arXiv subjects

Per Hedegård

Publications and source records attributed to Per Hedegård.

24 records · Page 2Linked to original sources

arXiv2010

Interaction-induced negative differential resistance in asymmetric molecular junctions

Combining insights from quantum chemistry calculations with master equations, we discuss a mechanism for negative differential resistance (NDR) in molecular junctions, operated in the regime of weak tunnel coupling. The NDR originates from an interplay of orbital spatial asymmetry and strong electron-electron interaction, which causes the molecule to become trapped in a non-conducting state above a voltage threshold. We show how the desired asymmetry can be selectively introduced in individual orbitals in e.g., OPE-type molecules by functionalization with a suitable side group, which is in linear conjugation to one end of the molecule and cross-conjugated to the other end.

cond-mat.mes-hall↗

arXiv1999

SO(5) theory of insulating vortex cores in high-$T_c$ materials

We study the fermionic states of the antiferromagnetically ordered vortex cores predicted to exist in the superconducting phase of the newly proposed SO(5) model of strongly correlated electrons. Our model calculation gives a natural explanation of the recent STM measurements on BSCCO, which in surprising contrast to YBCO revealed completely insulating vortex cores.

cond-mat.supr-con↗

arXiv1998

On loss of quantum coherence in an interacting Fermi gas

We clarify the path integral calculation, recently suggested by Golubev and Zaikin, and show, contrary to their claim, that quasiparticles become fully coherent quantum particles in the $T \to 0$ limit. The important physical point is the inclusion of the recoil of the quasiparticle when interacting with fluctuations in the rest of the Fermi gas.

cond-mat.mes-hall↗

arXiv1994

Two dimensional electron transport in disordered and ordered distributions of magnetic flux vortices

We have considered the conductivity properties of a two dimensional electron gas (2DEG) in two different kinds of inhomogeneous magnetic fields, i.e.\ a disordered distribution of magnetic flux vortices, and a periodic array of magnetic flux vortices. The work falls in two parts. In the first part we show how the phase shifts for an electron scattering on an isolated vortex, can be calculated analytically, and related to the transport properties through the differential cross section. In the second part we present numerical results for the Hall conductivity of the 2DEG in a periodic array of flux vortices found by exact diagonalization. We find characteristic spikes in the Hall conductance, when it is plotted against the filling fraction. It is argued that the spikes can be interpreted in terms of ``topological charge'' piling up across local and global gaps in the energy spectrum.

cond-mat↗

arXiv1993

Theory of the Eigler-swith

We suggest a simple model to describe the reversible field-induced transfer of a single Xe-atom in a scanning tunneling microscope, --- the Eigler-switch. The inelasticly tunneling electrons give rise to fluctuating forces on and damping of the Xe-atom resulting in an effective current dependent temperature. The rate of transfer is controlled by the well-known Arrhenius law with this effective temperature. The directionality of atom transfer is discussed, and the importance of use of non-equlibrium-formalism for the electronic environment is emphasized. The theory constitutes a formal derivation and generalization of the so-called Desorption Induced by Multiple Electron Transitions (DIMET) point of view.

cond-mat↗

arXiv1993

Classical theory of the Hall-effect in an inhomogeneous magnetic field

Inspired by recent experiments by Geim et al. we discuss the classical theory of the Hall effect of a 2 dimensional electron gas in an inhomogeneous magnetic field. The field modulation is in the form of flux tubes created by a superconductor overlayer. We find that an approach, where the vortices are treated as individual scatterers contributing to the collision term in the Boltzman equation will not work --- it leads to a vanishing Hall constant at $T=0$. If the field is treated as a smooth contribution to the driving term in the Boltzman equation, the classical Hall constant emerges, in agreement with experiments when the Fermi wavelength is short in comparison with all other lengths in the problem.

cond-mat↗