22 research outputs found
Universal bound to the amplitude of the vortex Nernst signal in superconductors
A liquid of superconducting vortices generates a transverse thermoelectric
response. This Nernst signal has a tail deep in the normal state due to
superconducting fluctuations. Here, we present a study of the Nernst effect in
two-dimensional hetero-structures of Nb-doped strontium titanate (STO) and in
amorphous MoGe. The Nernst signal generated by ephemeral Cooper pairs above the
critical temperature has the magnitude expected by theory in STO. On the other
hand, the peak amplitude of the vortex Nernst signal below is comparable
in both and in numerous other superconductors despite the large distribution of
the critical temperature and the critical magnetic fields. In four
superconductors belonging to different families, the maximum Nernst signal
corresponds to an entropy per vortex per layer of k.Comment: Accepted for publication in Phys. Rev. Let
Anomalous T-dependence of phonon lifetimes in metallic VO2
We investigate phonon lifetimes in VO2 single crystals. We do so in the
metallic state above the metal-insulator transition (MIT), where strong
structural fluctuations are known to take place. By combining inelastic X-ray
scattering and Raman spectroscopy, we track the temperature dependence of
several acoustic and optical phonon modes up to 1000 K. Contrary to what is
commonly observed, we find that phonon lifetimes decrease with decreasing
temperature. Our results show that pre-transitional fluctuations in the
metallic state give rise to strong electron-phonon scattering that onsets
hundreds of degrees above the transition and increases as the MIT is
approached. Notably, this effect is not limited to specific points of
reciprocal space that could be associated with the structural transition
Thermal and electrostatic tuning of surface phonon-polaritons in LaAlO<sub>3</sub>/SrTiO<sub>3</sub> heterostructures
Phonon polaritons are promising for infrared applications due to a strong light-matter coupling and subwavelength energy confinement they offer. Yet, the spectral narrowness of the phonon bands and difficulty to tune the phonon polariton properties hinder further progress in this field. SrTiO3 – a prototype perovskite oxide - has recently attracted attention due to two prominent far-infrared phonon polaritons bands, albeit without any tuning reported so far. Here we show, using cryogenic infrared near-field microscopy, that long-propagating surface phonon polaritons are present both in bare SrTiO3 and in LaAlO3/SrTiO3 heterostructures hosting a two-dimensional electron gas. The presence of the two-dimensional electron gas increases dramatically the thermal variation of the upper limit of the surface phonon polariton band due to temperature dependent polaronic screening of the surface charge carriers. Furthermore, we demonstrate a tunability of the upper surface phonon polariton frequency in LaAlO3/SrTiO3 via electrostatic gating. Our results suggest that oxide interfaces are a new platform bridging unconventional electronics and long-wavelength nanophotonics.</p
Metallicity and Superconductivity in Doped Strontium Titanate
Strontium titanate is a wide-gap semiconductor avoiding a ferroelectric instability thanks to quantum fluctuations. This proximity leads to strong screening of static Coulomb interaction and paves the way for the emergence of a very dilute metal with extremely mobile carriers at liquid-helium temperature. Upon warming, mobility decreases by several orders of magnitude. Yet, metallicity persists above room temperature even when the apparent mean free path falls below the electron wavelength. The superconducting instability survives at exceptionally low concentrations and beyond the boundaries of Migdal-Eliashberg approximation. An intimate connection between dilute superconductivity and aborted ferroelectricity is widely suspected. In this review, we give a brief account of ongoing research on bulk strontium titanate as an insulator, a metal, and a superconductor
Open Data to the publication "Isotope tuning of the superconducting dome of strontium titanate"
AbstractDielectric constant, Raman data, resistivity data, magnetic susceptibility, Curie temperatures, superconducting Tc, quantum oscillations, mobility, of doped and isotope-substituted SrTi(18O16O1−y)3−δ for 0 ≤ y ≤ 0.81 and carrier concentrations between 6×10^17 y and 2 × 10^20 cm−3 (δ < 0.02
Charge transport in a polar metal
The fate of electric dipoles inside a Fermi sea is an old issue, yet poorly explored. Sr1-xCaxTiO3 hosts a robust but dilute ferroelectricity in a narrow (0.0018 = n* (x), resistivity follows a T-square behavior together with slight upturns (in both Ca-free and Ca-substituted samples). The latter are reminiscent of Kondo effect and most probably due to oxygen vacancies