Linear Magnetoresistance Effect Research Articles

Nonequilibrium Green’s function approach to multi-band Cooper-pair transport: linear magnetoresistance effect due to nonunitary superconductivity

Many-body transport has emerged as an efficient tool for understanding interaction effects in quantum materials with a multi-band electronic structure. This paper proposes a formula for the two-particle transmission coefficient for Cooper-pair transport between multi-band normal and superconducting materials. The approach employs a tight-binding nonequilibrium Green’s function technique, allowing a direct calculation of the two-particle current, without invoking the paradigm of Andreev reflection. As an application of the theory, we demonstrate a low-field linear magnetoresistance effect for superconductors with an induced nonunitary order parameter. These results uncover an unexplored route for detecting unconventional nonunitary superconductivity in quantum materials of current theoretical and experimental interest.

Magneto-transport properties of Si1−xGex <B, Hf> whiskers

The field and temperature magnetoresistance dependences of the Si1−xGex (x = 0.05) whiskers at low temperatures were studied in the magnetic field range of 0−14 T with using of the Bitter magnet. The investigated whiskers with diameters 5−15 μm were grown by chemical vapour deposition with a doping concentration in the vicinity to the metal-insulator transition (Nc ≈ 7.8 ⋅ 1018 cm−3). The linear magnetoresistance effect of the solid solution Si1-xGex <B, Hf > whiskers was found in all range of the magnetic fields due to the surface coherence scattering of charge carriers as a result of conduction in the whisker core-shell structure.

Magnetotransport properties of tellurium under extreme conditions

This study investigates the transport properties of a chiral elemental semiconductor tellurium (Te) under magnetic fields and pressure. Application of hydrostatic pressure reduces the resistivity of Te, while its temperature dependence remains semiconducting up to 4 GPa, contrary to recent theoretical and experimental studies. Application of higher pressure causes structural as well as semiconductor-metal transitions. The resulting metallic phase above 4 GPa exhibits superconductivity at 2 K along with a noticeable linear magnetoresistance effect. On the other hand, at ambient pressure, we identified metallic surface states on the as-cleaved ($10\overline{1}0$) surfaces of Te. The nature of these metallic surface states has been systematically studied by analyzing quantum oscillations observed in high magnetic fields. We clarify that a well-defined metallic surface state exists not only on chemically etched samples that were previously reported, but also on as-cleaved ones.

Unsaturated linear magnetoresistance effect in high-quality free-standing InSb single-crystal nanosheets

Narrow band gap semiconductor InSb has attracted tremendous attention due to the high electron mobility, small electron effective mass, and large Landé g-factor, which makes InSb gain potential exploitation in novel electronic and spintronic devices. In addition, with lowering dimension and downscaling size, various quantum phenomena might emerge in low-dimensional InSb structures. In this work, the magneto-transport characteristics of high-quality free-standing InSb single-crystal nanosheets are systematically explored. A large and unsaturated linear magnetoresistance is observed at temperature ranging from 125 K to 300 K. And this linear magnetoresistance exhibits non-monotonic temperature dependence, which is different with previous studies. Further analysis indicates that this phenomenon could be understood by the quantum magnetoresistance model. Thus, the study on the linear magnetoresistance of InSb is helpful to develop the physical model in InSb nanostructure and might extend to low-dimensional semiconductors. Additionally, it could lay a foundation for the future application in magnetic sensors.

Non-Drude Magneto-Transport Behavior in a Topological Crystalline Insulator/Band Insulator Heterostructure.

The Drude model is one of the most fundamental models used to understand the electronic carrier transport in materials, including recently discovered topological materials. Here, we present a magneto-transport study revealing the non-Drude transport behavior in a heterostructure of topological crystalline insulator (TCI) SnTe and band insulator PbTe which exhibits a nonsaturating linear magneto-resistance (MR) effect, a novel phenomenon widely observed in topological materials with gapless dispersion. It is shown that in the van der Pauw geometry in which the longitudinal and transverse magneto-resistances are measured to extract the magneto-conductivity, the two-band Drude model is not sufficient to self-consistently describe both the longitudinal and transverse magneto-conductivities. Furthermore, in the Corbino geometry, which directly measures the longitudinal magneto-conductivity σ xx( B) for a straightforward comparison with the Drude model, the MR, 1/σ xx( B), still reveals a large linear MR effect, in direct discrepancy with the Drude model. While shining further light on the multiple-carrier transport in TCI, this study highlights an unusual magneto-transport character of topological materials that challenges the standard Drude picture of electron transport.

