54 research outputs found
Electronic nematic susceptibility of iron-based superconductors
We review our recent experimental results on the electronic nematic phase in
electron- and hole-doped BaFeAs and FeSe. The nematic susceptibility is
extracted from shear-modulus data (obtained using a three-point-bending method
in a capacitance dilatometer) using Landau theory and is compared to the
nematic susceptibility obtained from elastoresistivity and Raman data. FeSe is
particularly interesting in this context, because of a large nematic, i.e., a
structurally distorted but paramagnetic, region in its phase diagram. Scaling
of the nematic susceptibility with the spin lattice relaxation rate from NMR,
as predicted by the spin-nematic theory, is found in both electron- and
hole-doped BaFeAs, but not in FeSe. The intricate relationship of the
nematic susceptibility to spin and orbital degrees of freedom is discussed.Comment: Invited review article for a special issue on Fe-based
superconductors in Comptes Rendus Physiqu
Evolution of the specific-heat anomaly of the high-temperature superconductor YBa2Cu3O7 under influence of doping through application of pressure up to 10 GPa
The evolution of the specific-heat anomaly in the overdoped range of a single
crystal of the high-temperature superconductor YBa2Cu3O7 has been studied under
influence of pressure up to 10 GPa, using AC calorimetry in a Bridgman-type
pressure cell. We show that the specific-heat jump as well as the bulk Tc are
reduced with increasing pressure in accordance with a simple charge-transfer
model. This new method enables us through pressure-induced charge transfer to
study the doping dependence of the superconducting transition, as well as the
evolution of the superconducting condensation energy on a single stoichometric
sample without adding atomic disorder.Comment: final version: J. Phys.: Condens. Matter 17 (2005) 4135-414
‘Fragile Superconductivity': A Kinetic Glass Transition in the Vortex Matter of the High-temperature Superconductor YBa2 Cu3O7-δ
Using high-resolution thermal expansion and magnetization measurements, we provide experimental evidence for a kinetic glass transition in the vortex matter of YBa2Cu3O7-δ with some disorder. This transition, which represents the true superconducting transition in a magnetic field, exhibits many of the features of the usual glass transition found in supercooled structural liquids such as window glass. We demonstrate, using both kinetic and thermodynamic criteria, that this vortex matter is the most fragile system known to date, which we argue makes it possible to investigate the behavior very close to the Kauzmann temperature. Vortex matter, we suggest, may be a model system to study glassy behavior in general, which is expected to lead to a better understanding of the strong-fragile behavior in structural glasse
Large anisotropic uniaxial pressure dependencies of Tc in single crystalline Ba(Fe0.92Co0.08)2As2
Using high-resolution dilatometry, we study the thermodynamic response of the
lattice parameters to superconducting order in a self-flux grown
Ba(Fe0.92Co0.08)2As2 single crystal. The uniaxial pressure dependencies of the
critical temperature of Tc, calculated using our thermal expansion and specific
heat data via the Ehrenfest relation, are found to be quite large and very
anisotropic (dTc/dpa = 3.1(1) K/GPa and dTc/dpc = - 7.0(2) K/GPa). Our results
show that there is a strong coupling of the c/a ratio to superconducting order,
which demonstrates that Tc is far from the optimal value. A surprising
similarity with the uniaxial pressure effects in several other layered
superconductors is discussed.Comment: 11 pages, 4 Figure
3D-XY critical fluctuations of the thermal expansivity in detwinned YBa2Cu3O7-d single crystals near optimal doping
The strong coupling of superconductivity to the orthorhombic distortion in
YBa2Cu3O7-d makes possible an analysis of the superconducting fluctuations
without the necessity of subtracting any background. The present
high-resolution capacitance dilatometry data unambiguously demonstrate the
existence of critical, instead of Gaussian, fluctuations over a wide
temperature region (+/- 10 K) around Tc. The values of the amplitude ratio
A+/A-=0.9-1.1 and the leading scaling exponent |alpha|<0.018, determined via a
least-squares fit of the data, are consistent with the 3D-XY universality
class. Small deviations from pure 3D-XY behavior are discussed.Comment: 11 pages including three figure
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