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Charge transport nonlinearities in semiconductor quantum dots and nanorods are studied. Using a density matrix formalism, we retrieve the field-dependent nonlinear mobility and show the possibility of intra-pulse gain. We further demonstrate that the dynamics of master equations can be captured in an analytical formula for the field-dependent charge carrier mobility, e.g. for two-level systems. This equation extends the linear response theory based Kubo-Greenwood result to nonlinear processes at elevated field strength, easily reached in THz transport spectroscopy. With these tools we analyze the field strength, chirp, temperature and dephasing dependence of the charge carrier mobility in the model system of CdSe quantum dots and wires. Stark broadening and Rabi splitting result in strong alterations of the mobility spectra, pronounced at low temperatures. The mobility spectra are strongly temperature and pulse shape dependent in the nonlinear regime. The findings are of immediate interest e.g. for nonlinear THz generation, conversion and amplification in 6G technology and nano electronics. Our results further enable experimentalists to fit and understand measured charge transport nonlinearities with analytical expressions and to design nanosystems with engineered material properties. [ABSTRACT FROM AUTHOR]

The mechanical, electronic, magneto-optic and thermoelectric properties of CeBiPt compound have been calculated based on density functional theory (DFT) calculations. This compound has ground state point in the ferromagnetic phase with elastic stability by large bulk modulus of 88.565 GPa. Poisson's coefficient of 0.257 represents the ionic bonds between atoms, while the anisotropy coefficient indicates the elastic isotropic nature of this compound. Also, phonon dispersion emphasizes to the dynamic stability of this compound. By the mBJ approximation, this case exhibits ferromagnetic behavior with a magnetic moment of 0.98 μ B . Based on the magnetic behavior of this crystal, the Kerr effect angles ( θ k ) are 3.6∘ at 3 eV and − 3. 5 ∘ at 5.4 eV, respectively, therefore, the rotation angle of the ellipse light polarization ( γ k ) in the edge of ultraviolet region shows a large polarization of light in the visible region. The negative Seebeck coefficient of CeBiPt compound at low temperature refers to the hole transfer, also the magnitude of the power factor at higher temperatures indicates this compound is suitable for use in power generator applications. [ABSTRACT FROM AUTHOR]

From the canonical and rotating-wave transformations, we obtained the effective lower-polariton Hamiltonian depending on the applied magnetic field from the coupling of one of the quantum-well excitons and photons in a semiconductor microcavity. When the pump field is circularly polarized, the nonlinear interaction can induce a strong polariton blockade near the resonant peaks, which can be suppressed by a large pump in weak magnetic field situations. Thus, the platform behavior in the variation of the polariton occupation proves the polariton quantum blockade. On the other hand, when the pump field is linearly polarized, we achieve a single-photon emitter whose polariton polarization can be adjusted by an applied magnetic field. Polaritons with opposite spins, on the other hand, are anti-bunching in the lower excitation regime and become bunching only in weak magnetic field situations and a high excitation regime. Our findings constitute a potential step toward the realization of strongly coupled polaritonic systems. [ABSTRACT FROM AUTHOR]

Topology plays a crucial and multifaceted role in solid state physics, leading to a remarkable array of newly investigated materials and phenomena. In this Perspective, we provide a brief summary of well-established model materials with a particular focus on compensated magnets and highlight key phenomena that emerge due to the influence of topology in these systems. The overview covers various magneto-transport phenomena, with a particular focus on the extensively investigated anomalous magneto-transport effects. Furthermore, we look into the significance of topology in understanding elementary magnetic excitations, namely magnons, where the role of topology gained considerable attention from both theoretical and experimental perspectives. Since electrons and magnons carry energy, we explore the implications of topology in combined heat and spin transport experiments in compensated magnetic systems. At the end of each section, we highlight intriguing unanswered questions in this research direction. To finally conclude, we offer our perspective on what could be the next advancements regarding the interaction between compensated magnetism and topology. [ABSTRACT FROM AUTHOR]

