arXiv subjects

Petr Nemec

Publications and source records attributed to Petr Nemec.

8 recordsLinked to original sources

arXiv2026

Laser-Induced Rashba Spin-Orbit Torques in Multiferroic Semiconductor (Ge,Mn)Te

The multiferroic semiconductor GeMnTe exhibits ferroelectricity, strong Rashba spin-orbit coupling, and carrier-mediated magnetic order, making it a unique platform for exploring the interplay among electronic, structural, and magnetic degrees of freedom. In this study, we investigate the ultrafast magnetization dynamics of Ge0.85Mn0.15Te using time-resolved magneto-optical spectroscopy. By separating magnetic and nonmagnetic contributions in the transient response, we identify two distinct laser-induced magnetic phenomena, both resulting from photoinduced effective spin-orbit torque. Coherent magnetization precession arises from a laser-induced increase in hole concentration, which modifies the occupation of Rashba-split spin-locked valence band states and alters the magnetic easy axis. The transient change in magnetic ordering, observed as variations in the coercive field, is attributed to laser-induced modifications of the ferroelectric sublattice displacement, which affect the ferroelectric polarization and the associated Rashba spin-orbit interaction. While the first type of optical spin-orbit torque has already been observed in the diluted magnetic semiconductor (Ga,Mn)As, the second effect is unique to the multiferroic Rashba semiconductor (Ge,Mn)Te, opening new opportunities for all-optical manipulation of magnetic order and spin-orbit torque generation in spin-orbitronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Extended study of crystal structures, optical properties and vibrational spectra of polar 2-aminopyrimidinium hydrogen phosphite and bis(2-aminopyrimidinium) sulfate monohydrate and two 2-aminopyrimidinium hydrogen sulfate polymorphs

This study aimed primarily at completing and extending the characterization of the crystallographic, spectroscopic and optical properties of polar, biaxial, optically negative 2-aminopyrimidinium(1+) hydrogen phosphite. Besides the redetermination of the low-temperature crystal structure (space group P21), high-quality single crystals of this salt were grown from an aqueous solution, and their optical properties were studied. The determination of the refractive indices in the wavelength range of 435-1083 nm showed anomalous dispersion of the refractive indices, resulting in a point of uniaxiality. The crystal allows phase matching for collinear second harmonic generation (SHG) processes of both type I and type II in a broad wavelength range. SHG properties were studied for powdered size-fractioned samples and oriented single-crystal cuts. The optical damage threshold experiments confirmed excellent optical resistance - at least 220 TWm-2 and 70 TWm-2 for 800 and 1000 nm irradiation, respectively. The low-temperature crystallographic study was also extended for three monoclinic salts of 2-aminopyrimidine and sulfuric acid - i.e. bis(2-aminopyrimidinium(1+) sulfate monohydrate (space group P21/n) and two polymorphs of 2-aminopyrimidinium(1+) hydrogen sulfate (both with space group P21/c). The vibrational spectra of all title compounds were assigned using single-molecule quantum chemical computations (including Potential Energy Distribution analysis) in combination with the nuclear site group analysis. Spectroscopic results concerning sulfates of 2-aminopyrimidine provided valuable reference materials for the vibrational spectroscopic study and also addressed the question of their polymorphism. An optimal computational approach employing solid-state DFT calculations has also been sought to model the vibrational spectra of 2-aminopyrimidinium (1+) hydrogen phosphite crystals.

cond-mat.mtrl-sci↗

arXiv2023

Ultrafast Third-Order Nonlinear Optical Response of Charge Coupled Gold Nanoparticle-Ge24Se76 Heterostructure

The donor-acceptor interaction of a charge-coupled heterostructure encompassing a metal and an amorphous semiconductor subjected to a laser field has many potential applications in the realm of nonlinear optics. In this work, we fabricate an electron donor gold nanoparticle (AuNP) and acceptor amorphous Ge24Se76 heterostructure on a quartz substrate using a sequential thermal evaporation technique. In this charge-coupled heterostructure, we demonstrate the ultrafast third-order nonlinear absorptive and refractive response and their sign reversal compared to pristine Ge24Se76. Enhanced optical nonlinearity in these heterostructures of varying plasmonic wavelengths is due to charge transfer, verified by the Raman spectroscopy. Further, the ultrafast transient absorption measurements support the thesis of charge transfer in the AuNP/Ge24Se76 heterostructure. These findings open up exciting opportunities for developing novel device technologies with far-reaching applications in nonlinear optics.

cond-mat.mtrl-sci↗

arXiv2019

Imaging and writing magnetic domains in the non-collinear antiferromagnet Mn$_{\text{3}}$Sn

