Direct Spectroscopic Observation of a Shallow Hydrogenlike Donor State in Insulating<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>SrTiO</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Salman, Z.; Prokscha, T.; Amato, A.; Morenzoni, E.; Scheuermann, R.; Sedlák, Kamil; Suter, A.

doi:10.1103/physrevlett.113.156801

Cited by 26 publications

(23 citation statements)

References 52 publications

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“…There are some important discrepancies between this µ + SR study and the preceding work by Salman et al 18 They determined the principal values of the hyperfine coupling tensor A ′ as 1.4(1), 6.7(1), and 11.5(1) MHz from µ + SR frequencies observed at 25 K in ZF. Because the dipolar part in A ′ should be traceless, the coefficient of the isotropic part is estimated as Tr[A ′ ]/3 = 6.5(1) MHz, which is comparable in magnitude with the largest principal value.…”

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confidence: 79%

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Polaronic nature of a muonium-related paramagnetic center in SrTiO3

Ito

Higemoto

Koda

et al. 2019

Applied Physics Letters

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The hyperfine features and thermal stability of a muonium (Mu)-related paramagnetic center were investigated in the SrTiO 3 perovskite titanate via muon spin rotation spectroscopy. The hyperfine coupling tensor of the paramagnetic center was found to have prominent dipolar characteristics, indicating that the electron spin density is dominantly distributed on a Ti site to form a small polaron near an ionized Mu + donor. Based on a hydrogen-Mu analogy, interstitial hydrogen is also expected to form such a polaronic center in the dilute doping limit. The small activation energy of 30(3) meV found for the thermal dissociation of the Mu + -polaron complex suggests that the strain energy required to distort the lattice is comparable to the electronic energy gained by localizing the electron.Electron doping into an archetypal perovskite titanate, SrTiO 3 , results in intriguing physical properties such as superconductivity 1 and ferromagnetism, 2 and can help form a two-dimensional (2D) electron gas system at the LaAlO 3 /SrTiO 3 heterointerface. 3,4 This makes electrondoped SrTiO 3 a promising material for emerging oxide electronics. For many of its applications, it is crucial to determine whether excess electrons form either free or trapped carriers. However, experimental studies on (La, Nb)-doped or oxygen-deficient SrTiO 3 seem contradictory on this point. Optical conductivity and dc transport measurements showed that excess electrons behave as free carriers or large polarons having bandlike characteristics. 5,6 On the other hand, photoemission spectroscopy (PES) studies revealed an incoherent in-gap state, which can be associated with small polarons, and its coexistence with a coherent delocalized state. 7 The Kondo effect observed in an electric field-effect-induced 2D electron system in SrTiO 3 also suggests the coexistence of free and trapped carriers. 8 Although many theoretical studies have been conducted to understand such puzzling phenomena, 9-11 the origin of the dual electron behavior in n-type SrTiO 3 remains unclear.Interstitial hydrogen (H i ) also serves as a shallow donor in SrTiO 3 . 12 PES measurements on a SrTiO 3 (001) surface exposed to hot atomic hydrogen showed both in-gap and delocalized states. 13 This implies that small polarons can also exist in H i -doped SrTiO 3 . However, little is known about the microscopic nature of hydrogen dopants and doped electrons in bulk SrTiO 3 except for some insight provided by infrared (IR) and polarized Raman scattering spectroscopies 14-16 and positive muon spin rotation (µ + SR) spectroscopy. 17,18 . Further experimental investigations are required to fully elucidate the role of H i in bulk SrTiO 3 and better understand the behavior of excess electrons in n-type SrTiO 3 . a) ito.takashi15@jaea.go.jp Since hydrogen and muonium (Mu: a µ + -e − bound state) have almost the same reduced mass, the µ + SR technique has been extensively used for the study of hydrogen-related defects in condensed matter. [17][18][19][20][21][22][23] In this letter, we report a d...