We recently reported on a method to determine the easy axis position in a 10 nm thick film of the fully compensated antiferromagnet CuMnAs. The film had a uniaxial magnetic anisotropy and the technique utilized a magneto-optical pump and probe experiment [Saidl et al. Nat. Photonics 11, 91 (2017)]. In this contribution, we discuss the applicability of this method for the investigation of a broader set of epitaxial CuMnAs films having different thicknesses. This work reveals that the equilibrium magnetic anisotropy can be studied only in samples, where this anisotropy is rather strong. However, in the majority of CuMnAs films, the impact of a strong pump pulse induces nano-fragmentation of the magnetic domains and, therefore, the magnetic anisotropy measured by the pump–probe technique differs substantially from that in the equilibrium conditions. We also demonstrate that the optical pump–probe experiment can be used very efficiently to study the local heating and heat dissipation in CuMnAs epitaxial layers. In particular, we determined the electron–phonon relaxation time in CuMnAs. We also observed that, for a local film heating by a focused laser, the thinner films are heated more, but the heat is dissipated considerably faster than in the case of thicker films. This illustrates that the optical pump–probe experiment is a valuable characterization tool for the heat management optimization in the CuMnAs memory devices and can be applied in a similar way to those used during the heat-assisted magnetic recording technology development for the latest generation of hard drive disks. [ABSTRACT FROM AUTHOR]

Antiferromagnets are considered to be a promising host material for the next generation of magnetic storage due to their high stability and stray-field-free property. However, the absence of net magnetization in antiferromagnets renders conventional magnetometry ineffective, posing a great challenge in investigating microscopic antiferromagnetic (AFM) properties under magnetic or electric fields. In this Perspective, we provide an overview of various AFM domain imaging techniques and discuss the most promising optical imaging method based on the magneto-optical birefringence (MOB) effect. Additionally, we highlight recent advances in imaging AFM domains utilizing the MOB technique. This Perspective aims to provide a comprehensive review of the current research and potential future directions based on the MOB imaging technique, which could pave the way for the development of more efficient and reliable magnetic storage devices based on antiferromagnets. [ABSTRACT FROM AUTHOR]

Among antiferromagnetic materials, Mn2Au is one of the most intensively studied, and it serves as a very popular platform for testing various ideas related to antiferromagnetic magnetotransport and dynamics. Since recently, this material has also attracted considerable interest in the context of optical properties and optically-driven antiferromagnetic switching. In this work, we use first principles methods to explore the physics of charge photocurrents, spin photocurrents, and the inverse Faraday effect in antiferromagnetic Mn2Au. We predict the symmetry and magnitude of these effects and speculate that they can be used for tracking the dynamics of staggered moments during switching. Our calculations reveal the emergence of large photocurrents of spin in collinear Mn2Au, whose properties can be understood as a result of a non-linear optical version of the spin Hall effect, which we refer to as the photospin Hall effect, encoded into the relation between the driving charge and resulting spin photocurrents. Moreover, we suggest that even a very small canting in Mn2Au can give rise to colossal spin photocurrents that are chiral in flavor. We conclude that the combination of staggered magnetization with the structural and electronic properties of this material results in a unique blend of prominent photocurrents, which makes Mn2Au a unique platform for advanced optospintronics applications. [ABSTRACT FROM AUTHOR]

Half‐light and half‐matter exciton polaritons have demonstrated profound impacts on coherent quantum phenomena. Two‐dimensional (2D) organic−inorganic perovskite semiconductors, exhibiting large exciton binding energy and spin‐based behavior, are an excellent platform for the study of exciton polaritons at room temperature. However, the implementation of these fascinating coherent phenomena is still constrained by the lack of an understanding of the crucial polariton–polariton interaction effects. Here, an experimental observation of spin‐dependent polariton–polariton interactions in a prototype 2D organic−inorganic perovskite microcavity by circularly polarization‐resolved transient absorption (TA) measurements is reported. A power‐dependent blue shift of the lower polariton bands with the same spin is clearly revealed, whereas the energy band of the polariton bands with the opposite spin is almost not changed. Spectacularly, it is found that the energy band blue shift mainly takes place before the spin depolarization, which provides accurate evidence for the spin‐dependent polariton–polariton interactions. Furthermore, the strong coherent polariton–phonon coupling of perovskite microcavity has also been detected firstly in ultrafast TA dynamics. These results demonstrate that microcavity polaritons inheriting the matter properties from their excitonic constituents exhibit strong nonlinear interactions and pave the way for realizing coherent quantum phenomena at room temperature. [ABSTRACT FROM AUTHOR]

The discovery of current-induced spin–orbit torque (SOT) orthogonal reorientation, also known as orthogonal switching, of metallic Mn2Au and CuMnAs has opened the door for ultrafast writing of an antiferromagnet (AFM). A phenomenological theory predicts that the minimum field necessary for SOT switching—critical field—for ultrashort pulses increases inversely proportional to the pulse duration, thereby limiting the use of ultrafast stimulus as driving force for switching. We explore the possibility that by varying the working temperature, the critical field reduces enabling orthogonal switching in response to ultrashort pulses. To do so, we extend the previous theory to finite temperature and show that the critical field for orthogonal switching strongly depends on temperature. We determine how the temperature dependence of the critical field varies as a function of the pulse duration. For long pulses, the temperature dependence of the critical field is determined by the anisotropy field, and for ultrashort pulses, it is determined by the characteristic frequency of the AFM. We show that the short and long pulse duration limits for the critical field can be connected by an analytical expression. [ABSTRACT FROM AUTHOR]

