三维ZrN$_x$超导薄膜中的二维量子格里菲斯奇异性
Two-dimensional quantum Griffith singularity in three-dimensional ZrN$_x$ superconducting films
AI总结：
该研究在三维ZrN$_x$超导薄膜中观测到二维量子格里菲斯奇异性，揭示了无序诱导的非均匀性对量子相变临界行为的关键作用，为三维超导体中该奇异性的存在提供了实验证据。
AI中文摘要：
我们报道了在厚度约200纳米的外延ZrN$_x$超导薄膜中实验观测到的二维（2D）量子格里菲斯奇异性（QGS）。这些薄膜具有岩盐结构，在超导性方面属于三维（3D）体系。对于每个$x \blacktriangleright 1.30$的薄膜，在垂直和平行于薄膜平面的磁场下，低温磁阻等温线在较宽的磁场范围内交叉，而非在单一交叉点处交叉。尽管超导性具有宏观三维特性，但在选定的相邻温度下的磁阻等温线遵循二维超导体系的幂律标度理论预测，而非三维体系的预测。通过二维幂律标度分析磁阻等温线得到的有效临界指数$z\nu$随温度降低而增大，并在趋近量子相变时发散。此外，超导体-绝缘体或超导体-金属转变附近的电阻率数据符合描述由无限随机临界点主导的二维超导体系量子相变的激活标度形式。ZrN$_x$薄膜中的QGS归因于Zr空位和N间隙等本征缺陷诱导的淬火无序，这会产生空间非均匀的超导稀有区域。这些稀有区域的动力学在量子临界点附近可能表现出有效二维特性，主导量子相变附近体系的输运性质。我们的结果为三维超导体中QGS的存在提供了有力证据，并强调了无序诱导的非均匀性在决定量子相变临界行为中的关键作用。
英文摘要：
We report the experimental observation of two-dimensional (2D) quantum Griffiths singularity (QGS) in $\sim$200-nm-thick epitaxial ZrN$_x$ superconducting films. The films possess a rock-salt structure and are three-dimensional (3D) with respect to superconductivity. For each film with $x \gtrsim 1.30$, the low-temperature magnetoresistance isotherms under fields perpendicular and parallel to the film plane cross over at a broad magnetic field range independently rather than at a single crossing point. Despite the macroscopic 3D nature of the superconductivity, the magnetoresistance isotherms at selected adjacent temperatures follow the theoretical prediction of power-law scaling for 2D superconducting systems, rather than that for 3D systems. The effective critical exponent $zν$, obtained by analyzing the magnetoresistance isotherms using the 2D power-law scaling, increases with decreasing temperature and diverges as the quantum phase transition is approached. In addition, the resistivity data near the superconductor-insulator or superconductor-metal transitions obey an activated scaling form that describes the quantum phase transition of 2D superconducting systems governed by an infinite-randomness critical point. The QGS in the ZrN$_x$ films is attributed to quenched disorder induced by intrinsic defects, such as Zr vacancies and N interstitials, which creates spatially inhomogeneous superconducting rare regions. The dynamics of these rare regions, which may exhibit effective 2D characteristics near the quantum critical point, dominate the transport properties of the system near the quantum phase transition. Our results provide compelling evidence for the existence of QGS in 3D superconductors and highlight the crucial role of disorder-induced inhomogeneity in determining the critical behavior of quantum phase transitions.
