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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 ...

Université de Fribourg

Optical study of Dirac fermions and related phonon anomalies in the antiferromagnetic compound CaFeAsF

Xu, B. ; Xiao, H. ; Gao, B. ; Ma, Y. H. ; Mu, G. ; Mar?ík, Premysl ; Sheveleva, Evgeniia ; Lyzwa, F. ; Dai, Y. M. ; Lobo, R. P. S. M. ; Bernhard, Christian

In: Physical Review B, 2018, vol. 97, no. 19, p. 195110

We performed optical studies on CaFeAsF single crystals, a parent compound of the 1111-type iron-based superconductors that undergoes a structural phase transition from tetragonal to orthorhombic at Ts=121 K and a magnetic one to a spin density wave (SDW) state at TN=110 K. In the low-temperature optical conductivity spectrum, after the subtraction of a narrow Drude peak, we observe a...

Université de Fribourg

Lattice-mediated magnetic order melting in ${\mathrm{TbMnO}}_{3}$

Baldini, Edoardo ; Kubacka, Teresa ; Mallett, Benjamin P. P. ; Ma, Chao ; Koohpayeh, Seyed M. ; Zhu, Yimei ; Bernhard, Christian ; Johnson, Steven L. ; Carbone, Fabrizio

In: Physical Review B, 2018, vol. 97, no. 12, p. 125149

Recent ultrafast magnetic-sensitive measurements [Johnson et al., Phys. Rev. B 92, 184429 (2015); Bothschafter et al., Phys. Rev. B 96, 184414 (2017)] have revealed a delayed melting of the long-range cycloid spin order in TbMnO3 following photoexcitation across the fundamental Mott-Hubbard gap. The microscopic mechanism behind this slow transfer of energy from the photoexcited carriers to...

Université de Fribourg

In situ monitoring of atomic layer epitaxy via optical ellipsometry

Lyzwa, F. ; Marsik, Premysl ; Roddatis, V. ; Bernhard, Christian ; Jungbauer, M. ; Moshnyaga, V.

In: Journal of Physics D: Applied Physics, 2018, vol. 51, no. 12, p. 125306

We report on the use of time-resolved optical ellipsometry to monitor the deposition of single atomic layers with subatomic sensitivity. Ruddlesden–Popper thin films of SrO(SrTiO3) n=4 were grown by means of metalorganic aerosol deposition in the atomic layer epitaxy mode on SrTiO3(1 0 0), LSAT(1 0 0) and DyScO3(1 1 0) substrates. The measured time dependences of ellipsometric...

Université de Fribourg

Structural, magnetic and electronic properties of pulsed-laser-deposition grown SrFeO 3− δ thin films and SrFeO 3− δ /La 2/3 Ca 1/3 MnO 3 multilayers

Perret, Edith ; Sen, Kaushik ; Khmaladze, Jarji ; Mallett, Benjamin P. P. ; Yazdi-Rizi, Meghdad ; Maršík, Premysl ; Das, Saikat ; Marozau, Ivan ; Uribe-Laverde, Miguel Angel ; Andrés Prada, R. de ; Strempfer, J. ; Döbeli, Max ; Biškup, N. ; Varela, M. ; Mathis, Y.-L. ; Bernhard, Christian

In: Journal of Physics: Condensed Matter, 2017, vol. 29, no. 49, p. 495601

We studied the structural, magnetic and electronic properties of ${\rm SrFeO}_{3- \delta}$ (SFO) thin films and ${\rm SrFeO}_{3-\delta}$ /${\rm La}_{2/3}$ ${\rm Ca}_{1/3}$ MnO3 (LCMO) superlattices that have been grown with pulsed laser deposition (PLD) on ${\rm La}_{0.3}$ ${\rm Sr}_{0.7}$ ${\rm Al}_{0.65}$ ${\rm Ta}_{0.35}$ ${\rm O}_{3}$ (LSAT) substrates. X-ray reflectometry and scanning ...

Université de Fribourg

Superconductivity and charge-carrier localization in ultrathin ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_{4}/{\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$ bilayers

Sen, Kaushik ; Maršík, Premysl ; Das, Saikat ; Perret, E. ; Andres Prada, R. de ; Alberca, Aurora ; Biškup, N. ; Varela, M. ; Bernhard, Christian

In: Physical Review B, 2017, vol. 95, no. 21, p. 214506

La1.85Sr0.15CuO4/La2CuO4 (LSCO15/LCO) bilayers with a precisely controlled thickness of N unit cells (UCs) of the former and M UCs of the latter ([LSCO15_N/LCO_M]) were grown on (001)-oriented SrLaAlO4 (SLAO) substrates with pulsed laser deposition (PLD). X-ray diffraction and reciprocal space map (RSM) studies confirmed the epitaxial growth of the bilayers and showed that a [LSCO15_2/LCO_2]...

Université de Fribourg

Anomalous anisotropic exciton temperature dependence in rutile ${\mathrm{TiO}}_{2}$

Baldini, Edoardo ; Dominguez, Adriel ; Chiodo, Letizia ; Sheveleva, Evgeniia ; Yazdi-Rizi, Meghdad ; Bernhard, Christian ; Rubio, Angel ; Chergui, and Majed

In: Physical Review B, 2017, vol. 96, no. 4, p. 041204

Elucidating the details of electron-phonon coupling in semiconductors and insulators is a topic of pivotal interest, as it governs the transport mechanisms and is responsible for various phenomena such as spectral-weight transfers to phonon sidebands and self-trapping. Here, we investigate the influence of the electron-phonon interaction on the excitonic peaks of rutile TiO2, revealing a strong...

Université de Fribourg

Infrared ellipsometry study of photogenerated charge carriers at the (001) and (110) surfaces of $\mathrm{SrTi}{\mathrm{O}}_{3}$ crystals and at the interface of the corresponding $\mathrm{LaAl}{\mathrm{O}}_{3}/\mathrm{SrTi}{\mathrm{O}}_{3}$ heterostructures

Yazdi-Rizi, Meghdad ; Maršík, Premysl ; Mallett, Benjamin P. P. ; Sen, Kaushik ; Cerreta, A. ; Dubroka, Adam ; Scigaj, M. ; Sánchez, F. ; Herranz, G. ; Bernhard, Christian

In: Physical Review B, 2017, vol. 95, no. 19, p. 195107

With infrared (IR) ellipsometry and dc resistance measurements, we investigated the photodoping at the (001) and (110) surfaces of SrTiO3 (STO) single crystals and at the corresponding interfaces of LaAlO3/SrTiO3 (LAO/STO) heterostructures. In the bare STO crystals, we find that the photogenerated charge carriers, which accumulate near the (001) surface, have a similar depth profile and sheet...