Quantum Transport Properties Research Articles

Quantum transport properties of hybrid BN–C nanotubes: Strong spin filtering effect robust against Stone–Wales defects

Quantum transport properties of hybrid BN–C nanotubes: Strong spin filtering effect robust against Stone–Wales defects

Transport in a Two-Channel Nanotransistor Device with Lateral Resonant Tunneling.

We study field effect nanotransistor devices in the Si/SiO2 material system which are based on lateral resonant tunneling between two parallel conduction channels. After introducing a simple piecewise linear potential model, we calculate the quantum transport properties in the R-matrix approach. In the transfer characteristics, we find a narrow resonant tunneling peak around zero control voltage. Such a narrow resonant tunneling peak allows one to switch the drain current with small control voltages, thus opening the way to low-energy applications. In contrast to similar double electron layer tunneling transistors that have been studied previously in III-V material systems with much larger channel lengths, the resonant tunneling peak in the drain current is found to persist at room temperature. We employ the R-matrix method in an effective approximation for planar systems and compare the analytical results with full numerical calculations. This provides a basic understanding of the inner processes pertaining to lateral tunneling transport.

Electrical Transport Properties of PbS Quantum Dot/Graphene Heterostructures.

The integration of PbS quantum dots (QDs) with graphene represents a notable advancement in enhancing the optoelectronic properties of quantum-dot-based devices. This study investigated the electrical transport properties of PbS quantum dot (QD)/graphene heterostructures, leveraging the high carrier mobility of graphene. We fabricated QD/graphene/SiO2/Si heterostructures by synthesizing p-type monolayer graphene via chemical vapor deposition and spin-coating PbS QDs on the surface. Then, we used a low-temperature electrical transport measurement system to study the electrical transport properties of the heterostructure under different temperature, gate voltage, and light conditions and compared them with bare graphene samples. The results indicated that the QD/graphene samples exhibited higher resistance than graphene alone, with both resistances slightly increasing with temperature. The QD/graphene samples exhibited significant hole doping, with conductivity increasing from 0.0002 Ω-1 to 0.0007 Ω-1 under gate voltage modulation. As the temperature increased from 5 K to 300 K, hole mobility decreased from 1200 cm2V-1s-1 to 400 cm2V-1s-1 and electron mobility decreased from 800 cm2V-1s-1 to 200 cm2V-1s-1. Infrared illumination reduced resistance, thereby enhancing conductivity, with a resistance change of about 0.4%/mW at a gate voltage of 125 V, demonstrating the potential of these heterostructures for infrared photodetector applications. These findings offer significant insights into the charge transport mechanisms in low-dimensional materials, paving the way for high-performance optoelectronic devices.

Monolayer Penta-BeAs2: A Promising 2D Materials for Toxic Gas Sensor with High Selectivity.

The discovery of novel materials with high gas sensing selectivity is a key driver of gas sensor technology. Based on the recently reported two-dimensional (2D) pentagonal BeP2, we introduce penta-BeAs2 as a new member of the pentagonal family of materials for toxic gas sensors based on density functional theory (DFT). For electronic applications, a band structure calculation showed that penta-BeAs2 has indirect band gaps of 0.38 and 0.79 eV, using GGA-PBE or HSE functionals. Stability analysis confirmed that penta-BeAs2 is dynamically, mechanically, and thermally stable. The adsorption of toxic gases (CO, NO, and NO2) and nontoxic gases (H2, N2, H2O, and CO2) on the penta-BeAs2 monolayer was studied. The contrasting adsorption behavior observed between toxic and nontoxic gases on penta-BeAs2 (physisorption vs chemisorption) underscores its high selectivity for toxic gas-sensing applications. Adsorption energies for toxic gases fall within a moderate range (0.4-0.8 eV), indicating good reversibility and short recovery times at room temperature. Additionally, the quantum transport properties of penta-BeAs2 were studied using the nonequilibrium Green's function (NEGF) approach, confirming strong sensitivity and selectivity toward toxic gases.

