Putative hybridization gap in CaMn2Bi2 under applied pressure

Abstract

We report electrical transport measurements on CaMn2Bi2 single crystals under applied pressure. At ambient pressure and high temperatures, CaMn2Bi2 behaves as a single-band semimetal hosting Néel order at TN = 150 K. At low temperatures, multi-band behavior emerges along with an activated behavior typical of degenerate semiconductors. The activation gap is estimated to be ∆ ∼ 20 K. Applied pressure not only favors the antiferromagnetic order at a rate of 0.40(2) K/kbar, but also enhances the activation gap at 20 kbar by about 70 %. This gap enhancement is typical of correlated narrow-gap semiconductors such as FeSi and Ce3Bi4Pt3, and places CaMn2Bi2 as a Mn-based hybridization-gap semiconductor candidate. Ab initio calculations based on the density functional theory are shown to be insufficient to describe the ground state of CaMn2Bi2. arXiv:1907.09984v1 [cond-mat.str-el]

Competition between electronic correlations and hybridization in CaMn$_{2}$Bi$_{2}$

“…Additional recent transport studies find a small activation gap between 2 -4 meV. 20 Our calculations yield a larger magnetic moment and energy gap, however our results improve upon those obtained using the HSE06 hybrid functional. 20 Previous studies on transition metal solids, including Fe, Co, Ni, and Mn, where SCAN was employed yielded the complex charge and noncollinear magnetic ordering that occurs at low temperatures, but with a slight enhancement of the magnetization.…”

“…The band gap is indirect with the transition from the conduction band and the valence band characterized by a change in crystal momentum from Γ to M . Overall, the band structure resembles the same obtained by the generalized gradient approximation 18,20 , except with a finite band gap. In contrast, the conduction bands obtained by the HSE06 hybrid functional (Ref.…”

“…20 Our calculations yield a larger magnetic moment and energy gap, however our results improve upon those obtained using the HSE06 hybrid functional. 20 Previous studies on transition metal solids, including Fe, Co, Ni, and Mn, where SCAN was employed yielded the complex charge and noncollinear magnetic ordering that occurs at low temperatures, but with a slight enhancement of the magnetization. 30 The enhancement is attributed to an oversensitivity of the iso-orbital indicator, α, used to discern various chemical bonding environments and is currently being amended.…”

“…18,19 In line with this claim, lowtemperature electrical transport measurements find a slight increase of the gap under pressure. 20 This type of behavior is akin to Ce 3 Bi 4 Pt 3 and other heavy fermion compounds. [21][22][23] Therefore, CaMn 2 Bi 2 could provide a link between the cuprates, pnictides, and heavy fermion systems.…”

Pressure dependence of room-temperature structural properties of CaAl2Si2

“…We believe that such a difficulty in empirical demonstration does not rule out our argument regarding the structural metastability of CaAl 2 Si 2 since empirical evidences of HPHT-induced metastability-related transition in CaAl 2 Si 2 -type compounds are well documented in, e.g., the isomorphous SrAl 2 Si 2 [26] and SrMn 2 P 2 [27] as well as in BaAl 2 Si 2 [7] (more detailed analysis will be reported in reference [19]). It is worth mentioning that the isomorphous CaMn 2 Bi 2 manifests a pressure-induced, room-temperature structural P 3m1 → P2 1 /m transition at P c ≈ 2.35 GPa [28,29]: in contrast to CaAl 2 Si 2 , the occurrence of such a transition signals an absence of both a metastable character and an energy barrier, however it is left to be verified if an HPHT treatment would be capable of effecting another P2 1 /m → I4/mmm transition.…”