87 research outputs found
Condon Domain Phase Diagram for Silver
We present the Condon domain phase diagram for a silver single crystal
measured in magnetic fields up to 28 T and temperatures down to 1.3 K. A
standard ac method with a pickup coil system is used at low frequency for the
measurements of the de Haas-van Alphen effect (dHvA). The transition point from
the state of homogeneous magnetization to the inhomogeneous Condon domain state
(CDS) is found as the point where a small irreversibility in the dHvA
magnetization arises, as manifested by an extremely nonlinear response in the
pickup voltage showing threshold character. The third harmonic content in the
ac response is used to determine with high precision the CDS phase boundary.
The experimentally determined Condon domain phase diagram is in good agreement
with the theoretical prediction calculated by the standard Lifshitz-Kosevich
(LK) formula
Is ZrB12 two gap superconductor?
We report the measurements of the temperature dependence of the resistivity,
\rho(T), magnetic penetration depth,\lambda(T) the lower, Hc1(T), and upper,
Hc2(T), critical magnetic fields, for single crystals of dodecaboride ZrB12,
diboride ZrB2 and thin films of diboride MgB2. We observe a number of
deviations from conventional behavior in these materials. Although ZrB12
behaves like a simple metal in the normal state, the resistive Debye
temperature, 300 K, is three times smaller relative to that (800-1200 K)
calculated from the specific heat, C(T), data. We observe predominantly
quadratic temperature behavior of resistivity in ZrB12 below 25 K, and in ZrB2
below 100 K, indicating the possible importance of the electron-electron
interaction in these borides. Superfluid density of ZrB12 displays
unconventional temperature dependence with pronounced shoulder at T/Tc equal to
0.65. Contrary to conventional theories we found a linear temperature
dependence of Hc2(T) for ZrB12 from Tc down to 0.35 K. We suggest that both
\lambda(T) and Hc2(T) dependencies in ZrB12 can be explained by two band BCS
model with different superconducting gap and Tc.Comment: PDF file, 12 pages, 10 figures, submitted to Physical Review
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
Direct Observation of Condon Domains in Silver by Hall Probes
Using a set of micro Hall probes for the detection of the local induction,
the inhomogeneous Condon domain structure has been directly observed at the
surface of a pure silver single crystal under strong Landau quantization in
magnetic fields up to 10 T. The inhomogeneous induction occurs in the
theoretically predicted part of the H-T Condon domain phase diagram.
Information about size, shape and orientation of the domains is obtained by
analyzing Hall probes placed along and across the long sample axis and by
tilting the sample. On a beryllium surface the induction inhomogeneity is
almost absent although the expected induction splitting here is at least ten
times higher than in silver.Comment: 4 pages, 6 figures, submitted to PR
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
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
Raman study of the Verwey transition in Magnetite at high-pressure and low-temperature; effect of Al doping
We report high-pressure low-temperature Raman studies of the Verwey
transition in pure and Al-doped magnetite (Fe_3O_4). The low temperature phase
of magnetite displays a number of additional Raman modes that serve as
transition markers. These transition markers allow one to investigate the
effect of hydrostatic pressure on the Verwey transition temperature. Al-doped
magnetite Fe_2.8Al_0.2O_4 (TV=116.5K) displays a nearly linear decrease of the
transition temperature with an increase of pressure yielding dP/dT_V = -0.096
GPa/K. In contrast pure magnetite displays a significantly steeper slope of the
PT equilibrium line with dP/dT_V = -0.18 GPa/K. The slope of the PT equilibrium
lines is related to the changes of the molar entropy and molar volume at the
transition. We compare our spectroscopic data with that obtained from the
ambient pressure specific heat measurements and find a good agreement in the
optimally doped magnetite. Our data indicates that Al doping leads to a smaller
entropy change and larger volume expansion at the transition. Our data displays
the trends that are consistent with the mean field model of the transition that
assumes charge ordering in magnetite.Comment: 17 pages, 3 figure
N-acetyltransferase 2 (NAT2) Gene Polymorphisms and the Effectiveness of Infertility Treatment in Patients with Peritoneal Endometriosis
Today, infertility has become a global issue. WHO ranks it the fifth among the major diseases of those below 60 years, after alcoholism, depression, injuries and eyesight disorders. Numerous studies conducted on the problems of infertility in endometriosis still do not offer clear answers regarding the pathogenesis and mechanisms of this disease and its influences on fertility.
According to the survey results, point mutations of the NAT2 gene (NAT2*5 and NAT2*6) have been identified in 75.6% of the patients with infertility problems and the peritoneal form of endometriosis, that create “slow” allelic variants, which exceed the average index in the population.
The peculiarities of the NAT2 gene polymorphisms have been proven to be associated with the effectiveness of the infertility treatment of female patients with peritoneal endometriosis. In the group of non-pregnant patients, the presence of с.341Т>C, c.481C>T, c.590G>A and c.803A>G heterozygous point mutations are 73.2, 73.2, 5.4, and 62.5%, respectively. The significant difference in the comparison of the allelic polymorphism during the various stages of the endometriosis was not identified. At stage III-IV endometriosis the frequency of three and more point substitutions was significantly higher.
NAT2 gene polymorphisms can find use as an additional criterion for predicting the effectiveness of the infertility treatment of patients with peritoneal endometriosis
Normal-state electrical resistivity and superconducting magnetic penetration depth in Eu0.5K0.5Fe2As2
We report measurements of the temperature dependence of the electrical
resistivity, \rho(T), and magnetic penetration depth, \lambda(T), for
polycrystalline samples of Eu_0.5K_0.5Fe_2As_2 with Tc=31 K. follows
a linear temperature dependence above T_c and bends over to a weaker
temperature dependence around 150 K. The magnetic penetration depth, determined
by radio frequency technique displays an unusual minimum around 4 K which is
associated with short-range ordering of localized Eu3+ moments.Comment: 7 pages 4 figure
Conductance of a STM contact on the surface of a thin film
The conductance of a contact, having a radius smaller than the Fermi wave
length, on the surface of a thin metal film is investigated theoretically. It
is shown that quantization of the electron energy spectrum in the film leads to
a step-like dependence of differential conductance G(V) as a function of
applied bias eV. The distance between neighboring steps in eV equals the energy
level spacing due to size quantization. We demonstrate that a study of G(V) for
both signs of the voltage maps the spectrum of energy levels above and below
Fermi surface in scanning tunneling experiments.Comment: 15 pages, 5 figure
- …