Magneto-transport in the monolayer MoS2material system for high-performance field-effect transistor applications

Electronic transport in monolayer MoS2is significantly constrained by several extrinsic factors despite showing good prospects as a transistor channel material. Our paper aims to unveil the underlying mechanisms of the electrical and magneto-transport in monolayer MoS2. In order to quantitatively interpret the magneto-transport behavior of monolayer MoS2on different substrate materials, identify the underlying bottlenecks, and provide guidelines for subsequent improvements, we present a deep analysis of the magneto-transport properties in the diffusive limit. Our calculations are performed on suspended monolayer MoS2and MoS2on different substrate materials taking into account remote impurity and the intrinsic and extrinsic phonon scattering mechanisms. We calculate the crucial transport parameters such as the Hall mobility, the conductivity tensor elements, the Hall factor, and the magnetoresistance over a wide range of temperatures, carrier concentrations, and magnetic fields. The Hall factor being a key quantity for calculating the carrier concentration and drift mobility, we show that for suspended monolayer MoS2at room temperature, the Hall factor value is around 1.43 for magnetic fields ranging from 0.001 to 1 Tesla, which deviates significantly from the usual value of unity. In contrast, the Hall factor for various substrates approaches the ideal value of unity and remains stable in response to the magnetic field and temperature. We also show that the MoS2over an Al2O3substrate is a good choice for the Hall effect detector. Moreover, the magnetoresistance increases with an increase in magnetic field strength for smaller magnetic fields before reaching saturation at higher magnetic fields. The presented theoretical model quantitatively captures the scaling of mobility and various magnetoresistance coefficients with temperature, carrier densities, and magnetic fields.

Can magnetotransport properties provide insight into the functional groups in semiconducting MXenes?

Hall scattering factors of Sc₂CF₂, Sc₂CO₂ and Sc₂C(OH)₂ are calculated using Rode's iterative approach by solving the Boltzmann transport equation. This is carried out in conjunction with calculations based on density functional theory. The electrical transport in Sc₂CF₂, Sc₂CO₂ and Sc₂C(OH)₂ is modelled by accounting for both elastic (acoustic and piezoelectric) and inelastic (polar optical phonon) scattering. Polar optical phonon (POP) scattering is the most significant mechanism in these MXenes. We observe that there is a window of carrier concentration where the Hall factor acts dramatically; Sc₂CF₂ obtains an incredibly high value of 2.49 while Sc₂CO₂ achieves a very small value of approximately 0.5, and Sc₂C(OH)₂ achieves the so called ideal value of 1. We propose in this paper that such Hall factor behaviour has significant promise in the field of surface group identification in MXenes, an issue that has long baffled researchers.

Role of dephasing on the conductance signatures of Majorana zero modes

Conductance signatures that signal the presence of Majorana zero modes in a three terminal nanowire-topological superconductor hybrid system are analyzed in detail, in both the clean nanowire limit and in the presence of non-coherent dephasing interactions. In the coherent transport regime for a clean wire, we point out contributions of the local Andreev reflection and the non-local transmissions toward the total conductance lineshapes while clarifying the role of contact broadening on the Majorana conductance lineshapes at the magnetic field parity crossings. Interestingly, at largerB-field parity crossings, the contribution of the Andreev reflection process decreases which is compensated by the non-local processes in order to maintain the conductance quantum regardless of contact coupling strength. In the non-coherent transport regime, we include dephasing that is introduced by momentum randomization processes, that allows one to smoothly transition to the diffusive limit. Here, as expected, we note that while the Majorana character of the zero modes is unchanged, there is a reduction in the conductance peak magnitude that scales with the strength of the impurity scattering potentials. Dephasing due to fluctuating impurities is shown to affect the conductance lineshapes in ways that are distinguishable from the effects of contact-induced tunnel broadening. Most importantly our results reveal that the addition of dephasing in the set up does not lead to any notable length dependence to the conductance of the zero modes, contrary to what one would expect in a gradual transition to the diffusive limit. We believe this work paves a way for a systematic introduction of scattering processes into the realistic modeling of Majorana nanowire hybrid devices and assessing topological signatures in such systems in the presence of non-coherent scattering processes.

