Seminarium Oddziału Badań Magnetyków
sala nr 6 (bud. II)
Tuning of phase diagram and vortex pinning of iron-based superconductors by irradiation induced disorder
prof. Marcin Konczykowski
Laboratoire des Solides Irradiés, Ecole Polytechnique, Palaiseau, France
In my presentation I will discuss two applications of disorder controlled by energetic particle irradiation.
First in the exploration of composition – temperature (x-T) phase diagram of canonical iron-based superconductor Ba(FeAs1-xPx)2. Upon isovalent substitution of As by P, temperature of spin density wave (SDW) transition decreases and dome of superconducting phase appears. In the region of intersection of SDW transition line with superconducting dome several phenomena attract attention:
- Normal state exhibit non Fermi-liquid behavior
- Magnetism and superconductivity are supposed to coexist on microscopic scale.
- Putative quantum critical point (QCP) is hidden under superconducting dome.
I will present the investigation by electronic transport and magnetization of the phase diagram under the effect of point-like disorder induced by low temperature electron beam irradiation. The main observations are: (1) Downward shift of entire SDW transition line and extension of linear resistivity vs. temperature region pointing out to the displacement QCP under the effect of disorder. (2) Significant change of the vortex matter properties at the crossover from antiferromagnetic to paramagnetic normal state. (3) Lifshitz type transition at the origin of SDW state is robust against the disorder.
In the second axis, we explore vortex pining in irradiation controlled disorder landscape. Pristine samples exhibits strong pining regime by nanometer size defects. Low temperature electron irradiation leads to the emergence of weak collective pinning contribution due to uniform spread to point defects. Heavy ion irradiation (1.5 GeV U238 ions) of samples cooled down to 80K, results in disorder in form of columnar defects producing efficient anisotropic pining. Analysis of magnetic relaxation reveals various regimes of pining by columnar defects: collective with vortex distributed on several columns to individual with vortex localized on single column.
Within my presentation, I will present details of two experimental tools: (1) energetic particle beams for production of well controlled crystalline disorder, (2) local Hall sensor technique for space and time resolved magnetic measurements.
