Naik Subham, Kalaiarasan Somesh, Nath Ramesh C, Sarangi Sachindra N, Sahu Akshay K, Samal Debakanta, Biswal Himansu S, Samal Saroj L
Department of Chemistry, National Institute of Technology Rourkela, Rourkela 769008, India.
School of Physics, Indian Institute of Science Education and Research, Thiruvananthapuram 695551, India.
Inorg Chem. 2021 Apr 5;60(7):4588-4598. doi: 10.1021/acs.inorgchem.0c03545. Epub 2021 Mar 10.
2H-NbSe is a phonon-mediated, Fermi-surface topology-dependent multiband superconductor with an incommensurate charge-density wave (CDW) that coexists at a local level with superconductivity. Usually, the intercalation in 2H-NbSe enriches the CDW, enhances the -axis lattice parameter, and distorts the Fermi surface, which result in a decrease in the superconducting transition temperature (). The rate of decrease of depends on the electronic structure, size, valence, magnetic nature, and electronegativity of the intercalating species. Herein, we report an unusual effect of Mg intercalation on the superconductivity of 2H-MgNbSe ( = 0.0, 0.02, 0.06, 0.08, 0.10, and 0.12) synthesized by a high-temperature solid-state reaction method. Unlike other s- and p-block elements/species as intercalants (Rb, Sn, Ga, and Al) that have a sharp detrimental effect on the of 2H-NbSe within 1-5% of intercalation, Mg is found to be an exception. Upon Mg intercalation up to = 0.06, no remarkable changes in as compared to the parent 2H-NbSe ( ∼ 6.7 K) are observed, and further intercalation results in a small decrease in (for = 0.12, = 6.2 K). From heat-capacity measurements, it is inferred that superconducting Mg-intercalated 2H-NbSe exhibits strong electron-phonon coupling. Electronic structure calculations on two s-block element intercalated compounds of formula MNbSe ( = Mg, Rb) show that Rb s-, p-, and d-states completely overlap with the Nb d states, while the Mg s states lie in a low-energy region as compared to Nb d states, indicating a weak interaction between the intercalant and the Nb sublattice in MgNbSe as compared to RbNbSe. These results suggest that the electronic states of the Nb network in 2H-NbSe are least altered with Mg intercalation, which could be one of the reasons for the minimal effect on the with intercalation.
2H-NbSe₂是一种声子介导、依赖费米面拓扑结构的多带超导体，具有与超导在局部共存的非公度电荷密度波（CDW）。通常，2H-NbSe₂中的插层会使CDW富集，增大c轴晶格参数，并使费米面畸变，从而导致超导转变温度（Tₑ）降低。Tₑ的降低速率取决于插层物种的电子结构、尺寸、化合价、磁性和电负性。在此，我们报道了通过高温固相反应法合成的2H-MgₓNbSe₂（x = 0.0、0.02、0.06、0.08、0.10和0.12）中Mg插层对超导性的异常影响。与其他作为插层剂的s和p族元素/物种（Rb、Sn、Ga和Al）不同，它们在1 - 5%的插层范围内对2H-NbSe₂的Tₑ有明显的不利影响，而Mg是个例外。在插入Mg直至x = 0.06时，与母体2H-NbSe₂（Tₑ ∼ 6.7 K）相比，未观察到Tₑ有显著变化，进一步插层会导致Tₑ略有降低（对于x = 0.12，Tₑ = 6.2 K）。通过热容测量推断，插入Mg的超导2H-NbSe₂表现出强电子 - 声子耦合。对两种化学式为MNbSe₂（M = Mg、Rb）的s族元素插层化合物的电子结构计算表明，Rb的s、p和d态与Nb的d态完全重叠，而与Nb的d态相比，Mg的s态位于低能区，这表明与RbNbSe₂相比，MgNbSe₂中插层剂与Nb亚晶格之间的相互作用较弱。这些结果表明，2H-NbSe₂中Nb网络的电子态受Mg插层的影响最小，这可能是插层对Tₑ影响最小的原因之一。