Exact eigenvectors and eigenvalues of the finite Kitaev chain and its topological properties

We present a comprehensive, analytical treatment of the finite Kitaev chain for arbitrary chemical potential and chain length. By means of an exact analytical diagonalization in the real space, we derive the momentum quantization conditions and present exact analytical formulas for the resulting energy spectrum and eigenstate wave functions, encompassing boundary and bulk states. In accordance with an analysis based on the winding number topological invariant, and as expected from the bulk-edge correspondence, the boundary states are topological in nature. They can have zero, exponentially small or even finite energy. Further, for a fixed value of the chemical potential, their properties are ruled by the ratio of the decay length to the chain length. A numerical analysis confirms the robustness of the topological states against disorder.

Semi-classical electronic transport properties of ternary compound AlGaAs2: role of different scattering mechanisms

Using Rode's iterative method, we have investigated the semi-classical transport properties of the n-type ternary compound AlGaAs₂. Four scattering mechanisms have been included in our transport calculation, namely, ionized impurity, piezoelectric, acoustic deformation and polar optical phonon (POP). The scattering rates have been calculated in terms of ab initio parameters. We consider AlGaAs₂ to have two distinct crystal geometries, one in tetragonal phase (space group: [Formula: see text]), while the other one having body centered tetragonal crystal structure (space group: [Formula: see text]). Higher electron mobility has been observed in the body centered tetragonal phase, thereby making it more suitable for high mobility device application, over the tetragonal phase. In order to understand the differences in electron mobility for these two phases, curvatures of the E-k dispersion of the conduction bands for these phases have been compared. At room temperature, the dominant contribution in electron mobility was found to be provided by inelastic POP scattering. We have also noted that mobility is underestimated in relaxation time approximation compared with the Rode's iterative approach.

Manipulation of non-linear heat currents in the dissipative Anderson-Holstein model

The precise control of phonon heat currents will be of primary importance in emerging phononic devices. In this paper, a detailed analysis of electronically controled phonon transport is carried out using an Anderson-Holstein based dissipative quantum dot setup. We consider two relevant electronic bias situations: (a) a voltage bias in the absence of an electronic temperature gradient and (b) an electronic temperature gradient at zero voltage. It is shown that the direction of phonon transport in the non-linear regime is different in the two cases since the first case facilitates the accumulation of phonons in the dot and the second case leads to the absorption of phonons in the dot. In the linear regime, both the phonon and electronic transport get decoupled and Onsager's symmetry is verified. We explain the observed cumulative effects of voltage and electronic temperature gradients on the non-linear phonon currents by introducing a new transport coefficient that we term as the electron induced phonon thermal conductivity. It is demonstrated that under suitable operating conditions in Case (a) the dot can pump in phonons into the hotter phonon reservoirs and in Case (b) the dot can extract phonons out of the colder phonon reservoirs. Finally, as a corollary, we elaborate on how the non-linear electronic heat current can be stimulated and controlled by manipulating the temperature of the phonon reservoirs even under vanishing effective electronic charge flow.

Ab initio semi-classical electronic transport in ZnSe: the role of inelastic scattering mechanisms

We present a detailed ab initio study of semi-classical transport in n-ZnSe using Rode's iterative method. Inclusion of ionized impurity, piezoelectric, acoustic deformation and polar optical phonon scattering and their relative importance at low and room temperature for various n-ZnSe samples are discussed in depth. We have clearly noted that inelastic polar optical phonon scattering is the most dominant scattering mechanism over most of the temperature region. Our results are in good agreement with the experimental data for the mobility and conductivity obtained at different doping concentrations over a wider range of temperatures. Also we compare these results with the ones obtained with relaxation time approximation (RTA) which clearly demonstrate the superiority of the iterative method over RTA.

