Inelastic neutron scattering study on the electronic transition in ( Pr1−yYy)1−x

Abstract

The perovskite Co oxides Pr1−xCaxCoO3 exhibit at around x ∼ 0.5 an unusual transition at temperature TS [Tsubouchi et al. Phys. Rev. B 66 052418 (2002).] with no space group change and no long range magnetic order. We measured inelastic neutron scattering intensities of magnetic excitations I(Q, ω) for two single crystals of (Pr1−yYy)1−xCaxCoO3 in which the x-region of the transition is widened by the Pr-site doping, to study whether the recent proposal of the excitonic condensation model is relevant to this "hidden order transition" of the system. While the χ"(Q, ω) seems to have characteristics of strongly correlated Co 3d electrons above TS, it abruptly exhibits a weak feature reminiscent of a pseudogap-like structure at TS with decreasing T. The first peak of the Pr crystal-field-excitations has also been observed at low temperatures. Here, using a model of the coexistence of the exciton condensed phase (EC phase) with the nearly or weakly ferromagnetic one, we show that the EC phase appears as the collective transition in Pr1−xCaxCoO3.

Phase diagram of the (Pr1−ySmy)0.7Ca0.3CoBréard1, Veillon2, Hervé3 et al. 2022Phys. Rev. Materials1000View full textAdd to dashboardCite

“…Investigation of the closely related (Pr 1−y Eu y ) 0.7 Ca 3 CoO 3 showed the same qualitative behavior, with y crit ∼ 0.19 [11]. The most studied system in VSST literature is (Pr 1−y Y y ) 0.7 Ca 3 CoO 3 , owing to the fact that Y 3+ is nonmagnetic, which facilitates the analysis [10,14,27,30,32,[38][39][40]. However, the size difference with Pr 3+ is quite strong [41], which makes it difficult to follow the emergence of the VSST.…”

Strong enhancement of magnetic susceptibility induced by spin-nematic fluctuations in an excitonic insulating system with spin-orbit coupling

“…We expect that the fluctuations appear as a gapped mode due to the SOC. Indeed, a low-energy gapped excitation has been observed by the inelastic neutron scattering [52]. This might correspond to the fluctuation of the spin nematicity of the HS or IS states but the detailed relationship remains a future issue.…”

Emergence of pure spin current in doped excitonic magnets

“…A number of transition-metal oxides have been regarded as candidates for the excitonic magnets. For example, some kinds of cobalt oxides with the d 6 electron configuration were suggested to be the spin-triplet excitonic magnets [19][20][21][22][23], where the electrons in the e g orbitals and holes in the t 2g orbitals form excitonic pairs. Also, Ca 2 RuO 4 with the d 4 electron configuration was suggested to be an excitonic magnet [24][25][26].…”