34 research outputs found
Suppressed Andreev Reflection at the Normal-Metal / Heavy-Fermion Superconductor CeCoIn Interface
Dynamic conductance spectra are taken from Au/CeCoIn point contacts in
the Sharvin limit along the (001) and (110) directions. Our conductance
spectra, reproducibly obtained over wide ranges of temperature, constitute the
cleanest data sets ever reported for HFSs. A signature for the emerging
heavy-fermion liquid is evidenced by the development of the asymmetry in the
background in the normal state. Below , an enhancement of the sub-gap
conductance arising from Andreev reflection is observed, with the magnitude of
13.3 % and 11.8 % for the (001) and the (110) point contacts,
respectively, an order of magnitude smaller than those observed in conventional
superconductors but consistent with those in other HFSs. Our zero-bias
conductance data for the (001) point contacts are best fit with the extended
BTK model using the d-wave order parameter. The fit to the full conductance
curve of the (001) point contact indicates the strong coupling nature
(). However, our observed suppression of both the
Andreev reflection signal and the energy gap indicates the failure of existing
models. We provide possible directions for theoretical formulations of the
electronic transport across an N/HFS interface. Several qualitative features
observed in the (110) point contacts provide the first clear spectroscopic
evidence for the symmetry.Comment: 13 pages, 7 figures, LaTeX, paper invited and submitted to SPIE
Conference on Strongly Correlated Electron Materials: Physics and
Nanoengineering, in San Diego, California, July 31 - August 4, 200
Imaging the formation of high-energy dispersion anomalies in the actinide UCoGa
We use angle-resolved photoemission spectroscopy (ARPES) to image the
emergence of substaintial dispersion anomalies in the electronic
renormalization of the actinide compound UCoGa which was presumed to belong
to a conventional Fermi liquid family. Kinks or abrupt breaks in the slope of
the quasiparticle dispersion are detected both at low (130 meV) and high
(1 eV) binding energies below the Fermi energy, ruling out any
significant contribution of phonons. We perform numerical calculations to
demonstrate that the anomalies are adequately described by coupling between
itinerant fermions and spin fluctuations arising from the particle-hole
continuum of the spin-orbit split states of uranium. These anomalies are
resemble the `waterfall' phenomenon of the high-temperature copper-oxide
superconductors, suggesting that spin fluctuations are a generic route toward
multiform electronic phases in correlated materials as different as
high-temperature superconductors and actinides.Comment: 10 pages including supplementary material, Accepted for publication
in PR
Photoexcited electron dynamics in Kondo insulators and heavy fermions
We have studied the photoexcited carrier relaxation dynamics in the Kondo
insulator SmB6 and the heavy fermion metal YbAgCu4 as a function of temperature
and excitation level. The dynamic response is found to be both strongly
temperature dependent and nonlinear. The data are analyzed with a
Rothwarf-Taylor bottleneck model, where the dynamics are governed by the
presence of a narrow gap in the density of states near the Fermi level. The
remarkable agreement with the model suggests that carrier relaxation in a broad
class of heavy electron systems (both metals and insulators) is governed by the
presence of a (weakly temperature dependent) hybridization gap.Comment: accepted for publication in Physical Review Letter
Optical study of the electronic phase transition of strongly correlated YbInCu_4
Infrared, visible and near-UV reflectivity measurements are used to obtain
conductivity as a function of temperature and frequency in YbInCu_4, which
exhibits an isostructural phase-transition into a mixed-valent phase below
T_v=42 K. In addition to a gradual loss of spectral weight with decreasing
temperature extending up to 1.5 eV, a sharp resonance appears at 0.25 eV in the
mixed-valent phase. This feature can be described in terms of excitations into
the Kondo (Abrikosov-Suhl) resonance, and, like the sudden reduction of
resistivity, provides a direct reflection of the onset of coherence in this
strongly correlated electron system.Comment: 4 pages, 3 figures (to appear in Phys. Rev. B
The Kondo Dynamics of YbIn(1-x)AgxCu4
We present an infrared/optical study of the dynamics of the strongly
correlated electron system YbIn(1-x)AgxCu4 as a function of doping and
temperature for x ranging from 0 to 1, and T between 20 and 300 K. This study
reveals information about the unusual phase transition as well as the phases
themselves. Scaling relations emerge from the data and are investigated in
detail using a periodic Anderson model based calculation. We also provide a
picture in which to view both the low and high-energy x-dependent features of
the infrared data, including identification of high energy, temperature
dependent features.Comment: 12 pages, 11 figures, submitted Phys. Rev.
