Rare-earth pyrochlore iridates host two interlocking magnetic sublattices of corner-sharing tetrahedra and can harbour a unique combination of frustrated moments, exotic excitations and highly correlated electrons. They are also the first systems predicted to display both topological Weyl semimetal and axion insulator phases. We have measured the transport and magnetotransport properties of single-crystal Sm₂Ir₂O₇ up to and beyond the pressure-induced quantum critical point for all-in-all-out (AIAO) Ir order at p_c = 63 kbar previously identified by resonant X-ray scattering and close to which Weyl semimetallic behavior has been previously predicted. Our findings overturn the accepted expectation that the suppression of AIAO order should lead to metallic conduction persisting down to zero temperature. Instead, the resistivity-minimum temperature, which tracks the decrease in the AIAO ordering temperature for pressures up to 30 kbar, begins to increase under further application of pressure, pointing to the presence of a second as-yet unidentified mechanism leading to non-metallic behavior. The magnetotransport does track the suppression of Ir magnetism, however, with a strong hysteresis observed only within the AIAO phase boundary, similar to that found for Ho₂Ir₂O₇ and attributed to plastic deformation of Ir domains. Around p_c we find the emergence of a new type of electronic phase, characterized by a negative magnetoresistance with small hysteresis at the lowest temperatures, and hysteresis-free positive magnetoresistance above approximately 5 K. The temperature dependence of our low-temperature transport data are found to be best described by a model consistent with a Weyl semimetal across the entire pressure range.

稀土烧绿石虹彩拥有两个互锁的共享角四面体的磁性子晶格，并且可以拥有受抑矩、奇异激发和高度相关电子的独特组合。它们也是第一个预计显示拓扑外尔半金属相和轴子绝缘体相的系统。我们测量了单晶 Sm ₂ Ir ₂ O _{7的输运和磁输运特性，达到并超过先前确定的}p _c  = 63 kbar的全进全出 (AIAO) Ir 阶的压力诱导量子临界点通过共振 X 射线散射，与先前预测的 Weyl 半金属行为接近。我们的研究结果推翻了人们普遍接受的预期，即抑制 AIAO 秩序会导致金属传导持续至零温度。相反，电阻率最低温度（跟踪压力高达 30 kbar 时 AIAO 排序温度的降低）在进一步施加压力下开始增加，这表明存在第二种尚未确定的导致非金属的机制。行为。然而，磁输运确实跟踪了 Ir 磁性的抑制，仅在 AIAO 相界内观察到强磁滞，类似于 Ho ₂ Ir ₂ O ₇中发现的现象，并归因于 Ir 域的塑性变形。在p _c附近，我们发现出现了一种新型电子相，其特征是在最低温度下具有小磁滞的负磁阻，并且在大约 5 K 以上时具有无磁滞的正磁阻。我们的低温传输数据的温度依赖性为发现可以通过在整个压力范围内与 Weyl 半金属一致的模型来最好地描述。