We describe measurements of the uniaxial magnetic anisotropy and spin-flop rotation of the Néel vector in antiferromagnetic CuMnAs thin films using neutron diffraction. The suppression of the magnetic (100) peak under magnetic fields is observed for films as thin as 20 nm, indicating that they undergo a spin-flop transition. Good agreement is found between neutron diffraction and electrical transport measurements of the spin-flop rotation in the same layer with similar shape and hysteresis of the obtained curves, while the neutron measurements provide a quantitative determination of the spin flop extending throughout the antiferromagnet layer. [ABSTRACT FROM AUTHOR]

The intrinsic anomalous Nernst effect in a magnetic material is governed by the Berry curvature at the Fermi energy and can be realized in non-collinear antiferromagnets with vanishing magnetization. Thin films of (001)-oriented Mn3NiN have their chiral antiferromagnetic structure located in the (111) plane facilitating the anomalous Nernst effect unusually in two orthogonal in-plane directions. The sign of each component of the anomalous Nernst effect is determined by the local antiferromagnetic domain state. In this work, a temperature gradient is induced in a 50 nm thick Mn3NiN two micrometer-size Hall cross by a focused scanning laser beam, and the spatial distribution of the anomalous Nernst voltage is used to image and identify the octupole macrodomain arrangement. Although the focused laser beam width may span many individual domains, cooling from room temperature to the antiferromagnetic transition temperature in an in-plane magnetic field prepares the domain state, producing a checkerboard pattern resulting from the convolution of contributions from each domain. These images together with atomistic and micromagnetic simulations suggest an average macrodomain of the order of 1 μm2. [ABSTRACT FROM AUTHOR]

The coherent properties of a dense ensemble of triplet cyclotron magnetoexcitons in a quantum Hall insulator near the filling factor have been studied using shear interferometry methods. It has been found that a condensate of magnetoexcitons formed at fairly low temperatures by means of nonresonant photoexcitation has a higher degree of coherence compared to the gas of uncondensed magnetoexcitons: the transverse length of coherence reaches about 10 μm. The condensate can include up to 20% of all triplet magnetoexcitons. [ABSTRACT FROM AUTHOR]

The dynamics of magnetization is significantly determined by domain walls, which are currently considered as active elements of promising spintronic devices with ultrafast magnetization reversal. Studies of the dynamics of domain walls under the action of a magnetic field and spin-polarized currents in antiferromagnets and ferrimagnets in the region of compensation of the angular momentum have been reviewed. Solutions of the basic dynamic equations for domain walls in antiferromagnets and ferrimagnets that are obtained by solving the Landau–Lifshitz equations using the effective Lagrangian method make it possible to explain experimentally observed anomalies in the compensation area. The main mechanisms of the effect of spin-polarized currents on the dynamics of domain walls, as well as the prospects of further studies in this field, have been discussed. [ABSTRACT FROM AUTHOR]

Polarization singularities of vectorial electromagnetic fields locate at the positions where properties of polarization ellipses are not defined. First observed for conical diffraction in 1830s, polarization singularities have been studied systematically with the underlying concepts being reshaped and deepened by many pioneers of wave optics. Here we review the recent results on the generation and observation of polarization singularities in metaphotonics. We start with the discussion of polarization singularities in the Mie theory, where both electric and magnetic multipoles are explored from perspectives of local and global polarization properties. We then proceed with the discussion of various photonic-crystal structures, for which both near- and far-field patterns manifest diverse polarization singularities characterized by the integer Poincaré or more general half-integer Hopf indices (topological charges). Next, we review the most recent studies of conversions from polarization to phase singularities in scalar wave optics, demonstrating how bound states in the continuum can be exploited to generate directly optical vortices of various charges. Throughout our paper, we discuss and highlight several fundamental concepts and demonstrate their close connections and special links to metaphotonics. We believe polarization singularities can provide novel perspectives for light-matter manipulation for both fundamental studies and their practical applications. [ABSTRACT FROM AUTHOR]