Andreev reflection spectroscopy of the heavy-fermion superconductor CeCoIn along three different crystallographic orientations
Andreev reflection spectroscopy has been performed on the heavy-fermion
superconductor (HFS) CeCoIn single crystals along three different
crystallographic orientations, (001), (110), and (100), using Au tips as
counter-electrodes. Dynamic conductance spectra are reproducible over wide
temperature ranges and consistent with each other, ensuring the spectroscopic
nature. Features common to all directions are: i) asymmetric behaviors of the
background conductance, which we attribute to the emerging coherent
heavy-fermion liquid; ii) energy scales (~1 meV) for conductance enhancement
due to Andreev reflection; iii) magnitudes of enhanced zero-bias conductance
(10 - 13 %). These values are an order of magnitude smaller than the predicted
value by the Blonder-Tinkham-Klapwijk (BTK) theory, but comparable to those for
other HFSs. Using the d-wave BTK model, we obtain an energy gap of ~ 460 ueV.
However, it is found that extended BTK models considering the mismatch in Fermi
surface parameters do not account for our data completely, which we attribute
to the shift of spectral weight to low energy as well as to the suppressed
Andreev reflection. A qualitative comparison of the conductance spectra with
calculated curves shows a consistency with d-symmetry, providing
the first spectroscopic evidence for the order parameter symmetry and resolving
the controversy over the location of the line nodes.Comment: invited talk submitted to the 8th M2S conference to be held in
Dresden Germany, July 9-14, 2006, 4 pages, 3 figure
Localized-to-itinerant transition preceding antiferromagnetic quantum critical point and gapless superconductivity in CeRh0.5Ir0.5In5
A fundamental problem posed from the study of correlated electron compounds, of which heavy-fermion systems are prototypes, is the need to understand the physics of states near a quantum critical point (QCP). At a QCP, magnetic order is suppressed continuously to zero temperature and unconventional superconductivity often appears. Here, we report pressure T-c. (P)-dependent In-115 nuclear quadrupole resonance (NQR) measurements on heavy-fermion antiferromagnet