Excitons in Mott insulators

Wróbel, P.; Eder, R.

doi:10.1103/physrevb.66.035111

Cited by 28 publications

(37 citation statements)

References 11 publications

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“…18,19,20,21,22 The motion of a single particle is hindered by the interaction of its spin with the AF background. This can be described in terms of a spin polaron.…”

Section: B Hubbard Exciton and Orbital Ordermentioning

confidence: 99%

Mott-Hubbard exciton in the optical conductivity ofYTiO3andSmTiO3

et al. 2008

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In the Mott-Hubbard insulators YTiO3 and SmTiO3 we study optical excitations from the lower to the upper Hubbard band,The multi-peak structure observed in the optical conductivity reflects the multiplet structure of the upper Hubbard band in a multi-orbital system. Absorption bands at 2.55 and 4.15 eV in the ferromagnet YTiO3 correspond to final states with a triplet d 2 configuration, whereas a peak at 3.7 eV in the antiferromagnet SmTiO3 is attributed to a singlet d 2 final state. A strongly temperature-dependent peak at 1.95 eV in YTiO3 and 1.8 eV in SmTiO3 is interpreted in terms of a Hubbard exciton, i.e., a charge-neutral (quasi-)bound state of a hole in the lower Hubbard band and a double occupancy in the upper one. The binding to such a Hubbard exciton may arise both due to Coulomb attraction between nearest-neighbor sites and due to a lowering of the kinetic energy in a system with magnetic and/or orbital correlations. Furthermore, we observe anomalies of the spectral weight in the vicinity of the magnetic ordering transitions, both in YTiO3 and SmTiO3. In the G-type antiferromagnet SmTiO3, the sign of the change of the spectral weight at TN depends on the polarization. This demonstrates that the temperature dependence of the spectral weight is not dominated by the spin-spin correlations, but rather reflects small changes of the orbital occupation.

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“…18,19,20,21,22 The motion of a single particle is hindered by the interaction of its spin with the AF background. This can be described in terms of a spin polaron.…”

Section: B Hubbard Exciton and Orbital Ordermentioning

confidence: 99%

Mott-Hubbard exciton in the optical conductivity ofYTiO3andSmTiO3

et al. 2008

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“…This CT excitation creates a Cu 1+ ion and an oxygen 2p hole that forms a ZhangRice singlet (ZRS)with the neighboring copper spin, the two copper sites forming a bound state [1]. Over the years, exciton formation of these electron-hole pairs has been considered by several authors as a possible low energy elementary excitation in this half-filled copper oxide plane [2,3,4,5,6,7,8]. The strong magnetic interaction in this system has been pointed to as the origin of the exciton binding energy [2] as well as the large dispersion of the excitation [4].…”

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confidence: 99%

Charge-transfer exciton inLa2CuO4probed with resonant inelastic x-ray scattering

et al. 2008

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We report a high-resolution resonant inelastic x-ray scattering study of La2CuO4. A number of spectral features are identified that were not clearly visible in earlier lower-resolution data. The momentum dependence of the spectral weight and the dispersion of the lowest energy excitation across the insulating gap have been measured in detail. The temperature dependence of the spectral features was also examined. The observed charge transfer edge shift, along with the low dispersion of the first charge transfer excitation are attributed to the lattice motion being coupled to the electronic system. In addition, we observe a dispersionless feature at 1.8 eV, which is associated with a d-d crystal field excitation.PACS numbers: 78.70. Ck, 74.25.Jb, As the prototypical parent insulating compound, La 2 CuO 4 has drawn much attention as a starting point for the study of high-temperature superconductors. La 2 CuO 4 is well described as an antiferromagnetic insulator with a d x 2 −y 2 hole localized at the Cu site due to the strong electron correlations. In particular, this material is classified as a charge-transfer (CT) insulator, since the lowest energy charge excitation across the insulating gap corresponds to transferring an electron from oxygen to a neighboring copper. This CT excitation creates a Cu 1+ ion and an oxygen 2p hole that forms a ZhangRice singlet (ZRS)with the neighboring copper spin, the two copper sites forming a bound state [1]. Over the years, exciton formation of these electron-hole pairs has been considered by several authors as a possible low energy elementary excitation in this half-filled copper oxide plane [2,3,4,5,6,7,8]. The strong magnetic interaction in this system has been pointed to as the origin of the exciton binding energy [2] as well as the large dispersion of the excitation [4]. Indeed the apparently large dispersion observed in Sr 2 CuO 2 Cl 2 using electron energy loss spectroscopy (EELS) was attributed to a CT exciton with a small effective mass [9].Experimentally, optical spectroscopy and Raman scattering studies have been carried out to address the nature of the excitation spectrum near this CT gap [10,11,12,13]. Ohana et al. directly observed the coupling of the electronic excitations to the lattice system in the resonance of phonon Raman lines at laser energies around the CT energy (2.14 eV) and a low-energy shoulder at 1.9 eV [10]. Falck et al. found that a polaron model was able to reproduce their reflectivity data very well for a wide temperature range [11]. However, despite extensive experimental and theoretical studies to date, the nature of the CT exciton is still controversial. Outstanding questions include whether the electron-hole pair actually form a bound exciton state, or if they remain as a resonance state within the particle-hole continuum. Another question relates to the relative role played by magnetic interactions and/or phonons in the exciton formation and dispersion. For each of these questions, valuable information can be gained by studying the momentum d...

