The term quantum materials refers to materials whose properties are principally defined by quantum mechanical effects at macroscopic length scales and that exhibit phenomena and functionalities not expected from classical physics. Some key characteristics include reduced dimensionality, strong many-body interactions, nontrivial topology, and noncharge state variables of charge carriers. The field of quantum materials has been a topical area of modern materials science for decades, and is at the center stage of a wide range of modern technologies, ranging from electronics, photonics, energy, defense, to environmental and biomedical sensing. Over the past decade, much research effort has been devoted to the development of quantum materials with phenomena and functionalities that manifest at high temperature and feature unprecedented tunability with atomic-scale precision. This thriving research field has witnessed a number of seminal breakthroughs and is now poised to rise to the challenges in a new age of quantum information science and technology. This issue summarizes and reviews recent progress in selected topics, and also provides perspective for the future directions of emergent quantum materials in the years to come.

In probing quantum materials, thermal transport is less appreciated than electrical transport. This article aims to show the pivotal role that thermal transport may play in understanding quantum materials—longitudinal thermal transport reflects itinerant quasiparticles, even in an electrical insulating phase, while transverse thermal transport such as the thermal Hall and Nernst effects is tightly linked to nontrivial topology. We discuss three examples—quantum spin liquids wherein thermal transport identifies its existence, superconductors wherein thermal transport reveals the superconducting gap structure, and topological Weyl semimetals where the anomalous Nernst effect is a consequence of nontrivial Berry curvature. We conclude with an outlook on the unique insights thermal transport may offer to probe a much broader category of quantum phenomena.

Two-dimensional (2D) quantum materials offer a unique platform to explore mesoscopic phenomena driven by interfacial and topological effects. Their tunable electric properties and bidimensional nature enable their integration into sophisticated heterostructures with engineered properties, resulting in the emergence of new exotic phenomena not accessible in other platforms. This has fostered many studies on 2D ferromagnetism, proximity-induced effects, and quantum transport, demonstrating their relevance for fundamental research and future device applications. Here, we review ongoing progress in this lively research field with special emphasis on spin-related phenomena.

Low-dimensional superconductors have been at the forefront of physics research due to their rich physical properties such as high-temperature (Tc) superconductivity. In this article, we review the field of emergent high-Tc superconductivity at interfaces of heterostructures, focusing on the experimental advances and its physical mechanism. Charge transfer between constituent materials leads to two-dimensional carrier confinement that facilitates occurrence of superconductivity at the interface. We discuss the similarities between bulk high-Tc superconductors and interface systems, as well as implications from a survey of interface superconductors. We expect that the hybrid heterostructures and the ability to manipulate them on an atomic scale could be an enormously fertile ground to explore superconductivity with higher critical temperature Tc.

Topological quantum materials are a class of compounds featuring electronic band structures, which are topologically distinct from common metals and insulators. These materials have emerged as exceptionally fertile ground for materials science research. The topologically nontrivial electronic structures of these materials support many interesting properties, ranging from the topologically protected states, manifesting as high mobility and spin-momentum locking, to various quantum Hall effects, axionic physics, and Majorana modes. In this article, we describe different topological matters, including topological insulators, Weyl semimetals, twisted graphene, and related two-dimensional Chern magnetic insulators, as well as their heterostructures. We focus on recent materials discoveries and experimental advancements of topological materials, and their heterostructures. Finally, we conclude with prospects for the discovery of additional topological materials for studying quantum processes, quasiparticles and their composites, as well as exploiting potential applications of these materials.

An indirect exciton (IX), also known as an interlayer exciton, is a bound pair of an electron and a hole confined in spatially separated layers. Due to their long lifetimes, IXs can cool below the temperature of quantum degeneracy. This provides an opportunity to experimentally study cold composite bosons. This article overviews our studies of cold IXs, presenting spontaneous coherence and Bose–Einstein condensation of IXs and phenomena observed in the IX condensate, including the spatially ordered exciton state, commensurability effect of exciton density wave, spin textures, Pancharatnam–Berry phase, long-range coherent spin transport, and interference dislocations.

Gold nanoparticles (AuNPs) are one of the most versatile and accessible classes of nanomaterials. Their chemical stability, ease of colloidal synthesis, surface functionalization, and plasmonic resonance—tunable from the visible through the near-infrared—have made AuNPs the metal nanoparticle of choice for many applications. This article summarizes the chemical synthesis of AuNPs, particularly gold nanorods, with a focus on recent developments in shape control and surface modifications. Current applications using the photothermal properties of AuNPs, as well as AuNP connections to biology and the environmental sciences, will be discussed.