Direct probe of Mott-Hubbard to charge-transfer insulator transition and electronic structure evolution in transition-metal systems

Olalde-Velasco, P.; Jiménez-Mier, J.; Denlinger, Jonathan D.; Hussain, Zahid; Yang, Wanli

doi:10.1103/physrevb.83.241102

Cited by 61 publications

(80 citation statements)

References 30 publications

(21 reference statements)

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“…The optical conductivity shows an interesting structure: the absorption edge is around 3.3 and 3.6 eV for ZnCu 3 (OH) 6 6 Cl 2 , we find significant anisotropy.…”

Section: Cumentioning

confidence: 73%

“…To conclude, with this study we unveil the nature of optical excitations in the frustrated kagome-lattice Mott insulators ZnCu 3 (OH) 6 Cl 2 and Y 3 Cu 9 (OH) 19 Cl 8 by means of optical spectroscopy and density functional theory calculations. We identify the edge of the charge-transfer band at 3.3 and 3.6 eV in the experimental spectra, respectively, in good agreement with calculations corresponding to transitions from the ligand states to the Cu-d upper Hubbard band with an on-site Coulomb interaction of 8 eV.…”

Section: Cumentioning

confidence: 91%

“…3 (a), which appear inside the charge transfer gap (inset panel b). They are visible in the experiment as a double peak around 1-2 eV causing the blue-green color of the ZnCu 3 (OH) 6 Cl 2 and Y 3 Cu 9 (OH) 19 Cl 8 crystals. The intensity is small since, as discussed above, these transitions are only possible because the ligand orbitals penetrate the vicinity of the Cu site and get re-expanded into the l = 1 and l = 3 harmonics.…”

Section: Cumentioning

confidence: 92%

“…In other words, the tails of surrounding orbitals are re-expanded around the transition-metal site as a linear combination of the transition-metal s- This is, in a nutshell, the physics we want to address. We have chosen herbertsmithite-type compounds, ZnCu 3 (OH) 6 Cl 2 and Y 3 Cu 9 (OH) 19 Cl 8 as our testing ground, for the following reasons: (i) they have, as we will show, sizeable Mott-Hubbard correlation gaps of the order of 3 eV, and thus leave a window of transparency at lower energies where we expect the d-d excitations to manifest themselves; (ii) while intensively studied by magnetic and thermodynamic probes [7-10, 14, 23-29], optical investigations focused only on the low-energy excitations and phonons [30][31][32] and the details of the band structure of these materials have not been well characterized; even such basic parameters, extremely important for theoretical models, such as the Coulomb repulsion U and the hierarchy of the crystal field levels, have not been determined reliably in experiment so far. Hence, our goal is twofold: to fill a lacuna in the characterization of these intensely studied compounds and to gain insight into the physics of the local d-d optical excitations.…”

Section: Cumentioning

confidence: 99%

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Nature of optical excitations in the frustrated kagome compound herbertsmithite

et al. 2017

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Optical conductivity measurements are combined with density functional theory calculations in order to understand the electrodynamic response of the frustrated Mott insulators Herbertsmithite ZnCu3(OH)6Cl2 and the closely-related kagome-lattice compound Y3Cu9(OH)19Cl8. We identify these materials as charge-transfer rather than Mott-Hubbard insulators, similar to the high-Tc cuprate parent compounds. The band edge is at 3.3 and 3.6 eV, respectively, establishing the insulating nature of these compounds. Inside the gap, we observe dipole-forbidden local electronic transitions between the Cu 3d orbitals in the range 1-2 eV. With the help of ab initio calculations we demonstrate that the electrodynamic response in these systems is directly related to the role of on-site Coulomb repulsion: while charge-transfer processes have their origin on transitions between the ligand band and the Cu 3d upper Hubbard band, local d-d excitations remain rather unaffected by correlations.Since the discovery of high-T c cuprates, the physics of strongly correlated materials has been at the forefront of research in condensed matter physics. The relationship between correlations, unconventional superconductivity, quantum-spin-liquid behavior and other exotic states of matter has been intensely debated. While at the level of model theories one can introduce criteria to quantify the degree of correlation, such as the ratio U/W , where U is the on-site Coulomb repulsion and W is the singleparticle bandwidth, the quantification in many materials is not that straightforward. The effect of correlations usually shows up as mass renormalization, band narrowing, or as opening or enhancement of the band gap [1, 2]. Cu+2 ions are, arguably, the most strongly correlated among d transition metals [3][4][5][6]. They are key ingredients of high-T c cuprates and have been widely investigated in the last decades. A recent revival of interest in Cu-based materials was triggered by the discovery of geometrically frustrated cuprates that seem to exhibit spin-liquid properties [7][8][9][10][11][12][13][14][15][16] and may even harbor unconventional superconductivity with higher angular momenta than existing superconductors [17] or further topological phases [18] although synthesis seems to be difficult [19].In this work we investigate the origin of the optical excitations in the spin-liquid candidate Herbertsmithite and concentrate on the following conceptual issue: which measurable properties in correlated systems are strongly affected by correlation effects and which are not? We will show, experimentally and theoretically, that in a single experimental probe, namely optical conductivity, one can simultaneously observe properties dramatically influenced by Coulomb (Mott-Hubbard) correlation effects, and those that are hardly affected at all.One can distinguish two types of optical absorption processes, depicted in Fig. 1. On the one hand, we have the "charge-transfer process", that in its simple form can be described as creating a hole and an electron res...

