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García‐Fernández, Pablo; Sousa, Carmen; Aramburu, J. A.; Barriuso, M. T.; Moreno, M.

doi:10.1103/physrevb.72.155107

Cited by 27 publications

(27 citation statements)

References 37 publications

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“…While k′/k = 0.28 for NaCl:Rh 2+ , 61 a much higher value k′/k = 2.9 has been obtained for NaCl:Ni + . This result strongly supports that in the last case the NiCl 6 5− complex is elastically coupled to the rest of the lattice and thus it can reasonably be expected that g′ > g. This reasoning thus explains why V 3a is negative for NaCl:Rh 2+ while it can be positive for the present case.…”

Section: Inorganic Chemistrymentioning

confidence: 83%

“…A central point in the present analysis is to understand why the sign of the anharmonic parameter, V 3a , is found to be positive in NaCl:Ni + , while it is clearly negative for NaCl:Rh 2+ . As has been pointed out before, in NaCl:Rh 2+ the RhCl 6 4− complex is practically elastically decoupled from the rest of the lattice, 61,21 while this situation is likely not to be true for NaCl:Ni + , where Ni + and Na + are both monovalent ions. A simple model 61,21 for clarifying the two different situations is depicted in Figure 6.…”

Section: Inorganic Chemistrymentioning

confidence: 96%

“…As has been pointed out before, in NaCl:Rh 2+ the RhCl 6 4− complex is practically elastically decoupled from the rest of the lattice, 61,21 while this situation is likely not to be true for NaCl:Ni + , where Ni + and Na + are both monovalent ions. A simple model 61,21 for clarifying the two different situations is depicted in Figure 6. In such a figure, a given ligand, X, is attached to the impurity ion, M, as well as to the closest A host lattice cation along a ⟨100⟩ direction.…”

Section: Inorganic Chemistrymentioning

confidence: 96%

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Origin of Small Barriers in Jahn–Teller Systems: Quantifying the Role of 3d–4s Hybridization in the Model System NaCl:Ni⁺

Barriuso¹,

Ortiz-Sevilla²,

Aramburu³

et al. 2013

Inorg. Chem.

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Despite its relevance, the microscopic origin of the energy barrier, B, between the compressed and elongated geometries of Jahn−Teller (JT) systems is not well understood yet because of a lack of quantitative data about its various contributions. Seeking to clear up this matter, we have carried out both periodic and cluster ab initio calculations on the model system NaCl:Ni + . This system is particularly puzzling because, according to experimental data, its barrier is much smaller than that for other d 9 and d 7 ions in similar lattices. All calculations performed on the model system lead, in fact, to values |B| ≤ 160 cm −1 , which are certainly smaller than B = 500 cm −1 derived for NaCl:M 2+ (M = Ag, Rh) or B = 1024 cm −1 obtained for KCl:Ag 2+ . As a salient feature, analysis of calculations carried out as a function of the Q θ (∼3z 2 − r 2 ) coordinate unveils the microscopic origin of the barrier. It is quantitatively proven that the elongated geometry observed for NaCl:Ni + is due to the 3d−4s vibronic admixture, which is slightly larger than the anharmonicity in the e g JT mode that favors a compressed geometry. The existence of these two competing mechanisms explains the low value of B for the model system, contrary to cases where the complex formed by d 9 or d 7 ions is elastically decoupled from the host lattice. Although the magnitude of B for NaCl:Ni + is particularly small, the tunneling splitting, 3Γ, is estimated to be below 9 cm −1 , thus explaining why the coherence is easily destroyed by random strains and thus a static JT effect is observed experimentally. As a main conclusion, the barrier in JT systems cannot be understood neglecting the tiny changes of the electronic density involved in small distortions. The present calculations reasonably explain the experimental g tensor of NaCl:Ni + , pointing out that the d−d transitions in NiCl 6 5− are much smaller than those for CuCl 6 4− and the optical electronegativity of Ni + is only around 1.

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Section: Inorganic Chemistrymentioning

confidence: 83%

Section: Inorganic Chemistrymentioning

confidence: 96%

Section: Inorganic Chemistrymentioning

confidence: 96%

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Origin of Small Barriers in Jahn–Teller Systems: Quantifying the Role of 3d–4s Hybridization in the Model System NaCl:Ni⁺

Barriuso¹,

Ortiz-Sevilla²,

Aramburu³

et al. 2013

Inorg. Chem.

