122 research outputs found
M. M. Bakhtin in Russian Culture of the Twentieth Century (Translated by Ann Shukman)
This article by M.L.Gasparov was first published at Tartu in the Soviet Union in 1979 and has been translated and edited here with notes by Ann Shukman. Gasparov emphasizes four aspects of Bakhtin\u27s thought: his zeal for expropriating \u27the other\u27s word\u27 ; his zeal for dialogue ; a nihilistic selection of values ; the opposition of the novel to poetry. Ann Shukman\u27s commentary places Gasparov\u27s article in context
Electronic Raman scattering in Tl2Ba2CuO6+x: symmetry of the order parameter, oxygen doping effects, and normal state scattering
Single crystals of the optimally doped, moderately and strongly overdoped
high temperature superconductor Tl2Ba2CuO6+x (Tl-2201) with Tc=80, 56 and 30K,
respectively, have been investigated by polarized Raman scattering. By taking
the peak position of the B_1g component of electronic Raman scattering as
2Delta_0 we found that the reduced gap value (2Delta_0/k_BT_c) strongly
decreases with increasing doping. The behavior of the low frequency scattering
for the B_1g and B_2g scattering components is similar for optimally doped and
overdoped crystals and can be described by a w^3 - and w -law, respectively,
which is consistent with a d-wave symmetry of the order parameter. In contrast
to the optimally doped Tl-2201 in both, moderately and strongly overdoped
Tl-2201, the relative (compared to the B_1g) intensity of the A_1g scattering
component is suppressed. We suggest that the van Hove singularity is
responsible for the observed changes of Raman intensity and reduced gap value
with doping. Electronic Raman scattering in the normal state is discussed in
the context of the scattering from impurities and compared to the existing
infrared data. The scattering rate evaluated from the Raman measurements is
smaller for the overdoped samples, compared to the moderately overdoped
samples.Comment: 7 pages, 7 figure
Electron transport and anisotropy of the upper critical magnetic field in a Ba0.68K0.32Fe2As2 single crystals
Early work on the iron-arsenide compounds supported the view, that a reduced
dimensionality might be a necessary prerequisite for high-Tc superconductivity.
Later, however, it was found that the zero-temperature upper critical magnetic
field, Hc2(0), for the 122 iron pnictides is in fact rather isotropic. Here, we
report measurements of the temperature dependence of the electrical
resistivity, \Gamma(T), in Ba0.5K0.5Fe2As2 and Ba0.68K0.32Fe2As2 single
crystals in zero magnetic field and for Ba0.68K0.32Fe2As2 as well in static and
pulsed magnetic fields up to 60 T. We find that the resistivity of both
compounds in zero field is well described by an exponential term due to
inter-sheet umklapp electron-phonon scattering between light electrons around
the M point to heavy hole sheets at the \Gamma point in reciprocal space. From
our data, we construct an H-T phase diagram for the inter-plane (H || c) and
in-plane (H || ab) directions for Ba0.68K0.32Fe2As2. Contrary to published data
for underdoped 122 FeAs compounds, we find that Hc2(T) is in fact anisotropic
in optimally doped samples down to low temperatures. The anisotropy parameter,
{\gamma} = Habc2/Hcc2, is about 2.2 at Tc. For both field orientations we find
a concave curvature of the Hc2 lines with decreasing anisotropy and saturation
towards lower temperature. Taking into account Pauli spin paramagnetism we
perfectly can describe Hc2(T) and its anisotropy.Comment: 7 pages, 3 figure
Electron transport, penetration depth and upper critical magnetic field of ZrB12 and MgB2
We report on the synthesis and measurements of the temperature dependence of
resistivity, R(T), the penetration depth, l(T), and upper critical magnetic
field, Hc2(T), for polycrystalline samples of dodecaboride ZrB12 and diboride
MgB2. We conclude that ZrB12 as well as MgB2 behave like simple metals in the
normal state with usual Bloch-Gruneisen temperature dependence of resistivity
and with rather low resistive Debye temperature, TR=280 K, for ZrB12 (as
compared to MgB2 with TR=900 K). The R(T) and l(T) dependencies of ZrB12 reveal
a superconducting transition at Tc=6.0 K. Although a clear exponential
l(T)dependence in MgB2 thin films and ceramic pellets was observed at low
temperatures, this dependence was almost linear for ZrB12 below Tc/2. These
features indicate s-wave pairing state in MgB2, whereas a d-wave pairing state
is possible in ZrB12. A fit to the data gives a reduced energy gap
2D(0)/kTc=1.6 for MgB2 films and pellets, in good agreement with published data
for 3D \pi - sheets of the Fermi surface. Contrary to conventional theories we
found a linear temperature dependence of Hc2(T) for ZrB12 (Hc2(0)=0.15 T).Comment: 8 pages, 10 figures, submitted to JET
"Tesnota stichovogo rjada". Semantika i sintaksis
This collection brings together the articles dedicated to the 60th birthday of Professor Wolf Schmid, one of the foremost literary scholars of our times who made a crucial contribution to a wide range of scholarly fields: narratology, poetics, history of Russian and Slavic literature, Pushkin and Dostoevsky. The contributors form a distinguished international group of prominent scholars whose essays in this volume further develop Wolf Schmid\u27s narratological theory, shed new light on major works of literature and offer fascinating new insights into various periods of literary history.This collection brings together the articles dedicated to the 60th birthday of Professor Wolf Schmid, one of the foremost literary scholars of our times who made a crucial contribution to a wide range of scholarly fields: narratology, poetics, history of Russian and Slavic literature, Pushkin and Dostoevsky. The contributors form a distinguished international group of prominent scholars whose essays in this volume further develop Wolf Schmid\u27s narratological theory, shed new light on major works of literature and offer fascinating new insights into various periods of literary history
