Low Temperature Electrical Transport Research Articles

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.

Inducing a tunable skyrmion-antiskyrmion system through ion beam modification of FeGe films

Skyrmions and antiskyrmions are nanoscale swirling textures of magnetic moments formed by chiral interactions between atomic spins in magnetic noncentrosymmetric materials and multilayer films with broken inversion symmetry. These quasiparticles are of interest for use as information carriers in next-generation, low-energy spintronic applications. To develop skyrmion-based memory and logic, we must understand skyrmion-defect interactions with two main goals—determining how skyrmions navigate intrinsic material defects and determining how to engineer disorder for optimal device operation. Here, we introduce a tunable means of creating a skyrmion-antiskyrmion system by engineering the disorder landscape in FeGe using ion irradiation. Specifically, we irradiate epitaxial B20-phase FeGe films with 2.8 MeV Au4+ ions at varying fluences, inducing amorphous regions within the crystalline matrix. Using low-temperature electrical transport and magnetization measurements, we observe a strong topological Hall effect with a double-peak feature that serves as a signature of skyrmions and antiskyrmions. These results are a step towards the development of information storage devices that use skyrmions and antiskyrmions as storage bits, and our system may serve as a testbed for theoretically predicted phenomena in skyrmion-antiskyrmion crystals.

Modulation of the optical and transport properties of epitaxial SrNbO3 thin films by defect engineering

The discovery of strontium niobate (SNO) as a potentially new transparent electrode has generated much interest due to its implications in various optoelectronic devices. Pristine SNO exhibits exceptionally low resistivity (∼10−4 Ω cm) at room temperature. However, this low resistivity occurs due to large number of carrier concentration in the system, which significantly affects its optical transparency (∼40%) in the visible range and hinders its practical applications as a transparent electrode. Here, we show that modulating the growth kinetics via oxygen manipulation is a feasible approach to achieve the desired optoelectronic properties. In particular, epitaxial (001) SNO thin films are grown on (001) lanthanum aluminate by pulsed laser deposition at different oxygen partial pressures and are shown to improve the optical transparency from 40% to 72% (λ = 550 nm) at a marginal cost of electrical resistivity from 2.8 to 8.1 × 10−4 Ω cm. These changes are directly linked with the multi-valence Nb-states, as evidenced by x-ray photoelectron spectroscopy. Furthermore, the defect-engineered SNO films exhibit multiple electronic phases that include pure metallic, coexisting metal-semiconducting-like, and pure semiconducting-like phases as evidenced by low-temperature electrical transport measurements. The intriguing metal-semiconducting coexisting phase is thoroughly analyzed using both perpendicular and angle-dependent magnetoresistance measurements, further supported by a density functional theory-based first-principles study and the observed feature is explained by the quantum correction to the conductivity. Overall, this study shows an exciting avenue for altering the optical and transport properties of SNO epitaxial thin films for their practical use as a next-generation transparent electrode.

Low-temperature electrical transport in the normal-state of overdoped cuprate superconductors

The low-temperature electrical transport in the normal-state of overdoped cuprate superconductors is investigated based on the t-J model. The momentum relaxation due to the umklapp scattering between electrons by the exchange of the effective spin propagator is employed to evaluate the electrical resistivity within the framework of the Boltzmann transport theory. It is shown that the quadratic temperature dependence of the resistivity develops in the far-lower-temperature region, and is followed by a nonlinear temperature dependence of the resistivity in an extremely-narrow-crossover region and a linear temperature dependence of the resistivity in the low-temperature region. The obtained results also show that the same spin excitation governs both superconductivity and the electron umklapp scattering responsible for the low-temperature linear in temperature resistivity in the overdoped regime.

Low temperature electrical transport in thin carbon films deposited on SiO2/Si substrates by pulsed laser deposition

In this paper electrical transport studies are performed on thin carbon films deposited on SiO2/Si substrates by pulsed laser deposition (PLD) applying laser ablation of micro-crystalline graphite target. Experiments were carried out on 320 - 420 nm thick SiO2 on Si substrates as well as on hydrogenated diamond-like carbon (DLC) films deposited on SiO2/Si. Structural studies by means of XPS, SEM and Raman spectroscopy revealed that the films can be characterized as nano-sized carbon phases possessing different phase composition (i.e. the ratio sp3/sp2 hybridized carbon, etc.). The electrical conductivity/resistivity of the films was measured in the temperature range 10 K < T < 300 K. Four-contact Van der Pauw method as well as two contact schemes have been applied. Some films have low room temperature resistivity in the range ρ = (0.1–1.5)×10-3 Ω.·m and consist predominantly of sp2 hybridized carbon with Raman spectra, which resemble that of nano-sized graphene depending on the deposition conditions and substrates used. The thinnest only 0.5 nm layer deposited directly on SiO2 exhibits relatively low specific resistance (~10-3 Ω. m), which can be taken as an indication of good deposition conditions of graphene-like layers. The current flow mechanism was explored at temperatures from 300 K down to 10K. The temperature dependence reveals non-metallic behavior - the conductivity decreases at decreasing temperature as opposed to typical metal behaviour. A model of variable range hopping (VRH) mechanism is applied to explain the low temperature conductivity drawn from transport in nanocrystalline disordered systems.

