359 research outputs found
Muon-spin rotation measurements of the penetration depth of the Mo_3Sb_7 superconductor
Measurements of the magnetic field penetration depth \lambda in
superconductor Mo_3Sb_7 (T_c~2.1 K) were carried out by means of
muon-spin-rotation. The absolute values of \lambda, the Ginzburg-Landau
parameter \kappa, the first H_{c1} and the second H_{c2} critical fields at T=0
are \lambda(0)=720(100)nm, \kappa(0)=55(9), \mu_0H_{c1}(0)=1.8(3)mT, and
\mu_0H_{c2}(0)=1.9(2)T. The zero temperature value of the superconducting
energy gap \Delta(0) was found to be 0.35(1)meV corresponding to the ratio
2\Delta(0)/k_BT_c=3.83(10). At low temperatures \lambda^{-2}(T) saturates and
becomes constant below T~0.3T_c, in agreement with what is expected for s-wave
BCS superconductors. Our results suggest that Mo_3Sb_7 is a BCS superconductor
with the isotropic energy gapComment: 5 pages, 4 figure
Pressure effect on the in-plane magnetic penetration depth in YBa_2Cu_4O_8
We report a study of the pressure effect (PE) on the in-plane magnetic field
penetration depth lambda_{ab} in YBa_2Cu_4O_8 by means of Meissner fraction
measurements. A pronounced PE on lambda_{ab}^{-2}(0) was observed with a
maximum relative shift of \Delta\lambda^{-2}_{ab}/\lambda^{-2}_{ab}= 44(3)% at
a pressure of 10.2 kbar. It arises from the pressure dependence of the
effective in-plane charge carrier mass and pressure induced charge carrier
transfer from the CuO chains to the superconducting CuO_2 planes. The present
results imply that the charge carriers in YBa_2Cu_4O_8 are coupled to the
lattice.Comment: 4pages 3 figure
Comment on ``Muon-spin rotation studies of the superconducting properties of Mo_3Sb_7'', Phys.Rev.B 78, 172505 (2008)
In a recent article Tran et al. [Phys. Rev.B 78, 172505 (2008)] report on the
result of the muon-spin rotation (\muSR) measurements of Mo_3Sb_7
superconductor. Based on the analysis of the temperature and the magnetic field
dependence of the Gaussian relaxation rate \sigma_{sc} they suggest that
Mo_3Sb_7 is the superconductor with two isotropic s-wave like gaps. An
additional confirmation was obtained from the specific heat data published
earlier by partly the same group of authors in [Acta Mater. 56, 5694 (2008)].
The purpose of this Comment is to point out that from the analysis made by Tran
et al. the presence of two superconducting energy gaps in Mo_3Sb_7 can not be
justified. The analysis of \muSR data does not account for the reduction of
\sigma_{sc} with increasing temperature, and, hence, yields inaccurate
information on the magnetic penetration depth. The specific heat data can be
satisfactory described within the framework of the one-gap model with the small
residual specific heat component. The experimental data of Tran et al., as well
as our earlier published \muSR data [Phys. Rev. B 78, 014502 (2008)] all seem
to be consistent with is the presence of single isotropic superconducting
energy gap in Mo_3Sb_7.Comment: Comment on Phys.Rev.B 78, 172505 (2008
Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs
The recent discovery of pressure induced superconductivity in the binary
helimagnet CrAs has attracted much attention. How superconductivity emerges
from the magnetic state and what is the mechanism of the superconducting
pairing are two important issues which need to be resolved. In the present
work, the suppression of magnetism and the occurrence of superconductivity in
CrAs as a function of pressure () were studied by means of muon spin
rotation. The magnetism remains bulk up to ~kbar while its volume
fraction gradually decreases with increasing pressure until it vanishes at
7~kbar. At 3.5 kbar superconductivity abruptly appears with its
maximum ~K which decreases upon increasing the pressure. In the
intermediate pressure region (~kbar) the
