چكيده به لاتين
Exploiting the spin degree of freedom in addition to the charge of electrons, is the goal of spintronics for accomplishing and optimizing the efficiency of solid state devices. Besides, investigation of the topological properties of matters has played a leading role during the last decades. Furthermore, exploiting the material properties, persuades researchers in condensed matter and material physics to illustrate the responses of materials to all external interactions like mechanical ones.
In this dissertation, by using Su-Schrieffer-Heeger Hamiltonian and exploiting the Green’s function method in the framework of the Landauer-Büttiker formalism, the topological and spin dependent electron transport properties of a trans polyacetylene molecule are studied. It is found that molecules with the intracell single carbon-carbon bonding and the even number of monomers in their chains have two edge states and possess topological properties though their Hamiltonians do not respect the chiral symmetry. A perpendicular exchange magnetic field and two perpendicular and transverse electric fields are used to induce and manipulate the quantum spin dependent electron transport properties. The exchange field induces the spin polarization in different electron energy regions which are expanded by stronger exchange fields. Therefore this proposed device works as a perfect spin filter. The spin polarization can be manipulated by applying the perpendicular electric field and remains robust against the transverse electric field variations.
Moreover, utilizing the linear combination of atomic orbitals in the Slater–Koster approach in combination with the density functional theory band structure data, a new tight-binding Hamiltonian up to the third nearest neighbours for the dimerized trans polyacetylene is proposed. The effects of strain are also considered in the Hamiltonian by varying the distance between two successive CH groups along the molecular symmetry axis. Using this new Hamiltonian, the electronic transport properties in a trans polyacetylene chain in the presence and absence of strain are studied. It is shown that at a peculiar value of compression strain, the electron conductance shifts 0.27 eV in energy which is an exploitable magnitude for straintronic applications of the trans polyacetylene specially as strain sensors and strain switches.