Impurity metallic conduction below the critical concentration of metal-insulator transition in FeCo x Si

Analysis on very detailed measurements of resistivity (ρ) and thermoelectric power (S) of magnetic impurity (Co) substituted iron silicide (FeSi) has been presented in this report. The impurity valence electrons of Co dominate the whole physical properties at low temperatures below 35 K, below the critical concentration x c (≈0.02). The negative thermopower and the positive slope in the resistivity at low temperatures are exciting and show that the system is not entirely insulator below the critical concentration of metal–insulator transition (x c ). So, due to the external impurity electrons, the system’s magnetic ground state could change considerably compared to the parent compound FeSi. This report may help unveil the interesting low-temperature transport properties between x = 0 and x = 0.04 (FeCo x Si). Two band model and variable range hopping model were employed to explain the low-temperature electrical and thermal transport properties.

Low temperature electrical transport in microwave plasma fabricated free-standing graphene and N-graphene sheets

In this paper, the electrical transport in free-standing graphene and N-graphene sheets fabricated by a microwave plasma-based method is addressed. Temperature–dependent resistivity/conductivity measurements are performed on the graphene/N-graphene sheets compressed in pellets. Different measurement configurations reveal directional dependence of current flow—the room-temperature conductivity longitudinal to the pellet’s plane is an order of magnitude higher than the transversal one, due to the preferential orientation of graphene sheets in the pellets. SEM imaging confirms that the graphene sheets are mostly oriented parallel to the pellet’s plane and stacked in agglomerates. The high longitudinal electrical conductivity with values on the order of 103 S/m should be noted. Further, the current flow mechanism revealed from resistivity-temperature dependences from 300K down to 10K shows non-metallic behavior manifested with an increasing resistivity with decreasing the temperature usually observed for insulating or localized systems. The observed charge transport shows variable range hopping at lower temperatures and thermally activated behaviour at higher temperatures. This allows us to attribute the charge transport mechanism to a partially disordered system in which single graphene sheets are placed predominantly parallel to each other and stacked together.

Effects of Physical and Chemical Pressure on Charge Density Wave Transitions in LaAg1−xAuxSb2 Single Crystals

The structural characterization and electrical transport measurements at ambient and applied pressures of the compounds of the LaAg1−xAuxSb2 family are presented. Up to two charge density wave (CDW) transitions could be detected upon cooling from room temperature and an equivalence of the effects of chemical and physical pressure on the CDW ordering temperatures was observed with the unit cell volume being a salient structural parameter. As such LaAg1−xAuxSb2 is a rare example of a non-cubic system that exhibits good agreement between the effects of applied, physical, pressure and changes in unit cell volume from steric changes induced by isovalent substitution. Additionally, for LaAg0.54Au0.46Sb2 anomalies in low temperature electrical transport were observed in the pressure range where the lower charge density wave is completely suppressed.

Cesium-mediated electron redistribution and electron-electron interaction in high-pressure metallic CsPbI3

Electron-phonon coupling was believed to govern the carrier transport in halide perovskites and related phases. Here we demonstrate that electron-electron interaction enhanced by Cs-involved electron redistribution plays a direct and prominent role in the low-temperature electrical transport of compressed CsPbI3 and renders Fermi liquid (FL)-like behavior. By compressing δ-CsPbI3 to 80 GPa, an insulator-semimetal-metal transition occurs, concomitant with the completion of a slow structural transition from the one-dimensional Pnma (δ) phase to a three-dimensional Pmn21 (ε) phase. Deviation from FL behavior is observed upon CsPbI3 entering the metallic ε phase, which progressively evolves into a FL-like state at 186 GPa. First-principles density functional theory calculations reveal that the enhanced electron-electron coupling results from the sudden increase of the 5d state occupation in Cs and I atoms. Our study presents a promising strategy of cationic manipulation for tuning the electronic structure and carrier scattering of halide perovskites at high pressure.

