Layered MAX phases (M: transition metal, A: III-A, IV-A group elements, X: C or N) are the parent materials of MXenes, which have recently received attention as a new atomic layer system and are known as industrial materials for applications owing to their excellent properties, which combine the characteristics of both metals and ceramics. Meanwhile, the bulk electronic structure of MAX phases has primarily been investigated using computational methods, primarily because well-characterized single crystals are few. This review presents anomalous electronic states such as Dirac points and line nodes, which have been observed in recent electronic structure studies pertaining to MAX phase single-crystals using angle-resolved photoemission spectroscopy. These states are expected to result in unique topological quantum transport in MAX phases.

A device that converts thermal energy into extractable forms, such as mechanical energy, is termed as a heat engine. The operating medium that powers the heat engine is usually a physical system that follows classical physics. In recent years, research on heat engines, whose operating media follow quantum physics, has been progressing from theoretical and experimental perspectives. In this study, we focus primarily on the theoretical aspects, particularly on how the performance of this type of quantum heat engine improves with an increase in the size of the operating medium. We discuss the research background, recent trends in this field, and our latest findings. The results presented here suggest a significant potential for enhancing heat engine performance by leveraging quantum mechanics as the operating principle.