Landauer-Buttiker Formula Research Articles

Investigating magnetoresistance properties on a periodic poly(dA)-poly(dT) DNA structure

Magnetoresistance has been calculated for a range of magnetic fields. The calculation has been carried out using a periodic DNA structure. The magnetic field affects electron hopping constants in a tight-binding Hamiltonian regime through the Peierls phase. On the other hand, the internal electric field, as a result of the voltage difference across the molecule structure, affects the magnitude of electron hopping parameters. Green’s function method has been employed in computing the electron transmission probabilities. Then, the Landauer-Buttiker formula is used in computing currents at a certain voltage. The magnetoresistance was observed oscillating as the magnetic field increased, just like the current. At several voltages, the magnetoresistance changes sign with the change in the magnetic field.

Thermal transport of helical Majorana edge modes in a superconducting antiferromagnetic quantum spin Hall insulator

In the system composed of a two-dimensional antiferromagnetic quantum spin Hall insulator (AFQSHI) nanoribbon covered by s -wave superconductors, possessing helical Majorana edge mode (HMEM), and preserving effective time-reversal symmetry. Based on such the AFQSHI-SC hybrid system, we investigate the band structure and thermal transport properties. The two-terminal thermal conductance κ e l and electric conductance G are calculated by using the Landauer-Büttiker formula and the nonequilibrium Green’s function method. When a pair of intersecting edge states exists in the bulk band gap, a helical topological superconductor with Z 2 invariant ν = ± 1 is formed, which has a pair of Majorana edge states with opposite chirality, that is Majorana Kramer pairs, leading to a integer quantized thermal conductance plateau. We find that the quantized thermal conductance plateau is well preserved in a certain range of temperature. The presence and number of Majorana Kramer pairs in helical topological superconductor can be confirmed with the help of the quantized thermal conduction plateau, which is promising for the experimental detection of helical Majorana fermions. • In this manuscript, based on the Landauer-Buttiker formula and the nonequilibrium Green’s function method, we investigate the properties of helical Majorana fermions edge states thermal transport in a hybrid AFQSHI-SC structure. • When a pair of Majorana edge states with opposite chirality residing at the edge of the central topological superconductor region, a integer quantized thermal conductance plateau is discovered. • This quantized plateau can be used as strong evidence for the experimental detection of helical topological superconductors.

Revisiting the Electronic Structures and Phonon Properties of Thermoelectric Antimonide-Tellurides: Spin–Orbit Coupling Induced Gap Opening in ZrSbTe and HfSbTe

We report theoretical studies based on density functional theory within spin-orbit coupling to explore electronic structures, lattice dynamical properties of ZrSbTe and HfSbTe. With spin−orbit coupling included, our findings reveal that ZrSbTe and HfSbTe exhibit a semiconducting behavior with narrow indirect band gaps of 0.10 eV, and 0.15 eV, respectively. Besides, the lattice dynamical properties revealed that the explored materials based on antimonide−tellurides are dynamically stable. On the basis of electronic structures, the thermoelectric properties were computed using the Landauer-Buttiker formula by considering both electron and phonon contributions in the transport properties calculation. We employed Green’s-function method based on the Green-Kubo-Mori formula, where the thermoelectric properties such as the electrical conductivity σ and thermopower α were estimated in terms of the correlation functions. The present work could be viewed as a significant amendment of the electronic nature of ZrSbTe and HfSbTe that were reported to be metallic in literature.

Investigation of Electrical Behaviors Observed in Vertical GaN Nanowire Transistors Using Extended Landauer-Büttiker Formula

In this report, we study nonlinear electrical behaviors found in vertical-architecture transistors based on wrap-around-gated gallium nitride (GaN) nanowires (NWs) by extending a one-dimensional case of the Landauer-Buttiker formula. Here, the GaN NWs are considered “almost” one-dimensional ideal wires connecting the drain and source terminals, with the gate terminal serving to control the flowing current. Unlike previous models, which require several parameters and complex calculations, our proposed model only needs three parameters and simple calculations to match the experimental data. With this model, we confirm that the maximum current before saturation is a consequence of quasi-ballistic drain current. Thus, electron mobility has no effect in this device. Using a simple formulation, we discuss gating hysteresis in the device that is mediated by the selected oxide layer interface. We show that the memory effect of the device is attributed to time-delay current. The shorter gate length increases the transmission coefficient. As a result, the model can be employed to predict the next-generation NW transistor performance.