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“…Já nos pacientes que têm diabetes mellitus podem ocorrer alterações de paladar, como consequência de neuropatias relacionadas ao diabetes (9).…”

Section: Diabetes E Doença Renalunclassified

“…Existem também os chamados fantasmas de sabor (fantogeusia) já relatados em pacientes com epilepsia e esquizofrenia. Existe também a xerostomia, onde as glândulas salivares podem reduzir o fluxo de saliva e, desta forma, os alimentos não são diluídos e não atingem o receptor, o que pode resultar em uma comida com gosto ruim (4,8,9). Já as desordens do sistema olfativo podem ser classificadas em: anosmia, que é a perda total de sensibilidade aos odores; hiposmia, definida como a diminuição da sensibilidade a odores; disosmia, distorção do olfato para alguns ou todos os odores, ou a percepção de odor na ausência de quaisquer odores (alucinação olfatória); hiperosmia, aumento da sensibilidade ao odor de alguns ou todos os estimulantes (odorantes); agnosia, incapacidade total ou parcial para identificar, classificar ou contrastar o odorante verbalmente, apesar de uma capacidade de reconhecer e distinguir entre odorantes (5,10) O levantamento bibliográfico realizado teve como objetivo compilar informações referentes a diferentes fatores que podem alterar esta percepção de sabor, e com isso, diminuir a qualidade de vida dos pacientes.…”

Section: Introductionunclassified

Fatores Que Alteram a Percepção De Sabor

Strapasson

Barreira

Wille

et al. 2013

Infarma

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The sense of taste is generally regarded as less important compared with vision and hearing. However, disturbances in this direction greatly reduce the pleasures of life and can lead to serious problems and may attorney is a life-threatening. Since, people with sensitivity to taste and odor may try to compensate for reduced losses by increasing the intake substances that may be harmful if ingested in excess. Furthermore, the sensory properties of foods play a role not only in determining their consumption, but also in determining satiety, food intake and selection of a meal. KEYWORDS: perception of flavor, taste disturbance factors RESUMOO sentido do paladar é geralmente considerado como menos importante em comparação com visão e audição. No entanto, distúrbios neste sentido diminuem consideravelmente os prazeres da vida e podem levar a problemas sérios, podendo atétornar-se um perigo de vida., já que, pessoas com sensibilidade a gosto e odor reduzidos podem tentar compensar as perdas através do aumento da ingestão de substâncias que podem ser prejudiciais se ingeridas em excesso. Além disso, as propriedades sensoriais dos alimentos desempenham um papel não somente na determinação do seu consumo, como também na determinação da saciedade, ingestão e seleção do alimento numa refeição.PALAVRAS CHAVE: percepção de sabor; fatores de alteração do paladar. INTRODUÇÃOOs sentidos do paladar e do olfato transmitem as propriedades atraentes de alimentos promovendo e mantendo a ingestão destes. Porém, quando estes aparelhos sensoriais apresentam transtornos, diminuem ou distorcem estes sentidos. O gosto e o cheiro dos alimentos podem se tornar desinteressantes ou até mesmo repugnantes, o que pode provocar diminuição do apetite, levando à ingestão de alimentos reduzida e comprometimento do estado nutricional. Pessoas com sensibilidade a gosto e odor reduzidos podem tentar compensar as perdas através do aumento da ingestão de substâncias que podem ser prejudiciais se ingeridas em excesso. Por exemplo, a redução do limiar do sabor doce -que normalmente acompanha o envelhecimento -pode levar idosos diabé-ticos a ingerir muito açúcar; perdas relacionadas à idade na percepção do sabor salgado podem ser prejudiciais a pessoas com hipertensão. Assim como a diminuição no paladar e no olfato também pode expor os doentes a substâncias nocivas, como: contaminantes ambientais e comida estragada (1-6) Estas desordens podem estar associadas a uma variedade de condições incluindo: a terapia de fármacos, distúrbios do sistema nervoso (doença de Alzheimer e a de Parkinson), estados de doença (problemas renais crô-nicos ou doença hepática crônica, localizadas no ouvido, nariz ou garganta e infecções virais), distúrbios endó-crinos (diabetes mellitus, hipotireoidismo e síndrome de Cushing), deficiências nutricionais, como redução dos níveis de zinco e vitaminas B3 e B12 e problemas nutricionais relacionados ao câncer, envelhecimento normal e poluição. Estas geralmente podem ser classificadas por três grandes tipos de perdas: perdas de ...

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Excitons in Mott insulators

Cited by 28 publications

References 11 publications

Mott-Hubbard exciton in the optical conductivity ofYTiO3andSmTiO3

Mott-Hubbard exciton in the optical conductivity ofYTiO3andSmTiO3

Charge-transfer exciton inLa2CuO4probed with resonant inelastic x-ray scattering

Fatores Que Alteram a Percepção De Sabor

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