Non-ohmic Transport Research Articles

Tailoring the Photoresponse in Surface-Modified Graphene Oxide with Environmentally-Friendly Synthesized ZnS and CuS Nanoparticles

Notable progress has been achieved in the development of high-performance optoelectronics devices based on graphene oxide (GO) due to its distinctive electrical and optical attributes. This study furnishes an intriguing, eco-friendly approach for preparing nanocomposites comprising ZnS nanoparticles (NPs) embellished GO (ZnS-GO) and CuS NPs embellished GO (CuS-GO). Adhatoda vasica leaf extract acts as both a reducing agent and a linker, facilitating the attachment of ZnS and CuS NPs onto GO sheets. Thorough scrutiny was done on the materials deploying EDX, XPS, XRD, HRTEM, FESEM, PL, and FTIR techniques to endorse their elemental composition, phase purity, crystalline structure, surface morphology, and functional groups. Photodetectors prepared with Ag/ZnS-GO/Ag and Ag/CuS-GO/Ag configurations exhibited non-ohmic charge transport and photoconductive behavior in the visible spectrum. The tuning of these photodetectors was performed under illumination at wavelengths of 480 nm, 520 nm, and 670 nm across different bias voltages. Extensive on-off cycles were employed to evaluate the switching stability of the devices, demonstrating a clear photoresponse and photoswitching behavior. At a bias voltage of 30 V and an illumination wavelength of 480 nm, the ZnS-GO and CuS-GO photodetectors exhibited responsivities of 16.91 mA/W, 24.65 mA/W, and detectivities of 4.23 x 109 Jones, 10.08 x 109 Jones, respectively.

Nonlocal Electrodynamics in Ultrapure PdCoO2

The motion of electrons in the vast majority of conductors is diffusive, obeying Ohm’s law. However, the recent discovery and growth of high-purity materials with extremely long electronic mean free paths has sparked interest in non-Ohmic alternatives, including viscous and ballistic flow. Although non-Ohmic transport regimes have been discovered across a range of materials—including two-dimensional electron gases, graphene, topological semimetals, and the delafossite metals—determining their nature has proved to be challenging. Here, we report on a new approach to the problem, employing broadband microwave spectroscopy of the delafossite metal PdCoO2 in three distinct sample geometries that would be identical for diffusive transport. The observed differences, which go as far as differing power laws, take advantage of the hexagonal symmetry of the conducting Pd planes of PdCoO2. This permits a particularly elegant symmetry-based diagnostic for nonlocal electrodynamics, with the result favoring predominantly ballistic over strictly hydrodynamic flow. Furthermore, it uncovers a new effect for ballistic electron flow, owing to the highly faceted shape of the hexagonal Fermi surface. We combine our extensive data set with an analysis of the Boltzmann equation to characterize the nonlocal regime in PdCoO2, and we include out-of-plane impurity scattering as a source of apparent momentum-conserving scattering at low temperatures. More broadly, our results highlight the potential of broadband microwave spectroscopy to play a central role in investigating exotic transport regimes in the new generation of ultrahigh-conductivity materials. Published by the American Physical Society 2024

Superfluid Signatures in a Dissipative Quantum Point Contact.

We measure superfluid transport of strongly interacting fermionic lithium atoms through a quantum point contact with local, spin-dependent particle loss. We observe that the characteristic non-Ohmic superfluid transport enabled by high-order multiple Andreev reflections transitions into an excess Ohmic current as the dissipation strength exceeds the superfluid gap. We develop a model with mean-field reservoirs connected via tunneling to a dissipative site. Our calculations in the Keldysh formalism reproduce the observed nonequilibrium particle current, yet do not fully explain the observed loss rate or spin current.

Dominant andreev reflection through nonlinear radio-frequency transport

It is found that Andreev reflection provides a deterministic teleportation process at an ideal normal-superconductor interface, making it behave like an information mirror. However, it is challenging to control the Andreev reflection in a spatially-separated junction due to the mode mixing at the interface. We theoretically propose the laser-induced Andreev reflection between two-component Fermi superfluid and normal states without mode mixing via spatially-uniform Rabi couplings. By analyzing the tunneling current up to the fourth order, we find that the Andreev current exhibits unconventional non-Ohmic transport at zero temperature. The Andreev current gives the only contribution in the synthetic junction system at zero detunings regardless of the ratio of the chemical potential bias to the superfluid gap, which is in sharp contrast to that in conventional junctions. Our result may give a potential impact on theoretical and experimental study of quantum many-body phenomena, and also pave a way for understanding the black hole information paradox through the Andreev reflection as a quantum-information mirror.

The current-voltage measurements under flat-top pulsed magnetic fields for non-ohmic transport study.

