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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...

Université de Fribourg

Terahertz-driven phonon upconversion in SrTiO 3

Kozina, M. ; Fechner, M. ; Marsik, Premysl ; Driel, T. van ; Glownia, J. M. ; Bernhard, Christian ; Radovic, M. ; Zhu, D. ; Bonetti, S. ; Staub, U. ; Hoffmann, M. C.

In: Nature Physics, 2019, vol. 15, no. 4, p. 387–392

Direct manipulation of the atomic lattice using intense long-wavelength laser pulses has become a viable approach to create new states of matter in complex materials. Conventionally, a high-frequency vibrational mode is driven resonantly by a mid- infrared laser pulse and the lattice structure is modified through indirect coupling of this infrared-active phonon to other, lower-frequency...

Université de Fribourg

Signatures of the bonding-antibonding splitting in the $c$-axis infrared response of moderately underdoped bilayer and trilayer cuprate superconductors

Mallett, Benjamin P. P. ; Maršík, Premysl ; Munzar, Dominik ; Bernhard, Christian ; Dubroka, Adam

In: Physical Review B, 2019, vol. 99, no. 5, p. 054513

We report on results of our analysis of the c-axis infrared conductivity, σc(ω), of bilayer LnBa2Cu3O7−δ (Ln=La, Nd, Y) and trilayer Bi2Sr2Ca2Cu3O10+δ high-Tc superconductors. The analysis employs the multilayer model involving the conductivity of the bilayer or trilayer unit, σbl(ω), and that of the spacing layers separating the latter units, σint(ω). For the YBa2Cu3O7−δ sample...

Université de Fribourg

Temperature-driven topological phase transition and intermediate Dirac semimetal phase in ${\mathrm{ZrTe}}_{5}$

Xu, B. ; Zhao, L. X. ; Maršík, Premysl ; Sheveleva, E. ; Lyzwa, F. ; Dai, Y. M. ; Chen, G. F. ; Qiu, X. G. ; Bernhard, Christian

In: Physical Review Letters, 2018, vol. 121, no. 18, p. 187401

We present an infrared spectroscopy study of ZrTe5, which confirms a recent theoretical proposal that this material exhibits a temperature-driven topological quantum phase transition from a weak to a strong topological insulating state with an intermediate Dirac semimetal state around Tp ≃ 138 K. Our study details the temperature evolution of the energy gap in the bulk electronic structure....

Université de Fribourg

Coupled Cu and Mn charge and orbital orders in YBa₂Cu₃O₇/Nd 0.65 (Ca 1-y Sr y ) 0.35 MnO₃ multilayers

Perret, Edith ; Monney, Claude ; Johnston, S. ; Khmaladze, Jarji ; Lyzwa, Fryderyk ; Gaina, Roxana ; Dantz, M. ; Pelliciari, Jonathan ; Piamonteze, C. ; Mallett, B.P.P. ; Minola, M. ; Keimer, B. ; Schmitt, Thorsten ; Bernhard, Christian

In: Communications Physics, 2018, vol. 1, no. 1, p. 45

The observation of a charge density wave in the underdoped cuprate high Tc superconductors (Cu-CDW) raised a debate about its relationship with superconductivity. In bulk YBa2Cu3O7−δ the Cu-CDW is incipient and mainly pinned by defects. Nevertheless, a large magnetic field can induce a true long-range Cu- CDW order as it suppresses superconductivity. An enhanced Cu-CDW order was also ...