Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userConcomitant appearance of conductivity and superconductivity in (111)LaAlO3/SrTiO3 interface with metal capping
73
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
In polar-oxide interfaces, a certain number of monolayers (ML) is needed for conductivity to appear. This threshold for conductivity is explained by accumulating sufficient electric potential to initiate charge transfer to the interface. Here we study experimentally and theoretically the (111) SrTiO3/LaAlO3 interface where a critical thickness, tc, of nine epitaxial LaAlO3 ML is required to turn the interface from insulating to conducting and even superconducting. We show that tc decreases to 3ML when depositing a cobalt over-layer (capping) and 6ML for platinum capping. The latter result contrasts with the (100) interface, where platinum capping increases tc beyond the bare interface. The observed threshold for conductivity for the bare and the metal-capped interfaces is confirmed by our density functional theory calculations. Interestingly, for (111) SrTiO3/LaAlO3/Metal interfaces, conductivity appears concomitantly with superconductivity in contrast with the (100) SrTiO3/LaAlO3/Metal interfaces where tc is smaller than the critical thickness for superconductivity. We attribute this dissimilarity to the different orbital polarization of eg for the (111) versus dxy for the (001) interface.
rate research
Read More
When insulator LaAlO3 is grown by epitaxy onto a TiO2-terminated {100} surface of insulator SrTiO3, the resulting system has a metallic character. This phenomenon has been associated with an electrostatic frustration at the interface, as {100} surfaces of SrTiO3 are neutral while those of LaAlO3 are polar, but its microscopic mechanism is not quite understood. Here, we present a structural characterisation of this interface by aberration-corrected transmission electron microscopy. The unit cells at the interface appear elongated: we discuss this distortion in terms of electrostatic charge and extra carriers at the interface.
Recently superconductivity at the interface between the insulators LaAlO3 and SrTiO3 has been tuned with the electric field effect to an unprecedented range of transition temperatures. Here we perform a detailed finite size scaling analysis to explore the compatibility of the phase transition line with Berezinskii-Kosterlitz-Thouless (BKT) behavior and a 2D-quantum phase(QP)-transition. In an intermediate regime, limited by a gate voltage dependent limiting length, we uncover remarkable consistency with a BKT-critical line ending at a metallic quantum critical point, separating a weakly localized insulator from the superconducting phase. Our estimates for the critical exponents of the 2D-QP-transition, z=1 and nu=0.66, suggest that it belongs to the 3D-xy universality class.
LaAlO3 and SrTiO3 are insulating, nonmagnetic oxides, yet the interface between them exhibits a two-dimensional electron system with high electron mobility,1 superconductivity at low temperatures,2-6 and electric-field-tuned metal-insulator and superconductorinsulator phase transitions.3,6-8 Bulk magnetization and magnetoresistance measurements also suggest some form of magnetism depending on preparation conditions5,9-11 and suggest a tendency towards nanoscale electronic phase separation.10 Here we use local imaging of the magnetization and magnetic susceptibility to directly observe a landscape of ferromagnetism, paramagnetism, and superconductivity. We find submicron patches of ferromagnetism in a uniform background of paramagnetism, with a nonuniform, weak diamagnetic superconducting susceptibility at low temperature. These results demonstrate the existence of nanoscale phase separation as suggested by theoretical predictions based on nearly degenerate interface sub-bands associated with the Ti orbitals.12,13 The magnitude and temperature dependence of the paramagnetic response suggests that the vast majority of the electrons at the interface are localized, and do not contribute to transport measurements.3,6,7 In addition to the implications for magnetism, the existence of a 2D superconductor at an interface with highly broken inversion symmetry and a ferromagnetic landscape in the background suggests the potential for exotic superconducting phenomena.
In recent years, striking discoveries have revealed that two-dimensional electron liquids (2DEL) confined at the interface between oxide band-insulators can be engineered to display a high mobility transport. The recognition that only few interfaces appear to suit hosting 2DEL is intriguing and challenges the understanding of these emerging properties not existing in bulk. Indeed, only the neutral TiO2 surface of (001)SrTiO3 has been shown to sustain 2DEL. We show that this restriction can be surpassed: (110) and (111) surfaces of SrTiO3 interfaced with epitaxial LaAlO3 layers, above a critical thickness, display 2DEL transport with mobilities similar to those of (001)SrTiO3. Moreover we show that epitaxial interfaces are not a prerequisite: conducting (110) interfaces with amorphous LaAlO3 and other oxides can also be prepared. These findings open a new perspective both for materials research and for elucidating the ultimate microscopic mechanism of carrier doping.
Understanding the superconductivity at the interface of FeSe/SrTiO3 is a problem of great contemporary interest due to the significant increase in critical temperature (Tc) compared to that of bulk FeSe, as well as the possibility of an unconventional pairing mechanism and topological superconductivity. We report a study of the influence of a capping layer on superconductivity in thin films of FeSe grown on SrTiO3 using molecular beam epitaxy. We used in vacuo four-probe electrical resistance measurements and ex situ magneto-transport measurements to examine the effect of three capping layers that provide distinctly different charge transfer into FeSe: compound FeTe, non-metallic Te, and metallic Zr. Our results show that FeTe provides an optimal cap that barely influences the inherent Tc found in pristine FeSe/SrTiO3, while the transfer of holes from a non-metallic Te cap completely suppresses superconductivity and leads to insulating behavior. Finally, we used ex situ magnetoresistance measurements in FeTe-capped FeSe films to extract the angular dependence of the in-plane upper critical magnetic field. Our observations reveal an almost isotropic in-plane upper critical field, providing insight into the symmetry and pairing mechanism of high temperature superconductivity in FeSe.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
