arXiv subjects

M. Orlita

Publications and source records attributed to M. Orlita.

At least 37 records · Page 2Linked to original sources

arXiv2023

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 $Γ_{8}$ band inversion in GdPtBi by means of infrared spectroscopy.

cond-mat.mes-hall↗

arXiv2023

Magneto-optical sensing of the pressure driven magnetic ground states in bulk CrSBr

Competition between exchange interactions and magnetocrystalline anisotropy may bring new magnetic states that are of great current interest. An applied hydrostatic pressure can further be used to tune their balance. In this work we investigate the magnetization process of a biaxial antiferromagnet in an external magnetic field applied along the easy axis. We find that the single metamagnetic transition of the Ising type observed in this material under ambient pressure transforms under hydrostatic pressure into two transitions, a first-order spin flop transition followed by a second order transition towards a polarized ferromagnetic state near saturation. This reversible tuning into a new magnetic phase is obtained in layered bulk CrSBr at low temperature by varying the interlayer distance using high hydrostatic pressure, which efficiently acts on the interlayer magnetic exchange, and is probed by magneto-optical spectroscopy.

cond-mat.mes-hall↗

arXiv2023

EuCd$_2$As$_2$: a magnetic semiconductor

EuCd$_2$As$_2$ is now widely accepted as a topological semimetal in which a Weyl phase is induced by an external magnetic field. We challenge this view through firm experimental evidence using a combination of electronic transport, optical spectroscopy and excited-state photoemission spectroscopy. We show that the EuCd$_2$As$_2$ is in fact a semiconductor with a gap of 0.77 eV. We show that the externally applied magnetic field has a profound impact on the electronic band structure of this system. This is manifested by a huge decrease of the observed band gap, as large as 125~meV at 2~T, and consequently, by a giant redshift of the interband absorption edge. However, the semiconductor nature of the material remains preserved. EuCd$_2$As$_2$ is therefore a magnetic semiconductor rather than a Dirac or Weyl semimetal, as suggested by {\em ab initio} computations carried out within the local spin-density approximation.

cond-mat.mtrl-sci↗

arXiv2023

Magnon gap excitations in van der Waals antiferromagnet MnPSe$_3$

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.

cond-mat.mtrl-sci↗

arXiv2023

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.

cond-mat.mes-hall↗

arXiv2023

Evidence of 3D Dirac conical bands in TlBiSSe by optical and magneto-optical spectroscopy

TlBiSSe is a rare realization of a 3D semimetal with a conically dispersing band that has an optical response which is well isolated from other contributions in a broad range of photon eneries. 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 $v= 4.0\times 10^5$~m/s. % Finally, we provide a theoretical recipe to extract all parameters of the anisotropic Dirac band, including the Fermi energy and band degeneracy.

cond-mat.mtrl-sci↗

arXiv2023

Terahertz cyclotron emission from two-dimensional Dirac fermions

Since the emergence of graphene, we have seen several proposals for the realization of Landau lasers tunable over the terahertz frequency range. The hope was that the non-equidistance of the Landau levels from Dirac fermions would suppress the harmful non-radiative Auger recombination. Unfortunately, even with this non-equidistance an unfavorable non-radiative process persists in Landau-quantized graphene, and so far no cyclotron emission from Dirac fermions has been reported. One way to eliminate this last non-radiative process is to sufficiently modify the dispersion of the Landau levels by opening a small gap in the linear band structure. A proven example of such gapped graphene-like materials are HgTe quantum wells close to the topological phase transition. In this work, we experimentally demonstrate Landau emission from Dirac fermions in such HgTe quantum wells, where the emission is tunable by both the magnetic field and the carrier concentration. Consequently, these results represent an advance in the realization of terahertz Landau lasers tunable by magnetic field and gate-voltage.

cond-mat.mes-hall↗

arXiv2023

Temperature dependence of the energy band gap in ZrTe$_5$: implications for the topological phase

Using 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 $E_g=(5 \pm 1)$ meV at low temperatures and increases monotonously when the temperature is raised. This implies that ZrTe$_5$ is a weak topological insulator, with non-inverted ordering of electronic bands in the center of the Brillouin zone. Our magneto-transport experiments performed in parallel show that the resistivity anomaly in ZrTe$_5$ is not connected with the temperature dependence of the band gap.