Incoherent scattering can favorably influence energy filtering in nanostructured thermoelectrics

Investigating in detail the physics of energy filtering through a single planar energy barrier in nanostructured thermoelectric generators, we reinforce the non-trivial result that the anticipated enhancement in generated power at a given efficiency via energy filtering is a characteristic of systems dominated by incoherent scattering and is absent in ballistic devices. In such cases, assuming an energy dependent relaxation time τ(E) = kE^r, we show that there exists a minimum value r_min beyond which generation can be enhanced by embedding nanobarriers. For bulk generators with embedded nanobarriers, we delve into the details of inter sub-band scattering and show that it has finite contribution to the enhancement in generation. We subsequently discuss the realistic aspects, such as the effect of smooth transmission cut-off and show that for r > r_min, the optimized energy barrier is just sufficiently wide enough to scatter off low energy electrons, a very wide barrier being detrimental to the performance. Analysis of the obtained results should provide general design guidelines for enhancement in thermoelectric generation via energy filtering. Our non-equilibrium approach is typically valid in the absence of local quasi-equilibrium and hence sets the stage for future advancements in thermoelectric device analysis, for example, Peltier cooling near a barrier interface.

Proposal for a Domain Wall Nano-Oscillator driven by Non-uniform Spin Currents

We propose a new mechanism and a related device concept for a robust, magnetic field tunable radio-frequency (rf) oscillator using the self oscillation of a magnetic domain wall subject to a uniform static magnetic field and a spatially non-uniform vertical dc spin current. The self oscillation of the domain wall is created as it translates periodically between two unstable positions, one being in the region where both the dc spin current and the magnetic field are present, and the other, being where only the magnetic field is present. The vertical dc spin current pushes it away from one unstable position while the magnetic field pushes it away from the other. We show that such oscillations are stable under noise and can exhibit a quality factor of over 1000. A domain wall under dynamic translation, not only being a source for rich physics, is also a promising candidate for advancements in nanoelectronics with the actively researched racetrack memory architecture, digital and analog switching paradigms as candidate examples. Devising a stable rf oscillator using a domain wall is hence another step towards the realization of an all domain wall logic scheme.

Quantitative ethnomedicinal study of plants used in the Nelliyampathy hills of Kerala, India

ETHNOPHARMACOLOGICAL RELEVANCE

Inspite of tremendous advances made in allopathic medical practices, medicinal plants have played an important role throughout the world in treating and preventing a variety of diseases and hence there is urgency in recording such data. This is the first ethnobotanical study in which statistical calculations about plants are done by the Pearson correlation coefficient (PCC) method. The present study was aimed to identify plants collected for medicinal purposes by the traditional healers of Nelliyampathy hills, located in Palakkad district of Kerala, India and to document the traditional names, preparation and uses of these plants.

METHODS

The field study was carried out over a period of 2 years (2011-2013) using semi-structured interviews with 66 informants (most of the informants belonged to an age between 50 and 70 years) in six remote locations in the hills. Ethnomedicinal data was analyzed using frequency citation (FC), relative frequency of citation (RFC) and use value (UV) along with a Pearson correlation coefficient (PCC). Demographic characteristics of participants, ethnobotanical inventory of plants and data on medicinal application and administration were recorded.

RESULTS

A total of 85 medicinal plants belonging to 49 families were reported to be used against 19 different ailments in the hills. The maximum reported medicinal plant families were Cucurbitaceae with 6 species followed by Acanthaceae, Malvaceae and Fabaceae (each 5 species), Asteraceae, Lamiaceae, Moraceae and Myrtaceae (each 3 species), the most dominant life form of the species includes herbs (42) followed by tree (20), climber (15) and shrub (8), the most frequent used part was leaves (40%) followed by root (14%), seed and flowers (each12%), fruit (9%), bark (7%), stem (2%), latex (2%), rhizome and whole plant (each 1%), the most common preparation and administration methods were paste (32%), powder (22%), decoction and juice (each 20%) and raw (4%), infusion and inhalation (each1% ). The Pearson correlation coefficient between RFC and UV was 0.638 showing highly positive significant association.

