Charge-carrier localization induced by excess Fe in the superconductorFe1+yTe1−xSex

Abstract

We have investigated the effect of Fe nonstoichiometry on properties of the Fe 1+y (Te, Se) superconductor system by means of resistivity, Hall coefficient, magnetic susceptibility, and specific heat measurements. We find that the excess Fe at interstitial sites of the (Te, Se) layers not only suppresses superconductivity, but also results in a weakly localized electronic state. We argue that these effects originate from the magnetic coupling between the excess Fe and the adjacent Fe square planar sheets, which favors a short-range magnetic order.

Effect of Fe excess on structural, magnetic and superconducting properties of single-crystalline Fe1+xTe1−ySey

“…These results clearly show that reducing the excess of Fe in Fe 1+x Te 1−y Se y favors the occurrence of superconductivity. A similar conclusion is also drawn by Liu et al [16], based on the comparison of two samples with different Fe-contents and a fixed Se-doping level.…”

“…However, pure FeTe is not superconducting and the two end compounds of the "11" solid solution, FeSe and FeTe, even if structurally isomorphic, reveal to be substantially different. Both are off-stoichiometric, but whereas the off-stoichiometry in FeSe 1−y is preferably ascribed to Se-deficiency [11,12,13], in Fe 1+x Te excess Fe atoms occupy an additional site in the Fe-Te plane [14,15,16]. In Fe 1+x Te both magnetic (AFM) and structural (tetragonal to monoclinic) transitions occur at the same temperature T N 67 K [14], with the propagation vector aligned at 45 • from the nesting vector [17].…”

“…A systematic investigation of structural, magnetic, and superconducting properties as a function of both the Se-and Fe-content is mandatory, and is the aim of the present work. Single crystals of Fe 1+x Te 1−y Se y have been recently grown by several authors [15,16,20,21,22] and the role of excess Fe in increasing the charge localization has been recognized [16]. However, little attention has been paid to the actual Fe and Se doping levels in a more realistic 3-D phase diagram, and how different ground states can be driven by Fe and Se doping is not yet understood.…”

Effects of Iodine Annealing on Fe1+yTe0.6Se0.4

“…In addition, the 11 type is less toxic than iron pnictides and has small anisotropy [6], which is favorable for applications with high current-carrying capabilities. However, the excess iron that is located at the interstitial site in the Te/Se layer [7] has strong magnetism and acts as pair a breaker and suppresses superconductivity [8,9]. Thus, the as-grown Fe 1+y Te 1-x Se x single crystals only show filamentary superconductivity [10,11].…”

Site-selective electronic structure of pure and doped Ca2O3Fe3S2

“…In SmFeAsO 1−x F x [4], for example, suppression of superconductivity by high magnetic fields reveals a low temperature insulating behavior, similar to underdoped high-T c cuprates [5]. Interestingly, in some cases superconductivity arises directly from a normal state with insulating-like [6,7] resistivity above T c . Given telling similarities, along with notable differences, between the ironand cuprate-based superconductors [8], an especially important issue has been to confirm whether the parent compounds are itinerant metals or if they lie in close proximity to a Mott metal-to-insulator transition [7,9].…”