Vortices, occurring whenever a flow field 'whirls' around a one-dimensional core, are among the simplest topological structures, ubiquitous to many branches of physics. In the crystalline state, ...vortex formation is rare, since it is generally hampered by long-range interactions: in ferroic materials (ferromagnetic and ferroelectric), vortices are observed only when the effects of the dipole-dipole interaction are modified by confinement at the nanoscale
, or when the parameter associated with the vorticity does not couple directly with strain
. Here, we observe an unprecedented form of vortices in antiferromagnetic haematite (α-Fe
O
) epitaxial films, in which the primary whirling parameter is the staggered magnetization. Remarkably, ferromagnetic topological objects with the same vorticity and winding number as the α-Fe
O
vortices are imprinted onto an ultra-thin Co ferromagnetic over-layer by interfacial exchange. Our data suggest that the ferromagnetic vortices may be merons (half-skyrmions, carrying an out-of plane core magnetization), and indicate that the vortex/meron pairs can be manipulated by the application of an in-plane magnetic field, giving rise to large-scale vortex-antivortex annihilation.
Isostructural metal-insulator transition in VO 2 Lee, D.; Chung, B.; Shi, Y. ...
Science (American Association for the Advancement of Science),
11/2018, Letnik:
362, Številka:
6418
Journal Article
Recenzirano
The metal-insulator transition in correlated materials is usually coupled to a symmetry-lowering structural phase transition. This coupling not only complicates the understanding of the basic ...mechanism of this phenomenon but also limits the speed and endurance of prospective electronic devices. We demonstrate an isostructural, purely electronically driven metal-insulator transition in epitaxial heterostructures of an archetypal correlated material, vanadium dioxide. A combination of thin-film synthesis, structural and electrical characterizations, and theoretical modeling reveals that an interface interaction suppresses the electronic correlations without changing the crystal structure in this otherwise correlated insulator. This interaction stabilizes a nonequilibrium metallic phase and leads to an isostructural metal-insulator transition. This discovery will provide insights into phase transitions of correlated materials and may aid the design of device functionalities.
The tunneling magnetoresistance of Co70Fe30/AlO x /Co70Fe30 magnetic tunnel junctions with epitaxial bottom electrode annealed at different temperatures was studied. The TMR was significantly ...enhanced when the bottom electrodes were annealed at 300C and above. The interface roughness, barrier width and height are almost identical within the experimental uncertainty. However, high resolution reciprocal space mapping studies showed that the lattice distortion of the epitaxial bottom electrodes from body centered cubic to body centered tetragonal had the same trend as the TMR. The tetragonal lattice distortion is attributed to be the dominant factor for this spin polarization enhancement.
The isotropic, nonmagnetic doped BaBiO3 superconductors maintain some similarities to high-Tc cuprates, while also providing a cleaner system for isolating charge density wave (CDW) physics that ...commonly competes with superconductivity. Artificial layered superlattices offer the possibility of engineering the interaction between superconductivity and CDW. Here we stabilize a low-temperature, fluctuating short-range CDW order by using artificially layered epitaxial (BaPbO3)3m/(BaBiO3)m (m = 1-10 unit cells) superlattices that are not present in the optimally doped BaPb0.75Bi0.25O3 alloy with the same overall chemical formula. Charge transfer from BaBiO3 to BaPbO3 effectively dopes the former and suppresses the long-range CDW; however, as the short-range CDW fluctuations strengthen at low temperatures charge appears to localize and superconductivity is weakened. The monolayer structural control demonstrated here provides compelling implications to access controllable, local density wave orders absent in bulk alloys and manipulate phase competition in unconventional superconductors.
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