0000000000021673
AUTHOR
Andrei Pimenov
showing 9 related works from this author
Ion transport in the fragile glass former3KNO3-2Ca(NO3)2
1996
The molten salt ${3\mathrm{K}\mathrm{N}\mathrm{O}}_{3}$-2Ca(${\mathrm{NO}}_{3}$${)}_{2}$ has been studied in the frequency range 5 mHz40 GHz and for temperatures 10 KT500 K using impedance spectroscopy. It is found that in the microwave regime the dynamic conductivity traces the primary response. In the radio- and audio-frequency ranges the mobile ion relaxation becomes increasingly decoupled and the time scale and stretching of the response as determined from electrical modulus spectra differ from those obtained by spectroscopies probing the structural response. For T\ensuremath{\gtrsim}360 K minima are detected in the dielectric loss that make possible a comparison with recent mode-coupli…
Broadband infrared conductivity in an YBa2Cu3O6.7 thin film
2001
Infrared reflectivity of an oxygen reduced YBa2Cu3O6.7 thin film was measured in the frequency range 30 cm-1 < v < 7000 cm-1 and for temperatures 5 K < T < 300 K. At lower frequencies, 3 cm-1 < v < 40 cm-1, the complex conductivity σ*=σ1+iσ2 was measured directly using a transmission technique. Both data sets were combined to obtain the reflectivity in a broad frequency range and thus to improve substantially the quality of the Kramers-Kronig analysis at low frequencies. The analysis of the conductivity spectra reveals that the low-frequency spectral weight strongly depends on temperature directly above TC but saturates for T ≥ 150 K.
Ionic transport and heat capacity of glass-forming metalnitrate mixtures
1997
Abstract Ionic transport of the glass-forming metalnitrate mixtures [Ca(NO 3 ) 2 ] 0.44 [KNO 3 ] 0.56 (MKN), and [Mg(NO 3 ) 2 ] 0.44 [NaNO 3 ] 0.56 (MNN) was investigated near the glass transition using broadband spectroscopy of the complex conductivity to 300 MHz. The real part of the conductivity exhibits a transition from frequency independent to power law behavior as found in most ionic conductors. At high frequencies the frequency exponent approaches unity and becomes larger at low temperatures. In the real part of the dielectric constant, a relaxation step could be observed in CRN. A detailed evaluation of the results within the modulus formalism is presented. The imaginary part of t…
Direct observation of the quasiparticle relaxation in YBa2Cu3O7
1999
Abstract The real and imaginary parts of the optical conductivity ( σ 1 + iσ 2 ) in the superconducting state of YBa 2 Cu 3 O 7−δ thin films have been obtained by submillimeter spectroscopy for frequencies from 3 to 35 cm −1 . The quasiparticle relaxation can be directly observed in this frequency range. A Drude-type analysis allows to extract the temperature dependence of the scattering rate. The collapse of the relaxation rates provides clear experimental evidence that the spin fluctuations become gapped below T C .
Universal relationship between the penetration depth and the normal-state conductivity in YBaCuO
1999
The absolute values of the conductivity in the normal state sigma_n and of the low temperature penetration depths lambda(0) were measured for a number of different samples of the YBaCuO family. We found a striking correlation between sigma_n and 1/lambda^2, regardless of doping, oxygen reduction or defects, thus providing a simple method to predict the superconducting penetration depth and to have an estimate of the sample quality by measuring the normal-state conductivity.
Frequency-dependent relaxation rate in superconductingYBa2Cu3O6+δ
2000
The submillimeter-wave $3 {\mathrm{cm}}^{\ensuremath{-}1}l\ensuremath{\nu}l40 {\mathrm{cm}}^{\ensuremath{-}1}$ complex conductivity of the reduced ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+\ensuremath{\delta}}$ film ${(T}_{C}=56.5 \mathrm{K})$ was investigated for temperatures $4 \mathrm{K}lTl300 \mathrm{K}$ and compared to the properties of the same film in the optimally doped state. The frequency dependence of the effective quasiparticle scattering rate $1/{\ensuremath{\tau}}^{*}(\ensuremath{\nu})$ was extracted from the spectra. $1/{\ensuremath{\tau}}^{*}$ is shown to be frequency independent at low frequencies and high temperatures. A gradual change to $1/{\ensuremath{\tau}}^{…
Structural relaxation in a molten salt probed by time-dependent dc conductivity measurements
1998
Abstract Time-dependent dc conductivity was measured after cooling steps of about 2 K in the glass transformation range of 2Ca(NO 3 ) 2 -3RbNO 3 . The shape and time scale of the structural relaxation function was thus monitored for times 60 s t 6 s. The time scale could be compared with results from scanning calorimetry measurements and good agreement was found. From the heat capacity data and from the solid state conductivity the expected liquid state conductivity relaxation time was calculated using several models. The good compatibility of these calculations with the experimental results provides evidence that near the calorimetric glass transition the mobile ions perform concerted moti…
Optical conductivity inYBa2Cu3O7−δthin films
1999
The real and imaginary parts of the optical conductivity ${\ensuremath{\sigma}}_{1}+i{\ensuremath{\sigma}}_{2}$ of partly untwinned ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ thin films were measured by submillimeter spectroscopy for frequencies from 100 GHz to 1 THz. The frequency dependence of the conductivity below ${T}_{C}$ can be described by a narrow Drude-like peak with strongly temperature-dependent relaxation rates. ${\ensuremath{\sigma}}_{1}(\ensuremath{\nu})$ does not extrapolate to the universal d-wave value at 0 K. Impurity scattering significantly different to the unitary limit has to be assumed to achieve agreement with recent theor…
Relaxation times at the rate-dependent glass transition
1997
The structural relaxation time near the cooling rate dependent glass transition is determined self-consistently within the Moynihan-Narayanaswami formalism. In order to illustrate the method we analyze scanning calorimetry data from amorphous calcium-rubidium nitrate. A characteristic time scale of about 250 s is obtained at the conventionally defined glass transition. The occurrence of decoupled, faster relaxation modes is briefly discussed.