Physics of strongly correlated electron systems

Terahertz (THz) radiation is a powerful tool with widespread applications ranging from imaging, sensing, and broadband communications to spectroscopy and nonlinear control of materials. Future progress in THz technology depends on the development of efficient, structurally simple THz emitters that can be implemented in advanced miniaturized devices. Researchers at the Max Planck Institute for Solid State Research and their collaborators at the Universities of Stuttgart and Dresden have demonstrated the generation of terahertz radiation via the transverse thermoelectric effect in thin films of layered conducting transition metal oxides grown on offcut substrates, such that the highly conducting layers subtend an angle with the substrate plane.  Ultrafast out-of-plane temperature gradients induced by femtosecond lasers launch in-plane thermoelectric currents leading to intense THz emission. The film geometry allows efficient emission of the resulting THz field out of the film structure.  The experimental scheme does not require elaborate fabrication methods and complementary microstructure elements, and is not limited to a particular material or specific operational conditions. It thus offers a simple and promising avenue for versatile THz sources and integrable emitter elements.
Yordanov, P., Priessnitz, T., Kim, M.-J., Cristiani, G., Logvenov, G., Keimer, B., Kaiser, S., Generation of Terahertz Radiation via The Transverse Thermoelectric Effect. Adv. Mater. 2023, 2305622.
https://doi.org/10.1002/adma.202305622

Petar Yordanov, Tim Priessnitz, Min-Jae Kim, Stefan Kaiser, Bernhard Keimer, An Electromagnetic Radiation Source And Method For The Generation Of Terahertz Radiation Based On The Transverse Thermoelectric Effect. EP4086699A1, 2022.

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May 02, 2022
New neutron scattering method enables fast and precise determination of the hydrogen content in thin-film structures and electronic device.
Hydrogen as a green fuel will play a central role in future energy management. The production of hydrogen by electrolysis, the efficient storage in solid materials, and the conversion into electrical energy in fuel cells is based on the interaction of hydrogen at the surface of electrodes and storage materials. Understanding and optimizing these technologies requires quantitative information about the hydrogen concentration inside materials on nanometer scales, in particular close to the surface and in thin films.
A second rapidly developing research frontier is taking advantage of hydrogen intercalation to modify the electronic properties of solids and solid-state devices. Prominent examples include targeted modification of the lattice architecture and doping level of quantum materials, modulation of the exchange coupling and magnetic anisotropy of magnetic multilayers and devices, and solid state gas sensors. Artificial neural networks, the key component for machine learning algorithms, might gain efficiency by a synapse design with ultra low power consumption. The synapses are programmed by a gating voltage charging or discharging a thin conductive layer with hydrogen to modify its resistivity.
Neutron reflectometry (NR) is a distinguished method for the analysis of hydrogen distributions in thin films. By analogy with the optics of light, NR measures the neutron intensity reflected from the surface of a thin film as a function of the angle of incidence. Experimental reflectivity curves are then modeled to extract the depth dependence of the “neutron optical potential” ρ(z). Injection of hydrogen in the studied sample leads to a modification of ρ(z), which can be traced via the altered reflectivity. Hydrogen concentrations of 5 at.% with a depth resolution of one nanometer can be reliably measured by conventional NR, but real-time experiments remain limited by the required exposition times to slow processes on the scale of minutes to hours.
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