Freek Massee
     Laboratoire de Physique des Solides, CNRS

Iron based superconductors

vortex pinning due to heavy ion irradiationUpon irradiation with 249-MeV Au ions, two types of defects appear: large (columnar defects) and small (point defects), that virtually annihilate, respectively strongly suppress superconductivity.

Atomic-scale effects of high-energy ion irradiation

Maximizing the sustainable supercurrent density, JC, is crucial to high-current applications of superconductivity. To achieve this, preventing dissipative motion of quantized vortices is key. Irradiation of superconductors with high energy heavy ions can be used to create nanoscale defects that act as deep pinning potentials for vortices. This approach holds unique promise for high-current applications of iron-based superconductors because JC amplification persists to much higher radiation doses than in cuprate superconductors without significantly altering the superconducting critical temperature. However, for these compounds, virtually nothing is known about the atomic-scale interplay of the crystal damage from the high-energy ions, the superconducting order parameter, and the vortex pinning processes.

We visualize the atomic-scale effects of irradiating FeSexTe1−x with 249-MeV Au ions and find two distinct effects: compact nanometer-sized regions of crystal disruption or “columnar defects,” plus a higher density of single atomic site “point” defects probably from secondary scattering. We directly show that the superconducting order is virtually annihilated within the former and suppressed by the latter. Simultaneous atomically resolved images of the columnar crystal defects, the superconductivity, and the vortex configurations then reveal how a mixed pinning landscape is created, with the strongest vortex pinning occurring at metallic core columnar defects and secondary pinning at clusters of point-like defects, followed by collective pinning at higher fields.

For more information, see: Science Advances 1, e1500033 (2015).

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Other publications

M. P. Allan et al., Nature Physics 11, 177 (2015)
Identifying the ‘fingerprint’ of antiferromagnetic spin fluctuations in iron pnictide superconductors

M. P. Allan et al., Nature Physics 9, 220 (2013)
Anisotropic impurity states, quasiparticle scattering and nematic transport in underdoped Ca(Fe1−xCox)2As2

E. van Heumen et al., PRL 106, 027002 (2011)
Existence, character and origin of surface-related bands in the high temperature iron pnictide superconductor BaFe2-xCoxAs2

F. Massee et al., EPL 92, 57012 (2010)
Pseudogap-less high Tc superconductivity in BaCoxFe2-xAs2

S. de Jong et al., EPL 89, 27007 (2010)
Droplet-like Fermi surfaces in the anti-ferromagnetic phase of EuFe2As2, an Fe-pnictide superconductor parent compound

F. Massee et al., PRB 80, 140507(R) (2009)
Cleavage surfaces of the BaFe2-xCoxAs2 and FeySe1-xTex superconductors: A combined STM plus LEED study

F. Massee et al., PRB 79, 220517(R) (2009)
Nanoscale superconducting gap variations and lack of phase separation in optimally doped BaFe1.86Co0.14As2

S. de Jong et al., PRB 79, 115125 (2009)
A high resolution, hard X-ray photoemission investigation of BaFe2As2: moderate influence of the surface and evidence for a low degree of Fe 3d - As 4p hybridization of the near-EF electronic states