Strong coupling between light and the fundamental excitations of a two-dimensional electron gas (2DEG) is of foundational importance both to pure physics and to the understanding and development of ...future photonic nanotechnologies1–7. Here we study the relationship between spin polarization of a 2DEG in a monolayer semiconductor, MoSe2, and light–matter interactions modified by a zero-dimensional optical microcavity. We find pronounced spin-susceptibility of the 2DEG to simultaneously enhance and suppress trion-polariton formation in opposite photon helicities. This leads to observation of a giant effective valley Zeeman splitting for trion-polaritons (g-factor of >20), exceeding the purely trionic splitting by over five times. Going further, we observe clear effective optical nonlinearity arising from the highly nonlinear behaviour of the valley-specific strong light–matter coupling regime, and allowing all-optical tuning of the polaritonic Zeeman splitting from 4 meV to >10 meV. Our experiments lay the groundwork for engineering topological phases with true unidirectionality in monolayer semiconductors, accompanied by giant effective photonic nonlinearities rooted in many-body exciton–electron correlations.Researchers show spin-susceptibility in monolayer MoSe2 and demonstrate giant effective valley Zeeman splitting and nonlinearity for trion-polaritons.
Plasmonics allows light to be localized on length scales much shorter than its wavelength, which makes it possible to integrate photonics and electronics on the nanoscale. Magneto-optical materials ...are appealing for applications in plasmonics because they open up the possibility of using external magnetic fields in plasmonic devices. Here, we fabricate a new magneto-optical material, a magnetoplasmonic crystal, that consists of a nanostructured noble-metal film on top of a ferromagnetic dielectric, and we demonstrate an enhanced Kerr effect with this material. Such magnetoplasmonic crystals could have applications in telecommunications, magnetic field sensing and all-optical magnetic data storage.
Optical tools are promising for spin-wave generation because of the possibilities of ultrafast manipulation and local excitation. However, a single laser pulse can inject spin waves (SWs) only with a ...broad frequency spectrum, resulting in short propagation distances and low wave amplitudes. Here, we excite a magnetic garnet film by a train of fs-laser pulses with a 1-GHz repetition rate so that the pulse separation is shorter than the decay time of magnetic modes, which allows us to achieve a collective impact on the magnetization and establish a quasistationary source of spin waves, namely, a coherent accumulation of magnons (“magnon cloud”). This approach has several appealing features: (i) The magnon source is tunable, (ii) the SW amplitude can be significantly enhanced, (iii) the SW spectrum is quite narrow, providing long-distance propagation, (iv) the periodic pumping results in an almost constant-in-time SW amplitude for the distances larger than 20μm away from the source, and (v) the SW emission shows pronounced directionality. These results expand the capabilities of ultrafast coherent optical control of magnetization and pave the way for applications in data processing, including the quantum regime. The quasistationary magnon accumulation might also be of interest for applications in magnon Bose-Einstein condensates.
Hybrid structures synthesized from different materials have attracted considerable attention because they may allow not only combination of the functionalities of the individual constituents but also ...mutual control of their properties. To obtain such a control an interaction between the components needs to be established. For coupling the magnetic properties, an exchange interaction has to be implemented which typically depends on wavefunction overlap and is therefore short-ranged, so that it may be compromised across the hybrid interface. Here we study a hybrid structure consisting of a ferromagnetic Co layer and a semiconducting CdTe quantum well, separated by a thin (Cd, Mg)Te barrier. In contrast to the expected p-d exchange that decreases exponentially with the wavefunction overlap of quantum well holes and magnetic atoms, we find a long-ranged, robust coupling that does not vary with barrier width up to more than 30 nm. We suggest that the resulting spin polarization of acceptor-bound holes is induced by an effective p-d exchange that is mediated by elliptically polarized phonons.
Integration of magnetism into semiconductor electronics would facilitate an all-in-one-chip computer. Ferromagnet/bulk semiconductor hybrids have been, so far, mainly considered as key devices to ...read out the ferromagnetism by means of spin injection. Here we demonstrate that a Mn-based ferromagnetic layer acts as an orientation-dependent separator for carrier spins confined in a semiconductor quantum well that is set apart from the ferromagnet by a barrier only a few nanometers thick. By this spin-separation effect, a non-equilibrium electron-spin polarization is accumulated in the quantum well due to spin-dependent electron transfer to the ferromagnet. The significant advance of this hybrid design is that the excellent optical properties of the quantum well are maintained. This opens up the possibility of optical readout of the ferromagnet's magnetization and control of the non-equilibrium spin polarization in non-magnetic quantum wells.
Magneto-optical phenomena such as the Faraday and Kerr effects play a central role in controlling the polarization and intensity of optical fields propagating through a medium. Intensity effects in ...which the direction of light emission depends on the orientation of the external magnetic field are of particular interest, as they can be harnessed for routing light. Effects known so far for accomplishing such routing all control light emission along the axis parallel to the magnetic field. Here we report a new class of emission phenomena where directionality is established perpendicular to the externally applied magnetic field for light sources located in the vicinity of a surface. As a proof of principle for this effect, which we call transverse magnetic routing of light emission, we demonstrate the routing of emission for excitons in a diluted-magnetic-semiconductor quantum well. In hybrid plasmonic semiconductor structures, we observe significantly enhanced directionality of up to 60%.
