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Traditionally, metal-insulator phase transition (MIT) in most well-established quantum materials is governed by the Mott-Hubbard mechanism, where strong electronic repulsion in the transition metals drives the system from a metallic to an insulating state. In addition, structural instability (Peierl’s transition) and the presence of lattice defects/disorders (Anderson transition) are also known to cause MIT in some materials. Concomitant with the MIT, strongly correlated materials can also undergo structural and magnetic phase transition due to their coupled spin, charge, and lattice degrees of freedom. However, as the mechanisms mentioned above explain the origin of the phase transition as driven by a single/double order parameter (either electronic and/or structural), independent control of the MIT with other degrees of freedom, such as magnetic ordering or structural symmetry, is challenging. Recently, magnetic stress has been predicted to drive the metal-insulator transition in materials exhibiting strong spin-lattice coupling. However, this mechanism lacks experimental validation and an in-depth understanding.
In this presentation, we will demonstrate the existence of the magnetic-stress-driven MIT in an archetypal material, chromium nitride (CrN), exhibiting strong magnetostructural coupling. Structural, electronic transport characterization and first-principles modeling analysis show that the phase transition temperature in CrN is directly proportional to the strain-controlled anisotropic magnetic stress. The compressive strain increases the magnetic stress, leading to the much-coveted room-temperature transition. In contrast, tensile strain and the inclusion of non-magnetic cations weaken the magnetic stress and reduce the transition temperature. This discovery of a new physical origin of metal-insulator phase transition that unifies spin, charge, and lattice degrees of freedom in correlated materials marks a new paradigm and could lead to novel device functionalities.
References
1. B. Biswas, S. Rudra, R. S. Rawat, N. Pandey, S. Acharya, A. Joseph, A. I. K. Pillai, M. Bansal, M. de h-Óra, D. P. Panda, A. B. Dey, F. Bertram, C. Narayana, J. MacManus-Driscoll, T. Maity, M. Garbrecht, and B. Saha, "Magnetic stress-driven metal-insulator transition in strongly correlated antiferromagnetic CrN " Phys. Rev. Lett., 131, 126302 (2023).
2. B. Biswas, S. Chakraborty, A. Joseph, S. Acharya, A. I. K. Pillai, C. Narayana, V. Bhatia, M. Garbrecht and B. Saha, "Secondary Phase Limited Metal-Insulator Phase Transition in Chromium Nitride Thin Films", Acta Materialia 227, 117737 (2022).
3. B. Biswas, S. Chakraborty, O. Chowdhury, D. Rao, A. I. K. Pillai, V. Bhatia, M. Garbrecht, J. P. Feser and B. Saha "In-plane Cr2N-CrN metal-semiconductor heterostructure with improved thermoelectric properties" Phys. Rev. Materials, 5, 114605 (2021).
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