192 research outputs found
Dielectricly Enhanced T c in Underdoped Cuprates
It is proposed to create a multilayer structure in which an underdoped copper-oxide high-temperature superconductor is sandwiched between high-dielectric-constant insulator layers such as ferro- or ferri-electrics, thereby reducing the Coulomb repulsion between the intrinsically present clusters or stripes in the CuO2 layers of the pseudogap phase. This should lead to an increase in the size of such clusters, resulting in smaller distances between them and coherence at higher temperature, i.e., a higher T c with a smaller pseudogap (T ∗−T c
^25Mg NMR study of the MgB_2 superconductor
^25Mg NMR spectra and nuclear spin-lattice relaxation time, T_1, have been
measured in polycrystalline ^25MgB_2 with a superconducting transition
temperature T_c = 39.0 K in zero magnetic field. From the first order and
second order quadrupole perturbed NMR spectrum a quadrupole coupling frequency
nu_Q = 222(1.5) kHz is obtained. T_1T = 1090(50) sK and Knight shift K_c =
242(4) ppm are temperature independent in the normal conducting phase. The
^25Mg Korringa ratio equals to 0.95 which is very close to the ideal value of
unity for s-electrons. The comparison of the experimental nu_Q, T_1T, and K_c
with the corresponding values obtained by LDA calculations shows an excellent
agreement for all three quantities.Comment: 4 pages including 4 eps-figures, revtex
Correlation between the transition temperature and the superfluid density in BCS superconductor NbB_2+x
The results of the muon-spin rotation experiments on BCS superconductors
NbB_2+x (x = 0.2, 0.34) are reported. Both samples, studied in the present
work, exhibit rather broad transitions to the superconducting state, suggesting
a distribution of the volume fractions with different transition temperatures
(T_c)'s. By taking these distributions into account, the dependence of the
inverse squared zero-temperature magnetic penetration depth (\lambda_0^{-2}) on
T_c was reconstructed for temperatures in the range 1.5K<T_c<8.0K.
\lambda_0^{-2} was found to obey the power law dependence \lambda_0^{-2}\propto
T_c^{3.1(1)} which appears to be common for some families of BCS
superconductors as, {\it e.g.}, Al doped MgB_2 and high-temperature cuprate
superconductors as underdoped YBa_2Cu_3O_{7-\delta}.Comment: 9 pages, 7 figures. Accepted for publication in Phys. Rev.
Negative Oxygen Isotope Effect on the Static Spin Stripe Order in La_(2-x)Ba_xCuO_4 (x = 1/8)
Large negative oxygen-isotope (16O/18O) effects (OIE's) on the static
spin-stripe ordering temperature T_so and the magnetic volume fraction V_m were
observed in La_(2-x)Ba_xCuO_4 (x = 1/8) by means of muon spin rotation
experiments. The corresponding OIE exponents were found to be alpha_(T_so) =
-0.57(6) and alpha_(V_m) = -0.71(9), which are sign reversed to alpha_(T_c) =
0.46(6) measured for the superconducting transition temperature T_c. This
indicates that the electron-lattice interaction is involved in the stripe
formation and plays an important role in the competition between bulk
superconductivity and static stripe order in the cuprates.Comment: 5 pages, 4 figure
Tuning the structural instability of SrTiO_3 by Eu doping: The phase diagram of Sr_1-xEu_xTiO_3
The phase diagram of Sr_1-xEu_xTiO_3 is determined experimentally by electron
paramagnetic resonance and resistivity measurements and analyzed theoretically
within the self-consistent phonon approximation as a function of x
([0.03-1.0]). The transition temperature of the structural instability of the
system increases nonlinearly to higher temperatures with increasing x. This is
interpreted theoretically by a substantial alteration in the dynamics caused by
a change in the double-well potential from broad and shallow to narrow and
deep.Comment: 15 pages, 5 figure
Evidence for complex order parameter in La_{1.83}Sr_{0.17}CuO_4
The in-plane magnetic field penetration depth (\lambda_{ab}) in
single-crystal La_{1.83}Sr_{0.17}CuO_4 was investigated by means of the
muon-spin rotation (\muSR) technique. The temperature dependence of
\lambda^{-2}_{ab} has an inflection point around 10-15K, suggesting the
presence of two superconducting gaps: a large gap (\Delta_1^d) with d-wave and
a small gap (\Delta_2^s) with s-wave symmetry. The zero-temperature values of
the gaps at \mu_0H=0.02T were found to be \Delta_1^d(0)=8.2(2)meV and
\Delta_2^s(0)=1.57(8)meV.Comment: 5 pages, 3 figure
Dielectricly Enhanced Tc in Underdoped Cuprates
It is proposed to create a multilayer structure in which an underdoped copper-oxide high-temperature superconductor is sandwiched between high-dielectric-constant insulator layers such as ferro- or ferri-electrics, thereby reducing the Coulomb repulsion between the intrinsically present clusters or stripes in the CuO2 layers of the pseudogap phase. This should lead to an increase in the size of such clusters, resulting in smaller distances between them and coherence at higher temperature, i.e., a higher T c with a smaller pseudogap (T ∗−T c
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