Growth conditions, structure and superconductivity of pure and metal-dopedFeTe1 − xSex single crystals

Abstract

Superconducting single crystals of pureFeTe1 − xSex andFeTe0.65Se0.35 doped with Co, Ni, Cu, Mn, Zn, Mo, Cd, In, Pb, Hg, V, Ga, Mg, Al, Ti, Cr, Sror Nd into Fe ion sites have been grown applying Bridgman’s method. It hasbeen found that the sharpness of the transition to the superconducting state inFeTe1 − xSex is evidently inversely correlated with the crystallographic quality of the crystals.Among all of the studied dopants only Co, Ni and Cu substitute Fe ions inFeTe0.65Se0.35 crystals. The remaining ions examined do not incorporate into the crystal structure.Nevertheless, they form inclusions together with selenium, tellurium and/or iron, whichchange the chemical composition of the host matrix and therefore influence theTc value. The small disorder introduced into the magnetic sublattice, by partialreplacement of Fe ions by a slight amount of nonmagnetic ions of Cu (∼1.5 at.%) or by magneticions of Ni (∼2 at.%) and Co (∼5 at.%) with spin values different than that of the Fe ion, completely suppresses superconductivity in theFeTe1 − xSex system. This indicates that, even if superconductivity is observed in the systemcontaining magnetic ions, it cannot survive when the disorder in the magnetic ionsublattice is introduced, most likely because of magnetic scattering of Cooper pairs.