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Université de Fribourg

Backfolded acoustic phonons as ultrasonic probes in metal-oxide superlattices

Lyzwa, F. ; Chan, A. ; Khmaladze, Jarji ; Fürsich, K. ; Keimer, B. ; Bernhard, Christian ; Minola, M. ; Mallett, Benjamin P. P.

In: Physical Review Materials, 2020, vol. 4, no. 4, p. 043606

Ultrasonics have been an incisive probe of internal interfaces in a wide variety of systems ranging from stars to solids. For thin-film structures, however, ultrasound is largely ineffective because the signal is dominated by the substrate. Using confocal Raman spectromicroscopy, we show that multiple reflection of sound waves at internal interfaces of a metal-oxide superlattice generates...

Université de Fribourg

Electron–phonon-driven three-dimensional metallicity in an insulating cuprate

Baldini, Edoardo ; Sentef, Michael A. ; Acharya, Swagata ; Brumme, Thomas ; Sheveleva, Evgeniia ; Lyzwa, Fryderyk ; Pomjakushina, Ekaterina ; Bernhard, Christian ; van Schilfgaarde, Mark ; Carbone, Fabrizio ; Rubio, Angel ; Weber, Cédric

In: Proceedings of the National Academy of Sciences, 2020, vol. 117, no. 12, p. 6409-6416

The role of the crystal lattice for the electronic properties of cuprates and other high-temperature superconductors remains controversial despite decades of theoretical and experimental efforts. While the paradigm of strong electronic correlations suggests a purely electronic mechanism behind the insulator-to-metal transition, recently the mutual enhancement of the electron–electron and the...

Université de Fribourg

Magneto-transport in La2/3Sr1/3MnO3/YBa2Cu3O7/Alq3/Co spin-valves

Cerreta, Andrea ; Gaina, Roxana ; Nuccio, Laura ; Marozau, Ivan ; Sen, Kaushik ; De Andrés Prada, Roberto ; Sarkar, Subhrangsu ; Bernhard, Christian

In: EPL (Europhysics Letters), 2020, vol. 129, no. 3, p. 37002

We studied how an additional layer of the high superconductor YBCO affects the magneto-transport across a LSMO/Alq3/Co spin-valve structure. We found that up to a thickness of at least 10 nm the YBCO layer on top of LSMO hardly changes the spin-valve effect, since the device resistance still depends on the relative orientation of the LSMO and Co magnetization. The spin-valve effect persists...

Université de Fribourg

Optical signature of a crossover from Mott- to Slater-type gap in ${\mathrm{Sr}}_{2}{\mathrm{Ir}}_{1\ensuremath{-}x}{\mathrm{Rh}}_{x}{\mathrm{O}}_{4}$

Xu, Bîng ; Marsik, Premysl ; Sheveleva, Evgeniia ; Lyzwa, Fryderyk ; Louat, A. ; Brouet, V. ; Munzar, Dominik ; Bernhard, Christian ; 2020-01-15

In: Physical Review Letters, 2020, vol. 124, no. 2, p. 027402

With optical spectroscopy we provide evidence that the insulator-metal transition in Sr2Ir1−xRhxO4 occurs close to a crossover from the Mott- to the Slater-type. The Mott gap at x=0 persists to high temperature and evolves without an anomaly across the Néel temperature, TN. Upon Rh doping, it collapses rather rapidly and vanishes around x=0.055. Notably, just as the Mott gap vanishes yet...

Université de Fribourg

Growth and nanofabrication of all-perovskite superconducting/ferromagnetic/superconducting junctions

Andrés Prada, Roberto de ; Golod, T. ; Bernhard, Christian ; Krasnov, V. M.

In: Journal of Superconductivity and Novel Magnetism, 2019, vol. 32, no. 9, p. 2721–2726

We fabricate and study experimentally all-perovskite-oxide superconductor/ferromagnetic insulator/superconductor (S/FI/S) tunnel junctions made out of the high-temperature cuprate superconductor YBa2Cu3O7−y (YBCO) and the colossal magnetoresistive manganite LaMnO3 (LMO) in the ferromagnetic insulator state. YBCO/LMO/YBCO heterostructures with different LMO thicknesses (5, 10, and 20 nm)...

