Department of Magnetic Reseach Seminar
sala nr 6 (bud. II)
Composition-Temperature Phase Diagram of Iron-Based Superconductors Tuned by Disorder
prof. Marcin Konczykowski
Paryski Instytut Politechniczny w Palaiseau we Francji
Two phase transition lines forming composition temperature phase diagram of iron based superconductors ( IBS): antiferromagnetic Spin Density Wave (SDW) and superconducting (SC) can be tuned in large extend by controlled disorder. I will present the result of measurements of magnetization and electronic transport of Ba(FeAs 1 x P x 2 crystals, modified by point disorder induced by low temperature electron irradiation and by correlated disorder produced by swift heavy ions. Strong depression of SDW transition by both types of disorder sis consist ent with itinerant magnetism of IBS. SDW t ransition of Lifshitz type preserves its character even in strongly disordered material. Depression of superconducting transition temperature T c by point disorder is proportional to the dose and reach values below 1/3 of initial T c without saturation. In contrast, increase of normal state resistivity induced by columnar defects has almost no effect on T c . It is consistent with absence of pairbraiking effect of intraband scattering c hannel prevailing for this type of disorder landscape . The region of particular interest is that of slightly underdoped materials where magnetic and superconducting orders co exist. The sequence of transition s (in the function of temperature on cooling ) from normal, paramagnetic to antiferromagnetic and finally to superconducting state can be modified by disorder to direct transition from paramagnetic metal to superconductor. Extension of the SDW t ransition line can be traced inside of the superconducting dome by abrupt change of the critical current . This line follows the evolution with irradiation dose of SDW phase of the ground state and disappears at sufficiently high disorder. This confirms disorder induced downward shift in composition of putative Quantum Critical Point [1].
[1] Yuta Mizukami, et al . Journal of the Physical Society of Japan, 86, 083706 (2017)
