Alexander Thiess

Theory and Application of Chain Formation in Break Junctions

We introduce a generic model of chain formation in break junctions by formulating criteria for the stability and producibility of suspended monatomic chains based on total energy arguments. Using ab initio calculations including spin-polarization and spin-orbit coupling, we apply our model to the formation of monatomic 4d and 5d transition metal (TM) chains. We explain the physical origin of the experimentally observed general trend of increasing probability for the creation of long chains for late 5d TMs and suppressed chain formation for 4d TMs. We also clarify why the probability of chain elongation can be greatly enhanced by the presence of adsorbates in experiments.

Modeling impurity-assisted chain creation in noble-metal break junctions

In this work we present the generalization of the model for chain formation in break junctions, introduced by Thiess et al (2008 Nano Lett. 8 2144), to zigzag transition-metal chains with s and p impurities. We apply this extended model to study the producibility trends for noble-metal chains with impurities, often present in break junction experiments, namely, Cu, Ag and Au chains with H, C, O and N adatoms. Providing the material-specific parameters for our model from systematic full-potential linearized augmented plane-wave first-principles calculations, we find that the presence of such impurities crucially affects the binding properties of the noble-metal chains. We reveal that both the impurity-induced bond strengthening and the formation of zigzag bonds can lead to a significantly enhanced probability for chain formation in break junctions.

Magnetically hindered chain formation in transition-metal break junctions.

Based on first-principles calculations, we demonstrate that magnetism impedes the formation of long chains in break junctions. We find a distinct softening of the binding energy of atomic chains due to the creation of magnetic moments that crucially reduces the probability of successful chain formation. Thereby, we are able to explain the long standing puzzle why most of the transition metals do not assemble as long chains in break junctions and thus provide indirect evidence that in general suspended atomic chains in transition-metal break junctions are magnetic.

Competing magnetic anisotropies in atomic-scale junctions

Using first-principles calculations, we study the magnetism of

Structurally driven magnetic state transition of biatomic Fe chains on Ir(001)

5d

Effect of magnetism and light sp-dopants on chain creation in Ir and Pt break junctions

transition-metal atomic junctions including structural relaxations and spin-orbit coupling. Upon stretching monoatomic chains of W, Ir, and Pt suspended between two leads, we find the development of strong magnetism and large values of the magnetocrystalline anisotropy energy (MAE) of up to 30 meV per chain atom. We predict that switches of the easy magnetization axis of the nanocontacts upon elongation should be observable by ballistic anisotropic magnetoresistance measurements. Due to the different local symmetry, the contributions to the MAE of the central chain atoms and chain atoms in the vicinity of the leads can have opposite signs which reduces the total MAE. We demonstrate that this effect occurs independent of the chain length or geometry of the electrodes.

Massively parallel density functional calculations for thousands of atoms: KKRnano

Using first-principles calculations, we demonstrate that the magnetic exchange interaction and the magnetocrystalline anisotropy of biatomic Fe chains grown in the trenches of the

Systematic study of the exchange interactions in Gd-doped GaN containing N interstitials, O interstitials, or Ga vacancies

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Superparamagnetism in Gd-doped GaN induced by Ga-vacancy clustering

reconstructed Ir(001) surface depend sensitively on the atomic arrangement of the Fe atoms. Two structural configurations have been considered which are suggested from recent experiments. They differ by the local symmetry and the spacing between the two strands of the biatomic Fe chain. Since both configurations are very close in total energy they may coexist in experiment. We have investigated collinear ferro- and antiferromagnetic solutions as well as a collinear state with two moments in one direction and one in the opposite direction (

Preconditioning systems arising from the KKR Green function method using block-circulant matrices

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