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“…The optical conductivity shows an interesting structure: the absorption edge is around 3.3 and 3.6 eV for ZnCu 3 (OH) 6 6 Cl 2 , we find significant anisotropy.…”

Section: Cumentioning

confidence: 73%

Section: Cumentioning

confidence: 91%

Section: Cumentioning

confidence: 92%

Section: Cumentioning

confidence: 99%

See 2 more Smart Citations

Nature of optical excitations in the frustrated kagome compound herbertsmithite

et al. 2017

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“…(10) In the case of transitionmetal fluorides, a continuous transition from Mott-Hubbard to charge-transfer semiconductor has been observed across the first-row transition metals. (11) If the composition is changed from fluorine to oxygen, however, considering the electronegativity difference alone is not sufficient to define the type of semiconductor, because of the larger extent of orbital mixing through interatomic covalent bonding in the oxide compounds. Among various transition-metal oxides, the thermodynamic stability and surface redox reactivity make cobalt oxide (Co 3 O 4 ) an important catalyst for CO oxidation, (12) Fischer-Tropsch synthesis, (13) cyclohexane dehydrogenation, (14) and the oxygen evolution reaction in water splitting.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Photo-Induced Charge Transfer and Hot Carrier Relaxation Pathways in Spinel Cobalt Oxide (Co₃O₄)

et al. 2014

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The identities of photoexcited states in thin-film Co 3 O 4 and the ultrafast carrier relaxation dynamics of Co 3 O 4 are investigated with oxidation-state-specific pump−probe femtosecond core level spectroscopy. A thin-film sample is excited near the 2.8 eV optical absorption peak, and the resulting spectral changes at the 58.9 eV M 2,3edge of cobalt are probed in transient absorption with femtosecond highorder harmonic pulses generated by a Ti/sapphire laser. The initial transient state shows a significant 2 eV redshift in the absorption edge compared to the static ground state, which indicates a reduction of the cobalt valence charge. This is confirmed by a charge transfer multiplet spectral simulation, which finds the experimentally observed extreme ultraviolet (XUV) spectrum matches the specific O 2− (2p) → Co 3+ (e g ) charge-transfer transition, out of six possible excitation pathways involving Co 3+ and Co 2+ in the mixed-valence material. The initial transient state has a power-dependent amplitude decay (190 ± 10 fs at 13.2 mJ/cm 2 ) together with a slight redshift in spectral shape (535 ± 33 fs), which are ascribed to hot carrier relaxation to the band edge. The faster amplitude decay is possibly due to a decrease of charge carrier density via an Auger mechanism, as the decay rate increases when more excitation fluence is used. This study takes advantage of the oxidation-state-specificity of time-resolved XUV spectroscopy, further establishing the method as a new approach to measure ultrafast charge carrier dynamics in condensed-phase systems.

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Reversible Anionic Redox Activities in Conventional LiNi_1/3Co_1/3Mn_1/3O₂ Cathodes

Lee

Kim

et al. 2020

Angewandte Chemie

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Redox reactions of oxygen have been considered critical in controlling the electrochemical properties of lithium‐excessive layered‐oxide electrodes. However, conventional electrode materials without overlithiation remain the most practical. Typically, cationic redox reactions are believed to dominate the electrochemical processes in conventional electrodes. Herein, we show unambiguous evidence of reversible anionic redox reactions in LiNi1/3Co1/3Mn1/3O2. The typical involvement of oxygen through hybridization with transition metals is discussed, as well as the intrinsic oxygen redox process at high potentials, which is 75 % reversible during initial cycling and 63 % retained after 10 cycles. Our results clarify the reaction mechanism at high potentials in conventional layered electrodes involving both cationic and anionic reactions and indicate the potential of utilizing reversible oxygen redox reactions in conventional layered oxides for high‐capacity lithium‐ion batteries.

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Direct probe of Mott-Hubbard to charge-transfer insulator transition and electronic structure evolution in transition-metal systems

Cited by 61 publications

References 30 publications

Nature of optical excitations in the frustrated kagome compound herbertsmithite

Nature of optical excitations in the frustrated kagome compound herbertsmithite

Characterization of Photo-Induced Charge Transfer and Hot Carrier Relaxation Pathways in Spinel Cobalt Oxide (Co₃O₄)

Reversible Anionic Redox Activities in Conventional LiNi_1/3Co_1/3Mn_1/3O₂ Cathodes

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Direct probe of Mott-Hubbard to charge-transfer insulator transition and electronic structure evolution in transition-metal systems

Cited by 61 publications

References 30 publications

Nature of optical excitations in the frustrated kagome compound herbertsmithite

Nature of optical excitations in the frustrated kagome compound herbertsmithite

Characterization of Photo-Induced Charge Transfer and Hot Carrier Relaxation Pathways in Spinel Cobalt Oxide (Co3O4)

Reversible Anionic Redox Activities in Conventional LiNi1/3Co1/3Mn1/3O2 Cathodes

Contact Info

Product

Resources

About

Characterization of Photo-Induced Charge Transfer and Hot Carrier Relaxation Pathways in Spinel Cobalt Oxide (Co₃O₄)

Reversible Anionic Redox Activities in Conventional LiNi_1/3Co_1/3Mn_1/3O₂ Cathodes