Impurity affected transport properties of quantum well heterostructures with electronic and high-κ dielectric quantum screening

The effect of electronic and high-κ dielectric quantum screening (ES and DS) on the impurity-limited electron transport properties of quantum well/high-κ dielectric barrier type heterostructures with two-dimensional electron gas (2DEG) is studied theoretically. Characteristic of these heterosystems the 2D compound forms of screened impurity potential are employed for the first time. In the framework of 2D Debye-Hückel potential form an electron momentum relaxation time (τ) expression depending on the impurity 2D screening radius is obtained analytically. A numerical analysis of τ is carried out for the realistic HfO/InSb/HfO2QW heterostructure taking account both the finite mismatch of the energy bands at the heterointerface and the energy band non-parabolicity of InSb. The contributions of screened potential compound 2D forms to τ are established depending on QW width. A significant suppression of the scattering rate τ−1 (by an order of magnitude) is received with accounting of ES + DS combined effect.

Quantum Transport and Spectroscopy of 2D Perovskite/Graphene Heterostructures

AbstractUnderstanding the quantum transport properties of (Two‐dimensional) 2D perovskite heterostructures is key to interpreting their electronic performance and promoting optoelectronic devices. Here, it is shown that clear Shubnikov‐de Hass oscillation appears in the heterostructure of monocrystalline 2D perovskites and graphene, thanks to the clean interface. An efficient charge transfer between perovskite nanosheets and graphene is found, facilitating the separation of electrons and holes at the interface. The relation between the charge transfer efficiency and microscopic interface structures is quantitatively described. The evidence of photo‐assisted transport from the photo‐response of magnetoresistance is revealed, which happens between Landau levels of two graphene layers mediated by hot carriers in the perovskite layer, overcoming the barrier from the organic layers in the Ruddlesden‐Popper perovskite phase. These results provide a picture to understand the transport behavior of 2D perovskite/graphene heterostructure and a reference for the controlled design of interfaces in perovskite optoelectronic devices.

Nonvolatile ferroelectric control of electronic properties of Bi2Te3

Abstract Nonvolatile electric-field control of the unique physical characteristics of topological insulators (TIs) is essential for fundamental research and development of practical electronic devices. Electrically tunable transport properties through electrostatic gates have been extensively investigated. However, the relatively weak and volatile tunability limits its practical applications in spintronics. Here, we demonstrate the nonvolatile electric-field control of Bi2Te3 transport properties via constructing ferroelectric Rashba architectures, i.e., 2D Bi2Te3/α-In2Se3 ferroelectric field effect transistors. Through switching the polarization states of the α-In2Se3, the Fermi level, resistance, Fermi wave vector, carrier mobility, carrier density, and magnetoresistance (MR) of the Bi2Te3 film can be effectively modulated. Importantly, a shift of Fermi level toward band gap with surface state occurs as switching to negative polarization state, the contribution of the surface state to the conductivity increases, thereby increasing carrier mobility and electron coherence length significantly, and resulting in enhanced WAL effect. These results provide a nonvolatile electric-field control method to tune the electronic properties of TI and can further extend to the quantum transport properties.

Obtained Berry phase and cyclotron mass of Bi2Se3 topological insulator thin film through weak anti-localization and Shubnikov-de haas oscillation studies

Bi-based binary alloys have drawn enormous attention in modern condensed matter research for their novel topological property. Here, we have explored the quantum-transport properties of a 100 nm Bi2Se3 topological insulator thin film grown by an indigenously developed electron-beam-evaporator through co-deposition technique. A detailed study about the structural, elemental, and morphological analysis has been presented through the GI-XRD, Raman spectroscopy, XPS, EDX, SEM, and AFM characterization. Finally, we have investigated the angle and temperature-dependent magneto-conductance properties of our deposited films, which indicate the surface-electron dominated quantum-transport has occurred. Interestingly, our Bi2Se3 film exhibits 2D weak anti-localization and Subnikov-de Hass oscillation features. From which some novel topological parameters are explored, such as, Berry phase (β), phase-coherence-length (l ϕ ), Fermi velocity (vF), wave vector (kF), Dingle temperature (TD), quantum mobility (μ q), and cyclotron mass (mc). The estimated β = 0.7π and mc = 0.17me, indicate that the topologically protected massless Dirac particles can be achieved in this kind of system.