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“…These relevant facts, whose actual origin is discussed in Refs. 43,51,53 , support that in irradiated AgCl the hole is in a x 2 -y 2 -type orbital. Accordingly, as AgCl has the rocksalt structure the polaron motion should involve jumps from the hole in a x 2 -y 2 orbital in the initial site to x 2 -y 2 , x 2 -z 2 or y 2 -z 2 orbitals belonging to close silver sites.…”

Section: Non-degenerate Two-site Polaron Modelmentioning

confidence: 95%

“…This very common situation is called static Jahn-Teller effect. In this case, the introduction of a hole involves two distortions, one associated to the symmetric a1g breathing mode of the complex and another to the eg Jahn-Teller mode involved in the distortion of the octahedral complex towards a tetragonal symmetry 43 .…”

Section: Non-degenerate Two-site Polaron Modelmentioning

confidence: 99%

Stability and Polaronic Motion of Self-Trapped Holes in Silver Halides: Insight through DFT+UCalculations

et al. 2016

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Polarons and their associated transport properties are a field of great current interest both in chemistry and physics. In order to further our understanding of these quasi-particles, we have carried out first-principles calculations of self-trapped holes (STH) in the model compounds AgCl and AgBr, where extensive experimental information exists. Our calculations confirm that the STH solely stabilizes in AgCl but with a binding energy of only 165 meV, an order of magnitude smaller than that found for the Vk center in KCl. Key contributions to this stabilization energy come from the local relaxation along breathing (a1g) and Jahn-Teller (eg) modes in the AgCl6 4-unit. In order to study the transfer of the STH among silver sites we (i) use first-principles calculations to obtain the hopping barrier of the STH to first and second neighbors, involving eight distinct paths, using firstprinciples and (ii) construct a simple model, based on Slater-Koster parameters, that highlights the similarity of polaron transfer with magnetic superexchange. This allows one understanding why the movement of STH to second neighbors is highly enhanced with respect to closer ones. In agreement with experimental data and the model, the present calculations prove the existence of a dominant mechanism of polaronic motion that corresponds to the displacement of the STH to the next nearest sites in the <100> direction and a small barrier of 37 meV. This mechanism is dominated by the covalency inside a AgX6 4-complex (X:Cl;Br) thus explaining why the STH is not stabilized in AgBr following the increase of covalency due to the ClBr substitution. The present calculations confirm that ~10% of the charge associated with the STH in AgCl is lying outside the AgCl6 4-complex. This fact is behind the differences between optical and magnetic properties of the STH in AgCl and those observed in KCl:Ag 2+ .2

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A Genuine Jahn–Teller System with Compressed Geometry and Quantum Effects Originating from Zero‐Point Motion

et al. 2016

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First-principle calculations together with analysis of the experimental data found for 3d(9) and 3d(7) ions in cubic oxides proved that the center found in irradiated CaO:Ni(2+) corresponds to Ni(+) under a static Jahn-Teller effect displaying a compressed equilibrium geometry. It was also shown that the anomalous positive g∥ shift (g∥ -g0 =0.065) measured at T=20 K obeys the superposition of the |3 z(2) -r(2) ⟩ and |x(2) -y(2) ⟩ states driven by quantum effects associated with the zero-point motion, a mechanism first put forward by O'Brien for static Jahn-Teller systems and later extended by Ham to the dynamic Jahn-Teller case. To our knowledge, this is the first genuine Jahn-Teller system (i.e. in which exact degeneracy exists at the high-symmetry configuration) exhibiting a compressed equilibrium geometry for which large quantum effects allow experimental observation of the effect predicted by O'Brien. Analysis of the calculated energy barriers for different Jahn-Teller systems allowed us to explain the origin of the compressed geometry observed for CaO:Ni(+) .

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Coherent tunneling inCu2+- andAg2+-doped MgO and

Cited by 27 publications

References 37 publications

Origin of Small Barriers in Jahn–Teller Systems: Quantifying the Role of 3d–4s Hybridization in the Model System NaCl:Ni⁺

Origin of Small Barriers in Jahn–Teller Systems: Quantifying the Role of 3d–4s Hybridization in the Model System NaCl:Ni⁺

Stability and Polaronic Motion of Self-Trapped Holes in Silver Halides: Insight through DFT+UCalculations

A Genuine Jahn–Teller System with Compressed Geometry and Quantum Effects Originating from Zero‐Point Motion

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Coherent tunneling inCu2+- andAg2+-doped MgO and

Cited by 27 publications

References 37 publications

Origin of Small Barriers in Jahn–Teller Systems: Quantifying the Role of 3d–4s Hybridization in the Model System NaCl:Ni+

Origin of Small Barriers in Jahn–Teller Systems: Quantifying the Role of 3d–4s Hybridization in the Model System NaCl:Ni+

Stability and Polaronic Motion of Self-Trapped Holes in Silver Halides: Insight through DFT+UCalculations

A Genuine Jahn–Teller System with Compressed Geometry and Quantum Effects Originating from Zero‐Point Motion

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Origin of Small Barriers in Jahn–Teller Systems: Quantifying the Role of 3d–4s Hybridization in the Model System NaCl:Ni⁺

Origin of Small Barriers in Jahn–Teller Systems: Quantifying the Role of 3d–4s Hybridization in the Model System NaCl:Ni⁺