1,218 research outputs found
Hexagonal Rare-Earth Manganites as Promising Photovoltaics and Light Polarizers
Ferroelectric materials possess a spontaneous electric polarization and may
be utilized in various technological applications ranging from non-volatile
memories to solar cells and light polarizers. Recently, hexagonal rare-earth
manganites, h-RMnO (R is a rare-earth ion) have attracted considerable
interest due to their intricate multiferroic properties and improper
ferroelectricity characterized by a sizable remnant polarization and high Curie
temperature. Here, we demonstrate that these compounds can serve as very
efficient photovoltaic materials and, in addition, possess remarkable optical
anisotropy properties. Using first-principles methods based on
density-functional theory and considering h-TbMnO as a representative
manganite, we predict a strong light absorption of this material in the solar
spectrum range, resulting in the maximum light-to-electricity energy conversion
efficiency up to 33%. We also predict an extraordinary optical linear dichroism
and linear birefringence properties of h-TbMnO in a broad range of optical
frequencies. These results uncover the unexplored potential of hexagonal
rare-earth manganites to serve as photovoltaics in solar cells and as
absorptive and birefringent light polarizers.Comment: 26 pages, 8 figure
Prediction of a mobile two-dimensional electron gas at the LaScO3/BaSnO3(001) interface
Two-dimensional electron gases (2DEG) at oxide interfaces, such as LaAlO3/SrTiO3 (001), have aroused significant interest due to their high carrier density (∼1014 cm−2) and strong lateral confinement (∼1 nm). However, these 2DEGs are normally hosted by the weakly dispersive and degenerate d bands (e.g., Ti-3d bands), which are strongly coupled to the lattice, causing mobility of such 2DEGs to be relatively low at room temperature (∼1 cm2/Vs). Here, we propose using oxide host materials with the conduction bands formed from s electrons to increase carrier mobility and soften its temperature dependence. Using first-principles density functional theory calculations, we investigate LaScO3/BaSnO3 (001) heterostructure and as a model system, where the conduction band hosts the s-like carriers. We find that the polar discontinuity at this interface leads to electronic reconstruction resulting in the formation of the 2DEG at this interface. The conduction electrons reside in the highly dispersive Sn-5s bands, which have a large band width and a low effective mass. The predicted 2DEG is expected to be highly mobile even at room temperature due to the reduced electron-phonon scattering via the inter-band scattering channel. A qualitatively similar behavior is predicted for a doped BaSnO3, where a monolayer of BaO is replaced with LaO. We anticipate that the quantum phenomena associated with these 2DEGs to be more pronounced owing to the high mobility of the carriers
Effects of intermixing and oxygen vacancies on a two-dimensional electron gas at the polar (TbScO\u3csub\u3e3\u3c/sub\u3e/KTaO) (001) interface
3d-5d perovskite oxides, ABO3 (where A and B are 3d or 5d elements), form polar surfaces in the (001)- stacked thin films. As a result, the polar-polar (001) interface between two ABO3 insulators could create polar discontinuity potentially producing a two-dimensional electron gas of higher density and stronger spatial localization compared to the widely studied polar-nonpolar oxide interfaces, such as (001) LaAlO3/SrTiO3. Here, as a model system, we explore the interface between polar (001) TbScO3 and polar (001) KTaO3 using first-principles density functional theory.We find that the intermixed interface Ta0.75Sc0.25O2/Tb0.75K0.25O maintaining the bulk perovskite charge stacking (e.g., . . . + 1/ − 1/ + 1 . . .) is insulating and has a lower energy than the metallic interface TbO/TaO2 breaking such stacking. This intermixed interface is, however, prone to the formation of oxygen vacancies which make it conducting. We emphasize that the driving force for the formation of the two-dimensional electron gas (2DEG) here is not a built-in electric field stemming from the polar discontinuity but the interface stoichiometry. We find that the ratio of oxygen vacancy concentration is a factor of 30 times larger at the interface than in bulk KTO at room temperature. The oxygen vacancy-induced 2DEG resides on the Ta-5d electronic orbitals with dxy and dxz/yz occupation dominating overall charge density near and far away from the interface
Hexagonal rare-earth manganites as promising photovoltaics and light polarizers
