Gigantic transmission band edge resonance in periodic stacks of anisotropic layers

We consider Fabry-Perot cavity resonance in periodic stacks of anisotropic layers with misaligned in-plane anisotropy at the frequency close to a photonic band edge. We show that in-plane dielectric anisotropy can result in a dramatic increase in field intensity and group delay associated with the transmission resonance. The field enhancement appears to be proportional to forth degree of the number N of layers in the stack. By contrast, in common periodic stacks of isotropic layers, those effects are much weaker and proportional to N^2. Thus, the anisotropy allows to drastically reduce the size of the resonance cavity with similar performance. The key characteristic of the periodic arrays with the gigantic transmission resonance is that the dispersion curve omega(k)at the photonic band edge has the degenerate form Delta(omega) ~ Delta(k)^4, rather than the regular form Delta(omega) ~ Delta(k)^2. This can be realized in specially arranged stacks of misaligned anisotropic layers. The degenerate band edge cavity resonance with similar outstanding properties can also be realized in a waveguide environment, as well as in a linear array of coupled multimode resonators, provided that certain symmetry conditions are in place.Comment: To be submitted to Phys. Re

Slow wave resonance in periodic stacks of anisotropic layers

We consider transmission band edge resonance in periodic layered structures involving birefringent layers. Previously we have shown that the presence of birefringent layers with misaligned in-plane anisotropy can dramatically enhance the performance of the photonic-crystal Fabry-Perot resonator. It allows to reduce its size by an order of magnitude without compromising on its performance. The key characteristic of the enhanced photonic-crystal cavity is that its Bloch dispersion relation displays a degenerate photonic band edge, rather than only regular ones. This can be realized in specially arranged stacks of misaligned anisotropic layers. On the down side, the presence of birefringent layers results in the Fabry-Perot resonance being coupled only with one (elliptic) polarization component of the incident wave, while the other polarization component is reflected back to space. In this paper we show how a small modification of the periodic layered array can solve the above fundamental problem and provide a perfect impedance match regardless of the incident wave polarization, while preserving the giant transmission resonance, characteristic of a degenerate photonic band edge. Both features are of critical importance for a variety of practical applications, including antennas, light amplification, optical and microwave filters, etc.Comment: To be submitted to Phys. Rev.

Observation of Conduction Band Satellite of Ni Metal by 3p-3d Resonant Inverse Photoemission Study

Resonant inverse photoemission spectra of Ni metal have been obtained across the Ni 3$p$ absorption edge. The intensity of Ni 3$d$ band just above Fermi edge shows asymmetric Fano-like resonance. Satellite structures are found at about 2.5 and 4.2 eV above Fermi edge, which show resonant enhancement at the absorption edge. The satellite structures are due to a many-body configuration interaction and confirms the existence of 3$d^8$ configuration in the ground state of Ni metal.Comment: 4 pages, 3 figures, submitted to Physical Review Letter

Efficiency of tunable band-gap structures for single-photon emission

The efficiency of recently proposed single-photon emitting sources based on tunable planar band-gap structures is examined. The analysis is based on the study of the total and ``radiative'' decay rates, the expectation value of emitted radiation energy and its collimating cone. It is shown that the scheme operating in the frequency range near the defect resonance of a defect band-gap structure is more efficient than the one operating near the band edge of a perfect band-gap structure.Comment: 9 pages, 7 figure

Non-parabolicity of the conduction band of wurtzite GaN

Using cyclotron resonance, we measure the effective mass, $m$*, of electrons in AlGaN/GaN heterostructures with densities, $n_{2D}\sim 1-6\times10^{12}$cm$^{-2}$. From our extensive data, we extrapolate a band edge mass of $(0.208\pm0.002) m_e$. By comparing our $m$* data with the results of a multi-band \textbf{k.p} calculation we infer that the effect of remote bands is essential in explaining the observed conduction band non-parabolicity (NP). Our calculation of polaron mass corrections -- including finite width and screening - suggests those to be negligible. It implies that the behavior of $m*(n_{2D})$ can be understood solely in terms of NP. Finally, using our NP and polaron corrections, we are able to reduce the large scatter in the published band edge mass values

Parametric Excitation Of An Axially Moving Band By Periodic Edge Loading

Simple torsion parametric resonance and combination torsion-bending parametric resonance can be excited in an axially moving band by an in-plane periodic edge loading that is normal to the longitudinal axis of the band. The model simulates band saws, belts, magnetic tapes and like systems under edge forces. Sum combination instabilities, in particular, permit the excitation of low frequency resonances by higher frequency edge forces. Simple bending, combination torsion-torsion, combination bending-bending and difference type parametric instabilities are not excited by periodic normal edge forces. The space of band parameters leading to parametric instability shrinks with increasing axial tension and with increasing band velocity. © 1986 Academic Press Inc. (London) Limited

Electronic Density of States of a U(1)U\left(1\right) Quantum Spin Liquid with Spinon Fermi Surface. I. Orbital Magnetic Field Effects

Quantum spin liquid (QSL) with spinon Fermi surface is an exotic insulator that hosts neutral Fermi surfaces inside the gap. In an external magnetic field, it has been pointed out that the neutral Fermi surfaces are Landau quantized to form Landau levels (LLs) due to the induced emergent gauge magnetic field. In this work, we calculate the electronic density of states (DOS) of the QSL in an orbital magnetic field. We find that the LLs from the neutral Fermi surfaces give rise to a set of steps emerging at the upper and lower Hubbard band edges. Each of the Hubbard band edge steps further develop into a band edge resonance peak when a weak gauge binding from the gauge field fluctuations is taken into account. Importantly, each Hubbard band edge step and its resulting resonance peak in the weak gauge binding are found to have a correspondence LL from the neutral Fermi surfaces, so the Hubbard band edge steps and the band edge resonance peaks are the unique features that characterize the Landau quantization of the in-gap neutral Fermi surfaces. We further consider the strong gauge binding regime where the band edge resonance peaks move into the Mott gap and develop into true in-gap bound states. In the strong gauge binding regime, we solve the bound state LL spectrum. For the bound state with a Mexican hat like band dispersion, we find that the envelop energy to have a state excited from the bound state LL decreases quadratically with the magnetic field. The quadratic decrease behavior of the envelop energy is consistent with the intuition that applying magnetic field localizes the states and energetically promotes the in-gap bound states formation. Finally, we connect our results to the electronic DOS spectra measured in the layered 1T-TaS$_2$. We point out that a QSL with a quasi-bound state in the upper Hubbard band can give the DOS spectra similar to the one measured in the experiment.Comment: 17 pages, 10 figures, plus Supplementary Material. Comments are welcom