Electrical Transport Phenomena Research Articles

Understanding the transport properties of perovskite compounds as a function of temperature, frequency and DC-bias voltage using experimental measurements and appropriate theoretical models.

The present paper provides interesting measurements and methodologies to investigate the key factors controlling the electrical response of perovskite systems. The studied system was successfully prepared using a solid-state route. The chemical analysis and the X-ray diffraction results confirm the formation of the desired perovskite phase. As a result, the DC-resistivity analysis shows that the transport properties are governed by hopping mechanisms above the transition temperature. In this case, thermal agitation allows the charge-carriers to hop across the insulating barrier in the form of grain boundaries. Then, the dominance of the grain boundary contribution is proved. AC-resistivity spectra are investigated in terms of numerous power laws (UDR, SPL and NCL). Accordingly, the decrease in the resistivity values at high frequencies is explained through hopping and tunneling processes. Indeed, it is proved that the electrical transport phenomena are governed by QMT and CBH models. The coexistence of direct (C-C) and indirect (C-A-C) interactions explains the multi-behavior of the AC-resistivity. The scaling representation displays a single muster curve describing the universal dynamic response (UDR). Thus, it reveals the universality of the electrical resistivity of the system. However, the double Schottky barrier model is used to explain the grain boundary effects. A critical frequency "νc" is detected under temperature and DC-bias voltage effects. These observations disclose, in a different way, the separate contributions of the electro-active regions of the sample in the conduction phenomenon.

Enhanced Computational Study with Experimental Correlation on I-V Characteristics of Tantalum Oxide (TaOx) Memristor Devices in a 1T1R Configuration.

Memristors, non-volatile switching memory platform, has recently attracted significant interest, offering unique potential to enable the realization of human brain-like neuromorphic computing efficiency. Memristors also demonstrate excellent temperature tolerance, long-term durability, and high tunability with nanosecond pulses, making them highly attractive for neuromorphic computing applications. To better understand the material processing, microstructure, and property relationship of switching mechanisms in memristor devices, computational methodologies, and tools are developed to predict the I-V characteristics of memristor devices based on tantalum oxide (TaOx) resistive random-access memory (ReRAM) integrated with an n-channel metal-oxide-semiconductor (NMOS) transistor. A multiphysics model based on coupled partial differential equations for electrical and thermal transport phenomena is solved for the high- and low-resistance states during the formation, growth, and destruction of a conducting filament through SET and RESET stages. These stages effectively represent the migration of oxygen vacancies within an oxide exchange layer. A series of parametric studies and energy minimization calculations are conducted to determine probable ranges for key material and model parameters accounting for the experimental data. The computational model successfully predicted the measured I-V curves across various gate voltages applied to the NMOS transistor in the one transistor one resistance (1T1R) configuration.

Nonreciprocal transport in the superconducting state of the chiral crystal NbGe2

Due to the lack of inversion, mirror or other roto-inversion symmetries, chiral crystals possess a well-defined handedness which, when combined with time-reversal symmetry breaking from the application of magnetic fields, can give rise to directional dichroism of the electrical transport phenomena via the magnetochiral anisotropy. In this study, we investigate the nonreciprocal magneto-transport in microdevices of NbGe2, a superconductor with structural chirality. A giant nonreciprocal signal from vortex motions is observed during the superconducting transition, with the ratio of nonreciprocal resistance to the normal resistance γ reaching 6×105 T−1⋅A−1. Interestingly, the intensity can be adjusted and even sign-reversed by varying the current, the temperature, and the crystalline orientation. Our findings illustrate intricate vortex dynamics and offer ways of manipulation on the rectification effect in superconductors with structural chirality.

Giant magnetoresistance resulting from superzone gap in spin-frustrated rare-earth-based aluminide: DyFe2Al10.

The magnetic properties of orthorhombic aluminides have recently been the subject of investigation, revealing several intriguing phenomena within this class of materials. However, the exploration of their magnetic and electrical transport phenomena has remained somewhat limited. In this study, we delve into the magnetic and electrical transport characteristics of one such material from that group which is DyFe2Al10(DFA). Our findings go beyond classifying this material as a simple antiferromagnet; but it posses a short range ferromagnetic ordering apart from helical spin structure of Dy3+. It exhibits a metamagnetic transition and spin glass behavior below its Néel temperature (TN). Our analysis of electrical magnetotransport behavior indicates the emergence of an antiferromagnetic superzone gap, resulting in a significant enhancement in magnetoresistance effect. This discovery paves the way for a class of materials with complex interactions and notable magnetoresistance properties.

