Hanghui Chen

Engineering correlation effects via artificially designed oxide superlattices.

Ab initio calculations are used to predict that a superlattice composed of layers of LaTiO3 and LaNiO3 alternating along the [001] direction is a S=1 Mott insulator with large magnetic moments on the Ni sites, negligible moments on the Ti sites and a charge transfer gap set by the energy difference between Ni d and Ti d states, distinct from conventional Mott insulators. Correlation effects are enhanced on the Ni sites via filling the oxygen p states and reducing the Ni-O-Ni bond angle. Small hole (electron) doping of the superlattice leads to a two-dimensional single-band situation with holes (electrons) residing on the Ni d(x2-y2) (Ti d(xy)) orbital and coupled to antiferromagnetically correlated spins in the NiO2 layer.

Charge transfer driven emergent phenomena in oxide heterostructures

Complex oxides exhibit many intriguing phenomena, including metal-insulator transition, ferroelectricity/multiferroicity, colossal magnetoresistance and high transition temperature superconductivity. Advances in epitaxial thin film growth techniques enable us to combine different complex oxides with atomic precision and form an oxide heterostructure. Recent theoretical and experimental work has shown that charge transfer across oxide interfaces generally occurs and leads to a great diversity of emergent interfacial properties which are not exhibited by bulk constituents. In this report, we review mechanisms and physical consequence of charge transfer across interfaces in oxide heterostructures. Both theoretical proposals and experimental measurements of various oxide heterostructures are discussed and compared. We also review the theoretical methods that are used to calculate charge transfer across oxide interfaces and discuss the success and challenges in theory. Finally, we present a summary and perspectives for future research.

Phase diagram of Sr 1 − x Ba x MnO 3 as a function of chemical doping, epitaxial strain, and external pressure

We use ab initio calculations to systematically study the phase diagram of multiferroic

Spin-density functional theories and their+Uand+Jextensions: A comparative study of transition metals and transition metal oxides

{\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Ba}}_{x}{\mathrm{MnO}}_{3}

Antisite defects at oxide interfaces

(

Comparative study of exchange-correlation functionals for accurate predictions of structural and magnetic properties of multiferroic oxides

0\ensuremath{\le}x\ensuremath{\le}1

Design of new Mott multiferroics via complete charge transfer: promising candidates for bulk photovoltaics

) as a function of chemical doping, epitaxial strain, and external pressure. We find that by replacing Sr with Ba in cubic

Multiplicity of non symmetry-related polar states in perovskite Sr

{\mathrm{SrMnO}}_{3}

_{1-x}

and imposing epitaxial strain, the material can be tuned to the vicinity of a first order transition between two multiferroic phases, one antiferromagnetic with a smaller polarization and one ferromagnetic with a larger polarization. A giant effective magnetoelectric coupling and cross-field control (electric field control of magnetism or magnetic field control of polarization) can be achieved in the vicinity of the transition. The dependence of the theoretically computed transition point on the choice of exchange correlation functionals is determined and is found to be non-negligible. We also show that the perovskite structure of

Ba

{\mathrm{BaMnO}}_{3}