Effects of Co and Mn doping in K_0.8Fe_2−ySe₂revisited

Abstract

Accumulated evidence indicates that phase separation occurs in potassium intercalated iron selenides, a superconducting phase coexisting with the antiferromagnetic phase K2Fe4Se5, the so-called '245 phase'. Here, we report a comparative study of substitution effects by Co and Mn for Fe sites in K0.8Fe2-ySe2 within the phase separation scenario. Our results demonstrate that Co and Mn dopants have distinct differences in occupancy and hence in the suppression mechanism of superconductivity upon doping of Fe sites. In K0.8Fe2-xCoxSe2, Co prefers to occupy the lattice of the superconducting phase and suppresses superconductivity very quickly, obeying the magnetic pair-breaking mechanism or the collapse of the Fermi surface nesting mechanism. In contrast, in K0.8Fe1.7-xMnxSe2, Mn shows no preferential occupancy in the superconducting phase or the 245 phase. The suppression of superconductivity can be attributed to restraining of the superconducting phase and meanwhile inducing another non-superconducting phase by Mn doping.

Observations on the Resonant Mode in Superconducting KxFe2−ySe2

“…Magnetic susceptibility data show a superconducting transition at T c = 29 K (Fig. 1) in agreement with other published values [11].…”

Crystal growth, transport phenomena and two-gap superconductivity in the mixed alkali metal (K1−zNaz)xFe2−ySe2 iron selenide

“…The complex microstructure makes it difficult to study the effect of doping on the properties of the superconducting phase. Very recently it was shown that Co and Mn dopants have distinct differences in occupancy and hence in the mechanism of superconductivity suppression upon doping of Fe sites [28,29]. Taking into account a high sensibility of the superconducting phase to modifications in Fe sublattice, it is important to find a kind of substitution which allows increasing the superconducting volume fraction and to enhance the stability of the superconducting phase in the sample.…”

The crystal structure and physical properties of multiple components FeSe-based superconductors

“…(a) The high-resolution atomic image of K 0.8 Fe 2−y Se 2 , the schematic shows the ordered Fe vacancies [17] ; (b) the electron diffraction pattern taken along [001] zone axis [17] ; (c) the crystal structure of K 2 Fe 4 Se 5 [18] ; (d) the structural order and magnetic order parameters as a function of temperature [18] ; (e) the 2 × 2 superstructure as a function of temperature [19] ; (f) the Fe ordering of 2 × 2 superstructure [19] ; (g) the charge ordering in superconducting 2 × 5 order [21] ; (h) the schematic coexistence of KFe 2 Se 2 and K 2 Fe 4 Se 5 [21] 2 的电荷有序相, 超导相来自 2 × 5 的电荷有序 相 KFe 2 Se 2 (图 4(g))和 Se空位相KFe 2 Se 2 − z , 两者与 [22] . 同时, 对K 0.8 Fe 2−y Se 2 的Fe位进行了Mn和Co 掺杂研究, 发现了两种掺杂剂对超导截然不同的淬 灭效应 [23] . [22] ; (c), (d) 在K 0.8 Fe 2−y Se 2 中掺杂Co和Mn时, 超导转变温度和超导相含量随温度的关系曲线; (e), (f) K 0.8 Fe 2−y Se 2 中Co和Mn在超导相和绝缘相中的分布情况, 可以看出两种掺杂剂截然不同 的掺杂效应 [23] Figure 5 (Color online) The physical properties of doped K 0.8 Fe 2−y Se 2 .…”

“…同时, 对K 0.8 Fe 2−y Se 2 的Fe位进行了Mn和Co 掺杂研究, 发现了两种掺杂剂对超导截然不同的淬 灭效应 [23] . [22] ; (c), (d) 在K 0.8 Fe 2−y Se 2 中掺杂Co和Mn时, 超导转变温度和超导相含量随温度的关系曲线; (e), (f) K 0.8 Fe 2−y Se 2 中Co和Mn在超导相和绝缘相中的分布情况, 可以看出两种掺杂剂截然不同 的掺杂效应 [23] Figure 5 (Color online) The physical properties of doped K 0.8 Fe 2−y Se 2 . (a), (b) The T c of K 0.8 Fe 2−y SeS and its suppression by magnetic fields [22] ; (c), 相变温度区间为200~138 K, 该相变与其电子结构中 的费米面嵌套强度和矢量相关联 [24] .…”

“…此种新的费米面构型明显不同于 FeAs基化合物, 研究人员通过解析该电子结构发现 K 0.8 Fe 2−y Se 2 中不可能存在s±构型的超导对称性, 通过 随机相近似的方法, 推测K 0.8 Fe 2−y Se 2 中超导的能隙 构型可能为d波对称性 [28] . 同时, 对K 0.8 Fe 2−y Se 2 进行 Co元素掺杂, 发现超导转变温度迅速被杂质散射所 抑制, 也明显区别于FeAs基材料超导对杂质的响应 规律 [23] . [30] .…”