2D organic–inorganic hybrid Ruddlesden–Popper perovskites (RPPs) have recently attracted increasing attention due to their excellent environmental stability, high degree of electronic tunability, and natural multiquantum‐well structures. Although there is a rapid development of photoelectronic applications in solar cells, photodetectors, light emitting diodes (LEDs), and lasers based on 2D RPPs, the state‐of‐the‐art performance is far inferior to that of the existing devices because of the limited understanding on fundamental physics, especially special photophysics in carrier dynamics, excitonic fine structures, excitonic quasiparticles, and spin‐related effect. Thus, there is still plenty of room to improve the performances of photoelectronic devices based on 2D RPPs by enhancing knowledge on fundamental photophysics. This review highlights the special photophysics of 2D RPPs that is fundamentally different from the conventional 3D congeners. It also provides the most recent progress, debates, challenges, prospects, and in‐depth understanding of photophysics in 2D perovskites, which is significant for not only boosting performance of solar cells, LEDs, photodetectors, but also future development of applications in lasers, spintronics, quantum information, and integrated photonic chips. [ABSTRACT FROM AUTHOR]

Quasi two-dimensional perovskites have attracted great attention for applications in light-emitting devices and photovoltaics due to their robustness and tunable highly efficient photoluminescence (PL). However, the mechanism of intrinsic PL in these materials is still not fully understood. In this work, we have analysed the nature of the different emissive states and the impact of temperature on the emissions in quasi two-dimensional methyl ammonium lead bromide perovskite (q-MPB) and cesium lead bromide perovskite (q-CPB). We have used spatially resolved phase-modulated two-photon photoluminescence (2PPL) and temperature-dependent 2PPL to characterize the emissions. Our results show that at room temperature, the PL from q-MPB is due to the recombination of excitons and free carriers while the PL from q-CPB is due to the recombination of excitons only. Temperature-dependent measurements show that in both materials the linewidth broadening is due to the interactions between the excitons and optical phonons at high temperatures. Comparing the characteristics of the emissions in the two systems, we conclude that q-CPB is better suited for light emitting devices. With a further optimization to reduce the impact on the environment, q-CPB-based LEDs could perform as well as OLEDs. [ABSTRACT FROM AUTHOR]

A dramatic spectral line narrowing of the edge emission at room temperature from tris(quinolinolate) Al (Alq3), N,N′-diphenyl-N,N′-bis(1-naphthylphenyl)-1,1′-biphenyl-4,4′-diamine (NPD), 4,4′-bis(2,2′-diphenyl-vinyl)-,1′-biphenyl (DPVBi), and some guest-host small molecular organic light-emitting diodes (OLEDs), fabricated on indium tin oxide (ITO)-coated glass, is described. In all but the DPVBi OLEDs, the narrowed emission band emerges above a threshold thickness of the emitting layer, and narrows down to a full width at half maximum of only 5–10 nm. The results demonstrate that this narrowed emission is due to irregular waveguide modes that leak from the ITO to the glass substrate at a grazing angle. While measurements of variable stripe length l devices exhibit an apparent weak optical gain 0≤g≤1.86 cm-1, there is no observable threshold current or bias associated with this spectral narrowing. In addition, in the phosphorescent guest-host OLEDs, there is no decrease in the emission decay time of the narrowed edge emission relative to the broad surface emission. It is suspected that the apparent weak optical gain is due to misalignment of the axis of the waveguided mode and the axis of the collection lens of the probe. However, it is not clear if such a misalignment can account for all the effects of the observed evolution of the edge-emission spectra with l. [ABSTRACT FROM AUTHOR]

The optical properties of silica layers containing silicon nanocrystals are analyzed in terms of spectral filtering in absorbing planar waveguides (cutoff spectra), m-line measurements, and x-ray photoelectron spectroscopy (XPS). The effects of optical dispersion, approximation of weak guiding, and depth dependence of refractive index in a planar waveguide are studied. We compare the measured optical properties of silicon-rich silicon oxide samples with the values estimated by the Bruggeman theory using the XPS structural components. A good agreement between the measured and calculated refractive indices is found. The results for absorption suggest high transparency of the nanoscale-suboxide component in contrast to the corresponding bulk material. The Raman intensity of silicon nanocrystals is proportional to the XPS amount of bulk silicon. The extinction coefficient extracted for the Si component is between the values for crystalline and amorphous silicon. Annealing at higher temperatures decreases the Si component extinction coefficient, which is interpreted as a decrease in the amorphous Si fraction. The XPS method surprisingly suggests a large proportion of silicon suboxide even after annealing at 1200 °C. [ABSTRACT FROM AUTHOR]