CeRh0.5Ir0.5In5. These experiments reveal an antiferromagnetic (AF) QCP at P-c(AF) = 1.2 GPa where a dome of superconductivity reaches a maximum transition temperature Tc. Preceding P-c(AF), however, the NQR frequency nu(Q) undergoes an abrupt increase at P-c* = 0.8 GPa in the zero-temperature limit, indicating a change from localized to itinerant character of cerium's f-electron and associated small-to-large change in the Fermi surface. At P-c(AF) where T-c is optimized, there is an unusually large fraction of gapless excitations well below T-c that implicates spin-singlet, odd-frequency pairing symmetry
ΠΠ½ΡΠΎΡΠΌΠ°ΡΠΈΠΎΠ½Π½Π°Ρ ΡΠΈΡΡΠ΅ΠΌΠ° ΠΎΡΠ΅Π½ΠΊΠΈ ΡΠΈΡΠΊΠ° Π±Π°Π½ΠΊΡΠΎΡΡΡΠ²Π° ΠΏΡΠ΅Π΄ΠΏΡΠΈΡΡΠΈΡ Ρ ΠΏΠΎΠΌΠΎΡΡΡ Π½Π΅ΠΉΡΠΎΡΠ΅ΡΠ΅Π²ΠΎΠΉ ΠΌΠΎΠ΄Π΅Π»ΠΈ
ΠΠ±ΡΠ΅ΠΊΡΠΎΠΌ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ ΡΠ²Π»ΡΠ΅ΡΡΡ ΠΏΡΠΎΡΠ΅ΡΡ ΠΎΡΠ΅Π½ΠΊΠΈ ΡΠΈΡΠΊΠ° Π±Π°Π½ΠΊΡΠΎΡΡΡΠ²Π° ΠΏΡΠ΅Π΄ΠΏΡΠΈΡΡΠΈΡ. Π¦Π΅Π»ΡΡ ΡΠ°Π±ΠΎΡΡ ΡΠ²Π»ΡΠ΅ΡΡΡ ΠΏΡΠΎΠ΅ΠΊΡΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ ΠΈ ΡΠ°Π·ΡΠ°Π±ΠΎΡΠΊΠ° ΠΈΠ½ΡΠΎΡΠΌΠ°ΡΠΈΠΎΠ½Π½ΠΎΠΉ ΡΠΈΡΡΠ΅ΠΌΡ Π΄Π»Ρ ΠΎΡΠ΅Π½ΠΊΠΈ ΡΠΈΡΠΊΠ° Π±Π°Π½ΠΊΡΠΎΡΡΡΠ²Π° ΠΏΡΠ΅Π΄ΠΏΡΠΈΡΡΠΈΡ Π½Π° ΠΎΡΠ½ΠΎΠ²Π΅ Π½Π΅ΠΉΡΠΎΡΠ΅ΡΠ΅Π²ΠΎΠΉ ΠΌΠΎΠ΄Π΅Π»ΠΈ. Π ΠΏΡΠΎΡΠ΅ΡΡΠ΅ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ ΠΏΡΠΎΠ²ΠΎΠ΄ΠΈΠ»ΡΡ ΡΠ΅ΠΎΡΠ΅ΡΠΈΡΠ΅ΡΠΊΠΈΠΉ Π°Π½Π°Π»ΠΈΠ·, ΠΎΠ±Π·ΠΎΡ Π°Π½Π°Π»ΠΎΠ³ΠΎΠ², ΠΏΡΠΎΠ΅ΠΊΡΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ ΠΈ ΡΠ°Π·ΡΠ°Π±ΠΎΡΠΊΠ° ΠΈΠ½ΡΠΎΡΠΌΠ°ΡΠΈΠΎΠ½Π½ΠΎΠΉ ΡΠΈΡΡΠ΅ΠΌΡ. Π ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΠ΅ ΡΠ°Π±ΠΎΡΡ ΡΠΏΡΠΎΠ΅ΠΊΡΠΈΡΠΎΠ²Π°Π½Π° ΠΈΠ½ΡΠΎΡΠΌΠ°ΡΠΈΠΎΠ½Π½Π°Ρ ΡΠΈΡΡΠ΅ΠΌΠ° Π΄Π»Ρ ΠΎΡΠ΅Π½ΠΊΠΈ ΡΠΈΡΠΊΠ° Π±Π°Π½ΠΊΡΠΎΡΡΡΠ²Π° ΠΏΡΠ΅Π΄ΠΏΡΠΈΡΡΠΈΡ, ΡΠ΅Π°Π»ΠΈΠ·ΡΡΡΠ°Ρ ΡΠ»Π΅Π΄ΡΡΡΠΈΠ΅ ΡΡΠ½ΠΊΡΠΈΠΈ: ΡΠ°ΡΡΠ΅Ρ Π·Π½Π°ΡΠ΅Π½ΠΈΠΉ ΠΎΡΠ½ΠΎΠ²Π½ΡΡ
ΡΠΈΠ½Π°Π½ΡΠΎΠ²ΡΡ
ΠΏΠΎΠΊΠ°Π·Π°ΡΠ΅Π»Π΅ΠΉ ΠΈ ΠΏΠΎΡΡΡΠΎΠ΅Π½ΠΈΠ΅ Π½Π΅ΠΉΡΠΎΡΠ΅ΡΠ΅Π²ΠΎΠΉ ΠΌΠΎΠ΄Π΅Π»ΠΈ; ΠΎΡΠ΅Π½ΠΊΠ° ΡΠΈΡΠΊΠ° Π±Π°Π½ΠΊΡΠΎΡΡΡΠ²Π° Π½Π° ΠΎΡΠ½ΠΎΠ²Π΅ ΠΌΠΎΠ΄Π΅Π»ΠΈ; Π°Π½Π°Π»ΠΈΠ· ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΠΎΠ² ΠΎΡΠ΅Π½ΠΊΠΈ. ΠΠ° Π΄Π°Π½Π½ΡΠΉ ΠΌΠΎΠΌΠ΅Π½Ρ ΡΠΈΡΡΠ΅ΠΌΠ° ΠΏΡΠΎΡ
