Low-temperature solid-state cooling: from classical to quantum materials

Low-temperature environments are essential for advances in fundamental physics, materials science, and quantum technologies. From gas-compression refrigeration to modern solid-state cooling, the pursuit of lower temperatures reflects a deepening understanding of matter. Solid-state cooling harnesses entropy changes associated with various microscopic degrees of freedom in condensed-matter systems, offering the potential of high stability, compactness, and efficiency. Driven by the rise of quantum technology and the scarcity of helium, new principles and technologies of solid-state refrigeration have become increasingly important. This work reviews thermoelectric, magnetocaloric, and multicaloric effects from a thermodynamic perspective and their relationship, highlighting how quantum materials—with their coupled degrees of freedom and quantum fluctuations—open new pathways toward efficient low-temperature cooling.