Phase transformation from FeSe to Fe3Se4

We report on thermal atomic layer deposition of iron selenide (FeSe and Fe3Se4) thin films with four-inch wafer-scale uniformity using two precursors of iron bis(N, N′-diisopropylacetamidinato) [Fe(i-Pr-Me-AMD)2] and bis(triethysilyl) selenide [(Et3Si)2Se]. The temperature window is determined to be 350–400 °C. The transformation from tetragonal FeSe to monoclinic Fe3Se4 has been found. The tetragonal FeSe thin films exhibit a strong (00 l) texture deposited on amorphous silica glass, suggesting that the surface is partially parallel to the layered ab plane. By adjusting the ratio of iron and selenium, the thin films exhibit from conductors to semiconductors, and finally to insulators. All as-grown conductive samples appear metallic-like temperature dependence by low-temperature electrical transport measurements. This study opens the way to prepare various metal selenides by atomic layer deposition.

Low-temperature electrical transport and tunable optical properties of Mo-doped V2O3 thin films

This work reports the structural and low-temperature electrical transport properties of Mo doped V2O3 single-layer thin films (i.e., with compositions between Mo and V2O3 [V2−xMoxO3−δ (x = 0, 0.05–0.1)]) deposited on alumina (Al2O3) substrates by sol–gel dip-coating technique. The crystallinity of the V2O3 films is modified with the high concentration of Mo doping and exhibits a relatively defective structure compared to that of pure V2O3 films. The low temperature (i.e., over a temperature range of 253.15 to 273.15 K) electrical hysteresis curves reveal that the triggering of metal–insulator transition at low temperatures. The metal–insulator transition (MIT) temperature (Tc) values are found to be 258.49 and 261.11 K for 8 and 10 mol% Mo doped V2O3 films, respectively, which are higher than that of undoped V2O3 (Tc = 253.09 K). The experimental results contribute a promising method to develop a novel material for high-performance low-temperature engineering applications.

High-temperature solution growth of large size chalcogenide FeTxSe (T: Fe, Co) superconducting single crystals

We report the growth of high quality Fe excess and Co doped, Fe T x Se single crystals in nominal ratio via slow cooling method of high temperature solution growth technique and, their structural and physical properties through the X-ray diffraction, Raman spectroscopy, magnetic and transports measurements. Selective area electron diffraction (SAED) patterns and X-ray diffraction of cleavage piece confirm the growth of single crystals in ( h0l ) orientations. Observations of phonon vibration modes (A 1g and B 1g ) in Raman spectroscopy measurements mark the qualitative analysis of these single crystals. Low temperature magnetic and electrical transport studies manifest the superconducting nature of both single crystals.

Biomolecular control over local gating in bilayer graphene induced by ferritin

SummaryElectrical field-induced charge modulation in graphene-based devices at the nanoscale with ultrahigh density carrier accumulation is important for various practical applications. In bilayer graphene (BLG), inversion symmetry can simply be broken by an external electric field. However, control over charge carrier density at the nanometer scale is a challenging task. We demonstrate local gating of BLG in the nanometer range by adsorption of AfFtnAA (which is a bioengineered ferritin, an iron-storing globular protein with ∅ = 12 nm). Low-temperature electrical transport measurements with field-effect transistors with these AfFtnAA/BLG surfaces show hysteresis with two Dirac peaks. One peak at a gate voltage VBG = 35 V is associated with pristine BLG, while the second peak at VBG = 5 V results from local doping by ferritin. This charge trapping at the biomolecular length scale offers a straightforward and non-destructive method to alter the local electronic structure of BLG.

Low-Temperature Electrical Transport and Tunable Optical Properties of Mo-Doped V2o3 Thin Films

Low-Temperature Electrical Transport and Tunable Optical Properties of Mo-Doped V2o3 Thin Films

Experimental research progress of electronic band structure and low temperature transport based on molybdenum disulfide

Molybdenum disulfide is a layered transition metal chalcogenide semiconductor. It has many applications in the fields of two-dimensional spintronics, valleytronics and optoelectronics. In this review, molybdenum disulfide is taken as a representative to systematically introduce the energy band structures of single layer, bilayer and twisted bilayer molybdenum disulfide, as well as the latest experimental progress of its realization and low-temperature electrical transport, such as superconductivity and strong correlation phenomenon. Finally, two-dimensional transition metal chalcogenide moiré superlattice’s challenges in optimizing contact and sample quality are analyzed and the future development of this field is also presented.

