Type-I superconductivity in noncentrosymmetric <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>Nb</mml:mi><mml:msub><mml:mi>Ge</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
Baijiang Lv, Miaocong Li, Jia Chen, Yusen Yang, Siqi Wu, Lei Qiao, Feihong Guan, Hui Xing, Tao Qian, Guang‐Han Cao, Zhu‐An Xu
Abstract
Single crystals of $\mathrm{Nb}{\mathrm{Ge}}_{2}$ which crystallize in a noncentrosymmetric hexagonal structure with chirality are synthesized and their superconductivity is investigated. Type-I superconductivity is confirmed by dc magnetization, a field-induced second-to first-order phase transition in specific heat, and a small Ginzburg-Landau parameter ${\ensuremath{\kappa}}_{\text{GL}}=0.12$. The isothermal magnetization measurements show that there is a crossover from type-I to type-II/1 superconductivity with decreasing temperature and an unusually enhanced surface superconducting critical field (${H}_{c3}$) is discovered. The band structure calculations indicate the presence of Kramer-Weyl nodes near the Fermi level. These observations demonstrate that $\mathrm{Nb}{\mathrm{Ge}}_{2}$ is an interesting and rare example involving the possible interplay of type-I superconductivity, noncentrosymmetric structures, and topological properties.