Effect of Sb modification on dielectric and electrical properties of lithium bismuth titanate

Sb-modified alkali bismuth titanate Li0.5Bi0.5− x Sb x TiO3 (x = 0 and 0.1) compounds are prepared using the method of solid-state-reaction route. The XRD exploration in environmental conditions confirms the development of new compounds having single-phase orthorhombic crystal structures. Non-uniformly distributed grains are noticed in SEM micrographs for both compounds. The electric & dielectric behavior is analyzed by use of an impedance analyzer. The exploration of the dielectric behaviors of both compounds in a wide frequency range (100 Hz–1 MHz) & temperature range (30–500 °C) suggests that these characteristics are strongly dependent on frequency & temperature. Activation energy assessed from temperature variation of ac-conductivity in various zones recommends that the electric transport phenomenon obeys the Arrhenius equation and shows a mixed type of conductivity.

Electrical transport phenomena in two-dimensional metallic 2H-NbSe2: an experimental and theoretical study.

Two-dimensional (2D) metallic transition metal dichalcogenides (TMDCs) have attracted extensive interest in various fields owing to their unique electronic properties. However, studies on their transport properties and the modulation of these properties based on their band structure are limited. Herein, we studied the transport phenomena in 2D metallic 2H-NbSe2 using experimental and theoretical approaches. The transport properties, including electrical conductivity (σ) and Seebeck coefficient (S), of mechanically exfoliated 2H-NbSe2 nanosheets were measured. We observed field effect-dependent variations in σ and S of the 2H-NbSe2 nanosheets. Theoretical calculations of the electronic band structures and estimations of the transport properties of 2D 2H-NbSe2 crystals were conducted to verify and explain the experimental results. The superconducting transition temperature of the exfoliated NbSe2 nanosheets validated the reliability of the sample preparation procedures and indicated the high quality of the samples. Our findings provide a basis for understanding the electrical properties of metallic TMDCs intended for various applications.

Nonlinear electrical transport phenomena as fingerprints of a topological phase transition in ZrTe5

Topological phase transitions, influenced by magnetic fields, dopants, pressure, and temperature, create Berry curvature in band structures, challenging to detect due to resolution and scattering issues in spectroscopy and transport. Here, we propose nonlinear electrical transport phenomena as fingerprints of a topological phase transition in ZrTe5 under magnetic fields. Both a nonlinear longitudinal conductivity ΔσL in a magnetic-field-aligned electric field and a third-order nonlinear Hall (transverse) conductivity Δσxy in a magnetic-field-perpendicular electric field arise below a characteristic temperature T*. The sensitivity of nonlinear transport to the band topology allows the detection of a subtle change in the band topology hidden in linear transport coefficients. Extending the previous scaling theory between linear transport coefficients (σxx and σxy), we also propose scaling relations for both linear (σxx and σxy) and nonlinear (ΔσL and Δσxy) transport coefficients. These scaling relations will help understand the interplay between the mechanisms of nonlinear transport coefficients and the influence of Berry curvature.

Electrical transport phenomena and modulus behavior in lead-free Ba0.85Sr0.15Ti0.85Zr0.15O3 compound

In this work, the ceramic Ba0.85Sr0.15Ti0.85Zr0.15O3 is prepared using the conventional solid-state reaction method. The frequency dependence of the electrical conductivity, impedance, and electric modulus of Ba0.85Sr0.15Ti0.85Zr0.15O3 are investigated using numerous theoretical laws over a large temperature range. The X-ray diffraction (XRD) study confirms that this composition crystallizes in pseudo-cubic symmetry. In addition, it shows the good crystallization of our material. The appearance of semiconductor behavior is attributed to the activation of the small polaron hopping process. AC conductivity analysis confirms the presence of complex behaviors. Indeed, we found the contribution of several hopping and tunneling processes to the conduction properties. The Nyquist plots (Z” vs. Z’) confirm the important contribution of the microstructure to the transport and relaxation phenomena. The complex modulus analysis confirms the strong correlation between the movements of the mobile charge carriers and shows the thermal activation of the relaxation process in Ba0.85Sr0.15Ti0.85Zr0.15O3. As a result, the long-distance movement of the load carriers essentially determines the relaxation process at low frequencies. From the electric modulus results, it is observed that the system under study reveals a non-Debye character.