We report an unusual case of spectral filtering by a silica waveguide containing Si nanocrystals (Si-nc’s) deposited on a silica plate. For a number of Si-rich silica (SiOx) slab waveguides annealed at 1100 °C, the TE and TM waveguide mode cutoff positions are found in the inversed order with respect to the classical waveguide theory for an isotropic material. Using the cutoff and m-line spectra, this unusual behavior was explained assuming an optical birefringence of the material. For the highest Si content (x∼1.5), we estimated a maximal positive birefringence of ∼8%. The cutoff spectrum simulated with the optical parameters extracted from the m-line measurements corresponds well to the cutoff spectrum directly obtained by measuring waveguided luminescence. This agreement shows that the spectral filtering effect of silica layers containing Si-nc can be described within the quantitative model of delocalized waveguide modes. The possible origin for the observed birefringence is discussed. [ABSTRACT FROM AUTHOR]

We report on the study and modeling of the structural and optical properties of rib-loaded waveguides working in the 600–900-nm spectral range. A Si nanocrystal (Si-nc) rich SiO2 layer with nominal Si excess ranging from 10% to 20% was produced by quadrupole ion implantation of Si into thermal SiO2 formed on a silicon substrate. Si-ncs were precipitated by annealing at 1100 °C, forming a 0.4-μm-thick core layer in the waveguide. The Si content, the Si-nc density and size, the Si-nc emission, and the active layer effective refractive index were determined by dedicated experiments using x-ray photoelectron spectroscopy, Raman spectroscopy, energy-filtered transmission electron microscopy, photoluminescence and m-lines spectroscopy. Rib-loaded waveguides were fabricated by photolithographic and reactive ion etching processes, with patterned rib widths ranging from 1 to 8 μm. Light propagation in the waveguide was observed and losses of 11 dB/cm at 633 and 780 nm were measured, modeled and interpreted. [ABSTRACT FROM AUTHOR]

The temporal dynamics of a spinor exciton-polariton condensate in a high-quality anisotropic GaAs microcavity under pulsed resonant excitation with light possessing a nonzero orbital angular momentum is investigated. The phenomenon of spatial separation of the spin components of the polariton condensate upon pumping with a coherent superposition of two beams with opposite circular polarizations and orbital angular momenta is observed. The key factors for the observation of this effect are the lateral anisotropy of the microcavity that causes a splitting between the linear components of the polariton ground state and the occurrence of opposite orbital angular momenta for the two spin components of the condensate. The experimental results are in qualitative agreement with the theoretical model of the phenomenon developed in JETP Lett. 104, 827 (2016). [ABSTRACT FROM AUTHOR]

The second- and third-order coherence functions g(2)(0) and g(3)(0), the number distribution, and the phase distribution of a polariton condensate are calculated by a quantum Monte Carlo wavefunction method using a one-dimensional model. The second- and third-order coherence functions change from g(n)(0) = n! to unity as the pumping intensity increases, as is the case for an ideal photon laser. However, the number and phase distributions demonstrate that the polariton condensate is quite different from a coherent state; this is owing to polariton-polariton scattering. We investigate the effects of this scattering upon the statistical properties of the condensates. [ABSTRACT FROM AUTHOR]

Bosonic lasers represent a new generation of coherent light sources. In contrast to conventional, fermionic, lasers they do not require inversion of electronic population and do not rely on the stimulated emission of radiation. Bosonic lasers are based on the spontaneous emission of light by condensates of bosonic quasiparticles. The first realization of bosonic lasers has been reported in semiconductor microcavities where bosonic condensates of exciton-polaritons first studied several decades ago by K. B. Tolpygo can be formed under optical or electronic pumping. In this paper we overview the recent progress in the research area of polaritonics, address the perspective of realization of polariton devices: from bosonic cascade lasers to spin transistors and switches. Published by AIP Publishing. [ABSTRACT FROM AUTHOR]

Plasma-enhanced chemical vapor deposition is used to fabricate asymmetric planar luminescent waveguides (APWs) based on amorphous silicon-carbide films with submicron thickness on quartz substrates. Narrow peaks of linearly ( P and S) polarized radiation related to the emission in the APW leaky modes are detected in the APW emission spectra from the end surface of a substrate under excitation of photoluminescence. The dependence of the spectral positions of peaks on the angle at which the radiation is emitted from the end surface and the film thickness is analyzed. At grazing angles of emission, the radiation wavelength is almost independent of the angle. It is demonstrated that the difference between the wavelengths of the P- and S-polarized peaks in the PL spectra decreases with an increase in the waveguide thickness. The waveguide works as an optical microcavity for leaky modes. The amplitude of the S-polarized peak is higher than the amplitude of the P-polarized peak due to the fact that the Q factor for the S-polarized leaky modes is greater than the Q factor for the P-polarized leaky mode. The luminescent APWs can be used to generate optical beams with radial and azimuthal polarizations. [ABSTRACT FROM AUTHOR]