superconducting and the magnetic volume fractions are spatially phase separated
and compete for phase volume. Our results indicate that the less conductive
magnetic phase provides additional carriers (doping) to the superconducting
parts of the CrAs sample thus leading to an increase of the transition
temperature () and of the superfluid density (). A scaling of
with as well as the phase separation between magnetism and
superconductivity point to a conventional mechanism of the Cooper-pairing in
CrAs.Comment: 9 pages, 8 figure
Magnetic field dependence of the oxygen isotope effect on the magnetic penetration depth in hole-doped cuprate superconductors
The magnetic field dependence of the oxygen-isotope (^{16}O/^{18}O) effect
(OIE) on the in-plane magnetic field penetration depth \lambda_{ab} was studied
in the hole-doped high-temperature cuprate superconductors YBa_2Cu_4O_8,
Y_0.8Pr_0.2Ba_2Cu_3O_7-\delta, and Y_0.7Pr_0.3Ba_2Cu_3O_7-\delta. It was found
that \lambda_ab for the ^{16}O substituted samples increases stronger with
increasing magnetic field than for the ^{18}O ones. The OIE on \lambda_ab
decreases by more than a factor of two with increasing magnetic field from
\mu_0H=0.2 T to \mu_0H=0.6 T. This effect can be explained by the isotope
dependence of the in-plane charge carrier mass m^\ast_{ab}.Comment: 4 pages, two figure
Oxygen-isotope effect on the in-plane penetration depth in underdoped Y_{1-x}Pr_xBa_2Cu_3O_{7-delta} as revealed by muon-spin rotation
The oxygen-isotope (^16O/^18O) effect (OIE) on the in-plane penetration depth
in underdoped Y_{1-x}Pr_xBa_2Cu_3O_{7-delta} was studied by
muon-spin rotation. A pronounced OIE on was observed
with a relative isotope shift of
=-5(2)% for x =0.3 and -9(2)% for
x=0.4. It arises mainly from the oxygen-mass dependence of the in-plane
effective mass . The OIE exponents of T_{c} and of
exhibit a relation that appears to be generic for
cuprate superconductors.Comment: 4 pages, 4 eps figures, RevTex
Correlation between oxygen isotope effects on the transition temperature and the magnetic penetration depth in high-temperature superconductors close to optimal doping
The oxygen-isotope (^{16}O/^{18}O) effect (OIE) on the in-plane magnetic
penetration depth \lambda_{ab}(0) in optimally-doped YBa_2Cu_3O_{7-\delta} and
La_{1.85}Sr_{0.15}CuO_4, and in slightly underdoped YBa_2Cu_4O_8 and
Y_{0.8}Pr_{0.2}Ba_2Cu_3O_{7-\delta} was studied by means of muon-spin rotation.
A substantial OIE on \lambda_{ab}(0) with an OIE exponent
\beta_O=-d\ln\lambda_{ab}(0)/d\ln M_O\approx - 0.2 (M_O is the mass of the
oxygen isotope), and a small OIE on the transition temperature T_c with an OIE
exponent \alpha_O=-d\ln T_{c}/d \ln M_O\simeq0.02 to 0.1 were observed. The
observation of a substantial isotope effect on \lambda_{ab}(0), even in
cuprates where the OIE on T_c is small, indicates that lattice effects play an
important role in cuprate HTS.Comment: 6 pages, 4 figure
Muon-Spin-Rotation Measurements of the Penetration Depth in the Infinite-Layer Electron-Doped Cuprate Superconductor Sr0.9La0.1CuO2
Muon spin rotation (mSR) measurements of the in-plane penetration depth
lambda_ab have been performed in the electron-doped infinite layer high-Tc
superconductor (HTS) Sr0.9La0.1CuO2. Absence of the magnetic rare-earth ions in
this compound allowed to measure for the first time the absolute value of
lambda_ab(0) in electron-doped HTS using mSR. We found lambda_ab(0)=116(2) nm.
The zero-temperature depolarization rate sigma(0)?1/lambda_ab(0)^2=4.6(1) MHz
is more than four times higher than expected from the Uemura line. Therefore
this electron-doped HTS does not follow the Uemura relation found for
hole-doped HTS.Comment: to be published in Physical Review Letter
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