12 research outputs found
Disorder, critical currents, and vortex pinning energies in isovalently substituted BaFe(AsP)
We present a comprehensive overview of vortex pinning in single crystals of
the isovalently substituted iron-based superconductor
BaFe(AsP), a material that qualifies as an
archetypical clean superconductor, containing only sparse strong point-like
pins [in the sense of C.J. van der Beek {\em et al.}, Phys. Rev. B {\bf 66},
024523 (2002)]. Widely varying critical current values for nominally similar
compositions show that flux pinning is of extrinsic origin. Vortex
configurations, imaged using the Bitter decoration method, show less density
fluctuations than those previously observed in charge-doped
Ba(FeCo)As single crystals. Analysis reveals that the
pinning force and -energy distributions depend on the P-content . However,
they are always much narrower than in Ba(FeCo)As, a
result that is attributed to the weaker temperature dependence of the
superfluid density on approaching in
BaFe(AsP). Critical current density measurements and
pinning force distributions independently yield a mean distance between
effective pinning centers nm, increasing with
increasing P-content . This evolution can be understood as being the
consequence of the P-dependence of the London penetration depth. Further
salient features are a wide vortex free "Meissner belt", observed at the edge
of overdoped crystals, and characteristic chain-like vortex arrangements,
observed at all levels of P-substitution.Comment: 11 page
c-axis coupling in underdoped Bi(2)Sr(2)CaCu(2)O(8+δ) with varying degrees of disorder
c-axis coupling in underdoped Bi(2)Sr(2)CaCu(2)O(8+δ) with varying degrees of disorde
Nature of c-axis coupling in underdoped Bi2Sr2CaCu2O8 with varying degrees of disorder
The dependence of the Josephson Plasma Resonance (JPR) frequency in heavily
underdoped Bi2Sr2CaCu2O8+\delta on temperature and controlled pointlike
disorder, introduced by high-energy electron irradiation, is cross-correlated
and compared to the behavior of the ab-plane penetration depth. It is found
that the zero temperature plasma frequency, representative of the superfluid
component of the c-axis spectral weight, decreases proportionally with T_c when
the disorder is increased. The temperature dependence of the JPR frequency is
the same for all disorder levels, including pristine crystals. The reduction of
the c-axis superfluid density as function of disorder is accounted for by
pair-breaking induced by impurity scattering in the CuO2 planes, rather than by
quantum fluctuations of the superconducting phase. The reduction of the c-axis
superfluid density as function of temperature follows a T^{2}--law and is
accounted for by quasi-particle hopping through impurity induced interlayer
states.Comment: 10 pages, 9 Figure
Disorder and -axis quasiparticle dynamics in underdoped Bi2Sr2CaCu2O8
Contribution à LT25International audienceWe present measurements of the Josephson plasma frequency and the in-plane penetration depth of underdoped single crystalline Bi2Sr2CaCu2O8 with varying degrees of disorder introduced by irradiation with 2.3 MeV electrons. Increasing disorder drives T_c down, in agreement with in all model descriptions of high T_c superconductivity. However, the manner in which the JPR frequency, the square of which represents the zero-frequency spectral weight of the c-axis conductivity in the superconducting state, is driven down by disorder depends more strongly on the model description. We show that only the model of impurity assisted quasiparticle hopping in a d-wave superconductor, together with strongly scattering point defects in the superconducting layers, can explain the disorder dependence of the c-axis plasma frequency, the in-plane penetration depth, and T_c consistently. From the data, we extract the energy scale governing nodal quasiparticle excitations, Delta_0 ~ 2.5 k_BT_c
Emergent Rank-5 'Nematic' Order in URu2Si2
Novel electronic states resulting from entangled spin and orbital degrees of
freedom are hallmarks of strongly correlated f-electron systems. A spectacular
example is the so-called 'hidden-order' phase transition in the heavy-electron
metal URu2Si2, which is characterized by the huge amount of entropy lost at
T_{HO}=17.5K. However, no evidence of magnetic/structural phase transition has
been found below T_{HO} so far. The origin of the hidden-order phase transition
has been a long-standing mystery in condensed matter physics. Here, based on a
first-principles theoretical approach, we examine the complete set of multipole
correlations allowed in this material. The results uncover that the
hidden-order parameter is a rank-5 multipole (dotriacontapole) order with
'nematic' E^- symmetry, which exhibits staggered pseudospin moments along the
[110] direction. This naturally provides comprehensive explanations of all key
features in the hidden-order phase including anisotropic magnetic excitations,
nearly degenerate antiferromagnetic-ordered state, and spontaneous
rotational-symmetry breaking.Comment: See the published version with more detailed discussion
Disorder and c-axis quasiparticle dynamics in underdoped Bi2Sr2CaCu2O8
Disorder and c-axis quasiparticle dynamics in underdoped Bi2Sr2CaCu2O