Investigation of the non-ohmic transport behaviors under high magnetic fields can provide a new way to explore novel field-induced phenomena. We present the current-voltage measurements under high magnetic fields based on the flat-top pulsed magnetic field system. Two different measurement strategies were compared, given that the excitation current swept continuously or increased by a series of pulses. For the short duration of the flat-top pulsed field, the continuous current method was adopted and well optimized to reduce the Joule heating and achieve the quasi-static measurements. Finally, the non-ohmic behaviors of a quasi-one-dimensional charge density wave Li0.9Mo6O17 were successfully studied under the magnetic field up to 30T at 4.2K, which was the first current-voltage measurements carried out in pulsed magnetic fields.

Magnetoresistance retraction behaviour of Ag/p‐Ge:Ga/Ag device under pulsed high magnetic field

In non-magnetic semiconductor materials, unsaturated magnetoresistance (MR) effect has attracted lots of attention due to its physical interests and potential applications in electronic devices. Under the extremely high magnetic field, the stability and reliability of MR effects based on the non-ohmic transport has been rarely researched. In this paper, the transport properties of non-magnetic Ag/p-Ge:Ga/Ag devices under 45 T pulsed high magnetic field at 300 K are investigated. It is found that in ohmic conduction region ( I <5 mA) where the single dominant carrier is hole, the MR values increase with increasing the applied magnetic field, presenting a conventional unsaturated behavior. In the two non-ohmic regions (5 mA≤ I ≤ 100 mA) where the transport is dominated by bipolar (electrons and holes), a MR retraction has been obviously observed under pulsed high magnetic field. Combining the Hall measurement results and calculation of Hall effect with bipolar-driven transport model, the mechanism of the MR retraction is analysed, in which the MR retraction may be related to the strong regulation of electron-to-hole density ratio by pulsed high magnetic field. This work provides a reference for evaluating the stability and reliability of the properties of non-magnetic semiconductor based MR devices under the interference of strong magnetic pulses.

Photodetector based on liquid phase exfoliated SnSe quantum dots

Tremendous progress has been made in production of high-performance electronics and opto-electronics based on 2D-TMCs (Transition metal chalcogenides) due to their exotic band structure and unique physical properties. Herein, SnSe QDs, synthesized by liquid phase exfoliation, has an average size of 6 nm. Photodetector based on Ag/SnSe QDs/Ag shows non-ohmic charge transport with photoconducting behavior in visible to NIR spectral region. Photodetector shows quite distinct time resolved photoresponse with photoresponsivity of 401 μA/W in ambient environment and 36 μA/W in vacuum (10−3 torr) in illumination of 780 nm, 6 mW/cm2 light. Photoresponse with power law Iph α P0.7 shows that the photoresponse of detector is limited by defects in SnSe QDs. Photoswitching action is quite fast in vacuum than in ambient environment. Overall, the present findings demonstrate the influence of environmental oxygen on function of Ag/SnSe QDs/Ag photodetector.

Influence of the nanostructure on the electric transport properties of resistive switching cluster-assembled gold films

The use of Au clusters produced in the gas phase and deposited at low kinetic energy on a substrate allows the bottom-up fabrication of nanostructured metallic thin films with an extremely large number of interfaces, grain boundary junctions and crystal lattice defects. Cluster-assembled gold films exhibit non-ohmic electrical transport properties with a complex resistive switching behavior, exploring discrete resistance states which depend on their structural features (average thickness, resistance value reached on the percolation curve). Their electric conduction properties can be modelled in terms of complex networks of nanojunctions and used to perform binary classification of Boolean functions. The fabrication of devices based on cluster-assembled Au films and exploiting emergent complexity and collective phenomena requires a deep understanding of the influence of the nanoscale structure on the fundamental mechanisms of electrical conduction. Here we present a detailed study of the correlation between the nanostructure and the electrical properties of cluster-assembled gold films by a systematic characterization of the film growth from sub-monolayer to continuous layer beyond the electrical percolation threshold. The influence of different cluster size distributions on the onset of the electrical conduction and the role of defects is investigated by combining in situ and ex situ electrical and structural characterizations.

Mechanism of non-Ohmic conduction in a single Y3Fe5O12 nanofiber

We present a strong non-Ohmic transport characteristic in an individual Y3Fe5O12 (YIG) nanofiber at low temperature. The structural characterization reveals that the nanofiber consists of a multitude of nanoparticles stacked along the nanofiber axis. The non-Ohmic conductive behavior manifests itself by a strong input current dependence and the nonlinear I–V curves with a critical temperature around 160 K. The current measured at temperatures lower than 160 K follows the Simmons tunneling model, and the tunneling through the grain boundary is proposed to interpret the non-Ohmic feature in an individual YIG nanofiber. However, the observed resistance follows a T−1/4 variation in the high temperature range (&amp;gt; 160 K), suggesting a variable range hopping conduction.

