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Public access from Oct 18, 2021
Université de Fribourg

Total Angular Momentum Dichroism of the Terahertz Vortex Beams at the Antiferromagnetic Resonances

Sirenko, Andrei A. ; Marsik, Premysl ; Bugnon, Laurent ; Soulier, Mathias ; Bernhard, Christian ; Stanislavchuk, T. N. ; Xu, Xianghan ; Cheong, S.-W.

In: Physical Review Letters, 2021, vol. 126, no. 15, p. 157401

Terahertz vortex beams with different superposition of the orbital angular momentum $l={\pm}1$, ${\pm}2$, ${\pm}3$, and ${\pm}4$ and spin angular momentum ${\sigma}={\pm}1$ were used to study antiferromagnetic (AFM) resonances in TbFe$_3$(BO$_3$)$_4$ and Ni$_3$TeO$_6$ single crystals. In both materials we observed a strong vortex beam dichroism for the AFM resonances that are split in ...

Public access from Oct 6, 2021
Université de Fribourg

Infrared study of the multiband low-energy excitations of the topological antiferromagnet MnBi2Te4

Xu, Bing ; Zhang, Y. ; Alizade, E. H. ; Jahangirli, Z. A. ; Lyzwa, Fryderyk ; Sheveleva, Evgeniia ; Marsik, Premysl ; Li, Y. K. ; Yao, Y. G. ; Wang, Z. W. ; Shen, B. ; Dai, Y. M. ; Kataev, V. ; Otrokov, M. M. ; Chulkov, E. V. ; Mamedov, N. T. ; Bernhard, Christian

In: Physical Review B, 2021, vol. 103, no. 12, p. L121103

With infrared spectroscopy, we studied the bulk electronic properties of the topological antiferromagnet MnBi2Te4 with TN ≃ 25 K. With the support of band-structure calculations, we assign the intra- and interband excitations and determine the band gap of Eg ≈ 0.17 eV. We also obtain evidence for two types of conduction bands with light and very heavy carriers. The multiband free-carrier...

Université de Fribourg

Muon spin rotation and infrared spectroscopy study of Ba$_{1-x}$Na$_{x}$Fe$_{2}$As$_{2}$

Sheveleva, Evgeniia ; Xu, Bing ; Marsik, Premysl ; Lyzwa, Fryderyk ; Mallett, Benjamin P. P. ; Willa, K. ; Meingast, C. ; Wolf, Th. ; Shevtsova, T. ; Pashkevich, Yu. G. ; Bernhard, Christian

In: Physical Review B, 2020, vol. 101, no. 22, p. 224515

The magnetic and superconducting properties of a series of underdoped Ba 1 − x Na x Fe 2 As 2 (BNFA) single crystals with 0.19 ≤ x ≤ 0.34 have been investigated with the complementary muon-spin-rotation ( μ SR ) and infrared spectroscopy techniques. The focus has been on the different antiferromagnetic states in the underdoped regime and their competition with superconductivity,...

Université de Fribourg

Optical signatures of multifold fermions in the chiral topological semimetal CoSi

Xu, Bing ; Fang, Zhenyao ; Sánchez-Martínez, Miguel-Angel ; Venderbos, Jorn W. F. ; Ni, Zhuoliang ; Qiu, Tian ; Manna, Kaustuv ; Wang, Kefeng ; Paglione, Johnpierre ; Bernhard, Christian ; Felser, Claudia ; Mele, Eugene J. ; Grushin, Adolfo G. ; Rappe, Andrew M. ; Wu, Liang

In: Proceedings of the National Academy of Sciences, 2020, vol. 117, no. 44, p. 27104–27110

We report the optical conductivity in high-quality crystals of the chiral topological semimetal CoSi, which hosts exotic quasiparticles known as multifold fermions. We find that the optical response is separated into several distinct regions as a function of frequency, each dominated by different types of quasiparticles. The low-frequency intraband response is captured by a narrow Drude peak...

Université de Fribourg

Superconductivity-induced transverse plasma mode and phonon anomaly in the $c$-axis response of the bilayer compound ${\mathrm{RbCa}}_{2}{\mathrm{Fe}}_{4}{\mathrm{As}}_{4}{\mathrm{F}}_{2}$

Xu, Bing ; Munzar, Dominik ; Dubroka, Adam ; Sheveleva, Evgeniia ; Lyzwa, Fryderyk ; Maršík, Premysl ; Wang, C. N. ; Wang, Z. C. ; Cao, G. H. ; Bernhard, Christian

In: Physical Review B, 2020, vol. 101, no. 21, p. 214512

We studied the infrared response of polycrystalline samples of the iron arsenide superconductor (Rb,Cs)Ca2Fe4As4F2 (Rb,Cs-12442), which has a bilayer structure similar to the high-Tc cuprates YBa2Cu3O7 (YBCO) and Bi2Sr2CaCu2O8. The c-axis reflectivity spectra Rc have been derived from the reflectivity spectra of the polycrystalline samples Rpoly and the in-plane spectrum of a corresponding...

Université de Fribourg

Infrared spectroscopy study of the in-plane response of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.6}$ in magnetic fields up to 30 Tesla

Lyzwa, Fryderyk ; Xu, Bing ; Maršík, Premysl ; Sheveleva, Evgeniia ; Crassee, I. ; Orlita, M. ; Bernhard, Christian

In: Physical Review Research, 2020, vol. 2, no. 2, p. 023218

With terahertz and infrared spectroscopy we studied the in-plane response of an underdoped, twinned YBa2Cu3O6.6 single crystal with Tc=58(1)K in high magnetic fields up to B=30 Tesla (T) applied along the c axis. Our goal was to investigate the field-induced suppression of superconductivity and to observe the signatures of the three-dimensional (3D) incommensurate copper charge density wave...

Université de Fribourg

Backfolded acoustic phonons as ultrasonic probes in metal-oxide superlattices

Lyzwa, Fryderyk ; 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

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...