From antiferromagnetic insulator to correlated metal in pressurized and doped LaMnPO

Abstract

Widespread adoption of superconducting technologies awaits the discovery of new materials with enhanced properties, especially higher superconducting transition temperatures T c . The unexpected discovery of high T c superconductivity in cuprates suggests that the highest T c s occur when pressure or doping transform the localized and moment-bearing electrons in antiferromagnetic insulators into itinerant carriers in a metal, where magnetism is preserved in the form of strong correlations. The absence of this transition in Fe-based superconductors may limit their T c s, but even larger T c s may be possible in their isostructural Mn analogs, which are antiferromagnetic insulators like the cuprates. It is generally believed that prohibitively large pressures would be required to suppress the effects of the strong Hund's rule coupling in these Mn-based compounds, collapsing the insulating gap and enabling superconductivity. Indeed, no Mn-based compounds are known to be superconductors. The electronic structure calculations and X-ray diffraction measurements presented here challenge these long held beliefs, finding that only modest pressures are required to transform LaMnPO, isostructural to superconducting host LaFeAsO, from an antiferromagnetic insulator to a metallic antiferromagnet, where the Mn moment vanishes in a second pressure-driven transition. Proximity to these charge and moment delocalization transitions in LaMnPO results in a highly correlated metallic state, the familiar breeding ground of superconductivity. correlated electron systems | electronic delocalization transition S uperconductivity with high transition temperatures T c was first found near an electron delocalization transition (EDT) in the cuprates, and subsequently in systems as diverse as quasi-two dimensional organic layer compounds (1), heavy fermions (2, 3), and endohedrally doped fullerides (4). One obstacle to achieving a higher T c in the Fe-based superconductors may be that the parent compounds are metallic (5-7), albeit with quasiparticle mass enhancements (8) that suggest varying degrees of proximity to an EDT (9-11). So far no insulating parent compounds have been identified that can, by analogy to the cuprates, be doped to achieve higher superconducting transition temperatures. It is possible that the recently isolated K 2 Fe 4 Se 5 (12) and La 2 O 2 Fe 2 OðSe; SÞ 2 (13) phases may prove to be the first compounds of this type. In contrast, isostructural Mn-based compounds often have large insulating gaps and ordered moments (14, 15), suggesting their suitability as possible parent compounds. At present there are no known Mn-based superconductors, however, and it is generally believed that the Hund's rule coupling in Mn compounds is prohibitively strong, so that doping will not reduce the overall scale of the correlations to the point at which superconductivity may become possible. The electronic structure calculations and X-ray diffraction measurements presented here show how the interplay of Hund's rule interactions with incr...

Magnetic interactions in iron superconductors: A review

“…The specific heat enhancement is even larger in CsFe 2 As 2 and RbFe 2 As 2 [201,202], isovalent to KFe 2 As 2 . Moreover, half-filled Mn-compounds BaMn 2 As 2 and LaMnPO with 5 electrons in the 5 d-orbitals are insulators [203,204] and the strongly electron-doped compound BaCo 2 As 2 with 7 electrons in the 5 d-orbitals shows a small mass enhacement [205] m ∼ 1.4.…”

Antiferromagnetism in semiconductingSrMn2Sb2andBaMn2Sb2single crystals

“…They tend to have a simple checkerboard (G-type) AFM structure, indicating stronger ab-plane nearest-neighbor (NN) exchange interactions J 1 compared to twice the next-nearest-neighbor interactions J 2 , i.e., J 1 > 2J 2 [3]. A high-pressure measurement on LaMnPO showed a semiconductor to metal transition at a pressure of 10 GPa [38]. Fluorine-doped LaMnPO 1−x F x also exhibits an insulator-to-metal transition on doping which only weakly affects T N and μ [39], similar to La 1−x Sr x MnAsO [40].…”

Insulator-to-metal transition and large thermoelectric effect in La 1−x Sr x MnAsO

“…36 Another recent report shows evidence of metallization by F doping as well as under high pressures. 22 And it reveals that F doping in LaMnPO hardly changes the Neel temperature and the Mn local-moment. 22 Similarly, the Sr doping probably does not suppress the magnetic order of Mn so much in LMAO.…”

“…22 And it reveals that F doping in LaMnPO hardly changes the Neel temperature and the Mn local-moment. 22 Similarly, the Sr doping probably does not suppress the magnetic order of Mn so much in LMAO. This suggests that in most Mn-based pnictides the doping-induced carriers dominantly have the As 4p attribute, while the local moment of 3d electrons is preserved.…”

“…18 But it was only after the discovery of Fe-bsed superconductors that there has been growing research activities on this type of material. 10,11,[19][20][21][22][23][24][25][26] The apparent valence of Mn in LnMnP nO is 2+, thus the Mn ions have the electronic configuration of d 5 , i.e., the valence electrons fill half the 3d shell. Therefore, the Mn-based 1111 pnictides would be a Mott insulator, similar to the parent compound of cuprate superconductors, provided that the intrasite Coulomb correlation is high enough.…”