Unconventional quantum vortex matter state hosts quantum oscillations in the underdoped high-temperature cuprate superconductors

A central question in the underdoped cuprates pertains to the nature of the pseudogap ground state. A conventional metallic ground state of the pseudogap region has been argued to host quantum oscillations upon destruction of the superconducting order parameter by modest magnetic fields. Here, we use low applied measurement currents and millikelvin temperatures on ultrapure single crystals of underdoped [Formula: see text] to unearth an unconventional quantum vortex matter ground state characterized by vanishing electrical resistivity, magnetic hysteresis, and nonohmic electrical transport characteristics beyond the highest laboratory-accessible static fields. A model of the pseudogap ground state is now required to explain quantum oscillations that are hosted by the bulk quantum vortex matter state without experiencing sizable additional damping in the presence of a large maximum superconducting gap; possibilities include a pair density wave.

Energy loss rate and non-ohmic characteristics of a degenerate surface layer of compound semiconductors at low lattice temperatures

The rate of energy loss of the non-equilibrium electrons and their non-ohmic mobility characteristics have been analyzed here for a degenerate ensemble of two dimensional electron gas in a well of compound semiconductor, taking due account of some of the low temperature features. In place of the Fermi Dirac distribution function, a well-tested alternative form of the distribution function has been used here for mathematical simplicity. The numerical results thus obtained here for the wells of InSb, GaAs and GaN are compared with some available theoretical and experimental data. Our theoretical results are seen to be in quite reasonable agreement with the experimental data when some qualitative comparison is made between them. The results being interesting, the present work stimulates further studies in the same field. • At low temperatures, non-ohmic transport in quantum surfaces changes significantly. • Theory of energy loss rate and non-ohmic mobility are developed at low temperature. • In place of the Fermi-Dirac an alternative distribution is used for simplicity. • Degenerate surface layers of compounds like InSb, GaAs and GaN are studied. • Agreement with available experimental data for GaAs has been reasonable.

Non-Ohmic conduction in exfoliated La0.7Ca0.3MnO3 thin films

We present a strong non-Ohmic transport characteristic of the exfoliated La0.7Ca0.3MnO3 thin film obtained by growing a water-soluble sacrificial layer of Sr3Al2O6 between the SrTiO3 substrate and the La0.7Ca0.3MnO3 film. The non-Ohmic conduction manifests itself as a significant amount of electroresistance over a wide range of temperatures. The resistance shows a plateaulike feature at low temperatures, and the electroresistance reaches ∼50 000% at 10 K for input currents varying from 1024 nA to 125 pA. The structural characterization of the exfoliated film reveals the existence of antiphase boundaries, the tunneling through which appears to cause the non-Ohmic feature. Our results provide an avenue into colossal tunneling electroresistance mediated by crystallographic defects.

Characterization of nonOhmic electrical transport in double perovskite compounds through bias scale and nonlinearity exponent

Scaling analysis of nonOhmic electrical transport in double perovskite (DP) compounds like La2NiMnO6 and Sr2Fe0.3Mn0.7MoO6 is presented over a wide range of electric bias and temperatures. It is shown that the voltage V0(T) at which conductance deviates from its Ohmic value Σ0(T) scales with Σ0(T) as V0(T)∼Σ0(T)xT, xT being the onset exponent characterizing the onset of nonOhmic conduction. Interestingly, it was found that xT is negative and insensitive to the nature of conduction mechanism in DPs but is related to the characteristic temperature T0 and the mean hopping length Hm. We provide a scaling formalism in terms of the parameters V0(T) and xT in DPs for deeper understanding of the spintronic application and the electrode functioning in solid oxide fuel cells (SOFC). Inelastic multi-step tunneling is found to be the suitable mechanism of electronic transport characterized completely by these two parameters.

Intrinsic non-ohmic electronic transport properties of the transparent In–Zn–O compound nanobelts under ohmic contact and out of the space charge limited transport region

It is generally accepted that the nonlinear I–V characteristics for semiconductor nanostructures are mainly induced by the Schottky contacts or by the space charge limited transport mechanism. We perform I–V measurements on undoped and doped In–Zn–O compound nanobelts and confirm that their intrinsic non-ohmic transport behaviors are not caused by these mechanisms. A model based on the hopping assisted trap state electrons transport process is introduced to explain the nonlinear I–V characteristics and to extract their electrical parameters. An understanding of this trap-state influenced carrier transport can advance the progress of nanomaterials applications and enable us to distinguish their intrinsic transport behaviors from contact effects. The results also indicate that the material has good electrical properties and can be used as a potential substitute for In2O3.

