arXiv subjects

H. Kurt

Publications and source records attributed to H. Kurt.

11 recordsLinked to original sources

arXiv2023

Ru$_{2-x}$Mn$_{1+x}$Al thin films

The cubic Heusler alloy Ru$_{2-x}$Mn$_{1+x}$Al is grown in thin film form on MgO and MgAl$_2$O$_4$ substrates. It is a highly spin-polarised ferrimagnetic metal, with weak magnetocrystalline anisotropy. Although structurally and chemically similar to $\text{Mn}_2\text{Ru}_x\text{Ga}$, it does not exhibit ferrimagnetic compensation, or large magneto galvanic effects. The differences are attributed to a combination of atomic order and the hybridisation with the group 13 element Al or Ga. The spin polarisation is around 50 to 60 %. There is a gap in the density of states just above the Fermi level in fully ordered compounds.

cond-mat.mtrl-sci↗

arXiv2020

Topological phase transition of the centered rectangular photonic lattice

A Cm planar photonic material (two-dimensional) including the mirror reflection symmetry is explored where in the Dirac cones appeared at the high-symmetry points of the Brillouin zone boundary. By implementing the specific perturbation on the photonic crystal (PC), topological transition can make a bridge between the trivial PC (ordinary insulator) and the topological insulator including zero and non-zero spin Chern number (Cs), respectively. The perturbation can be realized through the rotation of the Cm photonic crystal around the nonzero angle to its initial position. Therefore, breaking the mirror symmetry of the unit cell leads to mismatch of the symmetry planes of the lattice. This modification results in the directional band gap & band inversion which is the signature of the topological transitions. The mentioned PC would be suitable for examination of the unidirectional transport of light at the topological interfaces.

physics.app-ph↗

arXiv2020

Robust Transport of the Edge Modes along the Photonic Topological Interfaces of Different Configurations

Two-dimensional photonic crystals made of six air holes on a core-shell dielectric material has been proposed to study the newly emerged photonic quantum spin Hall insulator. Specifically, radii modification of the air holes and core-shell without breaking time-reversal (TR) symmetry are supported by the C_6 point group symmetry upon a proposed scheme. It is shown that multiple topological transitions from an ordinary insulator with zero spin Chern number (Cs) to a topological insulator with a non-zero Cs can be achieved by modifying the geometry of the photonic structure. Studying the two counter-propagating helical edge modes which have the opposite group velocities are of individual importance for various optical purposes like scattering-free waveguides protected to various defects, disorders and strong light-matter interactions. We show that topological edge states demonstrate slow light characteristics. The findings emphasize the fact that exploring topological phase transition can be applied as a unique approach for realizing light transport, robust energy transportation and slow light in integrated photonic circuits and devices.

physics.app-ph↗

arXiv2020

Simulating Topological Robustness of Fano Resonance in Rotated Honeycomb Photonic Crystals

The Fano resonance with a distinctive ultra-sharp, asymmetric line shape and high quality factor Q, is a widely occurring phenomena that has a large variety of optical, plasmonic and microwave manifestations. In this paper, we explore the characteristic robustness of the Fano resonance mode, which is topologically protected by manufacturing band inversion induced by breaking the mirror symmetry of a two-dimensional honeycomb photonic crystal (HPC), associated with C_6 point group symmetry. So the dark and bright topological edge modes appear in the band gap made by opening of the Dirac cone. Destructive and constructive interference of the dark and bright modes leads to the asymmetric line shape of the Fano resonance. The Fano resonance mode which is very sensitive to the environmental and geometrical perturbations, can be applied to sensor design. Here we demonstrate that the topological Fano resonance mode preserves its asymmetric, ultra-sharp line shape in the presence of the disorder, defects and cavities, and this has useful optical device applications such as in low threshold lasers, and extremely precise interferometers

physics.app-ph↗

arXiv2020

Topological photonic states and directional emission of the light exiting from the photonic topological structure composed of two dimensional honeycomb photonic crystals with different point group symmetries

