Oxide-Heterostructures

Carefully controlled interfaces between two materials can give rise to novel physical phenomena and functionalities not exhibited by either of the constituent materials alone. Modern synthesis methods have yielded high-quantum heterostructures and superlattices of oxide materials with competing quantum many-body states. In order to explore new correlation-driven interface phenomena, our group seeks to understand and manipulate spin, charge and orbital order at oxide interfaces.

Epitaxial stabilization of cuprate compounds that are unstable in bulk form offers new opportunities to explore the interplay between superconductivity and charge order. Because of the nearly identical ionic radii of La and Ca (Fig. 8a), the La_2-xCa_xCuO₄ system is the least disordered among the archetypical “214” cuprate superconductors, but it is unstable in bulk form. Using oxide molecular beam epitaxy, we were able to synthesize homogeneous, highly overdoped La_2-xCa_xCuO₄ thin films and found that superconductivity persists up to a doping level of 50%. We also found that this system is an excellent platform for the investigation of atomic short-range order and charge order.

Interplay between electronic and atomic short-range order in La_2−𝑥Ca_𝑥CuO_4−𝛿 : Temperature and doping dependence
S. Hameed, Y. Liu, K. S. Rabinovich, G. Kim, M. Neumann, P. Wochner, G. Christiani, G. Logvenov, K. Higuchi, N. B. Brookes , E. Weschke, F. Yakhou-Harris, A. V. Boris, B. Keimer, and M. Minola
Physical Review B 112, L161114 (2025)
Optical conductivity and superconductivity in highly overdoped La_2−xCa_xCuO₄ thin films
Gideok Kim, Ksenia S. Rabinovich, Alexander V. Boris, Alexander N. Yaresko, Y. Eren Suyolcu, Yu-Mi Wu, Peter A. van Aken, Georg Christiani, Gennady Logvenov, Bernhard Keimer
PNAS 118, e2106170118 (2021)
 

The flexible and comparatively simple perovskite structure allows for straightforward chemical substitution and cube-on-cube combination of different compounds in atomically sharp epitaxial heterostructures. Many of the diverse physical properties of perovskites are determined by small deviations from the ideal cubic perovskite structure, which are challenging to control. We have shown that directional imprinting of atomic displacements in the antiferromagnetic Mott insulator YVO₃ can be achieved by depositing epitaxial films on different facets of the same isostructural substrate. Our results show that substrate-induced templating of lattice distortion patterns constitutes a pathway for materials design beyond established strain-engineering strategies.

Imprinted atomic displacements drive spin–orbital order in a vanadate perovskite
P. Radhakrishnan, K.S. Rabinovich, A.V. Boris, K. Fürsich, M. Minola, G. Christiani, G. Logvenov, B. Keimer, and E. Benckiser
Nature Physics 21, 126-131 (2025)
 

The detection and quantification of hydrogen is becoming increasingly important in research on
electronic materials and devices, following the identification of the hydrogen content as a potent
control parameter for the electronic properties. However, establishing quantitative correlations
between the hydrogen content and the physical properties of solids remains a formidable
challenge. We have established a resonance-enhanced neutron reflectometry method that
allows fast, direct, and non-destructive measurements of the hydrogen concentration in thin-film structures and thus offers new insights into the mechanisms underlying the influence of hydrogen in functional metal-oxide devices.

Understanding the Role of Hydrogen and Oxygen in Electronic Phase Changes of Nickelates
Laura Guasco, Rebecca Pons, David Cortie, Lars J. Bannenberg, Peter Wochner, Eberhard Goering, Peter Nagel, Stefan Schuppler, Shohei Hayashida, Rotraut Merkle, Bernhard Keimer, Thomas Keller, Eva Benckiser
Adv. Funct. Mater. 2419253 (2024)
Resonant neutron reflectometry for hydrogen detection
L. Guasco, Yu. N. Khaydukov, S. Pütter, L. Silvi, M. A. Paulin, T. Keller, B. Keimer
Nature Communications 13, 1486 (2022)
 

Devices with tunable magnetic non-collinearity are important components of spintronic and magnonic circuits. We have devised different means of generating tunable non-collinear magnetic ordering patterns in oxide thin-film structures. Recently, for instance, we have discovered surprisingly complex magnetic fan structures in spin-polarized neutron scattering experiments on simple La_1−xSr_xMnO₃ homojunction arrays with alternating doping levels x.

Emergent Magnetic fan Structures in Manganite Homojunction Arrays
Laura Guasco, Yury Khaydukov, Gideok Kim, Thomas Keller, Alexei Vorobiev, Anton Devishvili, Peter Wochner, Georg Christiani, Gennady Logvenov, Bernhard Keimer
Advanced Materials 34, 2202971 (2022)