Polaronic nature of a muonium-related paramagnetic center in SrTiO3

Ito, Takashi U.; Higemoto, Wataru; Koda, A.; Shimomura, K.

doi:10.1063/1.5125919

Cited by 12 publications

(12 citation statements)

References 27 publications

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“…Moreover, the emergence of the second Mu 0 states with a greater A d below ∼5 K coexisting with the diamagnetic state [53] recalls the situation in ZnO. Recent studies on Mu in SrTiO 3 have also reported electronic states similar to TiO 2 [55], where the localized moment at the Ti site is as large as ∼0.33µ B , suggesting a more strongly localized state (small polaron-like) than that in TiO 2 .…”

Section: Mu In Insulating/semiconducting Oxidessupporting

confidence: 56%

“…Thus, considering that the local atomic configuration of Mu/H is almost identical between ZnO and IGZO [58], the strong electron-phonon coupling is another important factor to enhance the localization of electrons around the OMu − complex. This invokes the precaution that the activation energy for the promotion from Mu 0 D to Mu + D cannot be simply attributed to ε + ; it includes the contribution of the adiabatic potential barrier for the electron between the localized state and the continuous state [55]. The effect of the electron-phonon coupling has also been theoretically investigated in terms of the duality of the conduction band carriers in TiO 2 and SrTiO 3 , which can be in both the continuous state and the deep level (self-trapped) state in the gap [95].…”

Section: Polaron States Mimicking Donor-like Mumentioning

confidence: 99%

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Ambipolar Property of Isolated Hydrogen in Oxide Materials Revealed by Muon

Hiraishi,

Okabe,

Koda

et al. 2021

Preprint

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The study on the electronic state of muon as pseudo-hydrogen (represented by the elemental symbol Mu) by muon spin rotation has long been appreciated as one of the few methods to experimentally access the electronic state of dilute hydrogen (H) in semiconductors and dielectrics. Meanwhile, theoretical predictions on the electronic state of H in these materials by first-principles calculations using density functional theory (DFT) do not always agree with the observed states of Mu, standing as an obstacle to integrating the findings of both Mu and H. In order to address this issue, we have re-examined the vast results of previous Mu studies in insulating/semiconducting oxides by paying special attention to the non-equilibrium character and the ambipolarity of Mu. As a result, we established a semi-quantitative model that enables systematic understanding of the electronic states of Mu in most oxides. First of all, Mu often occurs simultaneously in a neutral (Mu 0 ) and a diamagnetic state (Mu + or Mu − ) in wide-gap oxides, while DFT calculations predict that H is stable only for one of the charged states with the polarity determined by the equilibrium charge-transition level (E +/− ). Our model considers that Mu can form complex defects with both oxygen (Mu D ) and cations (Mu A ), resulting in a relaxed-excited state accompanying respective donor or acceptor levels (E +/0 or E −/0 ) corresponding to those predicted by the DFT calculations for H, and that their initial yields are determined by the interaction with Muinduced excitons. Furthermore, by introducing the assumption that the stability of these two states including their valence is determined by i) the relative position of E ±/0 in the energy band structure of the host and ii) a potential barrier associated with the transition between Mu D and Mu A , we find that the known experimental results can be explained systematically in accordance with E ±/0 . The model also reveals some common properties of Mu-related defects which were previously regarded as individual anomalies. One is the polaron-like nature of the electronic states associated with shallow donor Mu complexes, for which we argue a Copernican shift of the viewpoint to the Mu + D -bound excitons. Another is the fast diffusion of Mu 0 A , which is understood by the isolated feature of the acceptor-like electronic states. The possible impacts of these findings to a wide range of insulating compounds is discussed by drawing on examples including GaN, FeS 2 , and NaAlH 4 as key materials for the green technologies.

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Section: Mu In Insulating/semiconducting Oxidessupporting

confidence: 56%

Section: Polaron States Mimicking Donor-like Mumentioning

confidence: 99%

Ambipolar Property of Isolated Hydrogen in Oxide Materials Revealed by Muon

Hiraishi,

Okabe,

Koda

et al. 2021

Preprint

Self Cite

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“…Thus, we are confident in assigning S 1 to C + . This assignment directly implies that the f 2 → f 1 transition around 225 K corresponds to a charge-state transition from neutral to positive, which we characterize as a complex dissociation [30], i.e. a separation of the polaron and the oxygen-bound muon, rather than an ionization of the bound electron to the conduction band.…”

mentioning

confidence: 89%

“…Since isolated H is extremely hard to study directly, most information about its dopant characteristics comes from the study of muonium (Mu=[µ + e − ]), a light H analog with virtually identical electronic structure, which is experimentally accessible via the muon-spin-rotation (µSR) technique [24][25][26][27]. Recent µSR studies reported polaronic Mu centers in non-magnetic TMOs such as SrTiO 3 and TiO 2 [28][29][30], in which an oxygen-bound, positive muon and a small polaron located on a neighboring TM ion form an overall charge-neutral complex, suggesting that isolated H defects form analogous H-polaron centers. Recently, muon-polaron complexes have been shown to exist in the antiferromagnet Cr 2 O 3 [31].…”

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confidence: 99%

Local Electronic Structure and Dynamics of Muon-Polaron Complexes in Fe2O3

et al. 2021

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We perform detailed muon spin rotation (µSR) measurements in the classic antiferromagnet Fe2O3 and explain the spectra by considering dynamic population and dissociation of charge-neutral muonpolaron complexes. We show that charge-neutral muon states in Fe2O3, despite lacking the signatures typical of charge-neutral muonium centers in non-magnetic materials, have a significant impact on the measured µSR frequencies and relaxation rates. Our identification of such polaronic muon centers in Fe2O3 suggests that isolated hydrogen (H) impurities form analogous complexes, and that H interstitials may be a source of charge carrier density in Fe2O3.

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“…Such configurations have been observed recently in experiments on TiO 2 and SrTiO 3 . [17][18][19] The well-defined hyperfine lines of these states indicate that the muon -electron (polaron) complex is formed promptly (in the ns time range) after implantation. The muon -polaron concept was also applied in Ref.…”

mentioning

confidence: 98%