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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

Nonthermal excitonic condensation near a spin-state transition

Werner, Philipp ; Murakami, Yuta

In: Physical Review B, 2020, vol. 102, no. 2020-24, p. 241103

Recent experiments demonstrate the induction of long-range order in correlated electron systems via external perturbations, which calls for a better understanding of nonthermal ordered states and nonequilibrium symmetry breaking. Here, we reveal a mechanism based on entropy cooling and entropy trapping in a strongly correlated multiorbital system. We consider a two-orbital Hubbard model with...

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

${\eta}$-paired superconducting hidden phase in photodoped Mott insulators

Li, Jiajun ; Golez, Denis ; Werner, Philipp ; Eckstein, Martin

In: Physical Review B, 2020, vol. 102, no. 16, p. 165136

We show that a metastable η-pairing superconducting phase can be induced by photodoping doublons and holes into a strongly repulsive fermionic Hubbard model. The doublon-hole condensate originates from an intrinsic doublon-hole exchange interaction and does not rely on the symmetry of the half-filled Hubbard model. It extends over a wide range of doublon densities and effective temperatures....

Université de Fribourg

NESSi : The Non-Equilibrium Systems Simulation package

Schüler, Michael ; Golež, Denis ; Murakami, Yuta ; Bittner, Nikolaj ; Herrmann, Andreas ; U.R.Strand, Hugo ; Werner, Philipp ; Eckstein, Martin

In: Computer Physics Communications, 2020, vol. 257, no. 2020, p. 107484

The nonequilibrium dynamics of correlated many-particle systems is of interest in connection with pump–probe experiments on molecular systems and solids, as well as theoretical investigations of transport properties and relaxation processes. Nonequilibrium Green’s functions are a powerful tool to study interaction effects in quantum many-particle systems out of equilibrium, and to extract...

Université de Fribourg

Entropy and electronic orders of the three-orbital Hubbard model with antiferromagnetic Hund coupling

Yue, Changming ; Hoshino, Shintaro ; Werner, Philipp

In: Physical Review B, 2020, vol. 102, no. 19, p. 195103

An antiferromagnetic Hund coupling in multiorbital Hubbard systems induces orbital freezing and an associated superconducting instability, as well as unique composite orders in the case of an odd number of orbitals. While the rich phase diagram of the half-filled three-orbital model has recently been explored in detail, the properties of the doped system remain to be clarified. Here, we...

Université de Fribourg

Dynamical conductivity of lithium-intercalated hexagonal boron nitride films : A memory function approach

Rukelj, Zoran

In: Physical Review B, 2020, vol. 102, no. 20, p. 205108

This work is a study of dynamical conductivity of a quasi-two-dimensional heterostructure Li(BN)8. The conducting electrons have a free-electron-like parabolic dispersion and are assumed to scatter only on acoustic phonons. The approach used to derive the generalized Drude relation with frequency and temperature dependent relaxation consists of defining the induced current density as a...

Université de Fribourg

Nature of native atomic defects in ${\mathrm{ZrTe}}_{5}$ and their impact on the low-energy electronic structure

Salzmann, Bjoern ; Pulkkinen, Aki ; Hildebrand, Baptiste ; Jaouen, Thomas ; Zhang, S. N. ; Martino, E. ; Li, Q. ; Gu, G. ; Berger, Helmuth ; Yazyev, O. V. ; Akrap, Ana ; Monney, Claude

In: Physical Review Materials, 2020, vol. 4, no. 11, p. 114201

Over the past decades, investigations of the anomalous low-energy electronic properties of ZrTe5 have reached a wide array of conclusions. An open question is the growth method's impact on the stoichiometry of ZrTe5 samples, especially given the very small density of states near its chemical potential. Here we report on high- resolution scanning tunneling microscopy and spectroscopy...