Novel physical properties in 5d electronic materials (2024)

Along with the gradually expanding scope of material research, more and more 5d electronic-related materials are entering our vision. Particularly, the variation of the radial distribution function and strong spin-orbit coupling (SOC) effect of 5d lectrons enables the discovery of novel physical properties. Compared with 3d and 4d electrons, 5d electrons have their orbits further expanded in real space, thus forming competition between the strong spin-orbit coupling and electronic correlation, which results in a great number of novel quantum properties. Such strong spin-orbit coupling is accompanied by the splitting of energy levels and the generation of new electronic states, which subsequently triggers the breaking of space and time symmetry and brings about new quantum effects, including spin Hall effect, Rashba effect, topological surface state, magnetic skyrmion, and Weyl semi-metal [1], [2], [3], [4]. Of note, the excellent properties of 5d electronic materials have found unique applications. For example, the representative storage device HfO₂[5] and the representative transistor material WS2 [6,7] are considered the most powerful candidates of the next-generation material system in their respective industrial fields.

Owing to the complex behavior of 5d electrons and the lack of appropriate characterization methods, the physical mechanism of these novel physical properties of 5d electronic materials remains unclear. In terms of theoretical calculation, when using the first-principles methods (such as density functional theory) to calculate the energy band structure, the amount of calculation is usually increased by two orders of magnitude [8,9] due to the strong spin-orbit coupling of 5d electronic materials, which deters high-precision large system calculations. In addition to the correlation effect of the 5d electronic material system that cannot be simply ignored, we have to face an important problem of how to efficiently describe the electronic structure of 5d electronic materials and thus calculate the properties of ground and excited states. In terms of material preparation, despite the successful preparation of materials with theoretically excellent performance (such as WS₂), there is still a huge gap to bridge between their performance and the theoretical limit [10]. The characterization of more novel physical properties relies on the continued improvement of characterization technology. Further exploration is therefore needed to develop targeted detection methods for different properties, as well as to study the cooperative observation and correlation between various parameters of materials.

Although several systems of 5d electronic materials still have a long way to go towards practical application, it is necessary to sketch ahead a scientific research layout considering the huge potential of this field. In fact, 5d electronic material systems have received increasing widespread research attention and are set to become one of the key directions in material research. Benefiting from the synergistic development of advanced theoretical systems, precise material construction, comprehensive material characterization and excellent device applications, a top-down development trend in the field of 5d electronic materials research can be seen. However, it should not be overlooked that due to the specificity and complexity of 5d electrons, there are still lots of unknown aspects of 5d electronic materials from theory to application. Therefore, it is necessary to focus on the key scientific issues of 5d materials as well as deepen the interdisciplinary intersection between physics, materials, information and other disciplines to promote the development of 5d electronic materials field. This special topic of Fundamental Research, with its theme on novel physical properties in 5d electronic materials, collects three review articles concerning the theoretical design, material preparation and device application of 5d electronic system. Du etal. [11] focused on two-dimensional ferroelectric materials with 5d electrons, reviewed the latest progress in theoretical prediction of the system, and summarized the rational design strategy of two-dimensional ferroelectric materials. Yu etal. [12] introduced the representative progress in iridium oxide heterostructures in material preparation and field control, and commented on the existing problems and promising future directions. From the perspective of phase stability and domain structure, Zhou etal. [13] gave an overview of the applications of ferroelectric thin films and memory devices based on HfO₂, and discussed the latest progress and challenges of relevant ferroelectric storage devices. We hope that this collection may help further the understanding of 5d electronic materials, clarify the new effects and physical essence of the strong spin-orbit coupling of 5d electronic materials, and speed up the application of 5d electronic materials.

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