arXiv subjects

Maarten R. Wegewijs

Publications and source records attributed to Maarten R. Wegewijs.

21 records · Page 2Linked to original sources

arXiv2008

Nonequilibrium Dynamics of Anisotropic Large Spins in the Kondo Regime: Time-Dependent Numerical Renormalization Group Analysis

We investigate the time-dependent Kondo effect in a single-molecule magnet (SMM) strongly coupled to metallic electrodes. Describing the SMM by a Kondo model with large spin S > 1/2, we analyze the underscreening of the local moment and the effect of anisotropy terms on the relaxation dynamics of the magnetization. Underscreening by single-channel Kondo processes leads to a logarithmically slow relaxation, while finite uniaxial anisotropy causes a saturation of the SMM's magnetization. Additional transverse anisotropy terms induce quantum spin tunneling and a pseudospin-1/2 Kondo effect sensitive to the spin parity.

cond-mat.str-el↗

arXiv2006

Nuclear wave function interference in single-molecule electron transport

It is demonstrated that non-equilibrium vibrational effects are enhanced in molecular devices for which the effective potential for vibrations is sensitive to the charge state of the device. We calculate the electron tunneling current through a molecule accounting for the two simplest qualitative effects of the charging on the nuclear potential for vibrational motion: a shift (change in the equilibrium position) and a distortion (change in the vibrational frequency). The distortion has two important effects: firstly, it breaks the symmetry between the excitation spectra of the two charge states. This gives rise to new transport effects which map out changes in the current-induced non-equilibrium vibrational distribution with increasing bias voltage. Secondly, the distortion modifies the Franck-Condon factors for electron tunneling. Together with the spectral asymmetry this gives rise to pronounced nuclear wave function interference effects on the electron transport. For instance nuclear-parity forbidden transitions lead to differential conductance anti-resonances, which are stronger than those due to allowed transitions. For special distortion and shift combinations a coherent suppression of transport beyond a bias voltage threshold is possible.

cond-mat.mes-hall↗

arXiv2005

Vibration-assisted tunneling through competing molecular states

We calculate the non-linear tunneling current through a molecule with two electron-accepting orbitals which interact with an intramolecular vibration. We investigate the interplay between Coulomb blockade and non-equilibrium vibration-assisted tunneling under the following assumptions: (i) The Coulomb charging effect restricts the number of extra electrons to one. (ii) The orbitals are non-degenerate and couple asymmetrically to the vibration. (iii) The tunneling induces a non-equilibrium vibrational distribution; we compare with the opposite limit of strong relaxation of the vibration due to some dissipative environment. We find that a non-equilibrium feedback mechanism in the tunneling transitions generates strong negative differential conductance (NDC) in the model with two competing orbitals, whereas in a one-orbital model it leads only to weak NDC. In addition, we find another mechanism leading to weak NDC over a broader range of applied voltages. This pervasive effect is completely robust against strong relaxation of the vibrational energy. Importantly, the modulation of the electronic transport is based on an intramolecular asymmetry. We show that one can infer a non-equilibrium vibrational distribution when finding NDC under distinct gate- and bias-voltage conditions. In contrast, we demonstrate that any NDC effect in the one-orbital case is completely suppressed in the strong relaxation limit.

cond-mat.mes-hall↗