Optical Evidence for Symmetry Changes above the Néel Temperature of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>KCuF</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>

Deisenhofer, J.; Leonov, I.; Erëmin, M. V.; Kant, Ch.; Ghigna, Paolo; Mayr, F.; Iglamov, V. V.; Анисимов, В. И.; Marel, D. van der

doi:10.1103/physrevlett.101.157406

Cited by 50 publications

(48 citation statements)

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“…Such Hybrid functional ideas can also be used in the DFT+U method, where the U parameter was replaced with the adjustable Fock exchange 30 . As mentioned above, the anisotropic optical conductivity [16][17][18]20 could provide us with some useful information about orbital ordering. The inter-band optical conductivity is calculated from the converged Kohn-Sham wave functions |ψ nk and eigen values E n (k) by using the following Kubo formula 20,31 (in Ry units):…”

Section: Methods and Detailsmentioning

confidence: 99%

“…However, several experiments [14][15][16][17][18][19] have been developed to detect the anisotropy induced by the spin and orbital orderings. Among them, the measurement of anisotropic optical conductivity [16][17][18] using polarized light could provide us with some useful information. Here, we reported the optical conductivity calculated from first-principles 20 .…”

Section: Introductionmentioning

confidence: 99%

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First-principles study on the orbital ordering of KCrF3

Wang

Zheng

et al. 2011

Phys. Rev. B

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The electronic, magnetic and orbital structures of KCrF3 in its recently identified crystallographic phases (tetragonal and cubic) [S. Margadonna and G. Karotsis, J. Am. Chem. Soc. 128, 16436 (2006)] are studied by first principles method. In the tetragonal phase, both the generalized gradient approximation (GGA) and the GGA+U calculations show that the ground state is the A-type antiferromagnetic (A-AFM) configuration with G-type orbital ordering pattern. Our calculations show that the orbital structures and the magnetic configurations can be measured by the optical conductivity. In the cubic state, the GGA calculations show that the ground state is a ferromagnetic half metal state, while the GGA+U (U ef f =3.0 eV) calculations show that the A-AFM insulator phase is the ground state. Our calculations indicate that the electron-electron interactions rather than the electron-phonon interactions are the driving forces behind the orbital ordering.

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Section: Methods and Detailsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

First-principles study on the orbital ordering of KCrF3

Wang

Zheng

et al. 2011

Phys. Rev. B

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“…It is argued that these dynamic distortions freeze in at a temperature T S = 50 K, leading to an effectively lower symmetry and the occurrence of exciton-magnon sidebands in optical absorption experiments [27].…”

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confidence: 99%

Phononic and magnetic excitations in the quasi-one-dimensional Heisenberg antiferromagnet KCuF3

Gnezdilov

Lemmens

Wulferding

et al. 2012

Low Temperature Physics

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The Raman-active phonons and magnetic excitations in the orbitally ordered, quasi-one-dimensional Heisenberg antiferromagnet KCuF 3 are studied as a function of temperature in the range between 3 and 290 K in various scattering configurations. The low-energy E g and B 1g phonon modes show an anomalous softening (~25% and ~13%) between room temperature and the characteristic temperature T S = 50 K. In this temperature range a freezing-in of F -ion dynamic displacements is proposed to occur. In addition, the E g mode at about 260 cm -1 clearly splits below T S . The widths of the phonon lines above T S follow an activated behavior with an activation energy of about 50 K. Our observations clearly evidence a reduction of the lattice symmetry below T S and indicate a strong coupling of lattice, spin, and orbital fluctuations for T > T S . A strongly polarization dependent quasielastic scattering is observed at temperatures above T N = 39 K due to magnetic-energy fluctuations. For temperatures below T N a rich spectrum of additional modes is observed, with different lineshape, polarization and temperatures dependence. We attribute them to longitudinal and transverse magnetic modes as well as to a continuum of magnetic excitations.

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“…The JT effect is also a key ingredient for understanding the colossal magnetoresistance in manganites [10][11][12][13].…”

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confidence: 99%

Unusual ferroelectricity induced by the Jahn-Teller effect: A case study on lacunar spinel compounds

Xiang

2015

Phys. Rev. B

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The Jahn-Teller effect refers to the symmetry-lowering geometrical distortion in a crystal (or non-linear molecule) due to the presence of a degenerate electronic state.Usually, the Jahn-Teller distortion is not polar. Recently, GaV4S8 with the lacunar spinel structure was found to undergoes a Jahn-Teller distortion from cubic to ferroelectric rhombohedral structure at TJT = 38K. In this work, we carry out a general group theory analysis to show how and when the Jahn-Teller effect gives rise to ferroelectricity. On the basis of this theory, we find that the ferroelectric Jahn-Teller distort in GaV4S8 is due to the non-centrosymmetric nature of the parent phase and strong electron-phonon interaction related to two low-energy T2 phonon modes.Interestingly, GaV4S8 is not only ferroelectric, but also ferromagnetic with the magnetic easy axis along the ferroelectric direction. This suggests that GaV4S8 is a multiferroic in which an external electric field may control its magnetization direction.Our study not only explains the Jahn-Teller physics in GaV4S8, but also paves a new way for searching and designing new ferroelectrics and multiferroics.

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Optical Evidence for Symmetry Changes above the Néel Temperature ofKCuF3

Cited by 50 publications

References 32 publications

First-principles study on the orbital ordering of KCrF3

First-principles study on the orbital ordering of KCrF3

Phononic and magnetic excitations in the quasi-one-dimensional Heisenberg antiferromagnet KCuF3

Unusual ferroelectricity induced by the Jahn-Teller effect: A case study on lacunar spinel compounds

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