Stochastic and Quantum Thermodynamics of Driven RLC Networks

We develop a general stochastic thermodynamics of RLC electrical networks built on top of a graph-theoretical representation of the dynamics commonly used by engineers. The network is: open, as it contains resistors and current and voltage sources, nonisothermal as resistors may be at different temperatures, and driven, as circuit elements may be subjected to external parametric driving. The proper description of the heat dissipated in each resistor requires care within the white noise idealization as it depends on the network topology. Our theory provides the basis to design circuits-based thermal machines, as we illustrate by designing a refrigerator using a simple driven circuit. We also derive exact results for the low temperature regime in which the quantum nature of the electrical noise must be taken into account. We do so using a semiclassical approach which can be shown to coincide with a fully quantum treatment of linear circuits for which canonical quantization is possible. We use it to generalize the Landauer-Buttiker formula for energy currents to arbitrary time-dependent driving protocols.

Studi probabilitas transmisi dan karakteristik IV pada molekul DNA G4

[ The study of transmission probability and IV chracteristics of a G4 molecule ] In this era, there have been many theoretical and experimental studies conducted to enhance technological development. The development of technology continues to grow rapidly with electronic components that are getting smaller towards nano. Nanotechnology is becoming increasingly interesting because it can be created through DNA that is found in either the human body or other living things. This research was conducted to study DNA transport properties by calculating transmission probabilities and I-V characteristics. The DNA studied is DNA that has been modified consisting of 4 guanine bases arranged stacked to form a square called G4-DNA. G4-DNA is composed by having 32 base pairs and connected by electrodes at the end. The transport properties of G4-DNA were studied using the Hamiltonian tight binding approach. Transmission probability is calculated using the method of the Green Function Hamiltonian to determine the possibility of electrons flowing along the DNA pathway. This transmission probability is used in determining the I-V Characteristics based on the Landauer Buttiker formula. The result s are obtained that the electron transport process along the G4-DNA molecule is an increase in current to high voltage. The effects of I-V characteristics are seen by affecting the twisting motion frequency up to 5.12 meV which is a significant increase in current. The results of this study can provide information about the characteristics of DNA that can be applied in the future in manufacture of nanotechnology device .

Aharonov-Bohm-effect induced transparency and reflection in mesoscopic rings side coupled to a quantum wire

We demonstrate analytically and numerically the possibility of existence of the analogues of electromagnetic induced transparency (EIT) and electromagnetic induced reflection (EIR) in a simple mesoscopic structure. The latter consists of a ring of length 2d attached vertically to two semi-infinite leads (waveguide) by a wire of length d1. The ring is threaded by a magnetic flux Φ, the so-called Aharonov-Bohm effect. The number of dangling wire-ring resonators attached at the same point can be increased to N. First, we demonstrate analytically that in the absence of the magnetic flux (Φ=0) and for particular values of d1, the structure may present some states that are confined in the ring and do not interact with the waveguide states. These trapped states fall in the continuum states of the two leads and therefore represent bound in continuum (BIC) states. These states are characterized by a zero width resonance (i.e., infinite life-time) in the transmission and reflection spectra. In presence of a weak magnetic flux (Φ≠0), the BIC states transform to EIT or EIR resonances for specific values of the lengths d1and d of the wire and the ring respectively. In addition to the numerical results, we have developed Taylor expansion calculations of the transmission and reflection coefficients around EIT and EIR resonances to show that the latter can be written following a Fano shape. In particular, we have deduced the Fano parameter q and the quality factor Q of these resonances as function of N and the flux Φ. We have found that Q decreases as function of Φ for both EIT and EIR resonances, whereas it increases (decreases) as function of N for EIT (EIR) resonances. These results show the possibility of tuning EIT and EIR resonances by means of the magnetic flux Φ and the number of dangling resonators N. The effect of temperature on EIT and EIR resonances is also considered through an analysis of the Landauer-Buttiker conductance formula obtained from transmission. The theoretical results are obtained within the framework of the Green's function method which enables us to deduce analytically the dispersion relation, transmission and reflection coefficients. These results may have important applications for electronic transport in mesoscopic systems such as filters and demultiplexers.

