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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

Comparison of JT and AFD motions around the z axis; (a) in-phase  AFD motion ( mode); (b) in-phase  Jahn-Teller motion ( mode); (c) anti-phase  motion ( mode); (d) anti-phase  motion ( mode). Octahedras for the plane in z = 0 are plotted in red and in blue for the plane in z = c/2. The AFD motions can also appear around the y and z axes (not shown), whereas the Jahn-Teller motions only manifest around the z axis in the vanadates.
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f1: Comparison of JT and AFD motions around the z axis; (a) in-phase AFD motion ( mode); (b) in-phase Jahn-Teller motion ( mode); (c) anti-phase motion ( mode); (d) anti-phase motion ( mode). Octahedras for the plane in z = 0 are plotted in red and in blue for the plane in z = c/2. The AFD motions can also appear around the y and z axes (not shown), whereas the Jahn-Teller motions only manifest around the z axis in the vanadates.

Mentions: Whilst the V4+ perovskites (e.g. SrVO321) have been studied mainly for their interesting metallic properties, the V3+ perovskites are Mott insulators. A3+V3+O3 compounds have attracted much attention since the fifties when they were first synthesized22. During this time, many studies began to determine their magnetic, electronic and structural properties2324252627282930313233343536373839. A central theme at the core of these properties in vanadates is the so-called Jahn-Teller (JT) distortion. The famous Jahn-Teller theorem claims that a material with degenerate electronic states will be unstable towards undergoing a structural distortion lowering its symmetry to remove the electronic degeneracy. In other words, the Jahn-Teller effect is an electronic instability that can cause a structural and metal-insulator phase transition. For instance, in the cubic perovskite symmetry, the crystal field effect splits the d electron levels into a lower lying degenerate three-fold t2g and a higher lying degenerate two-fold eg state. Hence in 3d2 systems such as the rare-earth vanadates, a Jahn-Teller distortion is required to split the t2g levels in order to form a Mott insulating state. We note here the distinction between the Jahn-Teller effect and what we call the Jahn-Teller distortion in this study. Here we define the Jahn-Teller distortion by the symmetry of the atomic distortion as shown in Fig. 1b,d. Whilst a distortion of this symmetry will by definition remove the d electronic degeneracy, the origin of such a distortion does not necessarily need to appear from the Jahn-Teller effect. An important result of this study is that the Jahn-Teller distortion can instead be induced by structural anharmonic couplings, being therefore not only restricted to Jahn-Teller active systems40.


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

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

Comparison of JT and AFD motions around the z axis; (a) in-phase  AFD motion ( mode); (b) in-phase  Jahn-Teller motion ( mode); (c) anti-phase  motion ( mode); (d) anti-phase  motion ( mode). Octahedras for the plane in z = 0 are plotted in red and in blue for the plane in z = c/2. The AFD motions can also appear around the y and z axes (not shown), whereas the Jahn-Teller motions only manifest around the z axis in the vanadates.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Comparison of JT and AFD motions around the z axis; (a) in-phase AFD motion ( mode); (b) in-phase Jahn-Teller motion ( mode); (c) anti-phase motion ( mode); (d) anti-phase motion ( mode). Octahedras for the plane in z = 0 are plotted in red and in blue for the plane in z = c/2. The AFD motions can also appear around the y and z axes (not shown), whereas the Jahn-Teller motions only manifest around the z axis in the vanadates.
Mentions: Whilst the V4+ perovskites (e.g. SrVO321) have been studied mainly for their interesting metallic properties, the V3+ perovskites are Mott insulators. A3+V3+O3 compounds have attracted much attention since the fifties when they were first synthesized22. During this time, many studies began to determine their magnetic, electronic and structural properties2324252627282930313233343536373839. A central theme at the core of these properties in vanadates is the so-called Jahn-Teller (JT) distortion. The famous Jahn-Teller theorem claims that a material with degenerate electronic states will be unstable towards undergoing a structural distortion lowering its symmetry to remove the electronic degeneracy. In other words, the Jahn-Teller effect is an electronic instability that can cause a structural and metal-insulator phase transition. For instance, in the cubic perovskite symmetry, the crystal field effect splits the d electron levels into a lower lying degenerate three-fold t2g and a higher lying degenerate two-fold eg state. Hence in 3d2 systems such as the rare-earth vanadates, a Jahn-Teller distortion is required to split the t2g levels in order to form a Mott insulating state. We note here the distinction between the Jahn-Teller effect and what we call the Jahn-Teller distortion in this study. Here we define the Jahn-Teller distortion by the symmetry of the atomic distortion as shown in Fig. 1b,d. Whilst a distortion of this symmetry will by definition remove the d electronic degeneracy, the origin of such a distortion does not necessarily need to appear from the Jahn-Teller effect. An important result of this study is that the Jahn-Teller distortion can instead be induced by structural anharmonic couplings, being therefore not only restricted to Jahn-Teller active systems40.

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