| 1. |
- Singh-Bhalla, Guneeta, et al.
(författare)
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Unexpected termination switching and polarity compensation in LaAlO3/SrTiO3 heterostructures
- 2018
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Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 2:11
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Tidskriftsartikel (refereegranskat)abstract
- Polar crystals composed of charged ionic planes cannot exist in nature without acquiring surface changes to balance an ever-growing dipole. The necessary changes can manifest structurally or electronically as observed in semiconductors and ferroelectric materials through screening charges and/or domain wall formation. In the case of prototypical polar complex oxides such as the LaAlO3/SrTiO3 system the nature of screening charges for different interface terminations is not symmetric. Electron accumulation is observed near the LaAlO3/TiO2-SrTiO3 interface, while the LaAlO3/SrO-SrTiO3 stack is insulating. Here, we observe evidence for an asymmetry in the surface chemical termination for nominally stoichiometric LaAlO3 films in contact with the two different surface layers of SrTiO3 crystals, TiO2 and SrO. Using several element-specific probes, we find that the surface termination of LaAlO3 remains AlO2 irrespective of the starting termination of SrTiO3 substrate surface. We use a combination of cross-plane tunneling measurements and first-principles calculations to understand the effects of this unexpected termination on band alignments and polarity compensation of LaAlO3/SrTiO3 heterostructures. An asymmetry in LaAlO3 polarity compensation and resulting electronic properties will fundamentally limit atomic level control of oxide heterostructures.
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| 2. |
- Marinova, Maya, et al.
(författare)
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Depth Profiling Charge Accumulation from a Ferroelectric into a Doped Mott Insulator
- 2015
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 15:4, s. 2533-2541
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Tidskriftsartikel (refereegranskat)abstract
- The electric field control of functional properties is a crucial goal in oxide-based electronics. Nonvolatile switching between different resistivity or magnetic states in an oxide channel can be achieved through charge accumulation or depletion from an adjacent ferroelectric. However, the way in which charge distributes near the interface between the ferroelectric and the oxide remains poorly known, which limits our understanding of such switching effects. Here, we use a first-of-a-kind combination of scanning transmission electron microscopy with electron energy loss spectroscopy, near-total-reflection hard X-ray photoemission spectroscopy, and ab initio theory to address this issue. We achieve a direct, quantitative, atomic-scale characterization of the polarization-induced charge density changes at the interface between the ferroelectric BiFeO3 and the doped Mott insulator Ca1-xCexMnO3, thus providing insight on how interface-engineering can enhance these switching effects.
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| 3. |
- Nemsak, Slavomir, et al.
(författare)
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Element- and momentum-resolved electronic structure of the dilute magnetic semiconductor manganese doped gallium arsenide
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- The dilute magnetic semiconductors have promise in spin-based electronics applications due to their potential for ferromagnetic order at room temperature, and various unique switching and spin-dependent conductivity properties. However, the precise mechanism by which the transition-metal doping produces ferromagnetism has been controversial. Here we have studied a dilute magnetic semiconductor (5% manganese-doped gallium arsenide) with Bragg-reflection standing-wave hard X-ray angle-resolved photoemission spectroscopy, and resolved its electronic structure into element-and momentum-resolved components. The measured valence band intensities have been projected into element-resolved components using analogous energy scans of Ga 3d, Mn 2p, and As 3d core levels, with results in excellent agreement with element-projected Bloch spectral functions and clarification of the electronic structure of this prototypical material. This technique should be broadly applicable to other multi-element materials.
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| 4. |
- Östman, Erik, et al.
(författare)
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Hysteresis-free switching between vortex and collinear magnetic states
- 2014
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 16, s. 053002-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a lossless switching between vortex and collinear magnetic states in circular FePd disks arranged in a square lattice. Above a bifurcation temperature (Te) we show that thermal fluctuations are enough to facilitate flipping between the two distinctly different magnetic states. We find that the temperature dependence of the vortex annihilation and nucleation fields can be described by a simple power law relating them to the saturation magnetization.
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