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To manufacture an efficient thermoelectric device at the nanoscale and to get its controlled performance, we suggest a finite-width diamond ribbon in the presence of a perpendicular magnetic field. Contemplating the asymmetry in transmission function in a narrow conducting channel, the possibility of a gap around the energy band center in the presence of a magnetic field is discussed here. The eigenvalue spectrum and band structures show several interesting features. The different thermoelectric quantities are evaluated following the Landauer prescription. We show that the gap is tunable by controlling the strength of the magnetic field. Near the edge of the gap, our results exhibit a favorable thermoelectric response. We believe that our analysis of the proposed model can be experimentally tested in the laboratory and hope our study helps to construct an efficient thermoelectric device at the mesoscopic level.

The key requirement for an enhanced thermoelectric (TE) performance is the presence of asymmetry in transmission function. Focussing on this issue, we propose a unique idea to enhance TE performance in a graphene nanoribbon (GNR) that has not been explored so far to the best of our concern. In the present work, one part of the GNR is considered as a disordered region while the rest of the system is clean. Such an ordered-disordered separated structure yields more asymmetric transmission function over the conventional uniform disordered one. Finally, we include the effect of electron–electron (e–e) interaction to check whether it brings any non-trivial signature on TE performance. The e–e interaction is taken in the form of an on-site Hubbard model and we compute our results within a Hartree–Fock mean field approach. The results obtained in the present work exhibit quite remarkable TE performance along with some non-trivial features.

Generally, pristine graphene nanoribbons show poor thermoelectric (TE) performance. Several proposals are available to enhance the TE performance, which however requires some highly structural modifications of the system. In the present work, we explore a new prescription where a favorable TE response can be achieved by irradiating the ribbon. The electronic conductance, thermopower and thermal conductance due to electron are found to be highly sensitive to the irradiation. We obtain significantly enhanced thermopower along with highly suppressed thermal conductance for typical sets of irradiation parameters. As a result of this higher figure of merit is found. Therefore, we can suggest that a graphene nanoribbon can be used as an efficient energy conversion device in the presence of irradiation and hope that it will bear a significant impact in the energy market soon.

Electronic transport with a line (or a few lines) of Anderson type disorder in a zigzag graphene nanoribbon is investigated in presence of Rashba spin-orbit interaction. Such line disorders give rise to peculiar behavior in both charge as well as spin-polarized transmission in the following sense. In the weak disorder regime, the charge transport data show Anderson localization up to a certain disorder strength, beyond which the extended states emerge and start dominating over the localized states. These results are the hallmark signature of a selectively disordered (as opposed to bulk disorder) graphene nanoribbon. However, the spin-polarized transport shows a completely contradicting behavior. Further, the structural symmetries are shown to have an important role in the spintronic properties of the nanoribbons. Moreover, the edge-disorder scenario (disorder selectively placed at the edges) seems to hold promise for the spin-filter and switching device applications., 7 pages, 7 figures (Accepted for Publication in Europhysics Letters)

We investigate a novel way to manipulate the spin polarized transmission in a two terminal zigzag graphene nanoribbon in presence of Rashba spin-orbit (SO) interaction with circular shaped cavity engraved into it. A usual technique to control the spin polarized transport behaviour of a nanoribbon can be achieved by tuning the strength of the SO coupling, while we show that an efficient engineering of the spin polarized transport properties can also be done via cavities of different radii engraved in the nanoribbon. Simplicity of the technique in creating such cavities in the experiments renders an additional handle to explore transport properties as a function of the location of the cavity in the nanoribbon. Further, a systematic assessment of the interplay of the Rashba interaction and the dimensions of the nanoribbon is presented. These results should provide useful input to the spintronic behaviour of such devices. In addition to the spin polarization, we have also included an interesting discussion on the charge transmission properties of the nanoribbon, where, in absence of any SO interaction a metal-insulator transition induced by the presence of a cavity is observed., 7 pages, 9 figures (Accepted in Europhysics Letters)

We study the spin Hall effect in Y-shaped junction devices in presence of Rashba spin orbit coupling (RSOC). The voltage and the net spin current registered at one of the arms of the Y-junction are seen to increases although the spin Hall conductance (SHC) diminishes as the strength of the RSOC is increased. This implies the voltage increases further than that of the current, thereby causing a loss of the RSOC. Various other characteristic features obtained from our study include, a perfectly antisymmetric behaviour of the spin current and the SHC with respect to the zero bias, while the voltage shows a symmetric character. Finally a large RSOC completely destroys the SHC, owing to a complete disappearance of the local density of states, thereby reinforcing our earlier claim that RSOC emulates the effect of disorder on the quantum conductance of junction device.

In a system consisting of a metal-(s-wave) superconductor junction, we study the conductance characteristics in presence of Rashba spin orbit coupling (RSOC) and an external magnetic field applied along the plane of the sample. With a selective inclusion of the Rashba coupling either in the metallic or in both we note that there is a distinct effect with regard to the magnitude of the Andreev peak that occurs at a biasing voltage lower than the superconducting gap energy. The height of the peak is sensitive to the RSOC (increases with increase in RSOC) for RSOC to be present only in the metallic region, (same is true when RSOC is present throughout the junction), while the peak height is fairly independent when RSOC is solely present in the superconducting region. The in-plane magnetic field has very interesting effects which show up in the form of having a conductance peak at zero bias, thereby making it possible to realize a Majorana bound state.

Using the multi-probe Landauer-BUttiker formula and Green's function approach, we calculate the longitudinal conductance (LC) and spin Hall conductance (SHC) numerically in a two-dimensional junction system with the Rashba and Dresselhaus spin orbit coupling (SOC) and spin dependent disorder (SDD) in presence of both random onsite and hopping disorder strengths. It has been found that when the strengths of the RSOC and DSOC are same, the SHC vanishes. Further in presence of random onsite or hopping disorder, the SHC is still zero when the strengths of the two types of SOC, that is Rashba and Dressselhaus are the same. This indicates that the cancellation of SHC is robust even in the presence of random disorder. Only with the inclusion of SDD (onsite or hopping), a non-zero SHC is found and it increases as the strength of SDD increases. The physical implication of the existence of a non-zero SHC has been explored in this work. Finally, we have compared the effect of onsite SDD and hopping SDD on both longitudinal and spin Hall conductances.