AC-Driven Transport Through Molecular Wires

Abstract

Abstract. We consider electrical transport properties of a molecular wire under the influence of time-dependent electromagnetic fields. A formalism based on Floquet theory is derived which allows one to calculate both the dc current through the molecular wire and the associated noise power. Approximations for the case of a weak wire-lead coupling are studied in detail. IntroductionOwing to the recent experimental progress in the fabrication and characterisation of nanostructures involving single or a few molecules, the research field of molecular electronics currently enjoys a vivid activity, as exemplified by the present volume. Thereby, the main focus has been put on contacting single molecules by nanoelectrodes. This allows one to apply a transport voltage and to measure the resulting electrical current [1][2][3][4][5][6][7][8]. For the corresponding theoretical investigations, two lines of research are presently followed. The one is the ab-initio computation of the orbitals relevant for the motion of excess charges through the molecular wire [9-12], as described in Chaps. 3-6. The other line employs rather universal models to gain a qualitative understanding of the transport mechanisms involved [13][14][15][16][17][18][19]. Two particular problems addressed within model calculations are the conduction mechanism in the presence of electron-phonon coupling [14] and the length dependence of the current-voltage characteristics [13,17]. The present work also employs rather general models: We describe the molecules by a linear arrangement of tight-binding levels with the terminating sites attached to leads.Typical energy scales of molecules lie in the infrared regime where most of today's lasers work. Hence, lasers represent a natural possibility to excite the electrons of the molecular wire and, thus, to study the corresponding changes of the conduction properties [20]. One particular question in this context is the influence of excitations by electromagnetic fields and oscillatory gate voltages on the electron transport. Such excitations bear intriguing phenomena like photon-assisted electron tunnelling [21][22][23] and quantum ratchet effects [24,25]. From a fundamental point of view, these effects are of interest because the external fields enable selective electron excitations and allow one to study their interplay with the underlying transport mechanism. In prac-

Dissipative effects in the electronic transport through DNA molecular wires

“…24,25,26,27,28,29,30,31,32,33,34 To complicate this picture, environmental effects such as the presence of water molecules and counterions which stabilize the molecular structure make ab initio calculations even more challenging. 26,27 Hence, Hamiltonian models 36,37,38,39,40,41,42,43,44,45 that isolate single factors affecting electron transport are still playing a significant role and can help to shed more light onto the above issues as well as guide first principle investigations. Recently, Cuniberti et al 41 proposed a minimal model Hamiltonian to explain the semiconducting behavior previously observed by Porath et al 13 in suspended short (up to 30 base-pairs) poly(dG)-poly(dC) molecules.…”

Driven Liouville von Neumann Equation in Lindblad Form

“…Steady-state transport properties of molecular junctions remain the main focus of both experimental and theoretical efforts in this field. Nevertheless, the study of dynamical transport phenomena in nanoscale junctions has recently gained increasing attention from the scientific community. − Research in this direction explores the effects of time-dependent perturbations such as alternating currents, bias pulses, and external electromagnetic fields on the transient response of the system. This involves complex physical processes that can be harnessed for the design of miniaturized electronic devices such as optoelectronic ultrafast molecular switches and nanoscale rectifiers. ,,,,− ,, …”

Optical Switching of Charge Transmission through a Single Molecule: Effects of Contact Excitations and Molecule Heating

“…Either the fields are supposed to induce molecular conformational transitions − or directly produce excited electronic states of the molecule. For the latter case, mechanisms were studied based on laser pulses from the infrared − or from the visible region (see refs − ). However, only a restricted number of experimental tests of all of these suggestions have been reported so far. − In any case, such a disturbance essentially influences the leads contacting the molecule.…”