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Register a new userThermoelectric effects at a Germanium-electrolyte interface: measuring 100 nK temperature oscillations at room temperature
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We describe measurements of 100 nK temperature oscillations at room temperature, driven at the complex interface between p-doped Germanium, a nm size metal layer, and an electrolyte. We show that heat is deposited at this interface by thermoelectric effects, however the precise microscopic mechanism remains to be established. The temperature measurement is accomplished by observing the modulation of black body radiation from the interface. We argue that this geometry offers a method to study molecular scale dissipation phenomena. The Debye layer on the electrolyte side of the interface controls much of the dynamics. Interpreting the measurements from first principles, we show that in this geometry the Debye layer behaves like a low frequency transmission line.
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A d-orbital electron has an anisotropic electron orbital and is a source of magnetism. The realization of a 2-dimensional electron gas (2DEG) embedded at a LaAlO3/SrTiO3 interface surprised researchers in materials and physical sciences because the 2DEG consists of 3d-electrons of Ti with extraordinarily large carrier mobility, even in the insulating oxide heterostructure. To date, a wide variety of physical phenomena, such as ferromagnetism and the quantum Hall effect, have been discovered in this 2DEG systems, demonstrating the ability of the d-electron 2DEG systems to provide a material platform for the study of interesting physics. However, because of both ferromagnetism and the Rashba field, long-range spin transport and the exploitation of spintronics functions have been believed difficult to implement in the d-electron 2DEG systems. Here, we report the experimental demonstration of room-temperature spin transport in the d-electron-based 2DEG at a LaAlO3/SrTiO3 interface, where the spin relaxation length is ca. exceeding 200 nm. Our finding, which counters the conventional understandings to d-electron 2DEGs, opens a new field of d-electron spintronics. Furthermore, this work highlights a novel spin function in the conductive oxide system.
Non-local carrier injection/detection schemes lie at the very foundation of information manipulation in integrated systems. This paradigm consists in controlling with an external signal the channel where charge carriers flow between a source and a well separated drain. The next generation electronics may operate on the spin of carriers instead of their charge and germanium appears as the best hosting material to develop such a platform for its compatibility with mainstream silicon technology and the long electron spin lifetime at room temperature. Moreover, the energy proximity between the direct and indirect bandgaps allows for optical spin injection and detection within the telecommunication window. In this letter, we demonstrate injection of pure spin currents (textit{i.e.} with no associated transport of electric charges) in germanium, combined with non-local spin detection blocks at room temperature. Spin injection is performed either electrically through a magnetic tunnel junction (MTJ) or optically, exploiting the ability of lithographed nanostructures to manipulate the distribution of circularly-polarized light in the semiconductor. Pure spin current detection is achieved using either a MTJ or the inverse spin-Hall effect (ISHE) across a platinum stripe. These results broaden the palette of tools available for the realization of opto-spintronic devices.
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Modulation of the grain boundary properties in thermoelectric materials that have thermally activated electrical conductivity is crucial in order to achieve high performance at low temperatures. In this work, we show directly that the modulation of the potential barrier at the grain boundaries in perovskite SrTiO3 changes the low-temperature dependency of the bulk materials electrical conductivity. By sintering samples in a reducing environment of increasing strength, we produced La0.08Sr0.9TiO3 (LSTO) ceramics that gradually change their electrical conductivity behavior from thermally activated to single-crystal-like, with only minor variations in the Seebeck coefficient. Imaging of the surface potential by Kelvin probe force microscopy found lower potential barriers at the grain boundaries in the LSTO samples that had been processed in the more reducing environments. A theoretical model using the band offset at the grain boundary to represent the potential barrier agreed well with the measured grain boundary potential dependency of conductivity. The present work showed an order of magnitude enhancement in electrical conductivity (from 85 to 1287 S cm-1) and power factor (from 143 to 1745 {mu}W m-1 K-2) at 330 K by this modulation of charge transport at grain boundaries. This significant reduction in the impact of grain boundaries on charge transport in SrTiO3 provides an opportunity to achieve the ultimate phonon glass electron crystal by appropriate experimental design and processing.
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