Electronic Raman scattering in Magnetite, Spin vs. Charge gap
We report Raman scattering data of single crystals of magnetite (Fe3O4) with
Verwey transition temperatures (Tv) of 123 and 117K, respectively. Both single
crystals reveal broad electronic background extending up to 900 wavenumbers
(~110 meV). Redistribution of this background is observed when samples are
cooled below Tv. In particular, spectra of the low temperature phase show
diminished background below 300 wavenumbers followed by an enhancement of the
electronic background between 300 and 400 wavenumbers. To enhance the effect of
this background redistribution we divide the spectra just below the transition
by the spectra just above the transition. A resultant broad peak-like feature
is observed, centered at 370 wavenumbers (45 meV). The peak position of this
feature does not scale with the transition temperature. We discuss two
alternative assignments of this feature to a spin or charge gap in magnetite.Comment: 4 figures, 1 tabl
Phonon anomaly at the charge ordering transition in 1T-TaS2
The infrared reflectance of the transition metal chalcogenide 1T-TaS2 has
been measured at temperatures from 30K to 360K over 30-45,000cm^-1
(4meV-5.5eV). The optical conductivity was obtained by Kramers-Kronig analysis.
At 360K only modest traces of the phonon lines are noticeable. The phonon modes
are followed by a pseudogap-like increase of the optical conductivity, with
direct optical transitions observed at frequencies above 1eV. As the
temperature decreases, the low frequency conductivity also decreases, phonon
modes become more pronounced and pseudogap develops into a gap at 800cm^-1
(100meV). We observe an anomalous frequency dependence of the 208cm^-1
infrared-active phonon mode. This mode demonstrates softening as the
temperature decreases below the 180K metal-to-insulator transition. The same
mode demonstrates strong hysteresis of the frequency and linewidth changes,
similar in its temperature behavior to the hysteresis in the dc-resistivity. We
discuss a possible relation of the observed softening of the mode to the
structural changes associated with the metal-to-insulator transition.Comment: 7 pages, 4 figures, 1 table; corrected typo
First Principles Study of the Electronic and Vibrational Properties of LiNbO2
In the layered transition metal oxide LiNbO the Nb () ion is
trigonal-prismatically coordinated with O ions, with the resulting crystal
field leading to a single band system for low energy properties. A
tight-binding representation shows that intraplanar second neighbor hopping
meV dominates the first neighbor interaction ( meV). The
first and third neighbor couplings are strongly modified by oxygen
displacements of the symmetric Raman-active vibrational mode, and
electron-phonon coupling to this motion may provide the coupling mechanism for
superconductivity in Li-deficient samples (where K). We calculate all
zone-center phonon modes, identify infrared (IR) and Raman active modes, and
report LO-TO splitting of the IR modes. The Born effective charges for the
metal ions are found to have considerable anisotropy reflecting the degree to
which the ions participate in interlayer coupling and covalent bonding. Insight
into the microscopic origin of the valence band density, composed of Nb
states with some mixing of O states, is obtained from examining
Wannier functions for these bands.Comment: 12 pages, 7 figures; Updated with reviewer comments; Updated
reference
Upper critical magnetic field in Ba_0.68K_0.32Fe_2As_2 and Ba(Fe_0.93Co_0.07)_2As_2
We report measurements of the temperature dependence of the radio-frequency
magnetic penetration depth in Ba_0.68K_0.32Fe_2As_2 and
Ba(Fe_0.93Co_0.07)_2As_2 single crystals in pulsed magnetic fields up to 60 T.
From our data, we construct an H-T phase diagram for the inter-plane (H || c)
and in-plane (H || ab) directions for both compounds. For both field
orientations in Ba_0.68K_0.32Fe_2As_2, we find a concave curvature of the
Hc2(T) lines with decreasing anisotropy and saturation towards lower
temperature. Taking into account Pauli spin paramagnetism we can describe
Hc2(T) and its anisotropy. In contrast, we find that Pauli paramagnetic pair
breaking is not essential for Ba(Fe_0.93Co_0.07)_2As_2. For this electron-doped
compound, the data support a Hc2(T) dependence that can be described by the
Werthamer Helfand Hohenberg model for H || ab and a two-gap behavior for H ||
c.Comment: 7 pages, 8 figure
Interaction of vortices in thin superconducting films and Berezinskii-Kosterlitz-Thouless transition
The precondition for the BKT transition in thin superconducting films, the
logarithmic intervortex interaction, is satisfied at distances short relative
to , is the London penetration depth of the
bulk material and is the film thickness. For this reason, the search for
the transition has been conducted in samples of the size . It is
argued below that film edges turn the interaction into near exponential
(short-range) thus making the BKT transition impossible. If however the
substrate is superconducting and separated from the film by an insulated layer,
the logarithmic intervortex interaction is recovered and the BKT transition
should be observable.Comment: 4 pages, no figure
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