Influence of the Fermi velocity on the transport properties of the 3D topological insulators

We explore the transport of the surface states quasielectrons in the 3D topological insulators through the barriers of various origin: the Fermi velocity and the electrostatic barriers. These barriers are believed to be the rectangular and one-dimensional ones. The transmission coefficient T as the function of the quasiparticle energy E and an angle of incidence θ (transmission spectra) is evaluated with the help of the effective Hamiltonian; the conductivity G is calculated on the base of the Landauer–Buttiker formula. It is shown that the value of T and G significantly depends on the ratio of the Fermi velocities in the barrier and out-of-barrier regions α = vF2/vF1. The dependence of these quantities on the strength of the electrostatic potential is analyzed. We find in particular that the effect of supertunneling manifests itself in the considered structure—being markedly dependent on the value of α. The formula which points out the energy value for which the effect of supertunneling takes place, for different α, is presented. For normal angle of the particle incidence, there is the effect analogous to the Klein paradox. The spectra T(E,θ) and G(E) substantially depend on the interplay of α, energy E and the magnitude of the electrostatic potential. Hence, by changing the problem parameters one can flexibly vary the spectra of T(E,θ) and G(E) in wide limits. The obtained results may be useful for the nanoelectronics based on the topological insulators.

Gate-Controlled Conductance in ABA-Stacked Trilayer Graphene

In this work, we theoretically consider the electron transport across a junction on monolayer, Bernal-stacked AB bilayer and ABA trilayer graphene. The electronic transmissions through the electrostatic barrier in trilayer and bilayer graphene are computed within the scattering matrix using Landauer–Buttiker formula. We theoretically evaluate the total conductance. We study the effect of gate potential on the band structures. Our findings show that the effect of the gate potential could open an energy gap and the charge current can be controlled by tuning the gate potential in the middle region that acts as a barrier. Trilayer graphene is chosen as better appropriate candidate for industrial applications. Our findings show that the charge current can be controlled by tuning the gate potential in the middle region trilayer graphene that acts as a barrier.

Anisotropic magnetoelectronic structures and magneto-transport properties of topological Dirac semimetal nanowires

Abstract The magnetoelectronic structures, and the charge and spin conductance spectra of topological Dirac semimetal (TDS) nanowires are calculated by adopting the tight-binding Hamiltonian model in combination with the Green’s-function-based Landauer-Buttiker formula. Anisotropic electronic structures and magneto-transport properties are found in TDS nanowires with different confinement and magnetic field directions. With respect to in-plane-confinement TDS nanowires, trivial surface/corner states are observed and they are split into two spin-polarized states with oppositive signs when a weak out-of-plane magnetic field is applied. Moreover, the spin-polarized surface states will be transformed into bulk and corner states as the magnetic field strength is increased. Therefore, quantized spin conductance energy windows and fully-spin-polarized conductance can be achieved in the normal/out-of-plane-magnetic-field-modulated/normal TDS system in the case of the weak and strong fields, respectively. However, chiral surface states are generated when an in-plane magnetic field is applied, resulting in the perfect charge conductance steps of the normal/in-plane-magnetic-field-modulated/normal TDS system. With respect to the TDS nanowire with both the in-plane and out-of-plane confinements, nontrivial spin-momentum-locked helical surface states are observed. However, the helical character of the surface states will be destroyed and nontrivial-trivial topological phase transition happens as a high in-plane magnetic field is applied. In addition, the energy position of the surface subband inside the bulk energy gap is shifted so that the surface state transport can be switched on or off by tuning the magnetic field strength. Interestingly, the surface subband situated inside the bulk energy gap is split into two subbands with opposite spin signs as an out-of-plane magnetic field is added. Therefore, the topological phase transition between the quantum spin Hall and spin-polarized quantum Hall phases in the TDS nanowire, and the spin-polarized transport in the normal/out-of-plane-magnetic-field-modulated/normal TDS system, can be controlled by varying the magnetic field strength. These effects may benefit both the fundamental understanding of the magneto-electronic characters of the TDS nanostructures and the design of low-dissipation (spin) electronic devices.

