We first present results for the 7 nm thick BP flake, in Figure 2. An optical image is shown in Figure 2e. FTIR spectra were taken using a Thermo Electron iS50 FTIR spectrometer and Continuum microscope for which the light source is a broadband, unpolarized tungsten glo- bar. To improve signal/noise and minimize spatial drift, we surrounded the sample with a 150 nm thick gold reflector which also served as the gate electrode. The extinction modulation results are presented in Figure 2a. We observe two major features in this flake at energies of 0.5 eV (I) and 0.9 eV (II). The dip in extinction at 0.5 eV is present for both positive and negative gate voltages, as the sample is increasingly hole or electron doped, respectively. It grows in strength as the doping is further increased at larger gate-biases. The same trend is true for the feature at 0.9 eV, where a smaller peak in extinction modulation is observed for both polarities of voltage. This peak also is strengthened as the gate voltage is increased to +/- 120V. To gain insights into this behavior, we measure gate-dependent transport, using a scheme in which a positive bias induces hole-doping, and a negative bias introduces electron-doping. We observe ambipolar transport at room temperature and atmospheric conditions, as shown in Figure 2b. Similar results have been shown in the literature with on/off ratios of ~10 4 for flakes thinner than the one considered here, at low temperature. 30, 63 From this, the CNP is observed to be at 20 V, and, using the parallel plate model described in the Supporting Information, the unbiased, n-type carrier concentration is estimated to be 1.5∙10 12 cm -2 . Further discussion on the depletion length and vertical charge
Abstract: Despite tremendous advances in the fundamentals and applications of cavity quantum electrodynamics (CQED), investigations in this field have primarily been limited to optical cavities composed of purely dielectric materials. Here, we demonstrate a hybrid metal- dielectric nanocavity design and realize it in the InAs/GaAs quantum photonics platform utilizing angled rotational metal evaporation. Key features of our nanometallic light-matter interface include: (i) order of magnitude reduction in mode volume compared to that of leading photonic crystal CQED systems; (ii) surface-emitting nanoscale cylindrical geometry and therefore good collection efficiency; and finally (iii) strong and broadband spontaneous emission rate enhancement (Purcell factor ~ 8) of single photons. This light-matter interface may play an important role in quantum technologies.
The potential for an order of magnitude improvement in size reduction of optoelectronic devices facilitated by plasmonic sub-diffraction-limit light confinement has intrigued researchers over the last decade. This directly addresses both the size mismatch between current electronic and photonic components, and furthermore promises substantial increases in modulation/switching speed, and potentially also lower energy consumption. Yet as described in the previous section, the unavoidable optical loss inherent in plasmonic light localization has to great extent hindered technological adoption of this approach. Since the physical limitations and parameter space for localisation and loss in plasmonic waveguides and nanostructures are well understood, focus has shifted to work on the underlying plasmonic materials for further improvements in performance. On the one hand, for the dominant plasmonic materials gold and silver, a substantial amount of research effort has been put into achieving higher crystallinity and hence less domain- and surface-induced optical losses. Examples include self-assembled-monolayer-assisted thin film growth for smoother films or back- etching of silicon in silicon/noble metal multilayers in order to expose an essentially single-crystal surface layer. At the same time, there is an active search for new plasmonic materials particularly in the near-infrared part of the spectrum underway. Here, materials with improved temperature stability such as TiN are attractive for applications such as Heat-assisted Magnetic Recording (HAMR), and also from the viewpoint of CMOS compatibility. Other candidate materials for applications in the near-to-mid-infrared are highly doped zinc oxides or perovskite-based ferroelectrics.
transmission, absorptions, and scattering. As refractive index consists of the most fundamental measure for light-matterinteractions, to gate photons is in essence to gate refractive index. None of the existing approaches for electrically gating refractive index may provide satisfactory tunability, tuning spectral range, speed, and compatibility with CMOS circuits. The most common strategy to electrically tune refractive index relies on the plasma dispersion effect of free charge carriers, in which the optical absorption of injected electrons or holes may give rise to changes in the refractive index.[54-61] But the density of the charge carriers that can be injected is limited, and this fundamentally limits the tunability in refractive index, usually in the scale of 0.1-1%.[54-58] While ionic gating has been recently reported to be able to enable larger tunability,[62-64] its nonlocal nature, inferior chemical stability, and intrinsically slow switching make it not ideal in terms of speed and compatibility with CMOS circuits.
