34 research outputs found
Comparative study of the effects of electron irradiation and natural disorder in single crystals of SrFe(AsP) (0.35) superconductor
London penetration depth, , was measured in single crystals of
SrFe(AsP) (0.35) iron - based superconductor. The
influence of disorder on the transition temperature, , and on
was investigated. The effects of scattering controlled by the annealing of
as-grown crystals was compared with the effects of artificial disorder
introduced by 2.5~MeV electron irradiation. The low temperature behavior of
can be described by a power-law function, , with the exponent close to one in pristine annealed samples, as
expected for superconducting gap with line nodes. Upon
\ecm irradiation, the exponent increases rapidly exceeding a dirty limit
value of 2 implying that the nodes in the superconducting gap are
accidental and can be lifted by the disorder. The variation of the exponent
with is much stronger in the irradiated crystals compared to the crystals
in which disorder was controlled by the annealing of the growth defects. We
discuss the results in terms of different influence of different types of
disorder on intra- and inter- band scattering
Using electron irradiation to probe iron - based superconductors
High energy electron irradiation is an efficient way to create
vacancy-interstitial Frenkel pairs in crystal lattice, thereby inducing
controlled non-magnetic point - like scattering centers. In combination with
London penetration depth and resistivity measurements, the irradiation was
particularly useful as a phase - sensitive probe of the superconducting order
parameter in iron - based superconductors lending strongest support to sign -
changing pairing. Here we review the key results on the effect of
electron irradiation in iron-based superconductors
Intermediate scattering potential strength in electron-irradiated from London penetration depth measurements
Temperature-dependent London penetration depth, , of a high
quality optimally-doped single
crystal was measured using tunnel-diode resonator. Controlled artificial
disorder was induced at low-temperature of 20~K by 2.5 MeV electron irradiation
at accumulating large doses of and
electrons per . The irradiation caused significant suppression
of the superconductor's critical temperature, , from 94.6 K to 90.0 K,
and then to 78.7 K, respectively. The low-temperature behavior of
evolves from a linear in pristine state to a
behavior after the irradiation, expected for a line-nodal wave
superconductor. However, the original theory that explained such behavior had
assumed a unitary limit of the scattering potential, whereas usually in normal
metals and semiconductors, Born scattering is sufficient to describe the
experiment. To estimate the scattering potential strength, we calculated the
normalized superfluid density,
,
varying the amount and the strength of non-magnetic scattering using a
self-consistent matrix theory. Fitting the obtained curves to a power-law,
, and to a polynomial, , and comparing
the coefficients in one set, and and in another with the
experimental values, we estimate the phase shift to be around 70 and
65, respectively. We correlate this result with the evolution of the
density of states with non-magnetic disorder
Electron irradiation effects on superconductivity in PdTe: an application of a generalized Anderson theorem
Low temperature ( 20~K) electron irradiation with 2.5 MeV relativistic
electrons was used to study the effect of controlled non-magnetic disorder on
the normal and superconducting properties of the type-II Dirac semimetal
PdTe. We report measurements of longitudinal and Hall resistivity, thermal
conductivity and London penetration depth using tunnel-diode resonator
technique for various irradiation doses. The normal state electrical
resistivity follows Matthiessen rule with an increase of the residual
resistivity at a rate of 0.77cm/. London penetration depth and thermal
conductivity results show that the superconducting state remains fully gapped.
The superconducting transition temperature is suppressed at a non-zero rate
that is about sixteen times slower than described by the Abrikosov-Gor'kov
dependence, applicable to magnetic impurity scattering in isotropic,
single-band -wave superconductors. To gain information about the gap
structure and symmetry of the pairing state, we perform a detailed analysis of
these experimental results based on insight from a generalized Anderson theorem
for multi-band superconductors. This imposes quantitative constraints on the
gap anisotropies for each of the possible pairing candidate states. We conclude
that the most likely pairing candidate is an unconventional
state. While we cannot exclude the conventional and the triplet
, we demonstrate that these states require additional assumptions about
the orbital structure of the disorder potential to be consistent with our
experimental results, e.g., a ratio of inter- to intra-band scattering for the
singlet state significantly larger than one. Due to the generality of our
theoretical framework, we think that it will also be useful for irradiation
studies in other spin-orbit-coupled multi-orbital systems.Comment: 22 pages, 12 figure
Competition between orthorhombic and re-entrant tetragonal phases in underdoped Ba1-xKxFe2As2 probed by the response to controlled disorder
Low-temperature (22 K) irradiation with 2.5-MeV electrons, creating point defects affecting elastic scattering, was used to study the competition between stripe C-2 and tetragonal C-4 antiferromagnetic phases which exist in a narrow doping range around x = 0.25 in hole-doped Ba1-xKxFe2As2. In nearby compositions outside of this range, at x = 0.22 and x = 0.19, the temperatures of both the concomitant orthorhombic/stripe antiferromagnetic transition T-C2 and the superconducting transition T-c are monotonically suppressed by added disorder at similar rates of about 0.1 K/mu Omega cm, as revealed through using resistivity variation as an intrinsic measure of scattering rate. In a stark contrast, a rapid suppression of the C-4 phase at the rate of 0.24 K/mu Omega cm is found at x = 0.25. Moreover, this suppression of the C-4 phase is accompanied by unusual disorder-induced stabilization of the C-2 phase, determined by resistivity and specific heat measurements. The rate of the C-4 phase suppression is notably higher than the suppression rate of the spin-vortex phase in the Ni-doped CaKFe4As4 (0.16 K/mu Omega cm)