Quantum transport in a single molecular transistor at finite temperature (original) (raw)
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This thesis presents a series of studies into the electronic, thermal and thermoelectric properties of molecular junctions containing single organic molecules. The exploration and understanding the electronic and phononic characteristics of molecules connected to metallic leads is a vital part of nanoscience if molecular electronics is to have a future. This thesis documents a study for various families of organic and organometallic molecules, studied using a combination of density functional theory (DFT), which is implemented in the SIESTA code, and the Green’s function formalism of transport theory. The main results of this thesis are as follows: To elucidate the nature of the high and low conductance groups observed in break-junction measurements of single 4,4-bipyridine molecules, I present a combined experimental and theoretical study of the electrical conductance of a family of 4,4-bipyridine molecules, with a series of sterically-induced twist angles α between the two pyridyl...
Journal of Applied Physics
Quantum magneto-transport in a dissipative single molecular transistor is investigated at finite temperature in the presence of electron correlation and electron–phonon interaction within the framework of the Anderson–Holstein–Caldeira–Leggett Hamiltonian. The electron–phonon interaction and dissipation are dealt with by canonical transformations and the Coulomb correlation is treated at the mean-field level. The transport properties such as spectral function, tunneling current, differential conductance, and spin polarization are determined using the Keldysh method.
Quantum magneto-transport in a dissipative single molecular transistor is investigated at finite temperature in the presence of electron correlation and electron-phonon interaction within the framework of the Anderson-Holstein-Caldeira-Leggett Hamiltonian. The electron-phonon interaction and dissipation are dealt with by canonical transformations and the Coulomb correlation is treated at the mean-field level. The transport properties such as spectral function, tunneling current, differential conductance and spin polarization are determined using the Keldysh method.
DAE SOLID STATE PHYSICS SYMPOSIUM 2018, 2019
The quantum transport properties of a single molecular transistor are studied in the presence of an external magnetic field using the Keldysh Green function technique. The Anderson-Holstein-Caldeira-Leggett model is used to describe the single molecular transistor that consists of a molecular quantum dot (QD) coupled to two metallic leads and placed on a substrate that acts as a heat bath. The local electron-phonon (el-ph) interaction in the QD is decoupled by the Lang-Firsov (LF) transformation and the effective Hamiltonian is used to study the effects of an external magnetic field on the tunneling current and spin polarization of a SMT at zero temperature.
Linear response quantum transport through interacting multi-orbital nanostructures
Cornell University - arXiv, 2022
Nanoelectronics devices, such as quantum dot systems or single-molecule transistors, consist of a quantum nanostructure coupled to a macroscopic external electronic circuit. Thermoelectric transport between source and drain leads is controlled by the quantum dynamics of the lead-coupled nanostructure, through which a current must pass. Strong electron interactions due to quantum confinement on the nanostructure produce nontrivial conductance signatures such as Coulomb blockade and Kondo effects, which become especially pronounced at low temperatures. In this work we first provide a modern review of standard quantum transport techniques, focusing on the linear response regime, and highlight the strengths and limitations of each. In the second part, we develop an improved numerical scheme for calculation of the ac linear electrical conductance through generic interacting nanostructures, based on the numerical renormalization group (NRG) method, and explicitly demonstrate its utility in terms of accuracy and efficiency. In the third part we derive low-energy effective models valid in various commonly-encountered situations, and from them we obtain simple analytical expressions for the low-temperature conductance. This indirect route via effective models, although approximate, allows certain limitations of conventional methodologies to be overcome, and provides physical insights into transport mechanisms. Finally, we apply and compare the various techniques, taking the two-terminal triple quantum dot and the serial multi-level double dot devices as nontrivial benchmark systems.
Scientific Reports
We consider a single molecular transistor in which a quantum dot with local electron–electron and electron–phonon interactions is coupled to two metallic leads, one of which acts like a source and the other like a drain. The system is modeled by the Anderson-Holstein (AH) model. The quantum dot is mounted on a substrate that acts as a heat bath. Its phonons interact with the quantum dot phonons by the Caldeira–Leggett interaction giving rise to dissipation in the dynamics of the quantum dot system. A simple canonical transformation exactly treats the interaction of the quantum dot phonons with the substrate phonons. The electron–phonon interaction of the quantum dot is eliminated by the celebrated Lang-Firsov transformation. The time-dependent current is finally calculated by the Keldysh Green function technique with various types of bias. The transient-time phase diagram is analysed as a function of the system parameters to explore regions that can be used for fast switching in dev...
Transport Through a Quantum Dot with Electron-Phonon Interaction
Materials Today: Proceedings
We theoretically study the electrical transport properties of a single level quantum dot connected to two normal conducting leads, which is coupled to the lattice vibrations. We determine the current through the quantum dot in two different situations: timeindependent and time-averaged. In all situations we consider three cases: when there is no electron-phonon interaction, when the dot electrons interact with optical phonons or when they interact with acoustic phonons. At finite temperatures we take into account the temperature dependence of the chemical potential. We treat the electron-phonon interaction by the canonical transformation method. In the case of electron-longitudinal optical phonon interaction the spectrum contains a subpeak. In the case of electronacoustic phonon interaction the spectrum is continuous. In the time-averaged situation many parasite peaks appear in the spectrum, due to the external time-modulation.
Many-body theory of electronic transport in single-molecule heterojunctions
Physical Review B Condensed Matter and Materials Physics, 2009
A many-body theory of molecular junction transport based on nonequilibrium Green’s functions is developed, which treats coherent quantum effects and Coulomb interactions on an equal footing. The central quantity of the many-body theory is the Coulomb self-energy matrix ΣC of the junction. ΣC is evaluated exactly in the sequential-tunneling limit, and the correction due to finite tunneling width is evaluated self-consistently using a conserving approximation based on diagrammatic perturbation theory on the Keldysh contour. Our approach reproduces the key features of both the Coulomb blockade and coherent transport regimes simultaneously in a single unified transport theory. As a first application of our theory, we have calculated the thermoelectric power and differential conductance spectrum of a benzenedithiol-gold junction using a semiempirical π -electron Hamiltonian that accurately describes the full spectrum of electronic excitations of the molecule up to 8-10 eV.
Temperature dependence of polaronic transport through single molecules and quantum dots
Physical Review B, 2002
Motivated by recent experiments on electric transport through single molecules and quantum dots, we investigate a model for transport that allows for significant coupling between the electrons and a boson mode isolated on the molecule or dot. We focus our attention on the temperature dependent properties of the transport. In the Holstein picture for polaronic transport in molecular crystals the temperature dependence of the conductivity exhibits a crossover from coherent (band) to incoherent (hopping) transport. Here, the temperature dependence of the differential conductance on resonance does not show such a crossover, but is mostly determined by the lifetime of the resonant level on the molecule or dot.