Currently spin waves are considered for computation and data processing as an alternative to charge currents. Generation of spin waves by ultrashort laser pulses provides several important advances ...with respect to conventional approaches using microwaves. In particular, focused laser spot works as a point source for spin waves and allows for directional control of spin waves and switching between their different types. For further progress in this direction it is important to manipulate with the spectrum of the optically generated spin waves. Here we tackle this problem by launching spin waves by a sequence of femtosecond laser pulses with pulse interval much shorter than the relaxation time of the magnetization oscillations. This leads to the cumulative phenomenon and allows us to generate magnons in a specific narrow range of wavenumbers. The wavelength of spin waves can be tuned from 15 μm to hundreds of microns by sweeping the external magnetic field by only 10 Oe or by slight variation of the pulse repetition rate. Our findings expand the capabilities of the optical spin pump-probe technique and provide a new method for the spin wave generation and control.
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Seasonal dynamics of phytoplankton production and structural characteristics was studied at two closely located stations in the open part of the Sevastopol Bay mouth, one of which was a mussel ...farm. The net primary production, chlorophyll
a
content, total phytoplankton biomass, the quantitative ratio between small and large algal cells, and their seasonal dynamics were the same for both stations. Linear dependencies were observed between the relevant parameters of the stations, with the angular regression coefficients close to 1. The phytoplankton production and biomass peaked during the summer period, reaching 350 ± 43 mg C/(m
3
day) and 450 ± 50 mg C/m
3
, respectively. Chlorophyll
a
content varied from 0.5 to 3 mg/m
3
, with the minimum in January‒February and the maximum in summer. The assimilation number values for chlorophyll
a
during the light period corresponded to those reported for production waters and correlated with the temperatures during the year. Total oxygen consumption by bacterio- and phytoplankton during the summer period was 30–70% of net photosynthesis. The data were obtained on seasonal biomass variations in three groups of algae (
Synechococcus
, picoeukaryotic phytoplankton, and nanophytoplanktom); on average, picoalgae constituted 30% of the phytoplankton biomass, with maxima during the winter-spring and summer periods. Bacterioplankton abundance was determined using flow cytometry and the SYBR Green I vital fluorochrome. A positive relation between bacterial abundance and water temperature was shown.
A comprehensive study of stress response of the green microalgae
Dunaliella salina
(Teod.) after the addition of copper oxide nanoparticles (0, 250, 665, 1330, 2000, 2500, and 3750 µg/L) and ions of ...copper (0, 15, 150, 200, 400, 580, 770 µg/L) was performed. It was found that the inhibitory effect of copper on the structural and functional characteristics of
D. salina
was less pronounced when algae were grown on an f/4 nutrient medium, which is explained by the high content of the chelating agent EDTA capable of binding metal ions dissolved in water into chelate complexes, thereby reducing their activity and toxic effect on cells and increasing bioavailability for algae in the medium. A different mechanism of action of ionic and nano copper on the physiology of algae was shown. It was found that the ionic form of copper has a cytotoxic effect on
Dunaliella salina
cells, while CuO nanoparticles have a mechanical effect on the cell surface. Cell growth retardation, a decrease in fluorescein diacetate (FDA) fluorescence, a decrease in the specific content of chlorophyll per cell, the efficiency of the photosynthetic apparatus, and an induction of ROS synthesis were observed when algae were cultivated on f/32 medium at a concentration of Cu
2+
in the medium above 400 μg/L. The negative effect of CuO nanoparticles (NPs) was found at a pollutant content above 700 µg/L. It had a greater effect on morphological changes in cells: a twofold enlargement of cells occurred, the number of spherical forms increased (up to 71%), and significant deformation and perforation of the plasmalemma and the predominance of deformed cells of irregular shape and cells agglomerated with nanoparticles were found. It has been shown that the maximum concentrations of toxicants studied do not lead to complete elimination of the population, which is probably explained by the presence of cells resistant to copper (approximately 10–15% according to FDA staining) and capable of ensuring the survival and subsequent restoration of the
Dunaliella salina
population at a high level of anthropogenic pollution of the environment.
The ability to store optical information is important for both classical and quantum communication. Achieving this in a comprehensive manner (converting the optical field into material excitation, ...storing this excitation, and releasing it after a controllable time delay) is greatly complicated by the many, often conflicting, properties of the material. More specifically, optical resonances in semiconductor quantum structures with high oscillator strength are inevitably characterized by short excitation lifetimes (and, therefore, short optical memory). Here, we present a new experimental approach to stimulated photon echoes by transferring the information contained in the optical field into a spin system, where it is decoupled from the optical vacuum field and may persist much longer. We demonstrate this for an n-doped CdTe/(Cd,Mg)Te quantum well, the storage time of which could be increased by more than three orders of magnitude, from the picosecond range up to tens of nanoseconds.
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