Harnessing the unique properties of non-collinear antiferromagnets (AFMs) will be essential for exploiting the full potential of antiferromagnetic spintronics. Indeed, many of the effects enabling ferromagnetic spintronic devices have a corresponding counterpart in materials with non-collinear spin structure. In addition, new phenomena such as the magnetic spin Hall effect were experimentally observed in non-collinear AFMs, and the presence of the equivalent to the ferromagnetic spin transfer torque via spin polarized currents was theoretically predicted. In spite of these developments, an interpretation of the rich physical phenomena observed in non-collinear antiferromagnets is challenging, since the microscopic spin arrangement, the magnetic domain distribution, and the domain orientations have proven notoriously difficult to access experimentally. This is all the more problematic, as imaging and writing magnetic domains is of central importance for applications. Successful imaging is a basic requirement to experimentally confirm the spin transfer torque acting on non-collinear domain walls and therefore of eminent interest. Here, we demonstrate that the local magnetic structure of the non-collinear AFM Mn3Sn films can be imaged by scanning thermal gradient microscopy (STGM). The technique is based on scanning a laser spot over the sample's surface, and recording the ensuing thermo-voltage. We image the magnetic structure at a series of different temperatures and show that at room temperature, the domain structure is not affected by the application of moderate magnetic fields. In addition to imaging, we establish a scheme for heat-assisted magnetic recording, using local laser heating in combination with magnetic fields to intentionally write domain patterns into the antiferromagnet.

cond-mat.mes-hall↗

arXiv2018

Experimental demonstration of plasmon-soliton waves

Controlling low power light beam self-confinement with ultrafast response time opens up opportunities for the development of signal processing in microdevices. The combination of highly nonlinear medium with the tight confinement of plasmonic waves offers a viable but challenging configuration to reach this goal. Here, we report the experimental observation of plasmon-soliton waves propagating in a chalcogenide-based four-layer planar geometry engineered to limit plasmon propagation losses while exhibiting efficient Kerr self-focusing at moderate power. The observations reveal a strongly enhanced self-focusing undergone by a self-trapped beam propagating inside the structure. As expected, only TM polarized waves exhibit such a behavior. Different experimental arrangements are tested that unambiguously reveal the nonlinear plasmon-soliton coupling which is corroborated by numerical simulations.

physics.optics↗

arXiv2016

Nano scale thermo-electrical detection of magnetic domain wall propagation

In magnetic nanowires with perpendicular magnetic anisotropy (PMA) magnetic domain walls (DW) are narrow and can move rapidly driven by current induced torques. This enables important applications like high-density memories for which the precise detection of the position and motion of a propagating DW is of utmost interest. Today's DW detection tools are often limited in resolution, or acquisition speed, or can only be applied on specific materials. Here, we show that the anomalous Nernst effect provides a simple and powerful tool to precisely track the position and motion of a single DW propagating in a PMA nanowire. We detect field and current driven DW propagation in both metallic heterostructures and dilute magnetic semiconductors over a broad temperature range. The demonstrated spatial resolution below 20 nm is comparable to the DW width in typical metallic PMA systems.

cond-mat.mes-hall↗

arXiv2012

Investigation of Optical Spin Transfer Torque in Ferromagnetic Semiconductor GaMnAs by Magneto-Optical Pump-and-Probe Method

We report on magnetization precession induced in (Ga,Mn)As by an optical spin transfer torque (OSTT). This phenomenon, which corresponds to a transfer of angular momentum from optically-injected spin-polarized electrons to magnetization, was predicted theoretically in 2004 and observed experimentally by our group in 2012. In this paper we provide experimental details about the observation of OSTT by a time-resolved pump-and-probe magneto-optical technique. In particular, we show that the precession of magnetization due to OSTT can be experimentally separated from that induced by the well known magnetic-anisotropy-related mechanism in a hybrid structure piezo-stressor/(Ga,Mn)As with an in situ electrical control of the magnetic anisotropy. We also illustrate that OSTT is clearly apparent in the measured dynamical magneto-optical signal in a large variety of (Ga,Mn)As samples with a Mn concentration from 3% to 9%.

cond-mat.mtrl-sci↗

arXiv2004

Hamiltonian selfdistributive quasigroups

The problem of the existence of non-medial distributive hamiltonian quasigroups is solved. Translating this problem first to commutative Moufang loops with operators, then to ternary algebras and, finally, to cocyclic modules over\linebreak $\Bbb Z[x,x^{-1},(1-x)^{-1}]$, it is shown that every non-medial distributive hamiltonian quasigroup has at least 729 elements and that there are just two isomorphism classes of such quasigroups of the least cardinality. The quasigroups representing these two classes are anti-isomorphic.

math.RA↗