Jožef Stefan Institute

About: Jožef Stefan Institute is a facility organization based out in Ljubljana, Slovenia. It is known for research contribution in the topics: Liquid crystal & Dielectric. The organization has 3828 authors who have published 12614 publications receiving 291025 citations.

Bad metallic transport in a cold atom Fermi-Hubbard system

Abstract: Strong interactions in many-body quantum systems complicate the interpretation of charge transport in such materials. To shed light on this problem, we study transport in a clean quantum system: ultracold lithium-6 in a two-dimensional optical lattice, a testing ground for strong interaction physics in the Fermi-Hubbard model. We determine the diffusion constant by measuring the relaxation of an imposed density modulation and modeling its decay hydrodynamically. The diffusion constant is converted to a resistivity by using the Nernst-Einstein relation. That resistivity exhibits a linear temperature dependence and shows no evidence of saturation, two characteristic signatures of a bad metal. The techniques we developed in this study may be applied to measurements of other transport quantities, including the optical conductivity and thermopower.

Sintering of Lead-Free Piezoelectric Sodium Potassium Niobate Ceramics

Abstract: The potassium sodium niobate, K0.5Na0.5NbO₃, solid solution (KNN) is considered as one of the most promising, environment-friendly, lead-free candidates to replace highly efficient, lead-based piezoelectrics. Since the first reports of KNN, it has been recognized that obtaining phase-pure materials with a high density and a uniform, fine-grained microstructure is a major challenge. For this reason the present paper reviews the different methods for consolidating KNN ceramics. The difficulties involved in the solid-state synthesis of KNN powder, i.e., obtaining phase purity, the stoichiometry of the perovskite phase, and the chemical homogeneity, are discussed. The solid-state sintering of stoichiometric KNN is characterized by poor densification and an extremely narrow sintering-temperature range, which is close to the solidus temperature. A study of the initial sintering stage revealed that coarsening of the microstructure without densification contributes to a reduction of the driving force for sintering. The influences of the (K + Na)/Nb molar ratio, the presence of a liquid phase, chemical modifications (doping, complex solid solutions) and different atmospheres (i.e., defect chemistry) on the sintering are discussed. Special sintering techniques, such as pressure-assisted sintering and spark-plasma sintering, can be effective methods for enhancing the density of KNN ceramics. The sintering behavior of KNN is compared to that of a representative piezoelectric lead zirconate titanate (PZT).

Chemical Compatibility between Silver Electrodes and Low-Firing Binary-Oxide Compounds: Conceptual Study

Abstract: The chemical compatibility of silver electrodes and low-firing ceramics has been considered, in terms of the existence of a tie line between silver (and/or Ag2O) and the binary oxide compound in the corresponding ternary phase diagram. The probability of the existence of the tie line is related to the conditions in the subordinated silver-based isothermal binary systems. Greater probabilities have been calculated for the systems with fewer silver-based binary compounds. Based on the concepts that have been developed, several silver-based isothermal binary systems have been investigated to identify the oxides suitable for the development of low-temperature cofired ceramics. The developed concept has been tested by investigating the phase relations in the Bi2O3–Nb2O5 and Bi2O3–V2O5 ternary systems with silver. X-ray and microstructural investigations of bismuth niobates and bismuth vanadates reveal that, as a result of the inertness of Bi2O3 and the reactivity of Nb2O5 and V2O5 toward silver, compounds that are rich in niobium or vanadium react with silver to form ternary Nb/V-Bi-Ag oxide compounds, whereas for compounds that are rich in bismuth, tie lines to silver and Ag2O do exist.

Tracing mercury contamination from the Idrija mining region (Slovenia) to the gulf of trieste using hg isotope ratio measurements.

Abstract: To demonstrate the power of precise isotope ratio measurements of Hg in environmental samples and, more particularly, to test the use of stable isotopes as distinct tracers of the contamination source, we investigated a well-documented system, the Hg mining region near Idrija, Slovenia. Sediments alongside the Idrijca River, the Soca/Isonzo River, and in the Gulf of Trieste were analyzed to determine the variation in Hg isotopic composition versus distance from the source. Similar Hg isotopic signatures were observed among samples collected from the rivers Idrijca, Soca/Isonzo, and around the river mouth in the Gulf of Trieste, suggesting that sediments throughout the watershed of the Soca/Isonzo River to the Gulf of Trieste are dominated by Hg exported from the headwaters of the Idrijca River. Only locations on the southern part of the gulf, outside the river plume, showed lower values of the isotopic composition comparable to the Hg isotopic signature of Adriatic Sea sediments. Using a simple binary mix...

Superconducting Gap Δ c , the Pseudogap Δ p , and Pair Fluctuations above T c in Overdoped Y 1 − x Ca x Ba 2 Cu 3 O 7 − δ from Femtosecond Time-Domain Spectroscopy

Abstract: The gap structure in ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ single crystals is investigated by real-time measurements of the quasiparticle (QP) relaxation dynamics with femtosecond optical spectroscopy. We find evidence for the coexistence of two distinct gaps. One is a $T$-independent pseudogap ${\ensuremath{\Delta}}_{p}$ and the other is a $T$-dependent gap ${\ensuremath{\Delta}}_{c}(T)$ with a BCS-like $T$ dependence. From QP relaxation time measurements above ${T}_{c}$ we ascertain that fluctuations associated with the latter are consistent with time-dependent Ginzburg-Landau theory and are distinct from the pseudogap whose presence is apparent well above ${T}_{c}$ for all $x$.