cond-mat.mes-hall↗

arXiv2022

Lorentz-boost-driven magneto-optics in a Dirac nodal-line semimetal

Optical response of crystalline solids is to a large extent driven by excitations that promote electrons among individual bands. This allows one to apply optical and magneto-optical methods to determine experimentally the energy band gap - a fundamental property crucial to our understanding of any solid - with a great precision. Here we show that such conventional methods, applied with great success to many materials in the past, do not work in topological Dirac semimetals with a dispersive nodal line. There, the optically deduced band gap depends on how the magnetic field is oriented with respect to the crystal axes. Such highly unusual behaviour is explained in terms of band-gap renormalization driven by Lorentz boosts.

cond-mat.mes-hall↗

arXiv2022

Spatially resolved optical spectroscopy in extreme environment of low temperature, high magnetic fields and high pressure

We present an experimental set-up developed to perform optical spectroscopy experiments (Raman scattering and photoluminescence measurements) with a micrometer spatial resolution, in an extreme environment of low temperature, high magnetic field and high pressure. This unique experimental setup, to the best of our knowledge, allows us to explore deeply the phase diagram of condensed matter systems by tuning independently these three thermodynamic parameters, while monitoring the low-energy excitations (electronic, phononic or magnetic excitations), to spatially map the Raman scattering response or to investigate objects with low dimensions. We apply this technique to bulk FePS3, a layered antiferromagnet with a Neel temperature of T = 120 K.

cond-mat.mtrl-sci↗

arXiv2021

Optical conductivity signatures of open Dirac nodal lines

We investigate the optical conductivity and far-infrared magneto-optical response of BaNiS$_2$, a simple square-lattice semimetal characterized by Dirac nodal lines that disperse exclusively along the out-of-plane direction. With the magnetic field aligned along the nodal line the in-plane Landau level spectra show a nearly $\sqrt{B}$ behavior, the hallmark of a conical-band dispersion with a small spin-orbit coupling gap. The optical conductivity exhibits an unusual temperature-independent isosbestic line, ending at a Van Hove singularity. First-principles calculations unambiguously assign the isosbestic line to transitions across Dirac nodal states. Our work suggests a universal topology of the electronic structure of Dirac nodal lines.

cond-mat.mtrl-sci↗

arXiv2021

Magnon-polarons in van der Waals antiferromagnet FePS3

The hybridization of magnons (spin waves) with phonons, if sufficiently strong and comprising long wavelength excitations, may offer a new playground when manipulating the magnetically ordered systems with light. Applying a magnetic field to a quasi-2D antiferromagnet, FePS3, we tune the magnon-gap excitation towards coincidence with the initially lower-in-energy phonon modes. Hybrid magnon-phonon modes, the magnon polarons are unveiled with demonstration of a pronounced avoided crossing between the otherwise bare magnon and phonon excitations. The magnon polarons in FePS3 are primary traced with Raman scattering experiments, but, as we show, they also couple directly to terahertz photons, what evokes their further explorations in the domain of antiferromagnetic optospintronics.

cond-mat.mtrl-sci↗

arXiv2020

Suppressed Auger scattering and tunable light emission of Landau-quantized massless Kane electrons

The Landau level laser has been proposed a long time ago as a unique source of monochromatic radiation, widely tunable in the THz and infrared spectral ranges using an externally applied magnetic field. In spite of decades of efforts, this appealing concept never resulted in the design of a reliable device. This is due to efficient Auger scattering of Landau-quantized electrons, which is an intrinsic non-radiative recombination channel that eventually gains over cyclotron emission in all materials studied so far: in conventional semiconductors with parabolic bands, but also in graphene with massless electrons. The Auger processes are favored in these systems by Landau levels (or their subsets) equally spaced in energy. Here we show that this scheme does not apply to massless Kane electrons in gapless HgCdTe alloy, in which undesirable Auger scattering is strongly suppressed and the sizeable cyclotron emission observed, for the first time in the case of massless particles. The gapless HgCdTe thus appears as a material of choice for future technology of Landau level lasers.

cond-mat.mes-hall↗

arXiv2020

Landau level spectroscopy of Bi$_2$Te$_3$

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 $Γ$ point where profound inversion exists andgives rise to relativistic-like surface states of Bi$_2$Te$_3$.