We now turn to a discussion of the nature of these transitions. For the lowest LL of BLG, the possible internal quantum state of electrons comprises an octet described by the SU(4) spin- valley space and the 0-1 LL orbital degeneracy. Since ν = 1 corresponds to filling 5 of the 8 degenerate states in the lowest LL, the system will necessarily be polarized in some direction of the SU(4) spin-valley space. The presence of a D = 0 transition for ν = 1 indicates that even at low displacement field, the ground state exhibits a layer polarization which changes as D goes through zero. At the same time, we expect that at large D the system is maximally layer polarized. We therefore propose that the transition at finite D is between a 1/5 layer- polarized state (e.g. 3 top layer, 2 bottom layer levels filled) and a 3/5 layer-polarized state (e.g. 4 top layer, 1 bottom layer levels filled) (32–34). Interestingly, the quantitative agreement of the transitions for ν = 2/3 and ν = 1, shown in Fig. 3c, strongly suggest that the composite fermions undergo a similar transition in layer polarization.
As with transient gratings , we can adapt and control the diffraction by simply changing the frequency of the ac field. This enhancement of diffraction and switching it on and off with ac field voltage and frequency provide a flexible control of diffraction, a function that could prove invaluable in switching applications. Since the large birefringence of nematic liquid crystals spans the entire visible to infrared spectrum , , these tunable gratings will be useful for a variety of broadband switching applications, including telecommunications. Indeed, we have recently  measured the refractive index changing coefficients of some dye-doped nematic liquid crystals in the 1.55- m region, and have shown that their values are as large as in the visible spectrum.
Abstract: When a magnetic film is excited by a femtosecond laser pulse, either with THz or with optical frequencies, then there is at least a partial demagnetization within a few hundred femtoseconds, followed by a remagnetization to the original state on a bit longer time scale. This phenomenon is caused by a complex interaction of light with quantummatter. This paper gives a review of the present knowledge of the underlying physics. It discusses first the situation of a direct change of the magnetization by its interaction with the electromagnetic wave of the laser pulse, which appears during THz laser pulses with small field amplitudes. Then it considers the situation of an indirect change which appears after THz laser pulses with large field amplitudes and after optical laser pulses. In these cases the laser photons primarily excite electrons, with subsequent modifications of their spin-angular momenta by spin-flip scatterings of these electrons at quasiparticles, either at other electrons or at phonons or at magnons. The contributions of these various spin-flip scatterings to demagnetization are investigated. Then the transfer of angular momentum from the electronic spin system to the lattice during ultrafast demagnetization is discussed by describing the lattice vibrations in terms of magnetoelastic spin-phonon modes. Finally, the effect of electronic correlations in the sense of the density-matrix theory is investigated.
How does the unusual level structure in the presence of attractive interactions on the QD reflect on transport through the QD? We begin by considering the case in which both the superconducting and the normal leads are weakly coupled to the QD. In this case, the electrons move by a series of resonant pair-tunneling processes: the electron pair tunnels from the source lead to the QD and then to the drain lead. In order for the resonant tunneling processes to take place, the two-electron excitation on the QD must be resonant with an occupied two-electron state in the source lead and an empty two-electron state in the drain lead. The two-electron spectral function in a superconduc- tor has a 4Δ gap, as compared to the one-electron spectral function that has a 2Δ gap. Taking into account this gap we find the conductance maps (see Fig. 3). We observe that in order to connect the two diamonds with a straight line, as we see in the experiment, we must have one lead gapless, resulting in a 4Δ=e gap, as shown in Fig. 2(a). We note that the electron pairs in the source and drain leads can still tunnel through the QD; however, the contributed conduct- ance is very small due to the low density of states. The
In this Letter, we report an interesting phenomenon where the average refractive index of an isotropic liquid crystal phase can be tuned over a remarkably wide range by an external electric field applied across the device. The iso- tropic phase under study is known as the dark conglomerate phase or the DC phase. The electro-optic phenomenon reported here could be exploited for number applications, where the applied electric field modulates the refractive index of the liquid crystal phase which in turn changes the nature of the propagating light wave. As the DC phase is optically isotropic (or exhibits very low birefringence in some cases) the advantages of the devices based on the DC phase mainly include no power loss due to scattering, no requirement of an alignment layer therefore ease of fabrica- tion, and no polarization sensitive effects.
