Nd₂Ir₂O₇ is a correlated semimetal with the pyrochlore structure, in which competing spin–orbit coupling and electron–electron interactions are believed to induce a time-reversal symmetry-broken Weyl semimetal phase characterized by pairs of topologically protected Dirac points at the Fermi energy^1,2,3,4. However, the emergent properties in these materials are far from clear, and exotic new states of matter have been conjectured^5,6,7. Here, we demonstrate optically that, at low temperatures, the free carrier spectral weight is proportional to T², where T is the temperature, as expected for massless Dirac electrons. However, we do not observe the corresponding T³ term in the specific heat. That the system is not in a Fermi liquid state is further corroborated by the charge carrier scattering rate approaching critical damping and the progressive opening of a correlation-induced gap at low temperatures. These observations cannot be reconciled within the framework of band theory of electron-like quasiparticles and point towards the effective decoupling of the charge transport from the single particle sector.

Nd ₂ Ir ₂ O ₇是具有烧绿石结构的相关半金属，据信其中竞争的自旋-轨道耦合和电子-电子相互作用可诱导时间逆转对称的Weyl半金属相，其特征是在成对的拓扑受保护的Dirac点对费米能量^1,2,3,4。然而，这些材料的新兴性质还远未弄清，并且已推测出奇异的物质新状态^5,6,7。在这里，我们从光学上证明，在低温下，自由载流子光谱权重与T ²成正比，其中T是无质量狄拉克电子所期望的温度。但是，我们没有观察到比热中相应的T ³项。该系统不处于费米液态的事实进一步得到了接近临界阻尼的电荷载流子散射速率和在低温下逐步打开由相关性引起的间隙的证实。这些观察不能在类电子准粒子的能带理论的框架内调和，并指出电荷传输与单个粒子扇区之间的有效解耦。