In this paper, long wavelength superluminal and subluminal properties of pulse propagation in a defect slab medium doped with four-level GaAs/AlGaAs multiple quantum wells (MQWs) with 15 periods of 17.5 nm GaAs wells and 15 nm barriers is theoretically discussed. It is shown that exciton spin relaxation (ESR) between excitonic states in MQWs can be used for controlling the superluminal and subluminal light transmissions and reflections at different wavelengths. We also show that reflection and transmission coefficients depend on the thickness of the slab for the resonance and nonresonance conditions. Moreover, we found that the ESR for nonresonance condition lead to superluminal light transmission and subluminal light reflection. [ABSTRACT FROM AUTHOR]

The first-order spatial correlation function g( r) and the polariton density distribution in the condensate of quasi-two-dimensional exciton polaritons formed in a high- Q semiconductor microcavity pillar under nonresonant optical pumping are investigated. It is found that the correlation function in certain regions of the micropillar decreases abruptly with increasing condensate density. It is shown that this behavior of the correlation function is caused by the formation of a localized dark soliton in these regions. A deep minimum of the polariton density and a shift in the phase of the condensate wavefunction by π occur within the soliton localization area. [ABSTRACT FROM AUTHOR]

The investigation of intrinsic interactions in polariton condensates is currently limited by the photonic disorder of semiconductor microcavity structures. Here, we use a strain compensated planar GaAs/AlAs0 9 8P0 0 2 microcavity with embedded InGaAs quantum wells having a reduced cross-hatch disorder to overcome this issue. Using real and reciprocal space spectroscopic imaging under non-resonant optical excitation, we observe polariton condensation and a second threshold marking the onset of photon lasing, i.e., the transition from the strong to the weak-coupling regime. Condensation in a structure with suppressed photonic disorder is a necessary step towards the implementation of periodic lattices of interacting condensates, providing a platform for on chip quantum simulations. [ABSTRACT FROM AUTHOR]

The magnetic dipole-dipole interaction does not prevent existence of half-quantum vortices in the polar phase of superfluid $$^{3}$$ He which can be stable in uniaxial anisotropic aerogel. Here we discuss this exotic possibility. After developing a phenomenological theory of phase transition from the normal to the polar superfluid state and then to axipolar superfluid state we calculate the NMR properties of such type superfluids at the rest or under rotation when liquid is filled by an array either single quantum or half quantum vortices. [ABSTRACT FROM AUTHOR]

Free energy signatures related to the measurement of an emergent force ((≈10-9N) due to the exciton condensate (EC) in Double Quantum Wells are predicted and experiments are proposed to measure the effects. The EC-force is attractive and reminiscent of the Casimir force between two perfect metallic plates, but also distinctively different from it by its driving mechanism and dependence on the parameters of the condensate. The proposed experiments are based on a recent experimental work on a driven micromechanical oscillator. Conclusive observations of EC in recent experiments also provide a strong promise for the observation of the EC-force. [ABSTRACT FROM AUTHOR]

We propose theoretically an optical diode based on exciton-polaritons in semiconductor microcavities. A flow of polaritons in the bistable regime is used to send signals through an asymmetric fixed potential that favours the bridging of particles in one direction. Through dynamic modelling of the coherent polariton field, we demonstrate the characteristics of an ideal diode, namely, that the forward signal is fully transmitted while the transmission in the reverse direction tends to zero, without any additional external control. Moreover, the system proves to be robust to the presence of disorder, intrinsic to microcavities, and can function at gigahertz repetition rates. [ABSTRACT FROM AUTHOR]

Unlike to superfluid 4He the superfluid 3He-A support the existence of vortices with half-quantum of circulation as well as single quantum vortices. The singular single quanta vortices as well as nonsingular vortices with 2 quanta of circulation have been revealed in rotating 3He-A. However, the half-quantum vortices in open geometry always possess an extra energy due to spin-orbit coupling leading to formation of domain wall at distances larger than dipole length ∼10-3 cm from the vortex axis. Fortunately the same magnetic dipole-dipole interaction does not prevent the existence of half-quantum vortices in the polar phase of superfluid 3He recently discovered in peculiar porous media 'nematically ordered' aerogel. Here we discuss this exotic possibility. The discoveries of half-quantum vortices in triplet pairing superconductor Sr2RuO4 as well in the exciton-polariton condensates are the other parts of the story about half-quantum vortices also described in the paper. [ABSTRACT FROM AUTHOR]