Université de Fribourg

Controlling the strength of ferromagnetic order in YBa2Cu3O7/La2/3Ca1/3MnO3 multilayers

Andrés Prada, Roberto de ; Gaina, Roxana ; Biškup, N. ; Varela, M. ; Stahn, J. ; Bernhard, Christian

In: Physical Review B, 2019, vol. 100, no. 11, p. 115129

With dc magnetization and polarized neutron reflectometry we studied the ferromagnetic response of YBa2Cu3O7/La2/3Ca1/3MnO3 (YBCO/LCMO) multilayers that are grown with pulsed laser deposition. We found that whereas for certain growth conditions (denoted as A type) the ferromagnetic moment of the LCMO layer is strongly dependent on the structural details of the YBCO layer on which it is ...

Université de Fribourg

Terahertz vortex beam as a spectroscopic probe of magnetic excitations

Sirenko, A. A. ; Maršík, Premysl ; Bernhard, Christian ; Stanislavchuk, T. N. ; Kiryukhin, V. ; Cheong, S.-W.

In: Physical Review Letters, 2019, vol. 122, no. 23, p. 237401

Circularly polarized light with spin angular momentum is one of the most valuable probes of magnetism. We demonstrate that light beams with orbital angular momentum (OAM), or vortex beams, can also couple to magnetism exhibiting dichroisms in a magnetized medium. Resonant optical absorption in a ferrimagnetic crystal depends strongly on both the handedness of the vortex and the direction of...

Université de Fribourg

Memory-functionality superconductor/ferromagnet/superconductor junctions based on the high- T c cuprate superconductors YBa 2 Cu 3 O 7 − x and the colossal magnetoresistive manganite ferromagnets La 2 / 3 X 1 / 3 MnO 3 + δ ( X = Ca , Sr )

Andrés Prada, R. de ; Golod, T. ; Kapran, O. M. ; Borodianskyi, E. A. ; Bernhard, Christian ; Krasnov, V. M.

In: Physical Review B, 2019, vol. 99, no. 21, p. 214510

Complex oxides exhibit a variety of unusual physical properties, which can be used for designing novel electronic devices. Here we fabricate and study experimentally nanoscale superconductor/ferromagnet/superconductor junctions with the high-Tc cuprate superconductors YBa2Cu3O7−x and the colossal magnetoresistive (CMR) manganite ferromagnets La2/3X1/3MnO3+δ (X=Ca or Sr). We demonstrate...

Université de Fribourg

Granular superconductivity and charge/orbital order in YBa 2 Cu 3 O 7 /manganite trilayers

Khmaladze, Jarji ; Sarkar, S. ; Soulier, M. ; Lyzwa, F. ; Prada, R. de Andres ; Perret, Edith ; Mallett, B.P.P. ; Minola, M. ; Keimer, B. ; Bernhard, Christian

In: Physical Review Materials, 2019, vol. 3, no. 8, p. 084801

We studied how the electronic, superconducting, and magnetic properties of YBa2Cu3O7/Nd1−x(Ca1−ySry )xMnO3 multilayers depend on the tolerance factor and the hole doping of the manganite. In particular, we investigated the granular superconducting state and the related magnetic-field-driven insulator-to- superconductor transition that was previously discovered in corresponding multilayers...

Université de Fribourg

Scaling of the Fano effect of the in-plane Fe-As phonon and the superconducting critical temperature in ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{K}}_{x}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$

Xu, Bing ; Cappelluti, E. ; Benfatto, Larra ; Mallett, Benjamin P. P. ; Marsik, Premysl ; Sheveleva, Evgeniia ; Lyzwa, F. ; Wolf, Thomas ; Yang, Rui ; Qiu, X. G. ; Dai, Y. M. ; Wen, H. H. ; Lobo, R. P. S. M. ; Bernhard, Christian

In: Physical Review Letters, 2019, vol. 122, no. 21, p. 217002

By means of infrared spectroscopy, we determine the temperature-doping phase diagram of the Fano effect for the in-plane Fe-As stretching mode in Ba1−xKxFe2As2. The Fano parameter 1=q2, which is a measure of the phonon coupling to the electronic particle-hole continuum, shows a remarkable sensitivity to the magnetic and structural orderings at low temperatures. Most strikingly, at elevated...