Quantum transport properties of AB bilayer graphene via tight-binding approach with NEGF formalisms

Quantum transport properties of AB bilayer graphene via tight-binding approach with NEGF formalisms

Chiral edge transport along domain walls in magnetic topological insulator nanoribbons

Quantum anomalous Hall insulators are topologically characterized by non-zero integer Chern numbers, the sign of which depends on the direction of the exchange field that breaks time-reversal symmetry. This feature allows the manipulation of the conducting chiral edge states present at the interface of two magnetic domains with opposite magnetization and opposite Chern numbers. Motivated by this broad understanding, the present study investigates the quantum transport properties of a magnetized Bi2Se3 topological insulator nanoribbon with a domain wall (DW) oriented either parallel or perpendicular to the transport direction. Employing an atomistic tight-binding model and a non-equilibrium Green’s function formalism, we calculate the quantum conductance and explore the nature of the edge states. We elucidate the conditions leading to exact conductance quantization and identify the origin of deviations from this behavior. Our analysis shows that although the conductance is quantized in the presence of the horizontal DW, the quantization is absent in the perpendicular DW case. Furthermore, the investigation of the spin character of the edge modes confirms that the conductance in the horizontal DW configuration is spin polarized. This finding underscores the potential of our system as a simple three dimensional spin-filter device.

Electric-field-controlled electronic structures and quantum transport in monolayer InSe nanoribbons

Electronic structures and quantum transport properties of the monolayer InSe nanoribbons are studied by adopting the tight-binding model in combination with the lattice Green function method. Besides the normal bulk and edge electronic states, a unique electronic state dubbed as edge-surface is found in the InSe nanoribbon with zigzag edge type. In contrast to the zigzag InSe nanoribbon, a singular electronic state termed as bulk-surface is observed along with the normal bulk and edge electronic states in the armchair InSe nanoribbons. Moreover, the band gap, the transversal electron probability distributions in the two sublayers, and the electronic state of the topmost valence subband can be manipulated by adding a perpendicular electric field to the InSe nanoribbon. Further study shows that the charge conductance of the two-terminal monolayer InSe nanoribbons can be switched on or off by varying the electric field strength. In addition, the transport of the bulk electronic state is delicate to even a weak disorder strength, however, that of the edge and edge-surface electronic states shows a strong robustness against to the disorders. These findings may be helpful to understand the electronic characteristics of the InSe nanostructures and broaden their potential applications in two-dimensional nanoelectronic devices as well.

High-Performance Sub-10 nm Two-Dimensional SbSeBr Transistors through Transport Orientation.

Exploring two-dimensional (2D) materials with a small carrier effective mass and suitable band gap is crucial for the design of metal oxide semiconductor field effect transistors (MOSFETs). Here, the quantum transport properties of stable 2D SbSeBr are simulated on the basis of first-principles calculations. Monolayer SbSeBr proves to be a competitive channel material, offering a suitable band gap of 1.18 eV and a small electron effective mass (me*) of 0.22m0. The 2D SbSeBr field effect transistor (FET) with 8 nm channel length exhibits a high on-state current of 1869 μA/μm, low power consumption of 0.080 fJ/μm, and small delay time of 0.062 ps, which can satisfy the requirements of the International Technology Roadmap for Semiconductors for high-performance devices. Moreover, despite the monolayer SbSeBr having an isotropic me*, the asymmetrical band trends enable SbSeBr FETs to display transport orientation, which emphasizes the importance of band trends and provides valuable insights for selecting channel materials.

Jiezi: An open-source Python software for simulating quantum transport based on non-equilibrium Green's function formalism

We present a Python-based open-source library named Jiezi, which provides the means of simulating the electronic transport properties of nanoscaled devices on the atomistic level. The key feature of Jiezi lies in its core algorithm, i.e., self-consistent orchestration between the non-equilibrium Green's function (NEGF) method and a Poisson's equation solver. Beyond the construction of the tight-binding (TB) Hamiltonian with empirical parameters for conventional materials, the package offers a comprehensive framework for constructing the Wannier-based Hamiltonian matrix, enabling the investigation of novel materials and their heterostructures. To expedite the solution of NEGF systems, a methodology based on renormalization theory is proposed for reducing the dimension of the Hamiltonian matrix. Additionally, we adopt a non-linear Poisson equation solver with no analytical approximation in this software. The software facilitates seamless integration with external tools for geometry and mesh generation and post-processing. In this paper, we present the main capabilities and workflow by demonstrating with a simulation for the carbon nanotube field-effect transistor (CNTFET). Program summaryProgram Title: JieziCPC Library link to program files:https://doi.org/10.17632/nk79kbtww4.1Developer's repository link:https://github.com/Jiezi-negf/JieziLicensing provisions: GPLv3Programming language: PythonNature of problem: Simulates the quantum transport property of nano-scaled transistors based on the predefined device structure and the material composition.Solution method: Solves the coupled Schrödinger equation and Poisson equation by NEGF and finite element method.