Disorder-dominated linear magnetoresistance in topological insulator Bi2Se3 thin films

The linear magnetoresistance (MR) effect is an interesting topic due to its potential applications. In topological insulator Bi2Se3, this effect has been reported to be dominated by the carrier mobility (μ) and hence has a classical origin. Here, we study the magnetotransport properties of Bi2Se3 thin films and observe the linear MR effect, which cannot be attributed to the quantum model. Unexpectedly, the linear MR does not show the linear dependence on μ, in conflict with the reported results. However, we find that the observed linear MR is dominated by the inverse disorder parameter 1/kFl, where kF and l are the Fermi wave vector and the mean free path, respectively. This suggests that its origin is also classical and that no μ-dominated linear MR effect is observed which may be due to the very small μ values in our samples.

Magnetic properties and magnetoresistance effect of La2Co1−xMg xMnO6 (0.1 ⩽ x ⩽ 1.0)

Double perovskite La2Co1−xMgxMnO6 samples with different compositions (x = 0.1, 0.2, 0.3, 0.5, 0.7, 1.0) were synthesized by the standard solid-state reaction method. The samples (x = 0.1, 0.2, 0.3, 0.5, 0.7) exhibit obvious ferromagnetic behavior. The remanent magnetization, coercive field and Curie temperature gradually decrease with increasing the Mg-substitution. The appropriate amount of Mg-substitution can increase the saturation magnetization. The types of interactions changed with Mg-substitution, which makes the La2MgMnO6 sample exhibit clear antiferromagnetism. A slightly enhanced negative magnetoresistance effect (approximately 17%) of the La2Co0.9Mg0.1MnO6 sample was observed at 200 K and 7 T. The pronounced linear magnetoresistance effect is attributed to the suppression of spin-fluctuations by the magnetic field.

The Model for Linear Magnetoresistance of Two-Dimensional Metal-Semiconductor Composites with Interfacial Shells **Supported by the China Postdoctoral Science Foundation under Grant No 2014MM551868, and the Science and Technology Development Guidance Program of Qingdao under Grant No KJZD-13-35-JCH.

A metal-semiconductor composite with the interfacial shells is investigated theoretically for the large linear magnetoresistance effect of high doping Ag2+δSe and Ag2+δTe materials. The magnetoresistance (MR) of composites is a function of the magnetic field, temperature, the conductivities of two phases without magnetic field, and the thickness and conductivity of the interfacial shells. The MR increases with the increase of the magnetic field and with the decrease of temperature, and no saturation is found even under the high magnetic field. Moreover, it is interestingly found that the interfacial shell is an important factor for the MR of the composites. The MR increases with the thickness and the conductivity of the interfacial shells. Lastly, the theoretical results on the MR are compared with the experimental data. It is found that the value of the MR of the composite with the interfacial shell is larger than that without the interfacial shell.

Linear magnetoresistance versus weak antilocalization effects in Bi2Te3

In chalcogenide topological insulator materials, two types of magneto-resistance (MR) effects are widely discussed: a positive MR dip around zero magnetic field associated with the weak antilocalization (WAL) effect and a linear MR effect which generally persists to high fields and high temperatures. We have studied the MR of topological insulator Bi2Te3 films from the metallic to semiconducting transport regime. While in metallic samples, the WAL is difficult to identify due to the smallness of the WAL compared to the samples' conductivity, the sharp WAL dip in the MR is clearly present in the samples with higher resistivity. To correctly account for the low field MR by the quantitative theory of WAL according to the Hikami-Larkin-Nagaoka (HLN) model, we find that the classical (linear) MR effect should be separated from the WAL quantum correction. Otherwise the WAL fitting alone yields an unrealistically large coefficient $\alpha$ in the HLN analysis.