Enhanced robustness of zero-line modes in graphene via magnetic field

We systematically studied the influence of magnetic field on zero-line modes (ZLMs) in graphene and demonstrated the physical origin of their enhanced robustness by employing nonequilibrium Green’s functions and the Landauer–Buttiker formula. We found that a perpendicular magnetic field can separate the wavefunctions of the counter-propagating kink states into opposite directions. Specifically, the separation vanishes at the charge neutrality point and increases as the Fermi level deviates from the charge neutrality point and can reach a magnitude comparable to the wavefunction spread at a moderate field strength. Such spatial separation of oppositely propagating ZLMs effectively suppresses backscattering and is more significant under zigzag boundary condition than under armchair boundary condition. Moreover, the presence of magnetic field enlarges the bulk gap and suppresses the bound states, thereby further reducing the scattering. These mechanisms effectively increase the mean free paths of the ZLMs to approximately 1 μm in the presence of a disorder.

The energy spectra of the graphene-based quasi-periodic superlattice

The spectra of the Dirac quasi-electrons transmission through the Fibonacci quasi-periodical superlattice (SL) are calculated and analyzed in the continuum model with the help of the transfer matrix method. The onedimensional SL based on a monolayer graphene modulated by the Fermi velocity barriers is studied. A new quasi-periodical factor is proposed to be considered. We show that the Fibonacci quasi-periodic modulation in graphene superlattices with the velocity barriers can be effectively realized by virtue of a difference in the velocity barrier values (no additional factor is needed and we keep in mind that not each factor can provide the quasi-periodicity). This fact is true for a case of normal incidence of quasi-electrons on a lattice. In contrast to the case of other types of the graphene SL spectra studied reveal the remarkable property, namely the periodic character over all the energy scale and the transmission coefficient doesn’t tend asymptotically to unity at rather large energies. Both the conductance (using the known Landauer-Buttiker formula) and the Fano factor for the structure considered are also calculated and analyzed. The dependence of spectra on the Fermi velocity magnitude and on the external electrostatic potential as well as on the SL geometrical parameters (width of barriers and quantum wells) is analyzed. Using the quasi-periodical SL one can control the transport properties of the graphene structures in a wide range. The obtained results can be used for applications in the graphene-based electronics.

Pure spin polarized current through a full magnetic silicene junction

Using the Landauer–Buttiker formula, we investigate electronic transport in silicene junction composed of ferromagnetic silicene. The direction of magnetization in the middle region may change in a plane perpendicular to the junction, whereas the magnetization direction keep fixed upward in silicene electrodes. We investigate how the various magnetization directions in the middle region affect the electronic transport. We demonstrate that conductance depends on the orientation of magnetizations in the middle region. It is found that by changing the direction of the magnetization in the middle region, a pure spin up current can be achieved. This achievement makes this full magnetic junction a good design for a full spin-up current polarizer.

Photo-induced spin and valley-dependent Seebeck effect in the low-buckled Dirac materials

Employing the Landauer-Buttiker formula we investigate the spin and valley dependence of Seebeck effect in low-buckled Dirac materials (LBDMs), whose band structure are modulated by local application of a gate voltage and off-resonant circularly polarized light. We calculate the charge, spin and valley Seebeck coefficients of an irradiated LBDM as functions of electronic doping, light intensity and the amount of the electric field in the linear regime. Our calculation reveal that all Seebeck coefficients always shows an odd features with respect to the chemical potential. Moreover, we show that, due to the strong spin-orbit coupling in the LBDMs, the induced thermovoltage in the irradiated LBDMs is spin polarized, and can also become valley polarized if the gate voltage is applied too. It is also found that the valley (spin) polarization of the induced thermovoltage could be inverted by reversing the circular polarization of light or reversing the direction the electric field (only by reversing the circular polarization of light).

Quantum-interference effect on the spin polarization driven by protein-like single-helical molecules

We report a theoretical study about the spin-dependent electron transport through a two-arm mesoscopic circuit in which two protein-like single-helical molecules connect serially with two normal metallic leads, respectively. Based on an effective-model Hamiltonian, the spin polarization is evaluated using the Landauer–Buttiker formula. Our results reveal that in comparison with the single-arm case, the spin-polarization efficiency can be enhanced in this system, by adjusting the length ratio of two molecules and the molecule–lead coupling manner. Besides, when local magnetic flux is introduced, the Aharonov–Bohm effect makes a nontrivial contribution to the spin polarization. These findings can be helpful for building the helical-molecule-based spin filters.

