Many transition metal oxides (TMOs) are Mott insulators due to strong Coulomb repulsion between electrons, and exhibit metal-insulator transitions (MITs) whose mechanisms are not always fully understood. Unlike most TMOs, minute doping in CaMnO₃ induces a metallic state without any structural transformations. This material is thus an ideal platform to explore band formation through the MIT. Here, we use angle-resolved photoemission spectroscopy to visualize how electrons delocalize and couple to phonons in CaMnO₃. We show the development of a Fermi surface where mobile electrons coexist with heavier carriers, strongly coupled polarons. The latter originate from a boost of the electron-phonon interaction (EPI). This finding brings to light the role that the EPI can play in MITs even caused by purely electronic mechanisms. Our discovery of the EPI-induced dichotomy of the charge carriers explains the transport response of Ce-doped CaMnO₃ and suggests strategies to engineer quantum matter from TMOs.

由于电子之间很强的库仑斥力，许多过渡金属氧化物（TMO）是Mott绝缘体，并表现出金属绝缘体过渡（MIT）的机理，人们对其机理并不总是很了解。与大多数TMO不同，CaMnO _3中的微小掺杂会诱导金属态，而没有任何结构转变。因此，该材料是探索通过MIT形成谱带的理想平台。在这里，我们使用角度分辨光发射光谱来观察电子如何在CaMnO _3中离域并耦合到声子。我们显示了费米表面的发展，其中移动电子与较重的载流子，强耦合极化子共存。后者源于电子-声子相互作用（EPI）的增强。这一发现揭示了EPI甚至可以由纯电子机制引起的在MIT中的作用。我们对EPI引起的电荷载体二分法的发现解释了Ce掺杂的CaMnO ₃的输运响应，并提出了从TMO改造量子物质的策略。