Prakash Parida

Electronic and magnetic properties of BNC nanoribbons: a detailed computational study

Using density functional theory (DFT), we perform a systematic study of the electronic structure of zigzag edge BNC nanoribbons, which have an equal number of boron, carbon and nitrogen atoms. We study two nanoribbon structures. One of them is terminated by carbon and nitrogen atoms on opposite edges, whereas the other is terminated by carbon and boron atoms on opposite edges. We explore the effect of passivation of the edge atoms on the electronic and magnetic properties of the nanoribbons. We also evaluate the changes in these effects brought about by varying the width of the nanoribbons. Our results show that, for ribbons of small width, the ones with a boron edge show semiconducting behaviour regardless of the nature of edge passivation, whereas nitrogen-edged nanoribbons display a range of conduction properties including half-metallic, metallic and semiconducting properties depending on the nature of edge passivation. On the other hand, ribbons of larger width show metallic behaviour. We also study the effect of external electric fields on the band structure of both boron-edged and nitrogen-edged nanoribbons and the trends in these effects with varying width. We find that both boron- and nitrogen-edged nanoribbons retain their zero-field conduction properties even in the presence of an electric field directed from the boron/nitrogen edge to the carbon edge. Our transport study of hydrogen-passivated carbon- and nitrogen-edged zigzag BNC nanoribbons reveals strong spin-filter properties.

Organometallic vanadium-borazine systems: efficient one-dimensional half-metallic spin filters

Using density functional theory, we have investigated the electronic and magnetic properties of finite-size as well as infinitely periodic organometallic vanadium-borazine systems (Vn(B3N3H6)n + 1 for their possible applications in spintronics devices. From our calculations, we find the Vn(B3N3H6)n + 1 systems to be structurally more stable in comparison to their isoelectronic benzene counterparts (Vn(C6H6)n + 1). All the Vn(B3N3H6)n + 1 systems are found to be ferromagnetically stabilized, with the infinite one-dimensional [V(B3N3H6)]∞ wire exhibiting robust half-metallic behaviour. The Vn(B3N3H6)n + 1clusters are also found to exhibit efficient spin filter properties when coupled to graphene electrodes.

Negative differential resistance in nanoscale transport in the Coulomb blockade regime

Motivated by recent experiments, we have studied the transport behavior of coupled quantum dot systems in the Coulomb blockade regime using the master (rate) equation approach. We explore how electron-electron interactions in a donor-acceptor system, resembling weakly coupled quantum dots with varying charging energy, can modify the systems response to an external bias, taking it from normal Coulomb blockade behavior to negative differential resistance (NDR) in the current-voltage characteristics.

Cyclopentadienyl–benzene based sandwich molecular wires showing efficient spin filtering, negative differential resistance, and pressure induced electronic transitions

Using density functional theory, we investigate TM–cyclopentadienyl–benzene sandwich molecular wires (SMWs) which are composites of TM–cyclopentadienyl and TM–benzene wires (TM = transition metal (V, Fe)). All the SMWs are found to be highly stable ferromagnetic half-metals, showing spin switching behavior. Transport calculations show that finite size clusters display spin filter property when coupled with Au electrodes on either side. I–Vb characteristics of all systems confirm the spin filter property, with Au–BzVCpVBz–Au displaying exceptionally high performance. In addition to spin filtering, the Au–BzFeCpFeBz–Au system also shows negative differential resistance (NDR). Compression causes an abrupt reduction in magnetic moment and a transition to a metallic phase, while stretching causes an increase in magnetic moment. Half-metallicity is preserved for modest amounts of stretching and compression.

Line defects at the heterojunction of hybrid boron nitride–graphene nanoribbons

Using ab initio molecular dynamics (AIMD) simulations, we have explored the structural reconstruction of a special kind of line defect, which is constructed from tetragonal rings and is implanted at the heterojunction of hybrid boron nitride–graphene (BN–C) nanoribbons. It appears that nanoribbons get reconstructed in various ways to form different kinds of line defect depending upon the nature of the atoms at the heterojunction. Along with 5–8–5, we also report two new kinds of line defects, 8–8–8 and 7–4–7, at the heterojunction. The electronic and magnetic properties of the reconstructed nanoribbons are calculated using density functional theory (DFT). These nanoribbons show a wide range of electronic structures ranging from semiconducting to spin polarized metallic behaviour.

Negative differential conductance in nanojunctions: a current constrained approach

A current constrained approach is proposed to calculate negative differential conductance in molecular nanojunctions. A four-site junction is considered where a steady-state current is forced by inserting only the two central sites within the circuit. The two lateral sites (representing, e.g., dangling molecular groups) do not actively participate in transport but exchange electrons with the two main sites. These auxiliary sites allow for a variable number of electrons within the junction, while as required by the current constrained approach, the total number of electrons in the system is kept constant. We discuss the conditions for negative differential conductance in terms of cooperativity, variability of the number of electrons in the junction, and electron correlations.

Spin-crossover molecule based thermoelectric junction

Using ab-initio numerical methods, we explore the spin-dependent transport and thermoelectric properties of a spin-crossover molecule (i.e., iron complex of 2-(1H-pyrazol-1-yl)-6-(1H-tetrazole-5-yl)pyridine) based nano-junction. We demonstrate a large magnetoresistance, efficient conductance-switching, and spin-filter activity in this molecule-based two-terminal device. The spin-crossover process also modulates the thermoelectric entities. It can efficiently switch the magnitude as well as spin-polarization of the thermocurrent. We find that thermocurrent is changed by ∼4 orders of magnitude upon spin-crossover. Moreover, it also substantially affects the thermopower and consequently, the device shows extremely efficient spin-crossover magnetothermopower generation. Furthermore, by tuning the chemical potential of electrodes into a certain range, a pure spin-thermopower can be achieved for the high-spin state. Finally, the reasonably large values of figure-of-merit in the presence and absence of phonon demonstrate a large heat-to-voltage conversion efficiency of the device. We believe that our study will pave an alternative way of tuning the transport and thermoelectric properties through the spin-crossover process and can have potential applications in generation of spin-dependent current, information storage, and processing.