Search

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., (© 2023. Springer Nature Limited.)

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 current I across its inner and outer radii. Combined changes inISand in eitherΔvor I generate 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., (© 2022 IOP Publishing Ltd.)

CuAl 2 O 4 is a ternary oxide spinel with Cu 2+ ions ([Formula: see text]) primarily populating the A-site diamond sublattice. The compound is reported to display evidence of spin glass behavior but possess a non-frozen magnetic ground state below the transition temperature. On the other hand, the spinel CuGa 2 O 4 displays spin glass behavior at ~ 2.5 K with Cu 2+ ions more readily tending to the B-site pyrochlore sublattice. Therefore, we investigate the magnetic and structural properties of the solid solution CuAl 2(1-x) Ga 2x O 4 examining the evolution of the magnetic behavior as Al 3+ is replaced with a much larger Ga 3+ ion. Our results show that the Cu 2+ ions tend to migrate from tetrahedral to octahedral sites as the Ga 3+ ion concentration increases, resulting in a concomitant change in the glassy magnetic properties of the solution. Results indicate glassy behavior for much of the solution with a general trend towards decreasing magnetic frustration as the Cu 2+ ion shifts to the B-site. However, the [Formula: see text] and 0.2 members of the system do not show glassy behavior down to our measurement limit (1.9 K) suggesting a delayed spin glass transition. We suggest that these two members are additional candidates for investigation to access highly frustrated exotic quantum states.

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.

We have carried out density-functional theory (DFT) calculations for the chromium pnictide BaCr 2 P 2 , which is structurally analogous to BaFe 2 As 2 , a parent compound for iron-pnictide superconductors. Evolutionary methods combined with DFT predict that the chromium analog has the same crystal structure as the latter. DFT also predicts Néel antiferromagnetic order on the chromium sites. Comparison with a simple electron-hopping model over a square lattice of chromium atoms suggests that it is due to residual nesting of the Fermi surfaces. We have confirmed the DFT predictions directly after the successful synthesis of polycrystalline samples of BaCr 2 P 2 . X-ray diffraction recovers the predicted crystal structure to high accuracy, while magnetic susceptibility and specific-heat measurements are consistent with a transition to an antiferromagnetically ordered state below [Formula: see text] K.

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.