Fano factor for Dirac electrons in a supperlattice of normal/ferromagnetic/normal silicene junction

We investigate the electron transport in the presence of electric field and gate potential in a supperlattice of normal/ferromagnetic/normal silicene junction. We compute the total conductance and Fano factor using the transfer matrix method and Landauer-Buttiker formula. The total conductance and Fano factor of the silicene contain interesting information of the transport properties of the charge carriers. The dependence of the Fano factor behavior on the electric field strength, the gate potential, the thickness of the ferromagnetic region and more importantly the dependence on the number of barriers have been plotted. Our aim is to achieve a more accurate picture of the dependence of the Fano factor on parameters mentioned above. In this junction, Fano factor oscillates with the thickness of the ferromagnetic region, the electric field strength and the gate voltage in the ferromagnetic regions. Also we found that diffusive transport (F=1/3) occurs by taking large enough length of the ferromagnetic regions and tiny electric field strength. Another remarkable point is that Fano factor attains the full Poissonian value (F=1), by controlling the electric field strength and the length of the ferromagnetic regions. We see that with remaining intact the conductance, we can change the transport from Poissonian to diffusive transport by controlling the length of the ferromagnetic regions. However, these findings occur exactly in the case of ΔzE=0.5 when the number of barriers is large enough. Moreover, with considering dependence of the Fano factor on the electrostatic potential and electric field strength, we have proved that these parameters are controllable parameters on the kind of transport. It is said that Fano factor is very sensitive to the mentioned parameters and can be controlled by these parameters. In fact, we show that the value of Fano factor is a valuable tool for distinguishing the behavior of transport whereas this kind of information cannot be extracted from the conductance.

Nonlocal resistance in multi-terminal graphene system

Since the nonlocal measurement is helpful in discovering nontrivial physics that is too difficult to detect directly, the nonlocal measurement has now become one of the research focuses in condensed matter physics. Recent experiments find the signal of the giant nonlocal resistance in an H-shaped multi-terminal graphene system. After excluding other possible transport mechanisms, such as the classic Ohmic diffusion and the edge states, researchers tend to believe that the nonlocal resistance signal originates from the spin/valley Hall effect existing in graphene sample. Based on the Landauer-Buttiker formula, the numerical results make a relatively perfect match with the experimental data in the same multi-terminal graphene system. However, though the theoretic research has made certain progress in explaining the existence of the nonlocal resistance, it is still difficult to understand some exotic behaviors of the nonlocal resistance, which exhibits properties even contradictory to the known classical theories. For instance, the nonlocal resistance decreases to zero much more rapidly than the local one, and the giant peak of the nonlocal resistance appears inside the energy gap of the graphene. In this review, the experiments focusing on the nonlocal resistance in multi-terminal graphene system are carefully reviewed. Besides, this review also shows the associated theoretic studies, and an overlook of the future study is also provided.

Fully Valley/spin polarized current and Fano factor through the Graphene/ferromagnetic silicene/Graphene junction

In this work, we study the transport properties of Dirac fermions through the ferromagnetic silicene which is sandwiched between the Graphene leads (G/FS/G). Spin/valley conductance, spin/valley polarization, and also Fano factor are theoretically calculated using the Landauer-Buttiker formula. We find that the fully valley and spin polarized currents through the G/FS/G junction can be obtained by increasing the electric field strength and the length of ferromagnetic silicene region. Moreover, the valley polarization can be tuned from negative to positive values by changing the electric field. We find that the Fano factor also changes with the spin and valley polarization. Our findings of high controllability of the spin and valley transport in such a G/FS/G junction the potential of this junction for spin-valleytronics applications.

Controllable spin and valley polarized current through a superlattice of normal/ferromagnetic/normal silicene junction

The spin and valley transports in a superlattice of normal/ferromagnetic/normal silicene junction are studied theoretically. Transport properties in particular valley-resolved conductance, spin and valley polarization have been computed by the Landauer Buttiker formula. We achieve fully valley and spin polarized current in the superlattice N/F/N structure. Our findings also imply that by increasing the number of ferromagnetic barriers, the onset of fully spin and valley polarized current always occur for lower values of staggered potential(ΔzE) and length of the ferromagnetic region (KfL) in the silicene supelattice structure as compared with N/F/N silicene junction. Fully spin and valley polarizations make silicene superlattice a suitable candidate for spin-valleytronics applications.

Spin dependent disorder in a junction device with spin orbit couplings

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.