Scaling of the Coulomb pseudopotential in s-wave narrow-band superconductors

Park, Tae-Ho; Choi, Han-Yong

doi:10.1103/physrevb.65.052504

Cited by 49 publications

(71 citation statements)

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“…For example, the moment of Co in anatase TiO 2 increases from 0.73 to 0.83 B by means of GGA+ U method. The magnetic behavior of Co, Mn, Fe, and Ni-doped anatase TiO 2 is similar to the findings of Park et al 16 The difference between numerical values of the magnetic moments calculated by us and these authors 16 may be due to the use of different muffin-tin radii.The relative phase stability changes when the dopant concentration is increased to 12.5%. Note that for this concentration, we have chosen two different sites for the dopants in both anatase and rutile structures ͑Fig.…”

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confidence: 85%

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Origin of the anatase to rutile conversion of metal-dopedTiO2

Jena

2009

Phys. Rev. B

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Extensive calculations using density functional theory enable us to explain the origin of the surprising room-temperature conversion of anatase to rutile phase of TiO 2 when doped with Co and Ni, but not with Cu. Contrary to earlier suggestion, neither high spin nor strain of the transition metals is found to be responsible for this phase conversion. The driving mechanism, instead, is attributed to the increased interaction between Co and Ni atoms forming a linear chain in the rutile phase. We predict that Cr and Mn which have even larger spins than Co and Ni cannot induce this phase conversion.Growing interest in the study of TiO 2 semiconductor stems from its current use in photovoltaics, 1 electrochromics, 2 sensors, 3 and photocatalysis. 4 In the ground state TiO 2 exists in the anatase phase and undergoes transition to the rutile phase at temperatures well in excess of 600°C. 5 Since the optical and electrical properties of anatase and rutile TiO 2 are distinctly different, it is desirable to be able to control phase content and conversion between these two phases. In particular, it has been suggested that, due to the novel semiconducting properties of the anatase/ rutile interface region, partial conversion from anatase to rutile phase may render TiO 2 with exciting photocatalytic properties. 6-8 Consequently, there has been considerable interest 9-11 in finding ways to induce this phase transition at lower temperatures. In a recent paper, Gole et al. 12 reported the surprising room-temperature phase conversion of anatase to rutile TiO 2 by using transition-metal ions with highly unpaired electron spins. They showed that Co, and to a lesser extent Ni, accomplishes this conversion, while it does not occur when Cu is used as a dopant. The authors attributed the origin of this phase conversion to the magnetic nature of Co and Ni.In this Rapid Communication we show that Ni in TiO 2 is nonmagnetic and Co doping continues to enable the phase conversion even after switching off the magnetic interaction. Furthermore, Cr and Mn whose atomic spins are larger than that of Co are also incapable of causing this phase transition. The origin of the phase conversion resulting from Co and Ni doping is found to be due to the increased interaction between these atoms as they form a linear chain in the rutile structure. Our studies also reveal some unusual magnetic behavior of Cu, Fe, and Cr when doped in TiO 2 : nonmagnetic Cu couples ferromagnetically, ferromagnetic ͑FM͒ Fe couples antiferromagnetically, and antiferromagnetic ͑AFM͒ Cr couples ferromagnetically.The relaxations in the lattice caused by the dopant atom͑s͒, the total energy, and the electronic structure were calculated using Vienna ab initio simulation package ͑VASP͒ ͑Ref. 13͒ and the projector augmented wave ͑PAW͒ ͑Ref. 14͒ method. The PAW generalized gradient approximation ͑GGA͒ ͑Ref. 15͒ potentials with the valence states 3d and 4s for Ti, Cr, Mn, Fe, Co, Ni, and Cu and 2s and 2p for O were used. High precision calculations with a cutoff energy of 400 eV for ...

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confidence: 85%

supporting

confidence: 85%

Origin of the anatase to rutile conversion of metal-dopedTiO2

Jena

2009

Phys. Rev. B

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“…If E binding is negative in the thermodynamic limit then the spinons will be confined, the first excitations will be integer spin excitations as expected in a Valence Bond Cristal. If E binding → 0 with ∆ spinon → ∆ 0 = 0 with increasing size, we then expect the spinons to be unconfined and the first excitations of the model are fractionalized [112,113,114,115,116,117,118] Using these three equations (Eqs. 5.5, 5.6, 5.7) for consecutive sizes one obtains an estimate of the binding energy for each sample size.…”

Section: Unconfined Spinons?mentioning

confidence: 99%

Frustrated Quantum Magnets

Lhuillier

Misguich

2002

High Magnetic Fields

140

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A description of different phases of two dimensional magnetic insulators is given.The first chapters are devoted to the understanding of the symmetry breaking mechanism in the semi-classical Néel phases. Order by disorder selection is illustrated. All these phases break SU (2) symmetry and are gapless phases with ∆S z = 1 magnon excitations.Different gapful quantum phases exist in two dimensions: the Valence Bond Crystal phases (VBC) which have long range order in local S=0 objects (either dimers in the usual Valence Bond acception or quadrumers..), but also Resonating Valence Bond Spin Liquids (RVBSL), which have no long range order in any local order parameter and an absence of susceptibility to any local probe. VBC have gapful ∆S = 0, or1 excitations, RVBSL on the contrary have deconfined spin-1/2 excitations. Examples of these two kinds of quantum phases are given in chapters 4 and 5. A special class of magnets (on the kagome or pyrochlore lattices) has an infinite local degeneracy in the classical limit: they give birth in the quantum limit to different behaviors which are illustrated and questionned in the last lecture.

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“…[30][31][32] A special case of the Kappa distribution is the general 3-parameter logistic distribution function FðxÞ:…”

Section: (B) Concentration Profilementioning

confidence: 99%

Thermodynamic Modeling of Polymer Solution Interface

Ghiass

Rey

2009

Macro Theory & Simulations

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A new method is presented to characterize the interfacial concentration field and interfacial tension between equilibrium polymer solution phases, using readily accessible equilibrium concentration data. The new method is tested and validated using experimental data from different polystyrene solutions and it consists of i) calculation of a universal expression for the concentration gradient coefficient based on the Cahn‐Hilliard model and the Wolf interfacial tension master equation, and ii) development of a highly accurate algebraic function (Kappa distribution) that, for a given equilibrium polymer concentration set, yields the essentially exact interfacial profile predicted by the classical gradient theory for polymer solutions.magnified image

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Scaling of the Coulomb pseudopotential in s-wave narrow-band superconductors

Cited by 49 publications

References 9 publications

Origin of the anatase to rutile conversion of metal-dopedTiO2

Origin of the anatase to rutile conversion of metal-dopedTiO2

Frustrated Quantum Magnets

Thermodynamic Modeling of Polymer Solution Interface

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