Highly efficient spin field-effect transistor based on nanographene and hBN heterostructures: spintronic and quantum transport properties

Intense efforts are being undertaken to design atomic-scale nanodevices in response to the demand for novel electronic/spintronic devices to address the problems facing the current devices. In this work, we construct new spintronic nanodevices based on 2D heterostructures from graphene and hBN quantum dots. The heterostructures are ferromagnetic spin-ordered semiconductors with nonzero spin originating from the unpaired edge electrons of the graphene quantum dots. The net spin and its distribution on different layers of the heterostructures are controllable. For instance, doping the hBN layer in the lateral graphene-hBN-graphene structure with C-atoms can boost the net spin and facilitate its distribution on the three layers. The electronic properties are also affected where half metallicity has been achieved in this system. The I-V characteristics of the lateral G-hBN heterostructure show an oscillating spin-up current that is significantly higher than the regular spin-down current. Doping G-hBN with C-atoms significantly enhances the current magnitude and removes the oscillation due to the decreased net spin by the dopants. We demonstrate a field effect transistor from the lateral G-hBN-G heterostructure that operates based on quantum tunneling from the G-layer through the hBN-layer. The device works as a spin filter at zero gate voltage. A significant enhancement of the drain current is achieved by applying a positive gate voltage. This device shows an ON/OFF ratio of up to 1010 making it an ideal applicant for future spintronic nanodevices.

Two-dimensional heterostars from nanographene and group-III nitrides for efficient spin filters: Spintronic and quantum transport properties

Two-dimensional (2D) heterostructures open the door toward novel applications, such as multiterminal transistors, by integrating the properties of the participant materials. Here we construct 2D heterostars from zigzag-triangular graphene (ZTG) and group-III nitrides. They are investigated using density functional theory and non-equilibrium Green’s function approaches. These heterostars are ferromagnetically spin-ordered devices that originate and distribute on ZTG. Further control over the net spin can be achieved by forming bilayer heterostars where spin can be increased, decreased, or removed. Single-layer heterostars are wide energy gap semiconductors of ∼3.5 eV that decrease to ∼1 eV in bilayers or are kept unchanged in other bilayers. Quantum transport calculations show that different spintronic devices can be constructed by connecting the source/drain voltage to different terminals of the nanostars. These devices are characterized by a low tunneling current through the potential barrier of group-III nitrides that significantly increased by applying gate voltage. A spin filter based on graphene-AlN nanostar with efficient separation of spin-up current is demonstrated. Also, a significant improvement in both the spin-up and spin-down currents can be achieved in the same nanostar but using other terminals. 2D heterostars are then potential candidates for building multi-terminal spintronic devices.

Numerical simulation of Rashba spin–orbit coupling effect on quantum Hall resistivity within tight-binding approximation

A numerical simulation of the effect of Rashba spin–orbit coupling (RSO) on quantum transport properties of electrons confined to a two-dimensional electron gas (2DEG) in the integer quantum Hall regime is presented. The mechanism of quantization and the dependence of the Hall resistivity (HR) on the system built-in and external parameters are studied using the non-equilibrium Green’s function (NEGF) technique. Relevant Green’s functions are computed numerically using spectral decomposition method in combination with recursive techniques. The tight-binding-like representation of the system Hamiltonian including magnetic field is obtained within the finite difference method, using Dirichlet boundary conditions. Corresponding formula linking the Hall resistivity with the transmission function of the system has been derived analytically within the NEGF formalism in a general form, in the sense that the formula can also be used beyond the linear response limit and for nonzero temperatures. In particular, it was shown explicitly that in the presence of the RSO coupling the even- and odd plateaus emerging in the magnetic-field dependence of the quantum Hall resistivity are related to different physical mechanisms.