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confidence: 79%

“…In Ref. [ 18 ], TF dependences of paramagnetic frequencies at 25 K below 12 mT were analyzed with A ′ expressed in the laboratory frame using two sets of Euler angles. The high-field extension of paramagnetic frequency shifts calculated with these parameters is shown in Fig.…”

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confidence: 99%

Polaronic nature of a muonium-related paramagnetic center in SrTiO3

Ito

Higemoto

Koda

et al. 2019

Applied Physics Letters

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“…Using a simple one-dimensional model allowed to determine the nearsurface/interface electric field profile inside the sample. This kind of investigation recently revealed the presence of a shallow hydrogen donor state in SrTiO 3 with decreasing ionization energy at the surface 61 . It can be extended to semiconductors or semiconductor heterostructures with not too high doping levels ( < ∼ 10 17 cm −3 ) and defect concentrations ( < ∼ 10 16 cm −3 ).…”

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confidence: 92%

Depth dependence of the ionization energy of shallow hydrogen states in ZnO and CdS

et al. 2014

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The characteristics of shallow hydrogen-like muonium (Mu) states in nominally undoped ZnO and CdS (0001) crystals have been studied close to the surface at depths in the range of 10 nm -180 nm by using low-energy muons, and in the bulk using conventional µSR. The muon implantation depths are adjusted by tuning the energy of the low-energy muons between 2.5 keV and 30 keV. We find that the bulk ionization energy Ei of the shallow donor-like Mu state is lowered by about 10 meV at a depth of 100 nm, and continuously decreasing on approaching the surface. At a depth of about 10 nm Ei is further reduced by 25 -30 meV compared to its bulk value. We attribute this change to the presence of electric fields due to band bending close to the surface, and we determine the depth profile of the electric field within a simple one-dimensional model.

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“…insulating regions). 31 Second, in the case of an undoped STO film, muonium formation was previously shown to occur at 70 K, 32 far from the 20 K upturn in the trilayer wTF data. Finally, muonium formation is often suppressed in metallic materials such as STO quantum wells that contain highly confined 2DELs.…”

Section: Resultsmentioning

confidence: 92%

Quasistatic antiferromagnetism in the quantum wells of SmTiO3/SrTiO3 heterostructures

et al. 2018

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High carrier density quantum wells embedded within a Mott insulating matrix present a rich arena for exploring unconventional electronic phase behavior ranging from non-Fermi-liquid transport and signatures of quantum criticality to pseudogap formation. Probing the proposed connection between unconventional magnetotransport and incipient electronic order within these quantum wells has however remained an enduring challenge due to the ultra-thin layer thicknesses required. Here we address this challenge by exploring the magnetic properties of high-density SrTiO 3 quantum wells embedded within the antiferromagnetic Mott insulator SmTiO 3 via muon spin relaxation and polarized neutron reflectometry measurements. The one electron per planar unit cell acquired by the nominal d 0 band insulator SrTiO 3 when embedded within a d 1 Mott SmTiO 3 matrix exhibits slow magnetic fluctuations that begin to freeze into a quasistatic spin state below a critical temperature T *. The appearance of this quasistatic well magnetism coincides with the previously reported opening of a pseudogap in the tunneling spectra of high carrier density wells inside this film architecture. Our data suggest a common origin of the pseudogap phase behavior in this quantum critical oxide heterostructure with those observed in bulk Mott materials close to an antiferromagnetic instability.

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Direct Spectroscopic Observation of a Shallow Hydrogenlike Donor State in InsulatingSrTiO3

Cited by 26 publications

References 52 publications

Polaronic nature of a muonium-related paramagnetic center in SrTiO3

Polaronic nature of a muonium-related paramagnetic center in SrTiO3

Depth dependence of the ionization energy of shallow hydrogen states in ZnO and CdS

Quasistatic antiferromagnetism in the quantum wells of SmTiO3/SrTiO3 heterostructures

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