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05:01 Leibniz Universität Hannover (LUH) German 2012

Quantenengineering

  • Published: 2012
  • Publisher: Leibniz Universität Hannover (LUH)
  • Language: German
04:02 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2012

From confinement to deconfinement of magnetic monopoles in artificial rectangular spin ices

We study a frustrated two-dimensional array of dipoles forming an artificial rectangular spin ice with horizontal and vertical lattice parameters given by a and b respectively. We show that the ice regime could be stabilized by appropriate choices for the ratio γ ≡ a/b. Our results show that for , i.e. when the centers of the islands form a triangular lattice, the ground state becomes degenerate. Therefore, while the magnetic charges (monopoles) are excitations connected by an energetic string for general rectangular lattices (including the particular case of a square lattice), they are practically free to move for a special rectangular lattice with . Besides that, our results show that for the system is highly anisotropic in such a way that, even for this range out of the ice regime, the string tension almost vanishes along a particular direction of the array. We also discuss the ground state transition and some thermodynamic properties of the system.
  • Published: 2012
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:44 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2013

Dynamics and hysteresis in square lattice artificial spin ice

Dynamical effects under geometrical frustration are considered in a model for artificial spin ice on a square lattice in two dimensions. Each island of the spin ice has a three-component Heisenberg-like dipole moment subject to shape anisotropies that influence its direction. The model has real dynamics, including rotation of the magnetic degrees of freedom, going beyond the Ising-type models of spin ice. The dynamics is studied using a Langevin equation solved via a second-order Heun algorithm. Thermodynamic properties such as the specific heat are presented for different couplings. A peak in specific heat is related to a type of melting-like phase transition present in the model. Hysteresis in an applied magnetic field is calculated for model parameters where the system is able to reach thermodynamic equilibrium.
  • Published: 2013
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:29 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2015

Bending and buckling of narrow armchair graphene nanoribbons via STM manipulation

Semiconducting graphene nanoribbons (GNRs) are envisioned to play an important role in future electronics. This requires the GNRs to be placed on a surface where they may become strained. Theory predicts that axial strain, i.e. in-plane bending of the GNR, will cause a change in the band gap of the GNR. This may negatively affect device performance. Using the tip of a scanning tunneling microscope we controllably bent and buckled atomically well-defined narrow armchair GNR and subsequently probed the changes in the local density of states. These experiments show that the band gap of 7-ac-GNR is very robust to in-plane bending and out-of-plane buckling.
  • Published: 2015
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
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