Lifshitz metal–insulator transition induced by the all-in/all-out magnetic order in the pyrochlore oxide Cd₂Os₂O₇

Abstract

We investigate the metal-insulator transition (MIT) of the osmium pyrochlore oxide Cd 2 Os 2 O 7 through transport and magnetization measurements. The MIT and a magnetic transition to the all-in/all-out (AIAO) order occur simultaneously at 227 K. We propose a mechanism based on a Lifshitz transition induced by the AIAO magnetic order probably via strong spin-orbit couplings in the specific semimetallic band structure. It is suggested, moreover, that two observed puzzles, a finite conductivity near T = 0 and an emergence of weak ferromagnetic moments, are not bulk properties but originate at magnetic domain walls between two kinds of AIAO domains.

Robust ferromagnetism carried by antiferromagnetic domain walls

“…Similar conducting MDWs have also been suggested in Cd 2 Os 2 O 7 1017. Interestingly, weak ferromagnetism is observed below T N in both compounds1011; the origin remains unclear and we speculate it related to the MDWs.…”

“…On the other hand, microwave impedance microscopy successfully visualized the MDWs of Nd 2 Ir 2 O 7 , which indicates that the MDWs remain conducting even when the domains themselves become insulating1516. Similar conducting MDWs have also been suggested in Cd 2 Os 2 O 7 1017. Interestingly, weak ferromagnetism is observed below T N in both compounds1011; the origin remains unclear and we speculate it related to the MDWs.…”

“…In these compounds, 5 d electrons are conducting at high temperatures, while are completely localized at low temperatures to induce AIAO type magnetic orders; the metal-insulator (MI) transitions and magnetic orderings occur almost simultaneously at ~227 K in the osmate910 and at 34–110 K in the iridates1112. The crystal structure of Cd 2 Os 2 O 7 is shown in Fig.…”

Optical Spectroscopic Studies of the Metal-Insulator Transition Driven by All-In–All-Out Magnetic Ordering in5dPyrochloreCd2OsSohn1, Jeong2, Jin3 et al. 2015Phys. Rev. Lett.Self Cite265310View full textAdd to dashboardCite

“…We fixed T ¼ 200 K as we focused on a narrow T region from 180 to 219 K. For simplicity, we assumed that both the valance and conduction bands were 3D parabolic with the same m, although previous Hall measurements revealed that m of electrons is slightly smaller than that of holes [34]. We found that calculations without these assumptions gave similar results [31].…”

Crossover from itinerant to localized magnetic excitations through the metal-insulator transition inNaOsO3

“…Notably these MITs do not appear to be associated with any spontaneous structural symmetry breaking, placing them outside of the aforementioned Mott-Hubbard paradigm. Examples include some of the 5d 5 pyrochlore iridates R 2 Ir 2 O 7 (R = Ln 3+ ) [8,9], plus the 5d 3 osmates Cd 2 Os 2 O 7 [10][11][12][13] and NaOsO 3 . Various mechanisms have been proposed to describe these MITs, notably the Lifshitz and Slater mechanisms.…”