B. P. Gorshunov

Dielectric spectra of some ceramics for microwave applications in the range of 1010–1014 Hz

Abstract The complex permittivity spectra of the alumina A12O3, mixed perovskites CaTiO3-La(Mg1/2Ti1/2)O3, (Zr,Sn)TiO4 and BaO. 4TiO2. Nd2-xSm x O3 ceramics have been determined employing various techniques in the 1010–1014 Hz range. In samples with minimized loss its origin is lattice phonon absorption in the whole spectral range. In not optimized samples the microwave losses are appreciably higher (probably due to localized hopping of charged defects) but submillimetre losses remain unaffected. Extrapolating the submillimetre loss using the proportionality e″“(v)x v allows one to estimate the lower limit of microwave loss achievable by any processing.

Circular-Polarization-Dependent Study of the Microwave Photoconductivity in a Two-Dimensional Electron System

The polarization dependence of the low field microwave photoconductivity and absorption of a two-dimensional electron system has been investigated in a quasioptical setup in which linear and any circular polarization can be produced in situ. The microwave induced resistance oscillations and the zero resistance regions are notably immune to the sense of circular polarization. This observation is discrepant with a number of proposed theories. Deviations between different polarizations occur only near the cyclotron resonance where an unprecedented large resistance response is observed.

Dielectric spectroscopy of Ba(B1/2’B1/2‘)O3 complex perovskite ceramics: Correlations between ionic parameters and microwave dielectric properties. II. Studies below the phonon eigenfrequencies (102–1012 Hz)

Dielectric spectroscopy in the submillimeter, millimeter, microwave, and radio frequency range has been performed between 300 and 600 K (for some cases below 300 K) on nine Ba(B1/2’B1/2‘)O3 complex perovskite ceramic compounds. The real part of the permittivity e’ decreases linearly with the increasing tolerance factor t<1 approaching unity. It is insensitive to imperfections in the ceramic, such as impurities, vacancies, etc., and entirely determined by polar lattice vibrations. Its temperature dependence is influenced by the presence of a structural phase transition observed in six of the investigated compounds. It is shown that the imaginary part of the permittivity e‘ in the submillimeter range is mainly of intrinsic origin. The e‘(f) dependences were fitted applying a microscopic theory using polar‐phonon parameters that have been determined in the phonon resonance region by infrared reflection spectroscopy (Part I). The theory allows the extrapolation of minimum intrinsic loss due to polar‐phonon co...

High-frequency dielectric spectra of AgTaO3-AgNbO3 mixed ceramics

This paper presents the results of dielectric susceptibility investigations performed in the radiowave, microwave, submillimetre wave and infrared (IR) regions on the AgTaO3-AgNbO3 solid solution with Nb contents of 0.3, 0.4 and 0.6. An intense dipolar relaxation, which is responsible for the temperature dependence of the static permittivity and which freezes out at low temperatures, has been evidenced in the submillimetre wave region.

Frequency-domain magnetic resonance spectroscopy of molecular magnetic materials

A brief review is presented of a novel method of high-frequency magnetic resonance spectroscopy, which sweeps the frequency at a fixed magnetic field, including zero field. We describe the main features of this frequency-domain spectrometer which works in the spectral range from 30 GHz to 1.5 THz and at magnetic fields up to 8 T; the temperature can be as low as 0.4 K. The versatility of this technique is demonstrated by means of a number of examples from the field of molecular magnetism.

Optical investigations of the normal and superconducting states reveal two electronic subsystems in iron pnictides

D. Wu, N. Barǐsić, P. Kallina, A. Faridian, B. Gorshunov, N. Drichko, L. J. Li, X. Lin, G. H. Cao, Z. A. Xu, N. L. Wang, and M. Dressel 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany Department of Physics, Zhejiang University, Hangzhou 310027, People’s Republic of China 3 Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China (Dated: December 18, 2009)

CaNdAlO4 perovskite substrate for microwave and far‐infrared applications of epitaxial high Tc superconducting thin films

Single‐crystal perovskite calcium‐neodymium aluminate CaNdAlO4 has been grown and tested as a substrate material for high Tc superconducting thin films. The material is chemically stable, can be fabricated into the form of large, twin‐free wafers, permits deposition of epitaxial Y‐Ba‐Cu‐O and Bi‐Sr‐Ca‐Cu‐O films, and exhibits low dielectric permittivity (e≂20) and very low losses (tan δ≂10−3 at 100 K) at sub‐THz frequencies. Its high potential in microwave applications of thin‐film high Tc superconductors is clearly demonstrated.

The Higgs mode in disordered superconductors close to a quantum phase transition

The Higgs mechanism is best known for generating mass for subatomic particles. Less well-known is that the idea originated in the study of superconductivity, and can be tested in the laboratory.

Direct observation of the superconducting energy gap in the optical conductivity of the iron pnictide superconductor Ba(Fe0.9Co0.1)2As2

The temperature-dependent optical reflectivity and complex transmissivity of an epitaxially grown Ba(Fe0.9Co0.1)2As2 thin film were measured and the optical conductivity and permittivity evaluated over a wide frequency range. The opening of the superconducting gap 2�0 = 3:7 meV below Tc � 20 K is directly observed by a completely vanishing optical conductivity. The temperature and frequency dependent electrodynamic properties of Ba(Fe0.9Co0.1)2As2 in the superconducting state agree well with the BCS predictions with no nodes in the order parameter. The spectral weight of

Observation of an intersublattice exchange magnon in CoCr2O4 and analysis of magnetic ordering

= 250÷1230 GHz = 1÷5meV)andattemperaturesbetween4and300K.Theradiationwaslinearlypolarized.Theabsolutevaluesofopticaltransmis-sion (normalized to the empty-channel measurements) wereobtained in essentially the same way as described, e.g., inRef. 19.A commercial split-coil magnet, embedded into an opticalcryostat, was utilized for measurements in magnetic fieldsup to 8 T. In these measurements, we used three differentgeometries: