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Coupling and electrical control of structural, orbital and magnetic orders in perovskites.

Varignon J, Bristowe NC, Bousquet E, Ghosez P - Sci Rep (2015)

Bottom Line: Perovskite oxides are already widely used in industry and have huge potential for novel device applications thanks to the rich physical behaviour displayed in these materials.Based on universal symmetry arguments, we determine new lattice mode couplings that can provide exactly this paradigm, and exemplify the effect from first-principles calculations.The proposed mechanism is completely general, however for illustrative purposes, we demonstrate the concept on vanadium based perovskites where we reveal an unprecedented orbital ordering and Jahn-Teller induced ferroelectricity.

View Article: PubMed Central - PubMed

Affiliation: Physique Théorique des Matériaux, Université de Liège (B5), B-4000 Liège, Belgium.

ABSTRACT
Perovskite oxides are already widely used in industry and have huge potential for novel device applications thanks to the rich physical behaviour displayed in these materials. The key to the functional electronic properties exhibited by perovskites is often the so-called Jahn-Teller distortion. For applications, an electrical control of the Jahn-Teller distortions, which is so far out of reach, would therefore be highly desirable. Based on universal symmetry arguments, we determine new lattice mode couplings that can provide exactly this paradigm, and exemplify the effect from first-principles calculations. The proposed mechanism is completely general, however for illustrative purposes, we demonstrate the concept on vanadium based perovskites where we reveal an unprecedented orbital ordering and Jahn-Teller induced ferroelectricity. Thanks to the intimate coupling between Jahn-Teller distortions and electronic degrees of freedom, the electric field control of Jahn-Teller distortions is of general relevance and may find broad interest in various functional devices.

No MeSH data available.


Related in: MedlinePlus

Projected density of states on the dyz (grey filled red curve) and dxz (unfilled blue dashed curve) orbitals of vanadium by imposing the Pb21m atomic positions and computing the energy with Pb21m symmetry (left) for the electronic wavefunction and by removing the symmetry (right) for the electronic wavefunction.dxy is not displayed for clarity. V1 (V3) and V2 (V4) are located within the same (001) plane as defined in Fig. 2. The percentage of total dyz (red) and dxz (blue) character on each vanadium is shown as a pie chart to illustrate the change from C-o.o to C + G-o.o. once the symmetry constraint for the wavefunction is lifted.
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f3: Projected density of states on the dyz (grey filled red curve) and dxz (unfilled blue dashed curve) orbitals of vanadium by imposing the Pb21m atomic positions and computing the energy with Pb21m symmetry (left) for the electronic wavefunction and by removing the symmetry (right) for the electronic wavefunction.dxy is not displayed for clarity. V1 (V3) and V2 (V4) are located within the same (001) plane as defined in Fig. 2. The percentage of total dyz (red) and dxz (blue) character on each vanadium is shown as a pie chart to illustrate the change from C-o.o to C + G-o.o. once the symmetry constraint for the wavefunction is lifted.

Mentions: In order to understand the nature of this electronic instability, we plot the projected density of states on vanadiums in Fig. 3. Starting from the projected density of states with Pb21m symmetry, consecutive atoms along the z direction (V1 and V3, V2 and V4 on Fig. 2) exhibit identical density of states. Consequently, the orbital ordering appears to be of C-type. When allowing the electronic structure to distort, several changes appear in the orbital occupations. Consecutive atoms along the z direction now prefer to occupy either more of the dxz or the dyz orbital, which results in a mixed G-type (G-o.o.) plus C-type orbital ordering (C-o.o.). The G-o.o. that appears, despite the absence of the motion, is allowed via the Kugel-Khomskii mechanism44. This mixed orbital ordering produces an asymmetry between the VO2 planes, as indicated by the two magnitudes of magnetic moments in each layer (1.816 ± 0.001 μB and 1.819 ± 0.001 μB). The mixed orbital ordering also appears in the bulk vanadates, such as the G-o.o. + C-o.o. ground state of LaVO3 or PrVO3 (previously thought to be just G-o.o. from experiments)2526. However, here it is not enough to break the inversion symmetry along the z axis yielding no out-of-plane polarization. The second necessary ingredient is the symmetry breaking due to the A and A’ ordering along the [001] direction in the superlattices. The combination of both effects (in the AO and VO2 planes) is required to break inversion symmetry along the z axis and to produce the out-of-plane polarization. The result is an orbital ordering induced ferroelectricity in vanadate superlattices.


Coupling and electrical control of structural, orbital and magnetic orders in perovskites.

Varignon J, Bristowe NC, Bousquet E, Ghosez P - Sci Rep (2015)

Projected density of states on the dyz (grey filled red curve) and dxz (unfilled blue dashed curve) orbitals of vanadium by imposing the Pb21m atomic positions and computing the energy with Pb21m symmetry (left) for the electronic wavefunction and by removing the symmetry (right) for the electronic wavefunction.dxy is not displayed for clarity. V1 (V3) and V2 (V4) are located within the same (001) plane as defined in Fig. 2. The percentage of total dyz (red) and dxz (blue) character on each vanadium is shown as a pie chart to illustrate the change from C-o.o to C + G-o.o. once the symmetry constraint for the wavefunction is lifted.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4612717&req=5

f3: Projected density of states on the dyz (grey filled red curve) and dxz (unfilled blue dashed curve) orbitals of vanadium by imposing the Pb21m atomic positions and computing the energy with Pb21m symmetry (left) for the electronic wavefunction and by removing the symmetry (right) for the electronic wavefunction.dxy is not displayed for clarity. V1 (V3) and V2 (V4) are located within the same (001) plane as defined in Fig. 2. The percentage of total dyz (red) and dxz (blue) character on each vanadium is shown as a pie chart to illustrate the change from C-o.o to C + G-o.o. once the symmetry constraint for the wavefunction is lifted.
Mentions: In order to understand the nature of this electronic instability, we plot the projected density of states on vanadiums in Fig. 3. Starting from the projected density of states with Pb21m symmetry, consecutive atoms along the z direction (V1 and V3, V2 and V4 on Fig. 2) exhibit identical density of states. Consequently, the orbital ordering appears to be of C-type. When allowing the electronic structure to distort, several changes appear in the orbital occupations. Consecutive atoms along the z direction now prefer to occupy either more of the dxz or the dyz orbital, which results in a mixed G-type (G-o.o.) plus C-type orbital ordering (C-o.o.). The G-o.o. that appears, despite the absence of the motion, is allowed via the Kugel-Khomskii mechanism44. This mixed orbital ordering produces an asymmetry between the VO2 planes, as indicated by the two magnitudes of magnetic moments in each layer (1.816 ± 0.001 μB and 1.819 ± 0.001 μB). The mixed orbital ordering also appears in the bulk vanadates, such as the G-o.o. + C-o.o. ground state of LaVO3 or PrVO3 (previously thought to be just G-o.o. from experiments)2526. However, here it is not enough to break the inversion symmetry along the z axis yielding no out-of-plane polarization. The second necessary ingredient is the symmetry breaking due to the A and A’ ordering along the [001] direction in the superlattices. The combination of both effects (in the AO and VO2 planes) is required to break inversion symmetry along the z axis and to produce the out-of-plane polarization. The result is an orbital ordering induced ferroelectricity in vanadate superlattices.

Bottom Line: Perovskite oxides are already widely used in industry and have huge potential for novel device applications thanks to the rich physical behaviour displayed in these materials.Based on universal symmetry arguments, we determine new lattice mode couplings that can provide exactly this paradigm, and exemplify the effect from first-principles calculations.The proposed mechanism is completely general, however for illustrative purposes, we demonstrate the concept on vanadium based perovskites where we reveal an unprecedented orbital ordering and Jahn-Teller induced ferroelectricity.

View Article: PubMed Central - PubMed

Affiliation: Physique Théorique des Matériaux, Université de Liège (B5), B-4000 Liège, Belgium.

ABSTRACT
Perovskite oxides are already widely used in industry and have huge potential for novel device applications thanks to the rich physical behaviour displayed in these materials. The key to the functional electronic properties exhibited by perovskites is often the so-called Jahn-Teller distortion. For applications, an electrical control of the Jahn-Teller distortions, which is so far out of reach, would therefore be highly desirable. Based on universal symmetry arguments, we determine new lattice mode couplings that can provide exactly this paradigm, and exemplify the effect from first-principles calculations. The proposed mechanism is completely general, however for illustrative purposes, we demonstrate the concept on vanadium based perovskites where we reveal an unprecedented orbital ordering and Jahn-Teller induced ferroelectricity. Thanks to the intimate coupling between Jahn-Teller distortions and electronic degrees of freedom, the electric field control of Jahn-Teller distortions is of general relevance and may find broad interest in various functional devices.

No MeSH data available.


Related in: MedlinePlus