A ZnO planar optical microcavity displaying room-temperature polariton lasing over a wide range of cavity-exciton detunings has been fabricated. The cavity combines optimum crystalline quality, given by a ZnO single-crystal substrate, and optimum photonic quality, obtained by the use of two dielectric SiO2/HfO2 Bragg mirrors. A maximum cavity quality factor of about 4000 has been measured. Typically, the polariton lasing transition is accompanied by an increase of the output intensity by more than two orders of magnitude, a reduction of the emission linewidth and a relatively small blueshift of the lower polariton branch (less than 5% of the Rabi splitting). [ABSTRACT FROM AUTHOR]

The semiconducting material silicon forms the heart of the current complimentary metal?oxide semiconductor (CMOS) technology. Over the last four decades, the productivity of silicon technology has increased by a factor of more than a billion [1]. This growth in silicon technology was made possible by a steady reduction in the feature size, which helps pack more functionality per cost in a microprocessor. Today, the silicon-based semiconductor industry is an approximately US$270 billion market [1]. This exponential growth of the semiconductor industry was first observed by Dr. Gordon Moore. In 1965, Moore observed that the computing power of a microprocessor doubled every 18?24 months, and this observation later became known as Moore?s law [2]. In essence, Moore?s law is an economic law that serves to guide long-term planning and to set targets for research and development in the semiconductor industry. However, quantum-mechanical laws dictate that there are fundamental challenges associated with scaling on-chip components to below 10 nm [3]. A revolutionary innovation in semiconductor technology would be needed to sustain Moore?s law for advanced technology nodes below 10 nm [1], [4]. We examine performance trends of on-chip devices and interconnects upon dimensional scaling. This is followed by a discussion on emerging technologies and the repercussions of interconnects for these novel technologies. [ABSTRACT FROM PUBLISHER]

We analyze time evolution of spatial coherence of a polariton ensemble in a quantum wire (1D channel) under constant uniform resonant pumping. Using the theoretical approach based on the Lindblad equation for a one-particle density matrix, which takes into account the polariton-phonon and excitonexciton interactions, we study the behavior of the first-order coherence function g for various pump intensities and temperatures in the range of 1-20 K. Bistability and hysteresis in the dependence of the first-order coherence function on the pump intensity is demonstrated. [ABSTRACT FROM AUTHOR]

Two semiconductor systems, quantum wells with spatially indirect dipolar excitons and exciton polaritons in semiconductor microcavities, exhibiting the Bose condensation of excitons, are discussed. [ABSTRACT FROM AUTHOR]

If bosonic particles are cooled down below the temperature of quantum degeneracy, they can spontaneously form a coherent state in which individual matter waves synchronize and combine. Spontaneous coherence of matter waves forms the basis of a number of fundamental phenomena in physics, including superconductivity, superfluidity and Bose-Einstein condensation. Spontaneous coherence is the key characteristic of condensation in momentum space. Excitons-bound pairs of electrons and holes-form a model system to explore the quantum physics of cold bosons in solids. Cold exciton gases can be realized in a system of indirect excitons, which can cool down below the temperature of quantum degeneracy owing to their long lifetimes. Here we report measurements of spontaneous coherence in a gas of indirect excitons. We found that spontaneous coherence of excitons emerges in the region of the macroscopically ordered exciton state and in the region of vortices of linear polarization. The coherence length in these regions is much larger than in a classical gas, indicating a coherent state with a much narrower than classical exciton distribution in momentum space, characteristic of a condensate. A pattern of extended spontaneous coherence is correlated with a pattern of spontaneous polarization, revealing the properties of a multicomponent coherent state. We also observed phase singularities in the coherent exciton gas. All these phenomena emerge when the exciton gas is cooled below a few kelvin. [ABSTRACT FROM AUTHOR]

We observe hybrid states of cavity photons and Tamm plasmons in an organic microcavity with an incorporated thin silver layer of increasing thickness up to 40 nm. Via μ-photoluminescence spectroscopy, we investigate their angular dependence. At oblique angles, we observe a TE-TM polarization splitting of more than 40 meV for each mode. An analytical model is developed to describe the coupling of Tamm plasmons and cavity photons and to account for the splitting of the orthogonally polarized resonances. [ABSTRACT FROM AUTHOR]

We review, aiming at an audience of final year undergraduates, the phenomena observed in, and properties of, microcavity exciton-polariton condensates. These are condensates of mixed light and matter, consisting of superpositions of photons in semiconductor microcavities and excitons in quantum wells. Because of the imperfect confinement of the photon component, exciton-polaritons have a finite lifetime, and have to be continuously re-populated. Therefore, exciton-polariton condensates lie somewhere between equilibrium Bose-Einstein condensates and lasers. We review in particular the evidence for condensation, the coherence properties studied experimentally, and the wide variety of spatial structures either observed or predicted to exist in exciton-polariton condensates, including quantised vortices and other coherent structures. We also discuss the question of superfluidity in a non-equilibrium system, reviewing both the experimental attempts to investigate superfluidity to date, and the theoretical suggestions of how it may be further elucidated. [ABSTRACT FROM AUTHOR]