Ferroelectric materials possess a spontaneous electric polarization and may be utilized in various technological applications ranging from nonvolatile memories to solar cells and light polarizers. Recently, hexagonal rareearth manganites, h-RMnO3 (R is a rare-earth ion), have attracted considerable interest due to their intricate multiferroic properties and improper ferroelectricity characterized by a sizable remnant polarization and high Curie temperature. Here we demonstrate that these compounds can serve as very efficient photovoltaic materials and, in addition, possess remarkable optical anisotropy properties. Using first-principles methods based on density functional theory and considering h-TbMnO3 as a representative manganite, we predict a strong light absorption of this material in the solar spectrum range, resulting in a maximum light-to-electricity energy conversion efficiency of up to 33%. We also predict an extraordinary optical linear dichroism and linear birefringence properties of h-TbMnO3 in a broad range of optical frequencies. These results uncover the unexplored potential of hexagonal rare-earth manganites to serve as photovoltaics in solar cells and as absorptive and birefringent light polarizers
Anomalous Hall Conductivity of a Non-Collinear Magnetic Antiperovskite
The anomalous Hall effect (AHE) is a well-known fundamental property of
ferromagnetic metals, commonly associated with the presence of a net
magnetization. Recently, an AHE has been discovered in non-collinear
antiferromagnetic (AFM) metals. Driven by non-vanishing Berry curvature of AFM
materials with certain magnetic space group symmetry, anomalous Hall
conductivity (AHC) is very sensitive to the specific type of magnetic ordering.
Here, we investigate the appearance of AHC in antiperovskite GaNMn as a
representative of broader materials family ANMn (A is a main group
element), where different types of non-collinear magnetic ordering can emerge.
Using symmetry analyses and first-principles density-functional theory
calculations, we show that with almost identical band structure, the nearly
degenerate non-collinear AFM and phases of
GaNMn have zero and finite AHC, respectively. In a non-collinear
ferrimagnetic -1 phase, GaNMn exhibits a large AHC due to the presence
of a sizable net magnetic moment. In the non-collinear antiperovskite magnets,
transitions between different magnetic phases, exhibiting different AHC states,
can be produced by doping, strain, or spin transfer torque, which makes these
materials promising for novel spintronic applications
Anomalous Hall conductivity of noncollinear magnetic antiperovskites
The anomalous Hall effect (AHE) is a well-known fundamental property of ferromagnetic metals, commonly associated with the presence of a net magnetization. Recently, an AHE has been discovered in noncollinear antiferromagnetic (AFM) metals. Driven by nonvanishing Berry curvature of AFM materials with certain magnetic space-group symmetry, anomalous Hall conductivity (AHC) is very sensitive to the specific type of magnetic ordering. Here, we investigate the appearance of AHC in antiperovskite materials family ANMn3 (A = Ga, Sn, Ni), where different types of noncollinear magnetic ordering can emerge. Using symmetry analyses and first-principles density-functional theory calculations, we show that with almost identical band structure the nearly degenerate noncollinear AFM Γ5g and Γ4g phases of GaNMn3 have zero and finite AHC, respectively. In a noncollinear ferrimagnetic M-1 phase, GaNMn3 exhibits a large AHC due to the presence of a sizable net magnetic moment. In the noncollinear antiperovskite magnets, transitions between different magnetic phases, exhibiting different AHC states, can be produced by doping, strain, or spin transfer torque, which makes these materials promising for novel spintronic applications
Spin-polarized two-dimensional electron gas at GdTiO3/SrTiO3 interfaces: Insight from first-principles calculations
Two-dimensional electron gases (2DEGs) at oxide interfaces have been a topic of intensive research due to their high carrier mobility and strong confinement. Additionally, strong correlations in the oxide materials can give rise to new and interesting physics, such as magnetism and metal-insulator transitions at the interface. Using first-principles calculations based on density functional theory, we demonstrate the presence of a highly spin-polarized 2DEG at the interface between the Mott insulator GdTiO3 and a band insulator SrTiO3. The strong correlations in the dopant cause ferromagnetic alignment of the interface Ti atoms and result in a fully spin-polarized 2DEG. The 2DEG consists of two types of carriers distinguished by their orbital character. The majority of the interface charge is strongly localized on the Ti dxy orbitals at the interface and a smaller fraction resides on the delocalized Ti dxz,yz states
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