids have made rapid progress and also offer unique advantages not available to conventional rigid inorganic thermoelectrics, namely: (1) low cost fabrication on rigid and flexible substrates, as well as (2) engineering complex conformal geometries for energy harvesting/cooling. While the number of reports of new classes of viable hybrid thermoelectric materials is growing, no group has reported a general approach for bottom-up design of both p- and n-type materials from one common base. Thus, unfortunately, the literature comprises mostly of disconnected discoveries, which limits development and calls for a first-principles approach for property manipulation analogous to doping in traditional semiconductor thermoelectrics. Here, molecular engineering at the organic/inorganic interface and simple processing techniques are combined to demonstrate a modular approach enabling de novo design of complex hybrid thermoelectric systems. We chemically modify the surfaces of inorganic nanostructures and graft conductive polymers to yield robust solution processable p- and n-type inorganic/organic hybrid nanostructures. Our new modular approach not only offers researchers new tools to perform true bottom-up design of thermoelectric hybrids, but also strong performance advantages as well due to the quality of the designed interfaces. For example, we obtain enhanced power factors in existing (by up to 500% in Te/PEDOT:PSS) and novel (Bi2S3/PEDOT:PSS) p-type systems, and also generate water-processable and air-stable high performing n-type hybrid systems (Bi2Te3/PEDOT:PSS), thus highlighting the potency of our ex situ strategy in opening up new material options for thermoelectric applications. This strategy establishes a unique platform with broad handles for custom tailoring of thermal and electrical properties through hybrid material tunability and enables independent control over inorganic material chemistry, nanostructure geometry, and organic material properties, thus providing a robust pathway to major performance enhancements.

This work demonstrates the first method for controlled growth of heterostructures within hybrid organic/inorganic nanocomposite thermoelectrics. Using a facile, aqueous technique, semimetal–alloy nanointerfaces are patterned within a hybrid thermoelectric system consisting of tellurium (Te) nanowires and the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS). Specifically, this method is used to grow nanoscale islands of Cu1.75Te alloy subphases within hybrid PEDOT:PSS-Te nanowires. This technique is shown to provide tunability of thermoelectric and electronic properties, providing up to 22% enhancement of the system’s power factor in the low-doping regime, consistent with preferential scattering of low energy carriers. This work provides an exciting platform for rational design of multiphase nanocomposites and highlights the potential for engineering of carrier filtering within hybrid thermoelectrics via introduction of interfaces with controlled structural and energe...

Defining the magnetic anisotropy for in-plane or out-of-plane easy axis in ferrimagnetic insulators films by controlling the strain, while maintaining high-quality surfaces, is desirable for spintronic and magnonic applications. We investigate ways to tune the anisotropy of amorphous sputtered ultrathin thulium iron garnet (TIG) films, and thus tailor their magnetic properties by the thickness (7.5 to 60 nm), substrate choice (GGG and SGGG), and crystallization process. We correlate morphological and structural properties with the magnetic anisotropy of post-growth annealed films. 30 nm thick films annealed at 600 {\deg}C show compressive strain favoring an in-plane magnetic anisotropy (IPMA), whereas films annealed above 800 {\deg}C are under a tensile strain leading to a perpendicular magnetic anisotropy (PMA). Air-annealed films present a high degree of crystallinity and magnetization saturation close to the bulk value. These results lead to successful fabrication of trilayers TIG/Au/TIG, with coupling between the TIG layers depending on Au thickness. These results will facilitate the use of TIG to create various in situ clean hybrid structures for fundamental interface exchange studies, and towards the development of complex devices. Moreover, the sputtering technique is advantageous as it can be easily scaled up for industrial applications., Comment: The following article has been accepted by Journal of Applied Physics