P. Ganesh, "Understanding phase-transitions in correlated quantum materials"

Abstract

One of the most promising route for manipulating the properties of correlated solids for technological applications is through controlled perturbations via atomic-defects, doping, stoichiometry, strain as well as heterostructuring. However the mechanisms that drive the electronic, magnetic and/or topological transitions in these materials and the specific role of these perturbations is not fully understood. For example, the perovskite SrCoO3 is a ferromagnetic metal, while the oxygen-deficient (n-doped) brownmillerite SrCoO2.5 is an antiferromagnetic insulator.  Similarly, 2D materials such as MnBi2Te4 and WTe2 show different topological phases depending on how they are stacked or heterostructured, while layered CuInP2S6 show layer dependent ferroelectricity with multi-well character, with large anharmonicity [1,2]. Inducing local strain via ion-implantation or dimensional confinement can modify magnetic and related properties in correlated metals such as PdCoO2 and TbMn6Sn6.  The challenge in predicting and understanding these behaviors from the intricate couplings of charge, spin, orbital, and lattice degrees of freedom. These at times challenge standard modeling approaches, requiring either significant empiricism or adoption of new methodologies to make progress. As such, in addition to using density functional theory,  we also outline our use of the highly accurate ab initio quantum Monte Carlo (QMC) approach to address these challenges. To control computational costs, we have developed a protocol of using QMC results to validate more scalable approaches via magnetic moments, charge densities, and thermodynamic properties. We present results for bulk and heterostructures of VO2[3,4], our model for how doping controls the metal-insulator transition in the correlated-perovskites[5], the role of defects in inducing transitions in MnBi2Te4 [6] and PdCoO2 systems, and effects of stacking and dimensional confinement in MnBi2Te4 and TbMn6Sn6  [8] following this protocol.  

References

1. Brehm etl al., Nature Materials, 19, 43 (2020)
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3. P. Ganesh et al. . Physical Review B 101 155129 (2020).
4. Q. Lu et al. Scientific Reports 10 1 (2020).
5. M. Bennett et al. Physical Review Research 4 L022005 (2022).
6. M. Bennett et al. https://arxiv.org/abs/2204.04268 (2022)
7. A. Annaberdiyev et. al., https://arxiv.org/abs/2302.01903 (2023)