Magnon gap excitations and spin-entangled optical transition in van der Waals antiferromagnet NiPS3

Optical magneto-spectroscopy methods (Raman scattering, far-infrared transmission, and photoluminescence) have been applied to investigate the properties of the NiPS3 semiconducting antiferromagnet. The fundamental magnon gap excitation in this van der Waals material has been found to be split into two components, in support of the biaxial character of the NiPS3 antiferromagnet. Photoluminescence measurements in the near-infrared spectral range show that the intriguing 1.475 eV-excitation unique to the NiPS3 antiferromagnetic phase splits upon the application of the in-plane magnetic field. The observed splitting patterns are correlated with properties of magnon excitations and reproduced with the simple model proposed. Possible routes toward a firm identification of the spin-entangled 1.475 eV-optical excitation in NiPS3, which can hardly be recognized as a coherent Zhang-Rice exciton, are discussed.Comment: 8 pages, 8 figure

Exchange gap in GdPtBi probed by magneto-optics

We measured the magneto-reflectivity spectra (4 - 90 meV, 0 - 16 T) of the triple-point semimetal GdPtBi and found them to demonstrate two unusual broad features emerging in field. The electronic bands of GdPtBi are expected to experience large exchange-mediated shifts, which lends itself to a description via effective Zeeman splittings with a large g factor. Based on this approach, along with an ab initio band structure analysis, we propose a model Hamiltonian that describes our observations well and allows us to estimate the effective g factor, g* = 95. We conclude that we directly observe the exchange-induced $\Gamma_{8}$ band inversion in GdPtBi by means of infrared spectroscopy.Comment: 9 pages, SM include

Magnon gap excitations in van der Waals antiferromagnet MnPSe3_3

Magneto-spectroscopy methods have been employed to study the zero-wavevector magnon excitations in MnPSe$_3$. Experiments carried out as a function of temperature and the applied magnetic field show that two low-energy magnon branches of MnPSe$_3$ in its antiferromagnetic phase are gapped. The observation of two low-energy magnon gaps (at 14 and 0.7 cm$^{-1}$) implies that MnPSe$_3$ is a biaxial antiferromagnet. A relatively strong out-of-plane anisotropy imposes the spin alignment to be in-plane whereas the spin directionality within the plane is governed by a factor of 2.5 $\times$ 10$^{-3}$ weaker in-plane anisotropy.Comment: 9 pages, 3 figure

Landau level spectroscopy of Bi2_2Te3_3

Here we report on Landau level spectroscopy in magnetic fields up to 34 T performed on a thin film of topological insulator Bi$_2$Te$_3$ epitaxially grown on a BaF$_2$ substrate. The observed response is consistent with the picture of a direct-gap semiconductor in which charge carriers closely resemble massive Dirac particles. The fundamental band gap reaches $E_g=(175\pm 5)$~meV at low temperatures and it is not located on the trigonal axis, thus displaying either six or twelvefold valley degeneracy. Notably, our magneto-optical data do not indicate any band inversion. This suggests that the fundamental band gap is relatively distant from the $\Gamma$ point where profound inversion exists andgives rise to relativistic-like surface states of Bi$_2$Te$_3$.Comment: 12 pages, 11 figures, to be published in Phys. Rev.

Magnon gap excitations and spin-entangled optical transition in the van der Waals antiferromagnet NiPS 3

International audienceOptical magneto-spectroscopy methods (Raman scattering, far-infrared transmission, and photoluminescence) have been applied to investigate the properties of the NiPS 3 semiconducting antiferromagnet. The fundamental magnon gap excitation in this van der Waals material has been found to be split into two components, in support of the biaxial character of the NiPS 3 antiferromagnet. Photoluminescence measurements in the near-infrared spectral range show that the intriguing 1.475 eV excitation unique to the NiPS 3 antiferromagnetic phase splits upon the application of the in-plane magnetic field. The observed splitting patterns are correlated with properties of magnon excitations and reproduced with the simple model proposed. Possible routes towards a firm identification of the spin-entangled 1.475 eV optical excitation in NiPS 3 , which can hardly be recognized as a coherent Zhang-Rice exciton, are discussed

Temperature dependence of the energy band gap in ZrTe 5 : Implications for the topological phase

International audienceUsing Landau-level spectroscopy, we determine the temperature dependence of the energy band gap in zirconium pentatelluride (ZrTe 5). We find that the band gap reaches E g = (5 ± 1) meV at low temperatures and increases monotonically when the temperature is raised. This implies that ZrTe 5 is a weak topological insulator, with noninverted ordering of electronic bands in the center of the Brillouin zone. Our magnetotransport experiments performed in parallel show that the resistivity anomaly in ZrTe 5 is not connected with the temperature dependence of the band gap

Transverse and longitudinal magnons in the strongly anisotropic antiferromagnet FePSe 3

International audienc

Polaronic interaction in a single modulation-doped GaAs quantum well with the Feynman-Hellwarth-Iddings-Platzman approximation

International audienceAbsolute far-infrared magnetotransmission experiments have been performed in magnetic fields up to 33.5 T on a series of single GaAs quantum wells doped with different electron concentrations. The transmission spectra have been simulated with a multilayer dielectric model. The imaginary part of the optical response function, which reveals singular features related to the electron-phonon interactions, has been extracted. In addition to the expected polaronic effects due to the longitudinal-optical phonon of GaAs, additional interactions with interface phonons are observed. The main interaction is analyzed quantitatively with the Feynman-Hellwarth-Iddings-Platzman model, which is shown to predict correctly the concentration of carriers beyond which the Fröhlich interaction is completely screened

Evidence for three-dimensional Dirac conical bands in TlBiSSe by optical and magneto-optical spectroscopy

TlBiSSe is a rare realization of a three-dimensional semimetal with a conically dispersing band that has an optical response which is well isolated from other contributions in a broad range of photon energies. We report optical and magneto-optical spectroscopy on this material. When the compound is chemically tuned into a state of the lowest carrier concentration, we find a nearly linear frequency dependence of the optical conductivity below 0.5 eV. Landau level spectroscopy allows us to describe the system with a massive Dirac model, giving a gap 2Δ=32 meV and an in-plane velocity parameter vxy=4.0×105 m/s