Noise Spectroscopy: A Tool to Understand the Physics of Solar Cells

Noise spectroscopy is essentially focused on the investigation of electric fluctuations produced by physical mechanisms intrinsic to conductor materials. Very complex electrical transport phenomena can be interpreted through the study of the fluctuation properties, which provide interesting information both from the point of view of basic research and of applications. In this respect, low-frequency electric noise analysis was proposed more than twenty years ago to determine the quality of solar cells and photovoltaic modules, and, more recently, for the reliability estimation of heterojunction solar cells. This spectroscopic tool is able to unravel specific aspects related to radiation damage. Moreover, it can be used for a detailed temperature-dependent electrical characterization of the charge carrier capture/emission and recombination kinetics. This gives the possibility to directly evaluate the system health state. Real-time monitoring of the intrinsic noise response is also very important for the identification of the microscopic sources of fluctuations and their dynamic processes. This allows for identifying possible strategies to improve efficiency and performance, especially for emerging photovoltaic devices. In this work are the reported results of detailed electrical transport and noise characterizations referring to three different types of solar cells (silicon-based, organic, and perovskite-based) and they are interpreted in terms of specific physical models.

Single polaron hopping in Fe doped glassy semiconductors: Structure–electrical transport relationship

The development of glassy nanocomposites, xFe-(1−x) (0.5 V2O5–0.4 CdO–0.1 ZnO) is particularly important not only for exploring their microstructures using x-ray diffraction, FT-IR, and UV–Vis techniques but also for exploring their electrical conduction mechanism in terms of hopping of small polarons. The presence of various nanophases, such as ZnO, CdO, Cd9.5Zn0.5, ZnV, and Zn3V2O8, have been identified and the size of estimated nanocrystallites is found to decrease with more incorporation of the Fe content in the compositions. As the value of lattice strain increases with the increase of the Fe content in the compositions, the present system becomes more and more unstable, which may be favorable for better electrical transport phenomena via the polaron hopping process. Electrical conductivity of the system has been analyzed using modified correlated barrier hopping model, Almond–West formalism, and the alternating-current conductivity scaling. Experimental data reveal that both optical photon and acoustical phonon transitions are responsible for the entire electrical conduction process. Polaron hopping is expected to be of percolation type, which has been validated from an estimated range of frequency exponents. All experimental data have been used to frame a schematic model to explore the conduction mechanism inside the present glassy system.

Multifunctional 2D g-C4N3/MoS2 vdW Heterostructure-Based Nanodevices: Spin Filtering and Gas Sensing Properties.

Two-dimensional (2D) magnetic materials are the key to the development of the new generation in spintronics technology and engineering multifunctional devices. Herein, the electronic, spin-resolved transmission, and gas sensing properties of the 2D g-C4N3/MoS2 van der Waals (vdW) heterostructure have been investigated by using density functional theory with non-equilibrium Green's function method. First, the g-C4N3/MoS2 vdW heterostructure demonstrates ferromagnetic half-metallicity and superior adsorption capacity for gas molecules. The spin-dependent electronic transport of the g-C4N3/MoS2-based nanodevice is obviously regulated by parallel or anti-parallel spin configuration in electrodes, leading to perfect single-spin conduction behavior with a nearly 100% spin filtering efficiency, a negative differential resistance effect, and other interesting electrical transport phenomena. Moreover, g-C4N3/MoS2 exhibits directional dependency and strong transport anisotropic behavior under bias windows, indicating that the electric current propagates more easily through the vertical direction than the horizontal direction. The physical mechanisms are revealed and analyzed by presenting the bias-dependent transmission spectra in combination with the projected local device density of states. Finally, the g-C4N3/MoS2-based gas sensor is more sensitive to CO, NO, NO2, and NH3 molecules with the chemisorption type. The strong chemical adsorption leads to the formation of electrons on the local scattering center and ultimately affects the transport properties, resulting in the maximum gas sensitivity reaching 6.45 for NO at the bias of 0.8 V. This work not only reveals that the g-C4N3/MoS2 vdW heterostructure with high anisotropy, perfect spin filtering, and outstanding gas sensitivity is a promising 2D material but also provides an insight into the further application in futuristic electronic nanodevices.

Imaging Vibrational Excitations in the Electron Microscope

Vibrational spectroscopy is a powerful tool for probing atomic motions in molecules and extended solids. Recent advances in aberration-corrected, monochromated-scanning transmission electron microscopy (STEM) now allow imaging of individual phonon modes at the nanoscale, overcoming the spatial limit imposed by diffraction-limited optical spectroscopy techniques. In this Perspective, we summarize the recent progress in high-resolution electron energy-loss spectroscopy (EELS), which now enables vibrational spectroscopy to be performed in the electron microscope. The high spatial and energy resolution of low-loss EELS can be used to directly image phonons inside or near inorganic and organic materials without considerable sample damage. Monochromated EELS can furthermore resolve isotope specific vibrational signatures and phonon modes arising from single-atom dopants. In parallel with these advances, we highlight the ability of spatial- and momentum-resolved EELS to measure the phonon dispersions at material interfaces, obtaining valuable knowledge about interfacial thermal and electrical transport phenomena. Before concluding, we illustrate how imaging infrared (IR) plasmons at high spatial resolution deepens our understanding of how plasmons interact with molecular vibrations. Taken together, these diverse studies illustrate the capability of monochromated STEM-EELS to image low-energy phonon and plasmon excitations at the nanoscale and the new insights from these studies can be leveraged to engineer the specific material properties needed for next-generation devices.

