arXiv subjects

German Hammerl

Publications and source records attributed to German Hammerl.

4 recordsLinked to original sources

arXiv2021

Magnetotransport of Functional Oxide Heterostructures Affected by Spin-Orbit Coupling: A Tale of Two-Dimensional Systems

Oxide heterostructures allow for detailed studies of 2D electronic transport phenomena. Herein, different facets of magnetotransport in selected spin-orbit-coupled systems are analyzed and characterized by their single-band and multiband behavior, respectively. Experimentally, temperature- and magnetic field-dependent measurements in the single-band system BaPbO$_3$/SrTiO$_3$ reveal strong interplay of weak antilocalization (WAL) and electron-electron interaction (EEI). Within a scheme which treats both, WAL and EEI, on an equal footing a strong contribution of EEI at low temperatures is found which suggests the emergence of a strongly correlated ground state. Furthermore, now considering multiband effects as they appear, e.g., in the model system LaAlO$_3$/SrTiO$_3$, theoretical investigations predict a huge impact of filling on the topological Hall effect in systems with intermingled bands. Already weak band coupling produces striking deviations from the well-known Hall conductivity that are explainable in a fully quantum mechanical treatment which builds upon the hybridization of intersecting Hofstadter bands.

cond-mat.mes-hall↗

arXiv2019

Electronic transport in thin films of BaPbO$_3$: Unraveling two-dimensional quantum effects

Recently, perovskite related BaPbO$_3$ has attracted attention due to its hidden topological properties and, moreover, has been used as a thin layer in heterostructures to induce two-dimensional superconductivity. Here we investigate the normal state electronic transport properties of thin films of BaPbO$_3$. Temperature and magnetic field dependent sheet resistances are strongly affected by two-dimensional quantum effects. Our analysis decodes the interplay of spin--orbit coupling, disorder, and electron--electron interaction in this compound. Similar to recently discussed topological materials, we find that weak antilocalization is the dominant protagonist in magnetotransport, whereas electron--electron interactions play a pronounced role in the temperature dependence. A systematic understanding of these quantum effects is essential to allow for an accurate control of properties not only of thin films of BaPbO$_3$, but also of topological heterostructures.

cond-mat.mes-hall↗

arXiv2017

Interface-Driven Two-Dimensional Superconductivity in Bilayers of BaBiO$_3$ and BaPbO$_3$

Besides the cuprate superconductors lead-doped barium bismuthate still attracts intense interest concerning its relatively high critical temperature and the nature of its superconductivity in vicinity to a charge density wave ordered topological insulator. Here we present bilayers of barium bismuthate and barium leadate and find two-dimensional superconductivity at their interfaces well described by current-voltage characteristics compatible with a Berezinskii-Kosterlitz-Thouless transition. Magneto-transport studies independently prove the two-dimensional character of the superconducting properties in these bilayers. The particular dependence of the superconducting transition temperature on the thickness of the barium leadate top layer suggests the formation of the superconducting state to be strain-induced through the interface.

cond-mat.supr-con↗

arXiv2015

Detection and imaging of the oxygen deficiency in single crystalline YBa$_{\text{2}}$Cu$_{\text{3}}$O$_{\text{7}-δ}$ thin films using a positron beam

Single crystalline YBa$_{\text{2}}$Cu$_{\text{3}}$O$_{\text{7}-δ}$ (YBCO) thin films were grown by pulsed laser deposition (PLD) in order to probe the oxygen deficiency $δ$ using a mono-energetic positron beam. The sample set covered a large range of $δ$ (0.191<$δ$<0.791) yielding a variation of the critical temperature $T_{\text{c}}$ between 25 and 90\,K. We found a linear correlation between the Doppler broadening of the positron electron annihilation line and $δ$ determined by X-ray diffraction (XRD). Both, the origin of the found correlation and the influence of metallic vacancies, were examined with the aid of ab-initio calculations that allowed us (i) to exclude the presence of Y vacancies and (ii) to ensure that positrons still probe $δ$ despite the potential presence of Ba or Cu vacancies. In addition, by scanning with the positron beam the spatial variation of $δ$ could be analyzed. It was found to fluctuate with a standard deviation of up to $0.079(5)$ within a single YBCO film.

cond-mat.mtrl-sci↗