polarization. Similar results are obtained from the same spot when measuring the transmission, T , spectra (Fig. 4(b)). We note that the transmission spectra are noisier than those taken in reflection, due to the reduction in the total intensity of the light transmitted through the resonator. Nevertheless, general trends in the behavior of reflection and transmission spectra are clearly seen from a comparison of Figs. 4(a) and 4(b). For both polarizations, the position of the minima in the transmission spectra corresponds to the maxima of the reflection spectra and vice versa.
5. In a very colorful physics demonstration, Mrs. Claire Voyance uses three colored spotlights - red, green and blue - with equal intensities to illuminate a sheet of paper with different colors of light. Before turning the spotlights on, she paints the paper with various combinations of primary pigments. She then asks her students to predict in advance the color(s) of light that the paper will absorb and the color that the paper will appear. Use your understanding to make the same prediction.
blocked . Here, a detailed study of the repulsive polaron lifetime is necessary in order to judge the feasibility of these models. In addition, as the impurity and majority atoms originate from different orbitals, a state-dependent lattice enables us to tune the effective mass of the polaron. Depending on the impurity to majority atom mass ratio, a rich phase diagram for the strongly interacting Fermi gas is predicted . Changing the wavelength of the state-dependent lattice allows us to continuously tune from a mobile to a static impurity. The two extremes, where impurities are much lighter than majority atoms or very heavy, i.e. static impurities, are of particular interest. Depending on the mass ratio, the ground state of the light impurities is expected to consist of trimers or to have non-zero momentum, an FFLO-like phase . The case of a static impurity immersed in a Fermi sea is also known as Anderson orthogonality catastrophe. In this regime, the quasi-particle picture of the impurity breaks down because the static impurity can excite multiple low-energy particle-hole pairs . These excitations give rise to a characteristic power-law singularity in the spectral response of the impurity. As the or- thogonality catastrophe belongs to the small group of solvable nonequilibrium many-body problems, a comparison between theory and experiment is particularly interesting.
In QuantumMatter all the constituent atoms and molecules are in a single quantum state and behave coherently as a single quantum object. It typically exists at temperatures less than one millionth of a degree above absolute zero. In the long term, quantummatter is expected to have applications in diverse areas ranging from high-precision measurement to quantum information.
incremented to change the wire confinement, while the top gate is accordingly adjusted so as to keep the wire conductance G and correspondingly, the Fermi energy and carrier density, the same. A clear focusing peak singlet is observed when the quantum wire is strongly confined, indicating that there is only one chain (row). The peak singlet evolves into two peaks which progressively move away from the central point as the confinement is weakened, indicating a transition into two chains (rows). The spatial separation between the two chains can be calculated from the focusing peak separation. It is estimated to be around 200 nm using equation 1, consistent with the theoretical predictions 4 . We also note that the corresponding conductance traces of the wire do not show a jump to 4e 2
Photon number-state filtering of a coherent input rep- resents a markedly different approach, which has the po- tential to generate both bunched, and antibunched non- classical light on demand. A coherent input state can be considered as a weighted sum of different number states . Selective enhancement or suppression of spe- cific number-states therefore enables conversion of the classical input into a quantum output state. This was first demonstrated in a semiconductor device by using the anharmonicity of the levels of a strongly-coupled, QD- cavity system to filter one- or two-photon states from a coherent input state [8–10]. More recently, photon- number-dependent constructive or destructive quantum interference in weakly-coupled QD-cavity devices has been used to achieve the same goal [11–13].