Systematic study of doping dependence on linear magnetoresistance in p-PbTe

We report on a large linear magnetoresistance effect observed in doped p-PbTe films. While undoped p-PbTe reveals a sublinear magnetoresistance, p-PbTe films doped with BaF2 exhibit a transition to a nearly perfect linear magnetoresistance behaviour that is persistent up to 30 T. The linear magnetoresistance slope ΔR/ΔB is to a good approximation, independent of temperature. This is in agreement with the theory of Quantum Linear Magnetoresistance. We also performed magnetoresistance simulations using a classical model of linear magnetoresistance. We found that this model fails to explain the experimental data. A systematic study of the doping dependence reveals that the linear magnetoresistance response has a maximum for small BaF2 doping levels and diminishes rapidly for increasing doping levels. Exploiting the huge impact of doping on the linear magnetoresistance signal could lead to new classes of devices with giant magnetoresistance behavior.

Magnetic properties and magnetoresistance effect of Pb2FeMoO6

Magnetic properties and magnetoresistance effect of Pb2FeMoO6, synthesized under high pressure at high temperature, were systematically studied. The sample shows ferromagnetic behavior with Curie temperature about 243 K. The field dependent of paramagnetic susceptibility was discussed by the magnetic inhomogeneous related to Fe/Mo ions disorder. Electrical resistivity of the sample exhibits a semiconductor behavior, which can be well understood by variable-range hopping model. A maximum magnetoresistance effect value about 15% was observed at 20 K and 70 kOe. The pronounced linear magnetoresistance effect is attributed to the suppression of spin-fluctuations by the magnetic field.

Two-step synthesis of silver selenide semiconductor with a linear magnetoresistance effect

A two-step synthesis method for polycrystalline β-silver selenide (β-Ag2Se) was developed. In the first step, nanopowder was prepared using a chemical conversion method at room temperature. In the second step, the nanopowder was compressed and then the bulk Ag2Se was fabricated by the solid-state sintering process. The crystalline phase and morphology were examined. The results showed that β-Ag2Se was fast fabricated at room temperature. The dense polycrystalline Ag-rich Ag2Se was synthesized successfully at 450 °C for 0.5 h under Argon flow. For the polycrystalline, the electronic properties and transverse magnetoresistance (TMR) in a pulsed magnetic field were investigated. The samples displayed n-type semiconducting behaviors and a critical temperature with a broaden temperature range of 140–150 K. Also, it presented a positive and nearly linear dependence on magnetic field H at H ≥ Hc (crossover field) ranging from 2 to 20 T. Moreover, the linear dependence of TMR at strong field was non-saturating up to 35 T. Combining with the observation of morphology, it is thought that this unusual TMR effect was caused by slightly excess Ag. This new synthesis method provided a potential route to synthesize nonstoichiometric silver selenide.

Magnetodielectric response in 0.36BiScO3-0.64PbTiO3/La0.7Sr0.3MnO3 thin films and the corresponding model modifications

Dielectric relaxation and magnetodielectric (MD) effects were observed in 0.36BiScO3-0.64PbTiO3/La0.7Sr0.3MnO3 thin films. The universal dielectric response and distribution of relaxation time modifications were introduced into the Maxwell-Wagner (MW) model. Based on modified MW model, the negative MD response at low frequencies was attributed to magnetostriction of La0.7Sr0.3MnO3, while the large positive response at high frequencies mainly to the magnetoresistance of La0.7Sr0.3MnO3, and these two factors canceled each other out at intermediate frequencies. Moreover, a giant room temperature MD response of 9.5% was observed, and the linear MD response at 52 kHz was ascribed to the linear magnetoresistance effects.

