Browsing by Author "Amanatidis, Ilias"

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Effects of Current-Induced Forces on Pt-Benzene-Pt Single-Molecule Junctions
(2014-02-06)
Hsu, Bailey C.
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Amanatidis, Ilias
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Liu, Wei-Lin
;
Tseng, Allen
;
Chen, Yu-Chang
From first-principles approaches, we investigate the torque exerted by the current-induced forces in a highly asymmetric molecular junction, where the benzene molecule is directly connected to the platinum electrodes. We observe that the curved flow of the current streamline around the tilted molecule can induce a net torque, which tends to rotate the benzene molecule, much like the way a stream of water rotates a waterwheel. The magnitude and direction of the net torque are determined by the detailed current density flowing through the molecular junction. Such an asymmetric molecular junction could offer an experimentally practical system for the exploration of an electrically controllable single-molecule motor. The idea given above is also supported by a simple physical model based on the Landauer-Buttiker formula in the tight-binding framework.
Geometrical spin manipulation in Dirac flakes
(2016-02-03)
Kleftogiannis, Ioannis
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Amanatidis, Ilias
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電子物理學系
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Department of Electrophysics
We investigate numerically the spin properties of electrons in flakes made of materials described by the Dirac equation, in the presence of intrinsic spin-orbit coupling (SOC). We show that electrons flowing along the borders of flakes via edge states become helically spin-polarized for strong SOC, for materials with and without a gap at the Fermi energy, corresponding to the massive and massless Dirac equation respectively. The helically spin-polarized electrons create spin-resolved transport, controlled by the flake\'s geometry in a multi-terminal device setup. A simple analytical model containing the basic ingredients of the problem is introduced to get an insight into the helical mechanism, along with our numerical results which are based on an effective tight-binding model.
Thermoelectric Efficiency of Single-Molecule Junctions: Phase Diagram Constructed from First-Principles Calculations
(2015-12-31)
Amanatidis, Ilias
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Kao, Jing-Yao
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Du, Li-Yang
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Pao, Chun-Wei
;
Chen, Yu-Chang
To understand the behavior of thermoelectric efficiency of single-molecule junctions from 0 K to room temperature, we investigated the thermoelectric properties of a dibenzenedithiol (DBDT) single-molecule junction. We investigated its Seebeck coefficient (S), electric conductance (sigma), and electron\'s thermal conductance (kappa(el)) in the framework of Ai/parameter-free density functional theory combined with the Lippmann Schwinger formalism in scattering approach. We observe that the nanojunction is p-type and the value of the Seebeck coefficient at room temperature is around 40 mu V/A, in agreement with the results of the experiment. In addition, we investigate the phonon\'s thermal conductance (kappa(ph)) using (i) the weak-link model suitable for ballistic phonon transport mechanism in the low-temperature quantum regime and (ii) the nonequilibrium molecular dynamics (NEMD) simulation in the high-temperature classical regime. We finally construct the phase diagram for ZT, where the value of ZT reveals the power law behavior that falls into four phases because of the competition between kappa(el) and kappa(ph) and the crossover from the quantum to classical phonon transport mechanism for kappa(ph). Our theory shows the following ZT proportional to T-alpha where x = 2, 0, 2.26, and 3 in different temperature regimes labeled by I, II, III, and IV, respectively.