Hot-phonon-assisted additional correlation in Al0.23Ga0.77N/GaN

The hot-phonon effect is considered for an Al0.23Ga0.77N/GaN structure with a two-dimensional electron gas subjected to an electric field applied in the plane of electron confinement. The hot-phonon accumulation is taken into account in the hot-phonon lifetime approximation for the quantum well model designed through a self-consistent solution of Schrödinger and Poisson equations. The field-dependent electron temperature and non-ohmic transport are obtained from the Monte Carlo simulation for a 3-subband model. The longitudinal tensor component of an additional correlation of electron velocities is estimated in the hotelectron temperature approximation and an essential dependence on the hot-phonon lifetime is demonstrated. The results are in a reasonable agreement with the experimental data for a similar structure with a two-dimensional electron gas.

Non-Ohmic Electrical Transport in the Vicinity of the Superconducting Transition: Implications for the Study of the Phase Diagram of the Underdoped Cuprate Superconductors

In this paper, we present a theoretical discus- sion of the non-ohmic regime of the electrical conductivity of a type-II planar superconductor near its superconduct- ing transition, focusing mainly in the region between the phase-coherence and the pair-condensation critical temper- atures, Tphase <T < T cond. For that purpose, we extend down to those temperatures existing calculations for the so- called Aslamazov-Larkin conductivity in presence of finite electric fields, and the resulting exponent α of the fluctu- ation voltage-current characteristics E∼j α . These results are then discussed by considering two possible scenarios for the phase diagram of the superconducting fluctuations in the underdoped high-temperature superconductors. Our results suggest that the strong phase fluctuations scenario (i.e., large Tcond − Tphase) leads to a plateau in the T - dependence of the exponent α near Tphase, and that the T -region over which this plateau extends becomes wider when the applied electric field is increased. These features are much smaller in the conventional fluctuations scenario (i.e., small Tcond − Tphase).

Theory of Low- and High-Field Transports in Metallic Single-Wall Nanotubes

Individual metallic single-wall carbon nanotubes show unsual non-Ohmic transport behaviors at high bias fields. For low resistance contact samples, the differential conductance dI/dV increases with increasing bias, reaching a maximum at $\sim$ 100mV. As the bias increases further, dI/dV drops dramatically [Yao et al., Phys. Rev. Lett. 84, 2941 (2000)]. The higher the bias, the system behaves in a more normal (Ohmic) manner. This so-called zero-bias anomaly is temperature-dependent (50--150K). We propose a new interpretation. Supercurrent runs in the graphene wall below $\sim$ 150K. The normal conduction-electron currents run outside the wall, which are subject to the scattering by phonons and impurities. The currents along the tube induce circulating magnetic fields and eventually destroy the supercurrent in the wall at high enough bias, and restore the Ohmic behavior. If the prevalent ballistic electron model is adopted, then the scattering effects cannot be discussed.

Non-ohmic Electrical Transport Properties Above the Critical Temperature in Optimally and Underdoped Superconducting YBa2Cu3O6+x

The resistivity and the Hall effect as a function of current density and temperature in the normal state of very thin films of YBa2Cu3O6+x are measured with a fast pulsed-current technique. The in-plane longitudinal and transverse (Hall) conductivities are reduced in intense current densities up to several $\mathrm{MA\,cm}^{-2}$ . In optimally-doped samples, this non-ohmic effect is limited to temperatures below 100 K. In a moderately underdoped sample, however, the non-linearity extends to the temperature range from T c =53 K to ∼150 K. The non-linear part of the Hall conductivity does not scale with a critical exponent, thus excluding classical amplitude fluctuations of the superconducting order parameter as possible origin.

Scaling description of non-Ohmic transport in manganites

The current–voltage characteristics of several manganite systems like La0.87MnO3–(Mn2O3)0.13, La0.60Y0.07Ca0.33MnO3 and Nd0.55Sm0.3375Sr0.1125MnO3 show non-Ohmic behaviour at different temperatures. The onset voltage V0(T) at which conductance starts deviating from its zero-bias value Σ0(T) scales as V0(T)∼Σ0(T)xT with xT being the onset exponent. A detailed scaling analysis with these manganite systems reveal that the onset exponents xT are different in the paramagnetic insulating and ferromagnetic metallic phases. Besides, the magnitudes of xT are different in different manganite systems. Non-Ohmic conduction and the onset exponent are described with the help of inelastic multi-step tunneling model and scaling concepts.

Effect of electrostatic screening due to non-equilibrium carriers on the lattice scattering rate at low temperatures

The intravalley acoustic scattering rate has been calculated here taking the screening by non-equilibrium electrons into account under the condition when the lifetime of the electrons is controlled by shallow attractive traps at low lattice temperature. The scattering rates now turn out to be field dependent and the characteristics are significantly different from what follows when the electron ensemble is in equilibrium with the lattice. The results indicate the possibility of interesting non-ohmic transport characteristics under these conditions. Numerical results are obtained for high purity samples of Si.