Recent discoveries of a new type of quantum criticality arising from Yb-valence fluctuations in Yb-based metal in periodic crystal and quasicrystal have opened a new class of quantum critical phenomena in correlated electron systems. To clarify whether this new concept can be generalized to other rare-earth-based semimetal and insulator, we study SmS which exhibits golden-black phase transition under pressure. By constructing the model for SmS, we show that Coulomb repulsion between 4 f and 5d orbitals at Sm drives first-order valence transition (FOVT) and semimetal-toinsulator transition (MIT) simultaneously, which explains the golden-black phase transition. We clarify the ground-state phase diagram for the FOVT and MIT by identifying the quantum critical point of the FOVT. We find that exciton condensates in both semimetal and insulator phases. Our result explains measured peak anomalies in the specific heat and compressibility in pressurized golden SmS and provides a cue to clarify recently-observed anomalies in black SmS.

中文翻译：

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SmS 中价态和半金属到绝缘体转变的相互作用

最近发现的一种新型量子临界性由周期晶体和准晶体中 Yb 基金属的 Yb 价态波动引起，开启了相关电子系统中一类新的量子临界现象。为了阐明这个新概念是否可以推广到其他基于稀土的半金属和绝缘体，我们研究了在压力下表现出金黑色相变的 SmS。通过构建 SmS 模型，我们表明 Sm 处 4 f 和 5d 轨道之间的库仑排斥同时驱动一阶价跃迁 (FOVT) 和半金属-绝缘体跃迁 (MIT)，这解释了金黑色相变。我们通过确定 FOVT 的量子临界点来阐明 FOVT 和 MIT 的基态相图。我们发现激子在半金属和绝缘体相中凝聚。