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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

Ultrafast coupled charge and spin dynamics in strongly correlated NiO

Gillmeister, Konrad ; Golež, Denis ; Chiang, Cheng-Tien ; Bittner, Nikolaj ; Pavlyukh, Yaroslav ; Berakdar, Jamal ; Werner, Philipp ; Widdra, Wolf

In: Nature Communications, 2020, vol. 11, no. 1, p. 4095

Charge excitations across an electronic band gap play an important role in opto- electronics and light harvesting. In contrast to conventional semiconductors, studies of above-band-gap photoexcitations in strongly correlated materials are still in their infancy. Here we reveal the ultrafast dynamics controlled by Hund’s physics in strongly correlated photoexcited NiO. By combining...

Université de Fribourg

Mapping the unoccupied state dispersions in ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$ with resonant inelastic x-ray scattering

Monney, Claude ; Herzog, Marc ; Pulkkinen, Aki ; Huang, Y. ; Pelliciari, Jonathan ; Olalde-Velasco, P. ; Katayama, Naoyuk ; Nohara, Minoru ; Takagi, Hide ; Schmitt, Thorsten ; Mizokawa, Takashi

In: Physical Review B, 2020, vol. 102, no. 8, p. 085148

The transition metal chalcogenide Ta2NiSe5 undergoes a second-order phase transition at Tc=328K involving a small lattice distortion. Below Tc, a band gap at the center of its Brillouin zone increases up to about 0.35 eV. In this work, we study the electronic structure of Ta2NiSe5 in its low-temperature semiconducting phase, using resonant inelastic x-ray scattering (RIXS) at the Ni L3 edge....

Université de Fribourg

High‐ TC interfacial ferromagnetism in SrMnO 3 LaMnO 3 superlattices

Keunecke, Marius ; Lyzwa, Fryderyk ; Schwarzbach, Danny ; Roddatis, Vladimir ; Gauquelin, Nicolas ; Müller‐Caspary, Knut ; Verbeeck, Johann ; Callori, Sara J. ; Klose, Frank ; Jungbauer, Markus ; Moshnyaga, Vasily

In: Advanced Functional Materials, 2020, vol. 30, no. 18, p. 1808270

Heterostructures of strongly correlated oxides demonstrate various intriguing and potentially useful interfacial phenomena. LaMnO3/SrMnO3 superlattices are presented showcasing a new high‐temperature ferromagnetic phase with Curie temperature, T C ≈360 K, caused by electron transfer from the surface of the LaMnO3 donor layer into the neighboring SrMnO3 acceptor layer. As a result, the...

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

Probing intraband excitations in ${\mathrm{ZrTe}}_{5}$: A high-pressure infrared and transport study

Santos-Cottin, D. ; Padlewski, M. ; Martino, E. ; David, S. Ben ; Mardelé, F. Le ; Capitani, F. ; Borondics, F. ; Bachmann, M. D. ; Putzke, C. ; Moll, P. J. W. ; Zhong, R. D. ; Gu, G. D. ; Berger, H. ; Orlita, M. ; Homes, C. C. ; Rukelj, Z. ; Akrap, Ana

In: Physical Review B, 2020, vol. 101, no. 12, p. 125205

Zirconium pentatetelluride, ZrTe5, shows remarkable sensitivity to hydrostatic pressure. In this work we address the high-pressure transport and optical properties of this compound, on samples grown by flux and chemical vapor transport. The high-pressure resistivity is measured up to 2 GPa, and the infrared transmission up to 9 GPa. The dc conductivity anisotropy is determined using a...

Université de Fribourg

Magneto-optics of a Weyl semimetal beyond the conical band approximation: case study of tap

Polatkan, S. ; Goerbig, M. O. ; Wyzula, J. ; Kemmler, R. ; Maulana, L. Z. ; Piot, B. A. ; Crassee, I. ; Akrap, Ana ; Shekhar, C. ; Felser, C. ; Dressel, M. ; Pronin, A. V. ; Orlita, M.

In: Physical Review Letters, 2020, vol. 124, no. 17, p. 176402

Landau-level spectroscopy, the optical analysis of electrons in materials subject to a strong magnetic field, is a versatile probe of the electronic band structure and has been successfully used in the identification of novel states of matter such as Dirac electrons, topological materials or Weyl semimetals. The latter arise from a complex interplay between crystal symmetry, spin-orbit...

Université de Fribourg

Low-energy excitations in type-II Weyl semimetal ${T}_{d}\text{\ensuremath{-}}{\mathrm{MoTe}}_{2}$ evidenced through optical conductivity

Santos-Cottin, David ; Martino, Edoardo ; Le Mardelé, Florian ; Witteveen, C. ; Rohr, F. O. von ; Homes, C. C. ; Rukelj, Z. ; Akrap, Ana

In: Physical Review Materials, 2020, vol. 4, no. 2, p. 021201

Molybdenum ditelluride, MoTe2, is a versatile material where the topological phase can be readily tuned by manipulating the associated structural phase transition. The fine details of the band structure of MoTe2, key to understanding its topological properties, have proven difficult to disentangle experientially due to the multiband character of the material. Through experimental optical...

Université de Fribourg

Classification and characterization of nonequilibrium Higgs modes in unconventional superconductors

Schwarz, L. ; Fauseweh, B. ; Tsuji, N. ; Cheng, N. ; Bittner, Nikolaj ; Krull, H. ; Berciu, M. ; Uhrig, G.S. ; Schnyder, A.P. ; Kaiser, S. ; Manske, D.

In: Nature Communications, 2020, vol. 11, no. 1, p. 1–9

Recent findings of new Higgs modes in unconventional superconductors require a classification and characterization of the modes allowed by nontrivial gap symmetry. Here we develop a theory for a tailored nonequilibrium quantum quench to excite all possible oscillation symmetries of a superconducting condensate. We show that both a finite momentum transfer and quench symmetry allow for an...

Université de Fribourg

Multiband nonequilibrium G W + EDMFT formalism for correlated insulators

Golež, Denis ; Eckstein, Martin ; Werner, Philipp

In: Physical Review B, 2019, vol. 100, no. 23, p. 235117

We study the dynamics of charge-transfer insulators after a photoexcitation using the three-band Emery model which is relevant for the description of cuprate superconductors. We provide a detailed derivation of the nonequilibrium extension of the multiband GW + EDMFT formalism and the corresponding downfolding procedure. The Peierls construction of the electron-light coupling is generalized...