Lifshitz Transitions in 122-Pnictides Under Pressure
Abstract
We demonstrate, using T=0 first principles total energy calculations, that observed pressure-driven anomalies in the entire 122-pnictides family (AFe2As2; A = alkali earth element Ca, Sr, Ba) can be understood as consequences of Lifshitz transitions (LTs) Lifshitz60. Our results for energy band dispersions and spectra, lattice parameters, enthalpies, magnetism, and elastic constants over a wide range of hydrostatic pressure provide a coherent understanding of multiple transitions in these compounds, namely, enthalpic, magnetic and tetragonal (T) - collapsed tetragonal (cT) transitions. In particular, the T-cT transition and anomalies in lattice parameters and elastic properties, observed at finite temperatures, are interpreted as arising from proximity to T=0 Lifshitz transitions, wherein pressure causes non-trivial changes in the Fermi surface topology in these materials.
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