Directional microwave emission from femtosecond-laser illuminated linear arrays of superconducting rings.

We examine the electromagnetic emission from two photo-illuminated linear arrays composed of inductively charged superconducting ring elements. The arrays are illuminated by an ultrafast infrared laser that triggers microwave broadband emission detected in the 1-26 GHz range. Based on constructive interference from the arrays a narrowing of the forward radiation lobe is observed with increasing element count and frequency demonstrating directed GHz emission. Results suggest that higher frequencies and a larger number of elements are achievable leading to a unique pulsed array emitter concept that can span frequencies from the microwave to the terahertz (THz) regime.

Self-Assembly of Uniaxial Fullerene Supramolecules Aligned within Carbon Nanotube Fibers.

The conductivity and strength of carbon nanotube (CNT) wires currently rival those of existing engineering materials; fullerene-based materials have not progressed similarly, despite their exciting transport properties such as superconductivity. This communication reveals a new mechanically robust wire of mutually aligned fullerene supramolecules self-assembled between CNT bundles, where the fullerene supramolecular internal crystal structure and outer surface are aligned and dispersed with the CNT bundles. The crystallinity, crystal dimensions, and other structural features of the fullerene supramolecular network are impacted by a number of important production processes such as fullerene concentration and postprocess annealing. The crystal spacing of the CNTs and fullerenes is not altered, suggesting that they are not exerting significant internal pressure on each other. In low concentrations, the addition of networked fullerenes makes the CNT wire mechanically stronger. More importantly, novel mutually aligned and networked fullerene supramolecules are now in a bulk self-supporting architecture.

Erratum: Size effects in energy transport between thermal contacts mediated by nanoparticles [Phys. Rev. E 99, 032141 (2019)].

This corrects the article DOI: 10.1103/PhysRevE.99.032141.

Type-II quantum spin Hall effect in two-dimensional metals.

The quantum spin Hall (QSH) effect has been observed in topological insulators and long quantum wells using spin-orbit coupling as the probe, but it has not yet been observed in a metal. An experiment is proposed to measure the different Type-II QSH effect of an electron or hole in a two-dimensional (2D) metal by using the previously unexplored but relativistically gauge-invariant form of the generated 2D QSH Hamiltonian. Instead of using the electric field in the surface of the spin-polarized bands of a topological insulator or across the quantum well width as the probe, ones uses an applied azimuthal vector potential and an applied radial electric field as the tools to generate a spontaneously quantized spin current in an otherwise spin unpolarized 2D metal. A long cylindrical solenoid lies normally through the inner radius of a 2D metallic Corbino disk. The currentISsurrounding the solenoid produces an azimuthal magnetic vector potential but no magnetic field in the disk. In addition, a radial electric field is generated across the disk by imposing either a potential differenceΔvor a radial charge currentIacross its inner and outer radii. Combined changes inISand in eitherΔvorIgenerate spontaneously quantized azimuthal charge and spin currents. The experiment is designed to measure these quantized azimuthal charge and spin currents in the disk consistently. The quantum Hamiltonians for both experiments are solved exactly. A method to control the Joule heating is presented, which could potentially allow the Type-II QSH measurements to be made at room temperature.

The Zeeman, spin-orbit, and quantum spin Hall interactions in anisotropic and low-dimensional conductors.

To construct a microscopic theory of electrons and holes in anisotropic conductors that self-consistently treats their band effective mass anisotropy with their interactions with applied electric and magnetic fields, the Dirac equation is extended for an electron or hole in an orthorhombically-anisotropic conduction band. Its covariance is established both by a modified version of the Klemm-Clem transformations to a space in which it is isotropic, and also in its fully anisotropic form by making the most general proper and improper Lorentz transformations, proving its validity in both the relativistic and non-relativistic limits. The appropriate Foldy-Wouthuysen transformations are extended to expand about the non-relativistic Hamiltonian limit to fourth order in the inverse of the particle's Einstein rest energy. The results have important consequences for magnetic measurements of many classes of clean anisotropic semiconductors, metals, and superconductors. In all of these cases, the Zeeman interaction is found to depend strongly upon the effective mass anisotropy. When an electron or hole is traveling in an atomically thin one-dimensional conduction band, its Zeeman, spin-orbit, and quantum spin Hall interactions are vanishingly small. Accurate expressions for the Zeeman, spin-orbit and quantum spin Hall interactions for two-dimensional conductors are provided.

Size effects in energy transport between thermal contacts mediated by nanoparticles.

We investigate size effects in phononic energy transport in a system of two nanoparticles interconnected by a molecule and attached to thermal contacts also by molecules. In the considered closed system, the nanoparticles and contacts are described by ensembles of finite numbers of harmonic oscillators within the Drude-Ullersma model. The macroscopic character of the contacts is simulated by a large value of the ratio Δ/Δ_{B}=n (n>100) of mode spacings Δ and Δ_{B} corresponding to the nanoparticles and contacts, respectively. Quasistatic energy transport on the timescale Δ^{-1} is investigated. Equations describing the dynamics of the averaged eigenmode energies that belong to the nanoparticles and contacts are derived and solved. The resulting expressions for the energy current exiting (entering) the contacts as well as the energy current between the nanoparticles are obtained and investigated. The latter current accounts for energy accumulation by (depletion from) the nanoparticles. The finite size effects result in reversibility features and peculiarities at time moments t=2πℓΔ^{-1} for non-negative integers ℓ. They are qualitatively the same as in a previously studied system of two equal nanoparticles mediated by a molecule, despite the presence of the macroscopic contacts. The thermal conductance of the whole nanojunction is derived and explored. The energy currents and thermal conductance of the nanojunction in a case when its parameters are known from the experiment are computed using the developed model.

Tunable Broadband Radiation Generated Via Ultrafast Laser Illumination of an Inductively Charged Superconducting Ring.

An electromagnetic transmitter typically consists of individual components such as a waveguide, antenna, power supply, and an oscillator. In this communication we circumvent complications associated with connecting these individual components and instead combine them into a non-traditional, photonic enabled, compact transmitter device for tunable, ultrawide band (UWB) radiation. This device is a centimeter scale, continuous, thin film superconducting ring supporting a persistent super-current. An ultrafast laser pulse (required) illuminates the ring (either at a point or uniformly around the ring) and perturbs the super-current by the de-pairing and recombination of Cooper pairs. This generates a microwave pulse where both ring and laser pulse geometry dictates the radiated spectrum's shape. The transmitting device is self contained and completely isolated from conductive components that are observed to interfere with the generated signal. A rich spectrum is observed that extends beyond 30 GHz (equipment limited) and illustrates the complex super-current dynamics bridging optical, THz, and microwave wavelengths.