The structural, magnetic, Raman and electrical transport properties of Mn intercalated Ti3C2 T X

The electronic and magnetic properties of the two-dimensional Ti3C2 MXenes have attracted a lot of interests due to its potential applications. In this paper, Ti3C2 T x MXenes and Mn-doped Ti3C2 T x MXenes are synthesized and investigated. The experimental data shows that Mn2+ ions are homogeneously and randomly intercalated between Ti3C2 sheets as function terminals, which increase the interlayer distance between Ti3C2 sheets and offer a mass of uncoupled magnetic moment. The temperature dependence of the electric resistivity of both samples show similar complex behavior although the resistivity increases dramatically as Mn doping. The inter-flake variable range hopping (VRH) dominates the low temperature electric transport behavior, while the inter-flake thermally activated hopping as well as the metallic intra-flake transport competing with the inter-flake VRH play important roles at high temperature. The increasing resistivity of the Mn-doped sample could be attributed to the increase of the interlayer distance and the enhancement of the localization of the transport electrons after Mn2+ ions intercalation.

Band convergence and thermoelectric performance enhancement of InSb via Bi doping

The thermoelectric performance of InSb has been significantly improved via defect engineering or nanostructuring to reduce thermal conductivity in the past decade; however, less attention has been paid to improve its electrical properties via other key factors, e.g., carrier scattering mechanism, bipolar effect, etc. Here, we show that Bi doping on the Sb site not only significantly suppresses the high-temperature bipolar effect, but also leads to band convergence which enhances the Seebeck coefficient. As a result, a maximum zT of ∼0.43 @ 675 K is achieved in InSb0.97Bi0.03, which is increased by ∼43% as compared to that of pure InSb. In addition, the comparison of Bi and Ga doping (J. Mater. Chem., 2011, 21, 12398–12401) on the low-temperature electrical transport properties reveals that Bi doping is more beneficial for achieving high power factor due to the mixed acoustic phonon and ionized impurity scattering. Finally, it is suggested that Bi should be an effective dopant for electrical optimization of InSb and a further experiment on co-doping of Ga and Bi will be a considerable alternative for thermoelectric performance enhancement of InSb-based materials.

Structural, Magnetic, and Low-Temperature Electrical Transport Properties of YIG Thin Films with Heavily Reduced Oxygen Contents

Structural, Magnetic, and Low-Temperature Electrical Transport Properties of YIG Thin Films with Heavily Reduced Oxygen Contents

High mobility field-effect transistors based on MoS2 crystals grown by the flux method

Two-dimensional (2D) molybdenum disulphide (MoS2) transition metal dichalcogenides (TMDs) have great potential for use in optical and electronic device applications; however, the performance of MoS2 is limited by its crystal quality, which serves as a measure of the defects and grain boundaries in the grown material. Therefore, the high-quality growth of MoS2 crystals continues to be a critical issue. In this context, we propose the formation of high-quality MoS2 crystals via the flux method. The resulting electrical properties demonstrate the significant impact of crystal morphology on the performance of MoS2 field-effect transistors. MoS2 made with a relatively higher concentration of sulphur (a molar ratio of 2.2) and at a cooling rate of 2.5 °C h−1 yielded good quality and optimally sized crystals. The room-temperature and low-temperature (77 K) electrical transport properties of MoS2 field-effect transistors (FETs) were studied in detail, with and without the use of a hexagonal boron nitride (h-BN) dielectric to address the mobility degradation issue due to scattering at the SiO2/2D material interface. A maximum field-effect mobility of 113 cm2 V−1 s−1 was achieved at 77 K for the MoS2/h-BN FET following high-quality crystal formation by the flux method. Our results confirm the achievement of large-scale high-quality crystal growth with reduced defect density using the flux method and are key to achieving higher mobility in MoS2 FET devices in parallel with commercially accessible MoS2 crystals.

Magnetic and electrical transport study of the antiferromagnetic topological insulator Sn-doped MnBi2Te4

Magnetism coupled with topological materials can offer a platform for realizing quite rich fascinating physical phenomena, including quantum anomalous Hall effect (QAHE), topological magnetoelectric effect, and giant anomalous Nernst effect. Recently, the discovery of the intrinsic magnetic topological insulator ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ has promoted the study of the physical phenomena of magnetic topological materials. Here, we grow single crystals of Sn-doped ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ in bulk with ratios of 25%, 33%, 50%, and 66% to probe the magnetic and electrical properties. We perform low-temperature magnetic and electrical transport measurements for Sn-doped ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ and find that the antiferromagnetic (AFM) character is clear in this material until the concentration rises to 66%, and mainly transport dominated carriers are n-type. Most of all, the transition points of ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ decrease upon Sn doping, providing an alternative approach to realize QAHE at lower magnetic field, which is essential for further application in AFM spintronics.