First-order phase transition vs. spin-state quantum-critical scenarios in strain-tuned epitaxial cobaltite thin films

J. E. Dewey; V. Chaturvedi; T. A. Webb; P. Sharma; W. M. Postiglione; P. Quarterman; P. P. Balakrishnan; B. J. Kirby; L. Figari; C. Korostynski; A. Jacobson; T. Birol; R. M. Fernandes; A. N. Pasupathy; C. Leighton

arXiv · 2311.06127

First-order phase transition vs. spin-state quantum-critical scenarios in strain-tuned epitaxial cobaltite thin films

J. E. Dewey·V. Chaturvedi·T. A. Webb·P. Sharma·W. M. Postiglione·P. Quarterman·P. P. Balakrishnan·B. J. Kirby·L. Figari·C. Korostynski·A. Jacobson·T. Birol·R. M. Fernandes·A. N. Pasupathy·C. Leighton

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Abstract

Pr-containing perovskite cobaltites exhibit unusual valence transitions, coupled to coincident structural, spin-state, and metal-insulator transitions. Heteroepitaxial strain was recently used to control these phenomena in the model (Pr$_{1-y}$Y$_y$)$_{1-x}$Ca$_x$CoO$_{3-\delta}$ system, stabilizing a nonmagnetic insulating phase under compression (with a room-temperature valence/spin-state/metal-insulator transition) and a ferromagnetic metallic phase under tension, thus exposing a potential spin-state quantum critical point. The latter has been proposed in cobaltites and can be probed in this system as a function of a disorder-free variable (strain). We study this here via thickness-dependent strain relaxation in compressive SrLaAlO$_4$(001)/(Pr$_{0.85}$Y$_{0.15}$)$_{0.70}$Ca$_{0.30}$CoO$_{3-\delta}$ epitaxial thin films to quasi-continuously probe structural, electronic, and magnetic behaviors across the nonmagnetic-insulator/ferromagnetic-metal boundary. High-resolution X-ray diffraction, electronic transport, magnetometry, polarized neutron reflectometry, and temperature-dependent magnetic force microscopy provide a detailed picture, including abundant evidence of temperature- and strain-dependent phase coexistence. This indicates a first-order phase transition as opposed to spin-state quantum-critical behavior, which we discuss theoretically via a phenomenological Landau model for coupled spin-state and magnetic phase transitions.

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J. E. Dewey, V. Chaturvedi, T. A. Webb, P. Sharma, W. M. Postiglione, P. Quarterman, P. P. Balakrishnan, B. J. Kirby, L. Figari, C. Korostynski, A. Jacobson, T. Birol, R. M. Fernandes, A. N. Pasupathy, C. Leighton. 2023-11-10. First-order phase transition vs. spin-state quantum-critical scenarios in strain-tuned epitaxial cobaltite thin films. https://arxiv.org/abs/2311.06127

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