Iridates provide a fertile ground to investigate correlated electrons in the presence of strong spin-orbit coupling. Bringing these systems to the proximity of a metal-insulator quantum phase transition is a challenge that must be met to access quantum critical fluctuations with charge and spin-orbital degrees of freedom. Here, electrical transport and Raman scattering measurements provide evidence that a metal-insulator quantum critical point is effectively reached in 5% Co-doped Sr₂IrO₄ with high structural quality. The dc-electrical conductivity shows a linear temperature dependence that is successfully captured by a model involving a Co acceptor level at the Fermi energy that becomes gradually populated at finite temperatures, creating thermally-activated holes in the J_eff = 1/2 lower Hubbard band. The so-formed quantum critical fluctuations are exceptionally heavy and the resulting electronic continuum couples with an optical phonon at all temperatures. The magnetic order and pseudospin-phonon coupling are preserved under the Co doping. This work brings quantum phase transitions, iridates and heavy-fermion physics to the same arena.

在强自旋轨道耦合的存在下，铱离子为研究相关电子提供了沃土。将这些系统带到金属绝缘体的量子相变附近是必须面对的挑战，以利用电荷和自旋轨道的自由度获得量子临界波动。在此，电传输和拉曼散射测量提供了证据，表明在具有高结构质量的5％Co掺杂Sr ₂ IrO _4中可以有效地达到金属-绝缘子的量子临界点。该DC-电气传导性示出了线性的温度依赖性，其成功地通过包括在费米能级变得逐渐在有限的温度下填充的钴受主能级的模型捕获，在建立热激活孔Ĵ _EFF  = 1/2下哈伯德频带。如此形成的量子临界波动异常严重，并且所产生的电子连续体在所有温度下都与光学声子耦合。在Co掺杂下保留了磁序和伪自旋-声子耦合。这项工作将量子相变，铱酸盐和重费米子物理学带到了同一个领域。