Pressure-Induced Site-Selective Mott Insulator-Metal Transition inFe2O3

Abstract

We provide experimental and theoretical evidence for a pressure-induced Mott insulator-metal transition in Fe 2 O 3 characterized by site-selective delocalization of the electrons. Density functional plus dynamical meanfield theory (DFT þ DMFT) calculations, along with Mössbauer spectroscopy, x-ray diffraction, and electrical transport measurements on Fe 2 O 3 up to 100 GPa, reveal this site-selective Mott transition between 50 and 68 GPa, such that the metallization can be described by ð VI Fe 3þHS Þ 2 O 3 ½R3c structure! 50 GPa ð VIII Fe 3þHS VI Fe M ÞO 3 ½P2 1 =n structure! 68 GPa ð VI Fe M Þ 2 O 3 ½Aba2=PPv structure. Within the P2 1 =n crystal structure, characterized by two distinct coordination sites (VI and VIII), we observe equal abundances of ferric ions (Fe 3þ) and ions having delocalized electrons (Fe M), and only at higher pressures is a fully metallic high-pressure structure obtained, all at room temperature. Thereby, the transition is characterized by delocalization/metallization of the 3d electrons on half the Fe sites, with a site-dependent collapse of local moments. Above approximately 50 GPa, Fe 2 O 3 is a strongly correlated metal with reduced electron mobility (large band renormalizations) of m à =m ∼ 4 and 6 near the Fermi level. Importantly, upon decompression, we observe a site-selective (metallic) to conventional Mott insulator phase transition ð VIII Fe 3þHS VI Fe M ÞO 3 ! 50 GPa ð VIII Fe 3þHS VI Fe 3þHS ÞO 3 within the same P2 1 =n structure, indicating a decoupling of the electronic and lattice degrees of freedom. Our results offer a model for understanding insulator-metal transitions in correlated electron materials, showing that the interplay of electronic correlations and crystal structure may result in rather complex behavior of the electronic and magnetic states of such compounds.

High-pressure magnetic, electronic, and structural properties ofMFe2O4(M=Mg,Greenberg1, Xu2, Nikolaevsky3 et al. 2017Phys. Rev. B312210View full textAdd to dashboardCite

“…These electronic transformations in Fe 3 O 4 coincide with another structural phase transition to the post-postspinel Pmma structure. All these features are characteristics of the multistage correlation breakdown process, confirming the concept of a site-selective Mott transition proposed recently in [44].…”

“…Thus, these postspinels remain, up to the highest pressures measured, semiconducting and paramagnetic with a mixed spin state: S = 5/2 and S = 1/2 for Fe 3+ populating eightcoordination and six-coordination sites, respectively. Recent studies of Fe 2 O 3 , hematite [44], provide experimental and theoretical evidence for a possible site-selective multistage correlation breakdown. They show that, in a material with a complex crystal structure, containing transition metal cation(s) in different environments (i.e.…”

Pressure-induced spin-state transition of iron in magnesiowüstite (Fe,Mg)O

“…The positions of the impurity atoms (Mg/Fe) were arranged to maximize the distance from each other [74] (Fe/Mg atoms are uniformly distributed over the unit cell; that is, we neglect the possible formation of the Fe/Mg clusters under pressure [75]). For simplicity, we neglect the local relaxation effects around the impurity Mg/Fe atoms, as well as the possible formation of a site-selective Mott-insulating phase with coexisting (within a unit cell) HS and LS iron sites [76]. In order to evaluate pressure, we fit our total-energy results to the third-order Birch-Murnaghan equation of state [77] separately for the HS and LS volume regions.…”

Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2019)

“…After DMFT had opened the way to study multi-band models, an "orbital selective" Mott MIT was identified [48]. Then, with the advent of DFT+DMFT, a "site selective" Mott MIT was found in Fe 2 O 3 [49]. We now illustrate the DFT+DMFT approach by its application to two paradigmatic materials, SrVO 3 and Fe.…”