Image: Strain gradients break lattice symmetry and result in polarization fields through an effect known as flexoelectricity.

 

Polarization, or electrical dipole moment per unit volume, is a basic property in condensed-matter systems and has widespread technological applications. All insulators become polarized in the presence of an electric field (dielectric screening). Some materials with sufficiently low symmetry have a spontaneous polarization in their ground state, even when no field is present. If the direction of this polarization can be switched by applying an electric field, then these materials are know as ferroelectrics, which have information storage applications. Even if the polarization cannot be switched, e.g., in pyroelectrics, it can be used in heterostructures to create high-density 2D electron gases for transistor applications. If mechanical strain creates or modifies the polarization of a material, then it is know as a piezoelectric, which have applications as sensors and transducers. Finally, in any insulator, the presence of a strain gradient will result in a polarization through the flexoelectric effect.

Our research focuses on exploring materials that have desirable polarization properties, and developing methodologies to calculate the properties accurately efficiently from first principles.

Related publications:

Cyrus E. Dreyer, Massimiliano Stengel, David Vanderbilt,
Current-density implementation for calculating flexoelectric coefficients,
Phys. Rev. B 98, 075153 (2018), Editor’s Suggestion, arXiv:1802.06390

Cyrus E. Dreyer, Anderson Janotti, Chris G. Van de Walle, and David Vanderbilt,
Correct implementation of polarization constants in wurtzite materials and impact on III-nitrides,
Physical Review X 6, 021038 (2016), arXiv:1605.07629

Collaborators:

David Vanderbilt, Rutgers University

Karin M. Rabe, Rutgers University

Massimiliano Stengel, ICREA and ICMAB-CSIC

Press coverage:

Correcting charge polarization calculations for III-nitrides
Semiconductor Today, July 6, 2016