cond-mat.mes-hall↗

arXiv2020

Distinguishing the gapped and Weyl semimetal scenario in ZrTe$_5$: insights from an effective two-band model

Here we study the static and dynamic transport properties of a low energy two-band model proposed previously in E. Martino et al. [PRL 122, 217402 (2019), arXiv:1905.00280], with an anisotropic in-plane linear momentum dependence, and a parabolic out-of-plane dispersion. The model is extended to include a negative band gap, which leads to the emergence of a Weyl semimetal (WSM) state, as opposed to the gapped semimetal (GSM) state when the band gap is positive. We calculate and compare the zero and finite frequency transport properties of the GSM and WSM cases. The $dc$ properties that are calculated for the GSM and WSM cases are Drude spectral weight, mobility and resistivity. We determine their dependence on the Fermi energy and crystal direction. The in- and out-of-plane optical conductivities are calculated in the limit of the vanishing interband relaxation rate for both semimetals. The main common features are an $ω^{1/2}$ in-plane and $ω^{3/2}$ out-of-plane frequency dependence of the optical conductivity. We seek particular features related to the charge transport that could unambiguously point to one ground state over the other, based on the comparison with the experiment. Differences between the WSM and GSM are in principle possible only at extremely low carrier concentrations, and at low temperatures.

cond-mat.mes-hall↗

arXiv2020

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

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 interaction and inverse ordering of electronic bands. Here, we report on unusual Landau-level transitions in the monopnictide TaP that decrease in energy with increasing magnetic field. We show that these transitions arise naturally at intermediate energies in time-reversal-invariant Weyl semimetals where the Weyl nodes are formed by a partially gapped nodal-loop in the band structure. We propose a simple theoretical model for electronic bands in these Weyl materials that captures the collected magneto-optical data to great extent.

cond-mat.mes-hall↗

arXiv2020

Flipping exciton angular momentum with chiral phonons in MoSe$_2$/WSe$_2$ heterobilayers

Identifying quantum numbers to label elementary excitations is essential for the correct description of light-matter interaction in solids. In monolayer semiconducting transition metal dichalcogenides (TMDs) such as MoSe$_2$ or WSe$_2$, most optoelectronic phenomena are described well by labelling electron and hole states with the spin projection along the normal to the layer (S$_z$). In contrast, for WSe$_2$/MoSe$_2$ interfaces recent experiments show that taking S$_z$ as quantum number is not a good approximation, and spin mixing needs to be always considered. Here we argue that the correct quantum number for these systems is not S$_z$, but the $z$-component of the total angular momentum -- J$_z$ = L$_z$ + S$_z$ -- associated to the C$_3$ rotational lattice symmetry, which assumes half-integer values corresponding modulo 3 to distinct states. We validate this conclusion experimentally through the observation of strong intervalley scattering mediated by chiral optical phonons that -- despite carrying angular momentum 1 -- cause resonant intervalley transitions of excitons, with an angular momentum difference of 2.

cond-mat.mes-hall↗

arXiv2020

Infrared spectroscopy study of the in-plane response of YBa2Cu3O6.6 in magnetic fields up to 30 Tesla

With Terahertz and Infrared spectroscopy we studied the in-plane response of an underdoped YBa2Cu3O6.6 single crystal with Tc=58(1) K in high magnetic fields up to B=30 Tesla 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 (Cu-CDW) which was previously shown to develop at such high magnetic fields. Our study confirms that a B-field in excess of 20 Tesla gives rise to a full suppression of the macroscopic response of the superconducting condensate. However, it reveals surprisingly weak signatures of the 3d Cu-CDW at high magnetic fields. At 30 Tesla there is only a weak reduction of the spectral weight of the Drude-response (by about 3%) that is accompanied by an enhancement of two narrow electronic modes around 90 and 240 cm-1, that are interpreted in terms of pinned phase modes of the CDW along the a- and b-direction, respectively, and of the so-called mid-infrared (MIR) band. The pinned phased modes and the MIR band are strong features already without magnetic field which suggests that prominent but short-ranged and slowly fluctuating (compared to the picosecond IR-time scale) CDW correlations exist all along, i.e., even at zero magnetic field.

cond-mat.supr-con↗