Superconductivity in Iron Telluride Thin Films under Tensile Stress

Abstract

By realizing in thin films a tensile stress state, superconductivity of 13 K was introduced into FeTe, a nonsuperconducting parent compound of the iron pnictides and chalcogenides, with a transition temperature higher than that of its superconducting isostructural counterpart FeSe. For these tensile stressed films, superconductivity is accompanied by a softening of the first-order magnetic and structural phase transition, and also, the in-plane extension and out-of-plane contraction are universal in all FeTe films independent of the sign of the lattice mismatch, either positive or negative. Moreover, the correlations were found to exist between the transition temperatures and the tetrahedra bond angles in these thin films.

Mobility Analysis of FeTe Thin Films

“…Trace of the tetragonalto-monoclinic structural phase transition is not observed in samples B and C. In bulk samples, resistivity exhibits a discontinuous jump at T tm = 68 K, 16,17) but samples B and C exhibit only a rounded peak in ρ around T = 80 K followed by a rather smooth decrease to low temperatures as reported. 18,19) However, except for the absence of sharp drop at T tm , overall temperature dependence of ρ is similar between the films and bulk crystals. Thus, crossover from tetragonal to monoclinic phases is likely to take place, and hence, we safely assume that an AFM long-range order is present in samples B and C at low temperatures.…”

Comparative Review on Thin Film Growth of Iron-Based Superconductors

“…However, because superconducting FeTe films can have both longer and shorter a-axis length [124], the mechanism seems not simple like the strain scenario by Han et al [122], whereas the superconducting properties of FeTe may be largely affected by the lattice strain, suggested by thermal expansion measurements [126]. Physical properties of the superconducting FeTe are similar to those of FeSe 1−x Te x : (1) strain largely affects the T c values [126]; (2) importance of both n-and p-type carriers for the superconductivity, suggested by the Hall effect [40,127,128]; (3) huge B c2 (> 30 T) [122,123,129]. These may suggest that the mechanism of the superconductivity is the same for both FeTe and FeSe 1−x Te x .…”

“…However, there are some reports on the growth of superconducting FeTe thin films [122][123][124][125]. Han et al reported superconductivity in FeTe thin films with T onset c of 13 K for the first time [122].…”

Micro Structural and Optical Properties of Ferrous Selenide Thin Films and Its Characterization

“…Modern researches on the tetragonal phase FeSe (spacegroupP4/ nmm) have exposed that they endure a structural phase transformation from 90 K(Ts), to orthorhombic phase (space group C mma), concerning chiefly a insignificant distortion in(a-b) plane, i.e., γ tetragonal angle slightly enlarged from 90°, as it turns out to be superconducting at 8K (Tc) [7,10,20]. Through varying the stoichiometry of FeSe, for instance totalling extra iron [10,12], or doping with alien atoms, like substitution of iron with copper [21], the low temperature structural distortion could be suppressed along with the c-axis.…”

“…The composition of FeSe thin films was analyzed using an energy dispersive analysis by Xrays (EDX) set up attached with scanning electron microscopy. Preliminary studies for photo electrochemical solar cells based on iron selenide thin films were carried out and the experimental observations are discussed [20][21][22].…”