Observation of Superconductivity in Tetragonal FeS

Abstract

The possibility of superconductivity in tetragonal FeS has attracted considerable interest because of its similarities to the FeSe superconductor. However, all efforts made to pursue superconductivity in tetragonal FeS have failed so far, and it remains controversial whether tetragonal FeS is metallic or semiconducting. Here we report the observation of superconductivity at 5 K in tetragonal FeS that is synthesized by the hydrothermal reaction of iron powder with sulfide solution. The obtained samples are highly crystalline and less air-sensitive, in contrast to those reported in the literature, which are meta-stable and air-sensitive. Magnetic and electrical properties measurements show that the samples behave as a paramagnetic metal in the normal state and exhibit superconductivity below 5 K. The high crystallinity and the stoichiometry of the samples play important roles in the observation of superconductivity. The present results demonstrate that tetragonal FeS is a promising new platform to realize high-temperature superconductors.

Upper critical field and quantum oscillations in tetragonal superconducting FeS

“…The latter suggested an additional closed hole pocket at Γ. The discrepancy can be attributed to the difference in the atomic position z S of S: while the experimental value of z S = 0.2523 [2] was used in the present work and [5], the relaxed value of z S = 0.2243 was used in [38]. The carrier density and Sommerfeld coefficient are estimated to be n e = n h = 0.185 carriers/Fe and γ band = 2.4 mJ/(K 2 mol).…”

“…A dilution refrigerator and superconducting magnet were used to generate low temperatures down to T = 0.03 K and high magnetic fields up to B = 17.8 T. The magnetic field direction θ was measured from the c axis. Relativistic electronic structure calculations were performed by using the WIEN2K code [31] with the experimental lattice parameters [2,32] III. RESULTS AND DISCUSSION Figure 1 shows the resistive transition curves for (a) B c and (b) B ab at selected temperatures and (c) selected field directions at T 0.04 K. We define B c2 by a midpoint criterion, as indicated in (a).…”

Electronic structure of FeS

“…The T c of FeSe 1−x Te x can reach 14 K [9], while that of FeSe 1−x S x is first enhanced by dilute S substitution, then decreases upon further substitution [10]. Recently, it was found that FeS, in which Se is totally substituted by S, is still superconducting with a T c of about 4.5 K [11,12]. During this process, the nematic (orthorhombic) phase transition temperature (T N ) in FeSe is suppressed, and there is no structural or nematic transition in FeS [10,[13][14][15].…”

On the Nanoscale Structure of KxFe2−yCh2 (Ch = S, Se): A Neutron Pair Distribution Function View

“…In Tables 1 and 2, we quantitatively compare various structural parameters derived from the single-phase I4/m VD model at 5 K, such as lattice parameters, interatomic Fe-Ch and Fe-Fe distances, anion heights, and ADP values. Most values are compared in reference to respective quantities obtained for non-intercalated FeSe [24] and FeS [25] parent materials. As expected, the lattice parameters and the interatomic distances (all Fe-Ch and the inter-cluster Fe-Fe lengths) are longer in the case of selenide, resulting in a large increase in the unit cell volume of ca.…”

“…Intercalation of K in between the FeSe layers induced an effective reduction in the anion height, shifting the value closer to the optimum, while simultaneously increasing the Fe-interlayer spacing from 5.316(1) Å to 7.001(1) Å, with a concomitant increase of T C from about 8 K to about 32 K. In the sulphide analogue, the K intercalation also increased the Fe interlayer spacing from 5.031(1) Å to 6.747(4) Å, but the anion height increased only slightly, and at 1.28 Å, is still substantially far from the optimum value for superconductivity. Whereas FeS is a superconductor with a T C~5 K [25], the K-intercalated compound exhibited a spin-glass behavior.…”