Weak antilocalization, spin\u2013orbit interaction, and phase coherence length of a Dirac semimetal Bi0.97Sb0.03

The present study develops a general framework for weak antilocalization (WAL) in a three-dimensional (3D) system, which can be applied for a consistent description of longitudinal resistivity rho_{xx} left( B right) and Hall resistivity rho_{xy} left( B right) over a wide temperature (T) range. Compared to the previous approach Vu et al. (Phys Rev B 100:125162, 2019), which assumes infinite phase coherence length (lϕ) and a zero spin–orbit scattering length (lSO), the present framework is more general, covering high T and the intermediate spin–orbit coupling strength. Based on the new approach, the rho_{xx} left( B right) and rho_{xy} left( B right) of the Dirac semimetal Bi0.97Sb0.03 was analyzed over a wide T range from 1.7 to 300 K. The present framework not only explains the main features of the experimental data but also enables one to estimate lϕ and lSO at different temperatures. The lϕ has a power-law T dependence at high T and saturates at low T. In contrast, the lSO shows negligible T dependence. Because of the different T dependence, a crossover occurs from the lSO-dominant low-T to the lϕ-dominant high-T regions. Accordingly, the hallmark features of weak antilocalization (WAL) in rho_{xx} left( B right) and rho_{xy} left( B right) are gradually suppressed across the crossover with increasing T. The present theory describes both low-T and high-T regions successfully, which is impossible in the previous approximate approach. This work offers insights for understanding quantum electrical transport phenomena and their underlying physics, particularly when multiple WAL length scales are competing.

The Importance of Electrical Impedance Spectroscopy and Equivalent Circuit Analysis on Nanoscale Molecular Electronic Devices

AbstractTo understand the electrical and charge transport phenomena in either single or large‐scale molecular junctions, direct current (DC) measurements are mainly utilized. The current–voltage data obtained from DC measurements on molecular junctions (MJs) are employed to infer charge transport parameters, including barrier height, contact resistance, attenuation factor (β), and underlying transport mechanisms. However, DC measurements can not separate the individual electrical components, as it produces a total current that flows in the molecular junctions. Contact resistance obtained from the DC measurements by extrapolating plot of resistance versus chain length can not make exact value. In addition, defected SAMs‐based MJs or junctions having a protective layer, DC measurements alone can predict neither proper electrical values nor the correct transport mechanisms and it lacks frequency response. Electrical impedance spectroscopy (EIS) along with the circuit model enables the identification of individual electrical components of the molecular junctions and faultless contact resistance values that facilitate the model of actual transport mechanisms. In this Review, the working principle of electrical impedance spectroscopy and circuit modeling to digitize the experimental results on various molecular junctions, is discussed. Overall, the EIS technique can serve as an excellent analytical tool for the proper electrical characterization that is highly desirable for molecular electronics.

Detecting topological phase transitions in cadmium arsenide films via the transverse magnetoresistance

Topological protection against localization causes electrical transport phenomena in disordered topological materials to differ from those in topologically trivial systems. For example, a transition between a regime of weak localization to one of weak antilocalization can occur in systems such as topological insulators and topological semimetals when an external potential is applied across the system. Here, we report on the transverse magnetoresistance of thin films of cadmium arsenide, a topologically nontrivial, as we tune the electronic states and the Fermi level. We show that the appearance of weak localization and weak antilocalization sensitively reflects the relative contributions of multiple transport channels involving both gapless (massless) and gapped (massive) Dirac fermion states present in these films. The data are consistent with expectations of the different topological states of these films. Weak (anti-)localization phenomena can, therefore, serve as a probe of the types of Dirac fermions present in topological semimetals.

