The search for electrolyte materials with high oxygen conductivities is a key step toward reducing the operation temperature of fuel cells, which is currently above 700°C. We report a high lateral ionic conductivity, showing up to eight orders of magnitude enhancement near room temperature, in yttria-stabilized zirconia (YSZ)/strontium titanate epitaxial heterostructures. The enhancement of the conductivity is observed, along with a YSZ layer thickness–independent conductance, showing that it is an interface process. We propose that the atomic reconstruction at the interface between highly dissimilar structures (such as fluorite and perovskite) provides both a large number of carriers and a high-mobility plane, yielding colossal values of the ionic conductivity.

We show magnetoresistance in excess of 1000% in trilayers containing highly spin-polarized ${\mathrm{L}\mathrm{a}}_{0.7}{\mathrm{C}\mathrm{a}}_{0.3}{\mathrm{M}\mathrm{n}\mathrm{O}}_3$ and high-$T_c$ superconducting ${\mathrm{Y}\mathrm{B}\mathrm{a}}_2{\mathrm{C}\mathrm{u}}_3{\mathrm{O}}_7$. This large magnetoresistance is reminiscent of the giant magnetoresistance (GMR) in metallic superlattices but with much larger values, and originates at spin imbalance due to the injection of spin-polarized carriers. Furthermore, in contrast to ordinary GMR, the magnetoresistance is intimately related to the superconductivity in the ${\mathrm{Y}\mathrm{B}\mathrm{a}}_2{\mathrm{C}\mathrm{u}}_3{\mathrm{O}}_7$ layer and vanishes in the normal state. This result, aside from its fundamental importance, may be of interest for the design of novel spintronic devices based on ferromagnet/superconductor structures.

The penetration of a superconducting current from a superconductor into a half-metallic ferromagnet is usually forbidden. Resonances in the conductance spectra of superconductor/half-metal heterostructures suggest this restriction is lifted by the occurrence of unconventional equal-spin Andreev reflection. Conventional superconductivity is incompatible with ferromagnetism, because the magnetic exchange field tends to spin-polarize electrons and breaks apart the opposite-spin singlet Cooper pairs1. Yet, the possibility of a long-range penetration of superconducting correlations into strong ferromagnets has been evinced by experiments that found Josephson coupling between superconducting electrodes separated afar by a ferromagnetic spacer2,3,4,5,6,7. This is considered a proof of the emergence at the superconductor/ferromagnetic (S/F) interfaces of equal-spin triplet pairing, which is immune to the exchange field and can therefore propagate over long distances into the F (ref. 8). This effect bears much fundamental interest and potential for spintronic applications9. However, a spectroscopic signature of the underlying microscopic mechanisms has remained elusive. Here we do show this type of evidence, notably in a S/F system for which the possible appearance of equal-spin triplet pairing is controversial10,11,12: heterostructures that combine a half-metallic F (La0.7Ca0.3MnO3) with a d-wave S (YBa2Cu3O7). We found quasiparticle and electron interference effects in the conductance across the S/F interfaces that directly demonstrate the long-range propagation across La0.7Ca0.3MnO3 of superconducting correlations, and imply the occurrence of unconventional equal-spin Andreev reflection. This allows for an understanding of the unusual proximity behaviour observed in this type of heterostructures12,13.

A study of the effect of correlated ion motion on the electrical conductivity relaxation in single-crystalline yttria-stabilized zirconia is presented. Complex admittance in the radio frequency range show power-law dependencies in the real part of the conductivity at high frequencies of the form ${\mathrm{\omega }}^{\mathrm{n}}$ and asymmetric electric modulus plots as a result of correlations. An analysis of the frequency dependence of the electric modulus is conducted to obtain time decay functions of the form exp[-(t/τ${)}^{\mathrm{{\rm B}}}$] from an analytical distribution of relaxation times. Correlation times, and parameters n and Β characterizing the relaxation in time and frequency domains are compared to show the equivalence of time and frequency representations. The common origin of ac and dc processes is discussed in view of the frequency dependence of the complex conductivity. From a macroscopic activation energy for ion motion E=1.16 eV and a Β value of 0.43, a single-ion microscopic activation energy ${\mathrm{E}}_{\mathrm{a}}$=0.5 eV is obtained as ΒE according to Ngai's coupling model. The microscopic activation energy is related to the association energy of oxygen vacancies.

Dielectric relaxation measurements were performed on propylene glycol (PG) and oligomers having different number of repeat units $\text{(N=2,}$ 3, and 69). The primary α-relaxation had the Kohlrausch–Williams–Watts (KWW) form, with a stretch exponent $\text{(1−n)}$ which decreased with increasing N. The temperature dependence of the α-relaxation time, as reflected in the fragility index, increased with N. A broad, rather symmetric secondary β-relaxation was observed at higher frequencies in the dielectric loss spectrum for all samples with $\text{N>1.}$ This is the first observation of the β-relaxation peak in dipropylene glycol $\text{(N=2)}$ and tripropylene glycol $\text{(N=3).}$ The separation between the α- and β-relaxations increased with increasing N. This trend indicates that the separation is minimal in PG, which makes it difficult to resolve the β-relaxation from the more intense α-relaxation. This, together with the fact that the strength of the β-relaxation decreases with the molecular weight of PPG, as found by Johari and coworkers, explains the absence of an observable β- peak or shoulder in isothermal or isochronal dielectric measurement on PG. It is proposed that the deviation of the dielectric loss peak for PG from either the KWW or the Cole–Davidson functions at higher frequencies is due to a β-relaxation masked by the α-process. The same conclusion was reached by Johari and co-workers, based on evidence from their “difference isochrone method.” Finally, we show that the data from oligomers of propylene glycol support the recently proposed correlation of ${\tau }_{\beta }{\mathrm{(T}}_g)$ with $\text{(1−n)}$ and the rough agreement between ${\tau }_{\beta }{\mathrm{(T}}_g)$ and the primitive relaxation time of the coupling model at temperatures above $T_g.$