With strong spin-orbit coupling, topological insulators have an insulating bulk state, characterized by a band gap, and a conducting surface state, characterized by a Dirac cone. Plasmons in topological insulators show high frequency-tunability in the mid-infrared and terahertz spectral regions with transverse spin oscillations, also called "spin-plasmons". This paper presents a discussion and review of the developments in this field from the fundamental theory of plasmons in bulk, thin-film, and surface-magnetized topological insulators to the techniques of plasmon excitation and future applications.

Abstract:The terahertz plasmon dispersion of a multilayer system consisting of graphene on dielectric and/or plasma thin layers is systematically investigated. We show that graphene plasmons can couple with other quasiparticles such as phonons and plasmons of the substrate; the characteristics of the plasmon dispersion of graphene are dramatically modified by the presence of the coupling effect. The resultant plasmon dispersion of the multilayer system is a strong function of the physical parameters of the spacer and the substrate, signifying the importance of the substrate selection in constructing graphene-based plasmonic devices.

PurposeThis study aims to examine the relationships among open innovation, organizational ambidexterity and firm performance. One important aspect of open innovation is that it enables a firm to develop its organizational ambidexterity capability and become more efficient in using this capability to improve its performance.Design/methodology/approachThe authors introduce a moderated mediation theoretical framework to reveal the bridging role of organizational ambidexterity in the effect of open innovation on firm performance. The theoretical model is empirically validated using survey data from 215 high-tech firms.FindingsThe authors find that open innovation plays a moderating role in the relationship between organizational ambidexterity and firm performance. Furthermore, organizational ambidexterity plays a significant mediating role in the relationship between open innovation and firm performance, and open innovation has a nonlinear, inverse U-shaped moderation effect on the relationship between organizational ambidexterity and firm performance.Research limitations/implicationsThis is one of the first studies to undertake a moderated mediation analysis by highlighting the mediating role of organizational ambidexterity and the moderating role of open innovation in influencing firm performance. The authors make a theoretical contribution to the field of open innovation and organizational behavior, and the authors provide concrete and feasible decision-making suggestions to decision makers adopting open innovation.Practical implicationsThe empirical results can help high-tech firm managers ascertain the organizational ambidexterity practices that can be employed and determine the level of open innovation to enhance firm performance.Originality/valueThis research provides new insights into whether and how firms can grasp the benefits of organizational ambidexterity to undertake open innovation activities. The findings not only contribute to advancing the mediating effect of organizational ambidexterity but also verify the inverse U-shaped moderation of open innovation in the relationship between organizational ambidexterity and firm performance.

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