CONCLUSIONS

In this study, we have documented considerable indigenous knowledge about the native medicinal plants in Nelliyampathy hills for treating common ailments. The plants such as further investigated phytochemically and pharmacologically which leads to natural drug discovery development may be based on the present study. The study has various socioeconomic dimensions which are associated with the local communities.

Role of dual nuclear baths on spin blockade leakage current bistabilities

Spin-blockaded electronic transport across a double quantum dot (DQD) system represents an important advancement in the area of spin-based quantum information. The basic mechanism underlying the blockade is the formation of a blocking triplet state. The bistability of the leakage current as a function of the applied magnetic field in this regime is believed to arise from the effect of nuclear Overhauser fields on spin-flip transitions between the blocking triplet and the conducting singlet states. The objective of this paper is to present the nuances of considering a two bath model on the experimentally observed current bistability by employing a self consistent simulation of the nuclear spin dynamics coupled with the electronic transport of the DQD set up. In doing so, we first discuss the important subtleties involved in the microscopic derivation of the hyperfine mediated spin flip rates. We then give insights as to how the differences between the two nuclear baths and the resulting difference Overhauser field affect the two-electron states of the DQD and their connection with the experimentally observed current hysteresis curve.

The role of many-particle excitations in Coulomb blockaded transport

We discuss the role of electron-electron and electron-phonon correlations in current flow in the Coulomb blockade regime, focusing specifically on non-trivial signatures arising from the breakdown of mean-field theory. By solving transport equations directly in Fock space, we show that electron-electron interactions manifest as gateable excitations experimentally observed in the current-voltage characteristic. While these excitations might merge into an incoherent sum that allows occasional simplifications, a clear separation of excitations into slow 'traps' and fast 'channels' can lead to further novelties such as negative differential resistance, hysteresis and random telegraph signals. Analogous novelties for electron-phonon correlation include the breakdown of commonly anticipated Stokes-anti-Stokes intensities, and an anomalous decrease in phonon population upon heating due to reabsorption of emitted phonons.

A "cleanup procedure" involving periodate oxidation in the enzymatic synthesis of chemically pure alpha-32P and alpha-33P labelled deoxyribonucleotides

Enzymatic synthesis of alpha-(32)P and alpha-(33)P labelled deoxyribonucleotides involves the transfer of radiolabelled phosphorus from either gamma-(32)P adenosine triphosphate (gamma-ATP) or gamma-(32)P guanosine triphosphate (gamma-GTP). Subsequent removal of these ribonucleotides is essential for the preparation of chemically pure deoxyribonucleotides. Agarose-phenyl boronate columns, which bind specifically to cis-diol moieties, have been used for the removal of ribonucleotide contaminants. However, this involves column losses and additional radiation exposure. In the present work we describe a chemical method for the improvement of the chemical purity, based on the preferential oxidation of ribose sugars by periodate. The cis-diol moiety of ribose is specifically oxidised to the dialdehyde. The excess periodate ions were destroyed using ethylene glycol. The phosphate group was then cleaved by beta-elimination using alkali. The product was purified using anion exchange chromatography. The efficiency of the process was validated using tracer gamma-(32)P ATP and alpha-(32)P dATP. Samples at various steps were analysed by TLC, autoradiography and HPLC. During the process ATP is oxidised whereas 2'-deoxyadenosine triphosphate (dATP) remains intact. The alpha-(32)P dATP synthesized by this process was assayed for its incorporation in lambda-DNA by the random priming method and was found to be effectively incorporated. The process developed is an efficient and convenient method for the preparation of chemically pure deoxyribonucleotides.