Electrical transport phenomenon and variable range hopping conduction in reduced graphene oxide/polystyrene composites

In this work, we investigate the temperature dependence of the electrical conductivity of a reduced graphene oxide (RGO)/polystyrene (PS) composites. We re-analysed, in our investigation, the experimental measurements of RGO/PS composites with different RGO concentrations obtained by W. Park et al. We show using two different methods: the Zabrodskii method and a numerical method based on the calculation of the percentage deviation; that the electrical conductivity follows, at the beginning, the Efros-Shklovskii Variable Range Hopping regime (ES VRH) with T−1/2 . This behavior showed that long range electron-electron interaction reduces the Density Of State of carriers (DOS) at the Fermi level and creates the Coulomb gap (CG). When the RGO concentration increases, we noticed that the temperature dependence of the electrical conductivity tends toward T−1/3 , which may suggest a possible crossover from ES VRH regime to the Mott VRH regime for high RGO concentration values. We also, calculated and represented the Density Of State (DOS) per energy and per area function for each sample. We noted that the width of parameter representing the half of CG width decreases by increasing the RGO concentration and the function tends toward the constant corresponding to the Mott VRH

Structural and electronic properties of C60 fullerene network self-assembled on metal-covered semiconductor surfaces.

Using first-principles density functional theory calculations, we made an accurate structural characterization of the C60 superstructures self-assembled on the Tl-adsorbed Si(111) and Ge(111) surfaces, which finds a good agreement with the recent scanning tunneling microscopy observations. Our band structure calculations revealed the semi-metallic character of the C60/Tl/Si(111) system, while the C60/Tl/Ge(111) system was found to show up the pronounced metallic character due to the cascade of the flat bands lying in the vicinity of the Fermi level. The latter is a fingerprint for strong correlation effects in the C60/Tl/Ge(111) system, which makes it a promising object for studying electrical transport phenomena and opens the prospects for its application in the molecular-based electronic devices. We elucidated the details of the molecule-substrate and intermolecular interactions and discussed the character of a charge transfer in both systems.

Influence of Ba2+ Doping on Structural and Electrical Transport Properties of YMnO3 Ceramics

The pristine and barium (Ba2+) doped YMnO3 (Y1−xBaxMnO3; x = 0.00 and 0.05) ceramic samples were synthesized through the solid-state reaction method. The X-ray diffraction, Raman spectroscopy, and scanning electron microscopy were performed for the structural and morphological studies. The electrical transport properties were investigated using dielectric and modulus spectroscopy. The XRD patterns of the titled ceramics have shown the monophasic hexagonal structure having P63cm space group symmetry. The average crystallite size is found to decrease on partial substitution of Ba2+ cation. Raman spectroscopy was performed to observe the local disorder and variation in the modes with the introduction of dopant in the pristine ceramic. The surface morphology displays the formation of non-uniform grains in the ceramics. The dielectric spectroscopy reveals a decreasing trend in both the dielectric constant and dissipation factor with increasing frequency. It indicates the significant role played by the space charge polarization. The electrical modulus study of the ceramics was also performed to explore the electrical transport phenomenon. The present study reports the enhanced dielectric nature of doped materials.

Weak antilocalization and two-carrier electrical transport in Bi1−xSbx single crystals (0%≤x≤17.0%)

Experimental investigation of the weak antilocalization (WAL) effect on the Hall resistivity is quite rare, because the WAL is known to have no influence on the Hall effect in a single-band system. We challenge this view in a system that has both electrons and holes by deriving a two-band model modified by the WAL effect and by applying it to the low-field magnetoresistance (MR) and Hall resistance (HR) of $\mathrm{B}{\mathrm{i}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{b}}_{x}$ single crystals $(0\ensuremath{\le}x\ensuremath{\le}17.0%)$. Simultaneous occurrence of a dip in MR and nonlinearity in HR suggests that the $\mathrm{B}{\mathrm{i}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{b}}_{x}$ is a rare three-dimensional system, in which WAL and two distinct charge carriers interplay. The modified two-band model describes all the main features of MR and HR that are not captured by the conventional theory. From the quantitative analysis based on the modified theory, the values of key parameters, such as carrier density and mobility of electrons and holes, are estimated. The modified two-band model provides a solid framework for understanding electrical transport phenomena of a material with strong spin-orbit interaction and multiple distinct charge carriers.

Variable Range Hopping in a Dilute GaAs/AlGaAs Hole System

In this work, we conducted an investigation concerning low-temperature electrical transport phenomena in a two-dimensional (2D) GaAs hole gas. The different carrier densities of the sample locate them on the insulating side of the metal-insulator transition (MIT). Two theoretical models of variable range hopping (VRH) conduction according to Mott (Mott VRH region) and according to Efros-Shklovskii (ES VRH region) are used in the modeling of the experimental measurements obtained by Qiuet et al. [Phys. Rev. Lett. 108, 106404 (2012)].