Moumita Dey

Effect of dephasing on electron transport in a molecular wire: Green’s function approach

Abstract The effect of dephasing on electron transport through a benzene molecule is carefully examined using a phenomenological model introduced by Buttiker. Within a tight-binding framework all the calculations are performed based on the Green’s function formalism. We investigate the influence of dephasing on transmission probability and current–voltage characteristics for three different configurations ( ortho , meta and para ) of the molecular system depending on the locations of two contacting leads. The presence of dephasing provides a significant change in the spectral properties of the molecule and exhibits several interesting patterns that have so far remain unexplored.

Magneto-transport in a mesoscopic ring with Rashba and Dresselhaus spin-orbit interactions

Electronic transport in a one-dimensional mesoscopic ring threaded by a magnetic flux is studied in the presence of Rashba and Dresselhaus spin-orbit interactions. A completely analytical technique within a tight-binding formalism unveils the spin-split bands in the presence of the spin-orbit interactions and leads to a method of determining the strength of the Dresselhaus interaction. In addition to this, the persistent currents for ordered and disordered rings have been investigated numerically. It is observed that the presence of the spin-orbit interaction, in general, leads to an enhanced amplitude of the persistent current. Numerical results corroborate the respective analytical findings.

Spin transport through a quantum network: Effects of Rashba spin-orbit interaction and Aharonov-Bohm flux

We address spin dependent transport through an array of diamonds in the presence of Rashba spin-orbit (SO) interaction where each diamond plaquette is penetrated by an Aharonov–Bohm (AB) flux ϕ. The diamond chain is attached symmetrically to two semi-infinite one-dimensional nonmagnetic metallic leads. We adopt a single particle tight-binding Hamiltonian to describe the system and study spin transport using Green’s function formalism. After presenting an analytical method for the energy dispersion relation of an infinite diamond chain in the presence of Rashba SO interaction, we study numerically the conductance-energy characteristics together with the density of states of a finite sized diamond network. At the typical flux ϕ=ϕ0/2, a delocalizing effect is observed in the presence of Rashba SO interaction, and, depending on the specific choices of SO interaction strength and AB flux the quantum network can be used as a spin filter. Our analysis may be inspiring in designing spintronic devices.

Spin-orbit interaction induced spin selective transmission through a multi-terminal mesoscopic ring

Spin dependent transport in a multi-terminal mesoscopic ring is investigated in presence of Rashba and Dresselhaus spin-orbit interactions. Within a tight-binding framework, we use a general spin density matrix formalism to evaluate all three components (Px, Py, and Pz) of the polarization vector associated with the charge current through the outgoing leads. It explores the dynamics of the spin polarization vector of current propagating through the system subjected to the Rashba and/or the Dresselhaus spin-orbit couplings. The sensitivity of the polarization components on the electrode-ring interface geometry is discussed in detail. Our present analysis provides an understanding of the coupled spin and electron transport in mesoscopic bridge systems.

Logical XOR gate response in a quantum interferometer: A spin dependent transport

Abstract. We examine spin dependent transport in a quantum interferometer composed of magnetic atomic sites based on transfer matrix formalism. The interferometer, threaded by a magnetic flux ϕ, is symmetrically attached to two semi-infinite one-dimensional (1D) non-magnetic electrodes, namely, source and drain. A simple tight-binding model is used to describe the bridge system, and, here we address numerically the conductance-energy and current-voltage characteristics as functions of the interferometer-to-electrode coupling strength, magnetic flux and the orientation of local the magnetic moments associated with each atomic site. Quite interestingly it is observed that, for ϕ = ϕ0/2 (ϕ0 = ch/e, the elementary flux-quantum) a logical XOR gate like response is observed, depending on the orientation of the local magnetic moments associated with the magnetic atoms in the upper and lower arms of the interferometer, and it can be changed by an externally applied gate magnetic field. This aspect may be utilized in designing a spin based electronic logic gate.

Magnetic quantum wire as a spin filter: An exact study

We propose that a magnetic quantum wire composed of magnetic and non-magnetic atomic sites can be used as a spin filter for a wide range of applied bias voltage. We adopt a simple tight-binding Hamiltonian to describe the model where the quantum wire is attached to two semi-infinite one-dimensional non-magnetic electrodes. Based on single particle Greens function formalism all the calculations which describe two-terminal conductance and current through the wire are performed numerically. Our exact results may be helpful in fabricating mesoscopic or nano-scale spin filter.

Magnetic field induced metal-insulator transition in a kagome nanoribbon

In the present work, we investigate two-terminal electron transport through a finite width kagome lattice nanoribbon in presence of a perpendicular magnetic field. We employ a simple tight-binding (T-B) Hamiltonian to describe the system and obtain the transmission properties by using Green’s function technique within the framework of Landauer-Buttiker formalism. After presenting an analytical description of energy dispersion relation of a kagome nanoribbon in presence of the magnetic field, we investigate numerically the transmittance spectra together with the density of states and current-voltage characteristics. It is shown that for a specific value of the Fermi energy, the kagome network can exhibit a magnetic field induced metal-insulator transition, which is the central investigation of this communication. Our analysis may be inspiring in designing low-dimensional switching devices.

Spin Hall effect in a Kagome lattice driven by Rashba spin-orbit interaction

Using four-terminal Landauer-Buttiker formalism and Green’s function technique, in this present paper, we calculate numerically spin Hall conductance (SHC) and longitudinal conductance of a finite size kagome lattice with Rashba spin-orbit (SO) interaction both in the presence and absence of external magnetic flux in clean limit. In the absence of magnetic flux, we observe that depending on the Fermi surface topology of the system SHC changes its sign at certain values of Fermi energy. Unlike the infinite system (where SHC is a universal constant ±e8π), here SHC depends on the external parameters like SO coupling strength, Fermi energy, etc. We show that in the presence of any arbitrary magnetic flux, periodicity of the system is lost and the features of SHC tend to get reduced because of elastic scattering. But again at some typical values of flux (ϕ=12, 14, 34…, etc.) the system retains its periodicity depending on its size and the features of spin Hall effect (SHE) reappears. Our predicted results may ...

Integer quantum Hall effect in a square lattice revisited

Abstract We investigate the phenomenon of integer quantum Hall effect in a square lattice, subjected to a perpendicular magnetic field, through Landauer–Buttiker formalism within the tight-binding framework. The oscillating nature of longitudinal resistance and near complete suppression of momentum relaxation processes are examined by studying the flow of charge current using Landauer–Keldysh prescription. Our analysis for the lattice model corroborates the finding obtained in the continuum model and provides a simple physical understanding.

Topological Effect on Spin Transport in a Magnetic Quantum Wire: Green's Function Approach

We explore spin dependent transport through a magnetic quantum wire which is attached to two non-magnetic metallic electrodes. We adopt a simple tight-binding Hamiltonian to describe the model where the quantum wire is attached to two semi-infinite one-dimensional non-magnetic electrodes. Based on single particle Greens function formalism all the calculations are performed numerically which describe two-terminal conductance and current-voltage characteristics through the wire. Quite interestingly we see that, beyond a critical system size probability of spin flipping enhances significantly that can be used to design a spin flip device. Our numerical study may be helpful in fabricating mesoscopic or nano-scale spin devices.