ΠΎΠ΄ΠΈΡ ΡΠ΅ΡΡΠΎΠ²ΡΠ΅ ΠΈΡΠΏΡΡΠ°Π½ΠΈΡ Π½Π° ΠΏΡΠ΅Π΄ΠΏΡΠΈΡΡΠΈΠΈ ΠΠ "Π‘ΠΈΠ±ΠΊΠ°Π±Π΅Π»Ρ", Π³. Π’ΠΎΠΌΡΠΊ.The object of study is the process of assessing the risk of bankruptcy. The aim of this work is the design and development of information system for assessing the risk of bankruptcy of the enterprise based on neural network model. In the process of research was conducted the theoretical analysis, a review of analogues, the design and development of information systems. As a result of work designed information system for assessing the risk of bankruptcy of the enterprise that implements the following functions: calculation of values of main financial indicators and the construction of neural network model; evaluate the risk of bankruptcy based on the model; analysis of the evaluation results. At the moment the system is being tested at the enterprise of JSC "Sibkabel", Tomsk
ΠΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΠ΅ ΡΠ΅Ρ Π½ΠΈΡΠ΅ΡΠΊΠΈΡ Ρ Π°ΡΠ°ΠΊΡΠ΅ΡΠΈΡΡΠΈΠΊ ΡΠ°Π·ΠΌΠ΅ΡΠΈΠ²Π°Π½ΠΈΡ ΠΈ ΠΏΡΠΎΠ΅ΠΊΡΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ ΠΎΠ±ΠΎΡΡΠ΄ΠΎΠ²Π°Π½ΠΈΡ Π΄Π»Ρ Π²ΡΠ·ΠΊΠΈΡ ΡΡΠ΅Π΄
Π‘ΡΡΠ΅ΡΡΠ²Π΅Π½Π½ΡΠΌ Π½Π΅Π΄ΠΎΡΡΠ°ΡΠΊΠΎΠΌ ΠΏΠΎΠ΄Ρ
ΠΎΠ΄ΠΎΠ² Ρ ΠΌΠ½ΠΎΠ³ΠΈΡ
ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°ΡΠ΅Π»Π΅ΠΉ ΡΠ²Π»ΡΠ΅ΡΡΡ Π±ΠΎΠ»ΡΡΠΎΠ΅ ΠΊΠΎΠ»ΠΈΡΠ΅ΡΡΠ²ΠΎ ΡΠΏΡΠΎΡΠ΅Π½ΠΈΠΉ ΡΠ°ΡΡΠ΅ΡΠ½ΡΡ
ΠΌΠΎΠ΄Π΅Π»Π΅ΠΉ ΠΈ Π½Π΅Π²ΠΎΠ·ΠΌΠΎΠΆΠ½ΠΎΡΡΡ ΡΠΎΡΠ½ΠΎΠΉ ΠΊΠΎΠ»ΠΈΡΠ΅ΡΡΠ²Π΅Π½Π½ΠΎΠΉ ΠΎΡΠ΅Π½ΠΊΠΈ ΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΠΎΠ² ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΠΏΡΠΎΡΠ΅ΡΡΠ° ΠΏΠ΅ΡΠ΅ΠΌΠ΅ΡΠΈΠ²Π°Π½ΠΈΡ. Π Π΄Π°Π½Π½ΠΎΠΉ ΡΠ°Π±ΠΎΡΠ΅, ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΡ ΠΏΠ΅ΡΠ΅ΠΌΠ΅ΡΠΈΠ²Π°Π½ΠΈΡ ΡΡΠ΅Ρ
Π²ΠΈΠ΄ΠΎΠ² ΠΈΠΌΠΏΠ΅Π»Π»Π΅ΡΠΎΠ² Π±ΡΠ»Π° ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½Π°. ΠΡΠ΅ ΡΠ°ΡΡΠ΅ΡΡ ΠΈ Π°Π½Π°Π»ΠΈΠ·Ρ Π±ΡΠ»ΠΈ ΠΏΡΠΎΠ²Π΅Π΄Π΅Π½Ρ Ρ ΠΏΠΎΠΌΠΎΡΡΡ Π½Π΅ ΡΠΎΠ»ΡΠΊΠΎ ΡΠΈΠ·ΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΌΠΎΠ΄Π΅Π»Π΅ΠΉ Π½ΠΎ ΠΈ Ansys v17.2, ΡΡΠΎ ΠΎΠ±Π΅ΡΠΏΠ΅ΡΠΈΠ» ΠΊΠ°ΡΠ΅ΡΡΠ²ΠΎ ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΠ° Π΄Π°Π½Π½ΠΎΠ³ΠΎ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ.In this study computational fluid dynamics (CFD) approach was used to study mixing in an Industrial tank. We use Ansys v17.2 to do the evaluation of fluid mixing efficiency. In this study we use three different mixer models to do the comparison. The objective was to analyze the extent of mixing in the tank by producing visual images of the various mixing zones in the tank domain