拓扑绝缘体$Bi_2Se_3$中$^{57}$ Fe取代基的穆斯堡尔参数
Mössbauer parameters of $^{57}$Fe substituents in the topological insulator $Bi_2Se_3$
摘要：
$^{57}$ Fe穆斯堡尔谱可以探测含铁体系的几种\emph{local}结构、电子和磁性。然而，为了建立这些性质与系统几何结构之间的直接关系，需要对实验穆斯堡尔参数进行\emph{via}电子结构计算分析。在此，铁取代基的结构，电子和磁效应的拓扑绝缘体$Bi_2Se_3$，作为唯一探测的$^{57}$ Fe穆斯堡尔谱，已确定\emph{via}自旋极化电子结构计算。铁离子取代基，\emph{nominal} Fe $^{3+}(S = 5/2)$氧化态和自旋态，明确地表明，取代用于穆斯堡尔测量的外延$Bi_2Se_3$薄膜中的Bi $^{3+}$网站。伴随着铁的取代，\emph{localized}结构重排发生，从而较长的Bi-Se键的天然系统被取代显着较短的Fe-Se对应物在含Fe系统。由此产生的扭曲的八面体环境的取代基铁离子引起的特征穆斯堡尔参数（$δ_{Fe} \approx$ 0.51 mm/s，$ΔE_{Q} \approx$ 0.20 mm/s），已计算出与Fe掺杂的$Bi_2Se_3$薄膜的测量值非常一致。与取代基Fe $^{3+}$离子的\emph{nominal}高自旋电子构型（$t_{2g}^{\uparrow \uparrow \uparrow} e_g^{\uparrow \uparrow}$）一致，已经建立了Fe中心的自旋密度，然而，该自旋密度向邻近的Se原子\emph{via}直接Fe-Se键合和伴随的Fe（d）-Se（p）杂化延伸。
英文摘要：
$^{57}$Fe Mössbauer spectroscopy can probe several \emph{local} structural, electronic and magnetic properties of Fe-containing systems. However, to establish a direct relationship between these properties and a system's geometric structure, the experimental Mössbauer parameters need to be analyzed \emph{via} electronic structure calculations. Herein, structural, electronic and magnetic effects of iron substituents in the topological insulator $Bi_2Se_3$, as uniquely probed by $^{57}$Fe Mössbauer spectroscopy, have been determined \emph{via} spin-polarized electronic structure calculations. The iron ion substituents, of \emph{nominal} Fe$^{3+}(S = 5/2)$ oxidation and spin state, are unequivocally shown to substitute Bi$^{3+}$ sites in epitaxial $Bi_2Se_3$ thin-films used for Mössbauer measurements. Concomitant with iron substitution, \emph{localized} structural rearrangements take place whereby the longer Bi-Se bonds of the native system are replaced by significantly shorter Fe-Se counterparts in the Fe-containing system. The resulting distorted-octahedral environment about substituent iron ions gives rise to characteristic Mössbauer parameters ($δ_{Fe} \approx$ 0.51 mm/s, $ΔE_{Q} \approx$ 0.20 mm/s) which have been calculated in excellent agreement with measured values for Fe-doped $Bi_2Se_3$ thin films. Consistent with a substituent Fe$^{3+}$ ion's \emph{nominal} high-spin electronic configuration ($t_{2g}^{\uparrow \uparrow \uparrow} e_g^{\uparrow \uparrow}$), an Fe-centered spin density has been established which, nevertheless, extends towards neighboring Se atoms \emph{via} direct Fe-Se bonding and concomitant Fe(d)-Se(p) hybridization.
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