Microstructure and magnetoresistance of heterogeneous gold-rich Ag 3Au 1.1Te 2

Dispersions of very small non-magnetic metal particles or inclusions in a non-magnetic semiconductor matrix are well known to produce unusually large and linear magnetoresistance effects. So far these materials were limited to the binary silver-rich chalcogenides Ag 2Se and Ag 2Te. In this contribution Ag 3AuTe 2 was selected as a first candidate for a ternary matrix material, thus offering enhanced capabilities for the generation of heterogeneous microstructure and spatially varying composition on the nanoscale. In gold-rich Ag 3Au 1.1Te 2 two kinds of inhomogeneities are present, namely Au deposits with a size on the micron scale and an inhomogeneous distribution of Au and Ag within the matrix. The matrix consists of micron-sized grains with the structure type of Ag 3AuTe 2 as studied by electron microscopy. Like the binary silver chalcogenide phases, the material also shows a large and linear magnetoresistance effect. The transversal magnetoresistance effect was measured between 20 K and 270 K in magnetic fields up to B = 5 T. The results are discussed on the basis of existing models for a large and linear positive MR effect.

Preparation and magnetoresistance of Ag2+xSe thin films deposited via pulsed laser deposition.

The preparation of Ag2+xSe thin films with thicknesses between 4 nm and 3 μm by pulsed laser deposition on single crystalline NaCl and MgO substrates is reported. The films are perfectly dense and show a good lateral uniformity with a small number of defects. The microstructure of the films corresponds to a nanoparquet, being composed of two different phases of silver selenide. One phase is identified as the Naumannite low temperature phase of silver selenide, the structure of the other phase has not been reported in detail before and probably represents a metastable phase. Silver-rich films contain silver precipitates with typical sizes on the nanoscale. Their presence and their size appears to be responsible for the large and linear magnetoresistance effect of silver-rich silver selenide.

Classical Hall transition and magnetoresistance in strongly inhomogeneous planar systems

The magneto-transport properties of planar and layered strongly inhomogeneous two-phase systems are investigated, using the explicit expressions for the effective conductivities and resistivities obtained by the exact dual transformation, connecting effective conductivities of in-plane isotropic two-phase systems with and without magnetic field. These expressions allow to describe the effective resistivity of various inhomogeneous media at arbitrary concentrations x and magnetic fields H. The corresponding plots of the x-dependence of the Hall constant R H ( x , H ) and the magnetoresistance R ( x , H ) are constructed for various values of magnetic field at some values of inhomogeneity parameters. These plots for strongly inhomogeneous systems at high magnetic fields show a sharp transition between partial Hall resistivities (or Hall conductivities) with different dependencies of R H on the phase concentrations. It is shown that there is a strong correlation between large linear magnetoresistance effect and this sharp Hall transition. Both these effects are a consequence of the exact duality symmetry. A possible physical explanation of these effects and their correlation is proposed.

Large linear magnetoresistivity in strongly inhomogeneous planar and layered systems

Explicit expressions for magnetoresistance R of planar and layered strongly inhomogeneous two-phase systems are obtained, using exact dual transformation, connecting effective conductivities of in-plane isotropic two-phase systems with and without magnetic field. These expressions allow to describe the magnetoresistance of various inhomogeneous media at arbitrary concentrations x and magnetic fields H. All expressions show large linear magnetoresistance effect with different dependencies on the phase concentrations. The corresponding plots of the x- and H-dependencies of R ( x , H ) are represented for various values, respectively, of magnetic field and concentrations at some values of inhomogeneity parameter. The obtained results show a remarkable similarity with the existing experimental data on linear magnetoresistance in silver chalcogenides Ag 2 + δ Se . A possible physical explanation of this similarity is proposed. It is shown that the random, stripe type, structures of inhomogeneities are the most suitable for a fabrication of magnetic sensors and a storage of information at room temperatures.

Linear magnetoresistance of potassium

Measurements of the linear magnetoresistance effect in pure potassium were made using two independent methods. Four-terminal measurements on straight narrow samples showed transverse and longitudinal effects of the same magnitude. An induced torque method was then used on large good single crystals. In these the magnetoresistance was of the same order of magnitude as in the narrow samples and it was isotropic. The presence of the linear variation of resistivity with field in this case of a probeless method, where no obvious boundary value problems occur, adds to the existing evidence that the effect is not a result of sample shape or contact configuration.