Two-Step Spin Crossover and Contact-Tunable Giant Magnetoresistance in Cyclopentadienyl Metalloporphyrin

In this article, we study the optimized structures, spin crossover, and coherent quantum transport properties of a series of cyclopentadienyl metalloporphyrin (PTMCp, TM = transition metal) complexes using the density functional theory combined with the non-equilibrium Green’s function method. The structure of the complexes can be classified into the sandwich type and the biplanar type. Energetic analyses of spin states reveal that the IS(intermediate-spin)-HS(high-spin) spin transition may appear in PMnCp and PFeCp, and the LS(low-spin)-IS(intermediate-spin)-HS(high-spin) two-step spin transition may appear in PCoCp under external stimulus. We predict that giant magnetoresistance may be observed in the ground-state sandwich PTMCp depending on the contact between the electrodes and the molecule in measurements. These results indicate that PTMCp complexes could be promising materials for spintronics.

Mechanical Control of Quantum Transport in Graphene.

2D materials (2DMs) are fundamentally electro-mechanical systems. Their environment unavoidably strains them and modifies their quantum transport properties. For instance, a simple uniaxial strain can completely turn off the conductance of ballistic graphene or switch on/off the superconducting phase of magic-angle bilayer graphene. This article reports measurements of quantum transport in strained graphene transistors which agree quantitatively with models based on mechanically-induced gauge potentials. A scalar potential is mechanically induced in situ to modify graphene's work function by up to 25 meV. Mechanically generated vector potentials suppress the ballistic conductance of graphene by up to 30% and control its quantum interferences. The data are measured with a custom experimental platform able to precisely tune both the mechanics and electrostatics of suspended graphene transistors at low-temperature over a broad range of strain (up to 2.6%). This work opens many opportunities to harness quantitative strain effects in 2DM quantum transport andtechnologies.

Quantum interference effects in a 3D topological insulator with high-temperature bulk-insulating behavior

The Bi2Se3-family of 3D topological insulators (3DTI) exhibit insulating bulk states and surface states presenting a Dirac cone. At low temperatures, the conduction channels through the bulk of the material are fully gapped, making 3DTIs perfect systems to study the 2D transport behavior of Dirac fermions. Here, we report a 3DTI Bi1.1Sb0.9STe2 with a reduced level of defects, and thus, high-temperature insulating behavior in its bulk states. The insulator-to-metal transition occurs at ∼250 K, below which the bulk contributions are negligible. Even at room temperature, the conductivity contribution from the bulk channel is less than 20%. Quantum transport properties of topological surface states are observed in the Bi1.1Sb0.9STe2 nanoflake devices, e.g., high Hall mobility (∼1150 cm2/V s at 3 K), strong Shubnikov–de Haas oscillations with π Berry phase, weak antilocalization, and electron–electron interaction. Notably, additional oscillation patterns with quasi-periodicity-in-B and field-independent amplitude features are observed. The surface dominant transport behavior up to room temperature suggests that Bi1.1Sb0.9STe2 is a room temperature topological insulator for electronic/spintronic applications.

Broken edge spin symmetry induces a spin-polarized current in graphene nanoribbon

Zigzag graphene nanoribbons (ZGNRs) are known to possess spin moments at the hydrogen-terminated edge carbon atoms; thus, spin-polarized electron transmission is expected, while the current is longitudinally passed through the ZGNRs. However, in pristine ZGNRs, spin-polarized transmission is not observed due to symmetric anti-parallel distributions of the spin densities between the edges. Here, the hypothesis is that any physical or chemical process that breaks such anti-parallel spin symmetry can induce spin-polarized transmission in ZGNRs. In this work, we have established this proof-of-concept by depositing the trimethylenemethane (TMM) radical on 6ZGNRH and investigating the quantum transport properties by employing density functional theory in conjunction with the nonequilibrium Green’s function method. Although TMM has a high magnetic moment ( 2μB ), it does not induce magnetization in 6ZGNRH when TMM is physisorbed. However, during the chemisorption of TMM, it forms the π−π bond with the 6ZGNRH in a particular geometric configuration, where the p z orbitals of carbon atoms of TMM have maximum overlap with the p z orbitals of carbon atoms of 6ZGNRH. The chemisorption of TMM transfers the spin moment to 6ZGNRH, which breaks the edge spin symmetry of pristine 6ZGNRH. The adsorption of the TMM radical results in transmission dips in the transmission spectra due to interference between localized states of TMM and 6ZGNRH states. This induces spin-polarized transmission with 60% spin-filtering efficiency at zero bias, which can further be enhanced up to 92% by applying a bias voltage of 1.0 V.