Quantum phase transition in NbN superconducting thin films

作者：Tianyu Jing, Ziyan Han, Zhihao He, Mingxin Shao, Peng Li, Zhi‐Qing Li · 发表于：Physical review. B./Physical review. B · 年份：2023 · DOI：10.1103/physrevb.107.184515 · 被引用次数：11 · 研究领域：Physics of Superconductivity and Magnetism、Quantum and electron transport phenomena、Electronic and Structural Properties of Oxides

We systematically investigated the low-temperature transport properties of two series of NbN epitaxial films. The first series of films with thickness ranging from $\ensuremath{\sim}2.0$ to $\ensuremath{\sim}4.0\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ are two-dimensional (2D) with respect to superconductivity, while another series with thickness around $\ensuremath{\sim}20\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ is quasi-three-dimensional (quasi-3D). Those 2D NbN films undergo a superconductor-insulator transition (SIT) with decreasing film thickness, and the critical sheet resistance for the SIT is close to the quantum resistance of Cooper pairs $h/4{e}^{2}$ (6.45 $\mathrm{k}\mathrm{\ensuremath{\Omega}}$). Besides the Berezinski-Koterlitz-Thouless transition, a magnetic-field-driven SIT is observed in those 2D superconducting films ($2.6\phantom{\rule{0.16em}{0ex}}\mathrm{nm}\ensuremath{\lesssim}t\ensuremath{\lesssim}4.0\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$). The field-driven quantum metal state does not appear in these 2D superconducting films. However, it is found that both in the 2D and quasi-3D superconducting films the low-temperature magnetoresistance isotherms do not cross at a very narrow region (generally treated as a single point) but cross at a well-distinguished wide region. The dynamical critical exponent obtained by analyzing these magnetoresistance isotherms is divergent as the quantum critical point is approached. The divergence of the dynamical critical e...