In this work, we investigate a two dimensional honeycomb photonic crystal (2D HPC) with C_6 symmetry point group, which is known to demonstrate a double Dirac cone at k=0 of the Brillion zone. Then we design two deformed PCs from the original one, by modifying the radius of the cylinders from the unit cell center in which the symmetry C_6 is reduced to the C_3\u{psion} group and new structure exhibits the photonic topological edge states. Consequently, the topologically protected propagation of the edge states with back scattering-immune feature is observed along the interfaces of the two deformed PCs without any defects or including cavities or bend. Furthermore, the directional surface modes exit from the photonic topological insulators (PTIs) including various defects, is investigated. As well as, we explore the propagation and coupling of light through the coupled photonic topological insulators (CPTIs).

physics.app-ph↗

arXiv2017

Directionality Fields generated by a Local Hilbert Transform

We propose a new approach based on a local Hilbert transform to design non-Hermitian potentials generating arbitrary vector fields of directionality, p(r), with desired shapes and topologies. We derive a local Hilbert transform to systematically build such potentials, by modifying background potentials (being either regular or random, extended or localized). In particular, we explore particular directionality fields, for instance in the form of a focus to create sinks for probe fields (which could help to increase absorption at the sink), or to generate vortices in the probe fields. Physically, the proposed directionality fields provide a flexible new mechanism for dynamically shaping and precise control over probe fields leading to novel effects in wave dynamics.

physics.optics↗

arXiv2004

Manipulating Current-Induced Magnetization Switching

We summarize our recent findings on how current-driven magnetization switching and magnetoresistance in nanofabricated magnetic multilayers are affected by varying the spin-scattering properties of the non-magnetic spacers, the relative orientations of the magnetic layers, and spin-dependent scattering properties of the interfaces and the bulk of the magnetic layers. We show how our data are explained in terms of current-dependent effective magnetic temperature.

cond-mat.mtrl-sci↗

arXiv2004

Current-Induced Magnetization Switching in Permalloy-based Nanopillars with Cu, Ag, and Au

We compare magnetoresistances (MR) and switching currents (I_s) at room temperature (295K) and 4.2K for Permalloy/N/Permalloy nanopillars undergoing current-induced magnetization switching (CIMS), with non-magnetic metals N = Cu, Ag, and Au. The N-metal thickness is held fixed at 10 nm. Any systematic differences in MR and I_s for the different N-metals are modest, suggesting that Ag and Au represent potentially viable alternatives for CIMS studies and devices to the more widely used Cu.

cond-mat.mtrl-sci↗

arXiv2004

Changes in magnetic scattering anisotropy at a ferromagnetic/superconducting interface

We show that some metals and alloys (X = Cu, Ag, FeMn, or Cu and Ag combined with each other), sputtered between ferromagnetic Co and superconducting Nb, produce no change in current-perpendicular-to-plane magnetoresistance (CPP-MR) in a carefully designed CPP-spin-valve. In contrast, other metals (Ru or Au) or combinations (Cu or Ag combined with Au, Ru, or FeMn) change the CPP-MR, in some cases even reversing its sign. We ascribe these changes to activation of magnetic scattering anisotropies at a ferromagnetic/superconducting interface, apparently by strong spin-flipping between the Co and Nb layers.

cond-mat.mtrl-sci↗

arXiv2003

Controlled normal and inverse magnetoresistance and current-driven magnetization switching in magnetic nanopillars

Combining pairs of ferromagnetic metals with different signs of scattering anisotropies, let us independently invert the magnetoresistance and the direction of current-driven switching in ferromagnetic/non-magnetic/ferromagnetic metal nanopillars. We show all four combinations of normal and inverse behaviors, at both room temperature and 4.2K. In all cases studied, the direction of switching is set by the net scattering anisotropy of the fixed (polarizing) ferromagnet. We provide simple arguments for what we see.

cond-mat.mtrl-sci↗

arXiv2003

Effect of Antiferromagnetic Interlayer Coupling on Current-Assisted Magnetization Switching

We compare magnetization switching in Co/Cu/Co nanopillars with uncoupled and dipole-field coupled Co layers. In uncoupled nanopillars, current-driven switching is hysteretic at low magnetic field H and changes to reversible, characterized by telegraph noise, at high H. We show that dipolar coupling both affects the switching current and causes the switching to become reversible at small H. The coupling thus changes the switching to reversible, hysteretic, and then reversible again as H increases. We describe our results in terms of current-assisted thermal activation.

cond-mat↗