Multilayered heterogeneous one-dimensional (1-D) nanostructures are important building blocks for nanodevice applications. A practical nanofabrication technique to produce heterogeneous nanostructures with arbitrary materials must have the ability to control the dimensions and uniformity, to control the alignment, and to control the interfacial properties of the heterogeneous nanostructures. In this paper, we demonstrate a simple but versatile method to fabricate three-dimensional (3-D) heterogeneous nanorod structures by multilayer dynamic shadowing growth (DSG). DSG is a process based on the geometric shadowing effect and substrate rotation in a physical vapor deposition system. By combining DSG and the sputtering technique, we successfully fabricated Au/Si matchstick nanorods which can further be developed as a novel biosensor for Respiratory Syncytial Virus (RSV) detection. By changing the source materials during the deposition, we demonstrate that complicated heterostructured nanorod arrays, such as Si/Ni multilayer nanosprings, can be easily produced, and they exhibit particular magnetic anisotropic behavior. We also use the DSG technique to coat a thin catalyst layer asymmetrically on the side of a nanorod backbone, and therefore design catalytic nanomotors with a variety of geometries capable of performing multiple desired motions in a fuel solution. This fabrication method reveals an optimistic step towards complex heteronanorod array design and fabrication. [ABSTRACT FROM PUBLISHER]

Layers of densely packed luminescent Si nanocrystals embedded in fused silica act as wavelength-specific planar waveguides that filter the wide-band spontaneous emission. The waveguides’ light output consists of two spectrally narrow (∼10 nm), orthogonally polarized, and spatially directed bands. This effect is shown to result from leaky modes of the lossy waveguides. The results have general applicability to lossy, asymmetric waveguides and show the way to produce spectrally narrow emission without the use of optical cavities. [ABSTRACT FROM AUTHOR]

A key prerequisite for low-threshold polariton lasing in organic or inorganic microcavity systems is the efficient population of the lower polariton ground state. Here, we report the observation of a resonant phonon-mediated relaxation process which gives rise to nonthermal polariton population with sub 100 fs build-up times. This mechanism is manifested by discrete maxima of the angular-resolved photoluminescence intensity, with corresponding shortening of the photoluminescence rise time at respective phonon resonances. The realization of enhanced relaxation rates in disordered J-aggregate systems is important for developing room temperature organic laser sources with less fabrication complexity than their crystalline counterparts. [ABSTRACT FROM AUTHOR]

We propose a scheme of a ZnO room-temperature polariton laser based on a photonic crystal slab. We predict a very low threshold density for optical pumping: 5 × 1016 cm-3. We have studied the threshold dependence on the parameters of the system, such as detuning. The main advantage of photonic-crystal-based polariton laser is expected to be the simplicity of production. [ABSTRACT FROM AUTHOR]

We report the observation of positive optical gain in silicon nanocrystals (Si-nc) embedded in silicon nitride measured by the variable stripe length technique. We evidence the onset of stimulated emission and report gain coefficients up to 52 cm-1 at the highest excitation power (6.5 W/cm2). Photoluminescence dynamics presents two distinct recombination lifetimes in the nanosecond and the microsecond ranges. This was interpreted in terms of fast carrier trapping in nitrogen-induced localized states in the Si-nc surface and subsequent slow radiative recombination, suggesting that carrier trapping in radiative surface states plays a crucial role in the optical gain mechanism of Si-nc. [ABSTRACT FROM AUTHOR]

We study the relaxation dynamics of spin-polarized exciton-polaritons using a technique in a pump-probe configuration: According to their total angular momentum, exciton-polaritons can be excited by circularly polarized light of either σ+ or σ- helicities. In addition, a bound state of two excitons may exist to which the transition is only allowed when using two photons of opposite helicities. After excitation by a pump pulse of σ+ helicity, additional polaritons from a probe pulse of σ- helicity may be absorbed to excite biexcitons, while absorption of those with σ+ helicity becomes possible only after a spin-flip process. It is characterized by a time-constant τs, which can be determined by a time-resolved study of the induced transmission changes at the exciton–biexciton transition. We demonstrate this method using bulk CuCl, in which the biexciton binding energy is large and in which effects due to polariton propagation can be nicely evidenced. We thus identify a spectral region where the spin-flip process is dominating, which is situated just below the polariton bottleneck. [ABSTRACT FROM AUTHOR]