A paradigm system of quantum mechanics which may exhibit intriguing quantum proper- ties like entanglement and non-locality are two spins. By increasing the number of spins, more complex behavior may emerge. In fact, a large variety of condensed matter phe- nomena, ranging from metal-insulator transition to superﬂuidity or superconductivity, are successfully described by mapping the relevant low-energy Hilbert space onto a spin model . Moreover, spin models may describe spin-liquid phases which exhibit topolog- ical order. In recent years, technological progress in manipulating atoms on the quantum level has allowed to explicitly engineer spin models . This has opened the opportunity for testing the foundations of quantum mechanics, for simulating complex many-body behavior, and for studying the dynamics of interacting spin chains [–].
Biomaterials are now drawing more and more attention since they often present special properties which are not easily obtained from traditional inorganic or organic materials. In addition, biomaterials come from renewable resources and are usually biodegradable. Among biomate- rials, researches have been interested in DNA for various reasons, such as potential applications of DNA assem- bly in molecular electronic devices , nanoscale robotics , and DNA-based computation . One of the most interesting applications in DNA is to use DNA as a kind of optoelectronic material. Thin ﬁlm of DNA-CTMA has been used successfully in various applications such as organic light emitting diodes, a cladding and host material in nonlinear optical devices, and organic ﬁeld-eﬀect tran- sistors because of its nature of large dielectric constant and large band gap . DNA-based polymers are utilized in optically pumped organic solid-state lasers . A better understanding of the nonlinear optical properties of DNA materials will undoubtedly lead us to more exciting appli- cations. So, many researches on nonlinear optical prop- erties of DNA materials have been undertaken. Samoc et al. have studied the nonlinear refractive index and the two-photon absorption coeﬃcient of native (sodium salt)
A theoretical model and a design of a magnetic field tunable CdMnTe/CdMgTe terahertz quan- tum well infrared photodetector are presented. The energy levels and the corresponding wave- functions were computed from the envelope function Schr¨ odinger equation using the effective mass approximation and accounting for Landau quantization and the giant Zeeman effect induced by magnetic confinement. The electron dynamics were modeled within the self-consistent coupled rate equations approach, with all relevant electron-longitudinal optical phonon and electron-longitudinal acoustic phonon scattering included. A perpendicular magnetic field varying between 0 T and 5 T, at a temperature of 1.5 K, was found to enable a large shift of the detection energy, yielding a tuning range between 24.1 meV and 34.3 meV, equivalent to 51.4 µm to 36.1 µm wavelengths. For magnetic fields between 1 T and 5 T, when the electron population of the QWIP is spin-polarized, a reasonably low dark current of ≤ 1.4 × 10 −2 A/cm 2 and a large responsivity of 0.36
However, selecting the most suitable material to enhance process performance for a specific application, rather than just simplify fabrication, is no trivial task. A number of material properties have to be taken into account, such as mechanical strength, thermal stability, chemical inert- ness, optical transmission, electrical insu- lation, and dielectric and surface properties. In addition, operational parameters such as the choice of solvent, temperatures, and pressure will need to be considered when selecting a suitable substrate. The aim of this article is to review the common types of materials that are currently used to fab- ricate microfluidic devices and consider how these influence the eventual perform- ance of the final device. In particular, the physical, chemical, and biological attrib- utes of such materials will be considered, as these will ultimately lead to the future generation of more highly functionalized and integrated systems.
In conclusion, we have utilized a Green’s function-based model to calculate the outcoupling efficiency of IR-QDLED using CNT anode. The calculations suggest that it is relatively simple to use CNT anode to increase the light outcoupling efficiency by a factor ∼ 4. So, CNT is an ideal choice for IR-QDLEDs. Also we have investigated the effect of metal cathode material types on the optical characteristics of IR QD-LEDs. We have found that the application of Al and Au as cathode materials is better than Mg/Ag and Ni as cathode materials from optical characteristics point view point, especially in the case of SWCNT anode.