arXiv subjects

Jörg Lehmann

Publications and source records attributed to Jörg Lehmann.

24 records · Page 2Linked to original sources

arXiv2002

Rectification of laser-induced electronic transport through molecules

We study the influence of laser radiation on the electron transport through a molecular wire weakly coupled to two leads. In the absence of a generalized parity symmetry, the molecule rectifies the laser induced current, resulting in directed electron transport without any applied voltage. We consider two generic ways of dynamical symmetry breaking: mixing of different harmonics of the laser field and molecules consisting of asymmetric groups. For the evaluation of the nonlinear current, a numerically efficient formalism is derived which is based upon the Floquet solutions of the driven molecule. This permits a treatment in the non-adiabatic regime and beyond linear response.

cond-mat.mes-hall↗

arXiv2002

Laser controlled molecular switches and transistors

We investigate the possibility of optical current control through single molecules which are weakly coupled to leads. A master equation approach for the transport through a molecule is combined with a Floquet theory for the time-dependent molecule. This yields an efficient numerical approach to the evaluation of the current through time-dependent nano-structures in the presence of a finite external voltage. We propose tunable optical current switching in two- and three-terminal molecular electronic devices driven by properly adjusted laser fields, i.e. a novel class of molecular transistors.

physics.chem-ph↗

arXiv2002

Molecular Wires Acting as Coherent Quantum Ratchets

The effect of laser fields on the electron transport through a molecular wire being weakly coupled to two leads is investigated. The molecular wire acts as a coherent quantum ratchet if the molecule is composed of periodically arranged, asymmetric chemical groups. This setup presents a quantum rectifier with a finite dc-response in the absence of a static bias. The nonlinear current is evaluated in closed form within the Floquet basis of the isolated, driven wire. The current response reveals multiple current reversals together with a nonlinear dependence (reflecting avoided quasi-energy crossings) on both, the amplitude and the frequency of the laser field. The current saturates for long wires at a nonzero value, while it may change sign upon decreasing its length.

cond-mat.mes-hall↗

arXiv2001

Incoherent charge transport through molecular wires: interplay of Coulomb interaction and wire population

The influence of Coulomb interaction on the electron transport through molecular wires is studied in the regime of incoherent tunneling. In the limit of strong Coulomb repulsion, the current for spinless electrons is determined. It is shown that the voltage profile along the wire crucially influences the dependence of the current on the wire length. Upon inclusion of the spin degree of freedom one finds a blocking effect which depends both on the interaction strength and on the population of the wire. For finite Coulomb interaction, the temperature dependence of the blocking is studied and it is shown that several regimes with different blocking strength may exist.

physics.chem-ph↗

arXiv2000

Surmounting Oscillating Barriers: Path-integral approach for Weak Noise

We consider the thermally activated escape of an overdamped Brownian particle over a potential barrier in the presence of periodic driving. A time-dependent path-integral formalism is developed which allows us to derive asymptotically exact weak-noise expressions for both the instantaneous and the time-averaged escape rate. Our results comprise a conceptionally new, systematic treatment of the rate prefactor multiplying the exponentially leading Arrhenius factor. Moreover, an estimate for the deviations at finite noise-strengths is provided and a supersymmetry-type property of the time averaged escape rate is verified. For piecewise parabolic potentials, the rate-expression can be evaluated in closed analytical form, while in more general cases, as exemplified by a cubic potential, an action-integral remains to be minimized numerically. Our comparison with very accurate numerical results demonstrates an excellent agreement with the theoretical predictions over a wide range of driving strengths and driving frequencies.

cond-mat.stat-mech↗

arXiv1999

Surmounting Oscillating Barriers

Thermally activated escape over a potential barrier in the presence of periodic driving is considered. By means of novel time-dependent path-integral methods we derive asymptotically exact weak-noise expressions for both the instantaneous and the time-averaged escape rate. The agreement with accurate numerical results is excellent over a wide range of driving strengths and driving frequencies.

cond-mat.stat-mech↗