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The magnetoresistance (MR) in nonmagnetic materials continues to be a fertile research area in materials science. The search for giant, positive MR has been limited to a rather small window of materials such as high‐mobility semimetals in single‐crystalline form. Here, the observation of a very large positive MR in metallic Pt5P2 in polycrystalline form is reported. The observations reveal that improvement of the crystallinity results in a significant enhancement of the positive MR, exceeding 10 000% at 9 T, comparable to high‐mobility semimetals. Based on first‐principles calculations combined with magnetotransport and thermoelectric measurements, the Fermi surface of Pt5P2 is found to consist of a collection of multiple electron and hole pockets compensating one another, along with a characteristic pocket continuously connected to the adjacent Brillouin zone, together with possible topologically protected band crossings. This work extends the landscape of high MR candidate materials to polycrystalline metals, which demonstrates the importance of crystallinity and purity of the samples for the optimization of the MR. [ABSTRACT FROM AUTHOR]

Abstract The magnetoresistance (MR) in nonmagnetic materials continues to be a fertile research area in materials science. The search for giant, positive MR has been limited to a rather small window of materials such as high‐mobility semimetals in single‐crystalline form. Here, the observation of a very large positive MR in metallic Pt5P2 in polycrystalline form is reported. The observations reveal that improvement of the crystallinity results in a significant enhancement of the positive MR, exceeding 10 000% at 9 T, comparable to high‐mobility semimetals. Based on first‐principles calculations combined with magnetotransport and thermoelectric measurements, the Fermi surface of Pt5P2 is found to consist of a collection of multiple electron and hole pockets compensating one another, along with a characteristic pocket continuously connected to the adjacent Brillouin zone, together with possible topologically protected band crossings. This work extends the landscape of high MR candidate materials to polycrystalline metals, which demonstrates the importance of crystallinity and purity of the samples for the optimization of the MR.

Magnetotransport measurements have been carried out for pristine and irradiated Y Ba 2 Cu 3 O 7 − x films. The measurements reveal a crossover from the clean superconducting limit to the dirty one with an increase in the impurity scattering rate Γ produced by a certain dose of irradiation. For the clean limit, the critical temperature T c 0 decreases with Γ , while the initial slope K = | d H c 2 / d T | T c 0 increases. We find a nice agreement between these experimental data and a model of d -wave superconductors with anisotropic impurity scattering. Such dose-dependencies of T c 0 and K reveal the superconducting coherence length ξ 0 to be quasi-invariant in the clean limit. For the dirty limit, ξ 0 increases with Γ due to a decrease in both the quantities T c 0 and K. Though, this decrease appears slower than predicted by the textbook picture of d -wave superconductors. Such discrepancy can be produced by an irradiation-induced modulated disorder responsible for the formation of (d + s) -wave pairing. • The initial slope K = | d H c 2 / d T | T c 0 increases with irradiation dose for low ion fluences, whereas for higher ion fluences it suffers a slow decay. • Clean-to-dirty crossover occurs in the superconducting state of Y BCO films at a certain dose of xenon ion irradiation. • The superconducting coherence length ξ 0 remains quasi-invariant in the clean limit, while in the dirty limit it increases with irradiation dose. [ABSTRACT FROM AUTHOR]

Layered transition metal dichalcogenides (TMDCs) have been extensively studied owing to their unique physical and chemical properties. Weak van der Waals (vdW) interactions between the stacking layers of TMDCs allow intercalation of various species including monovalent alkali, divalent alkaline earth and multivalent metal ions, zero-valent transition metals, as well as organic molecules, all of which can drastically alter fundamental properties of the TMDCs. The urge to understand the phenomena and the desire to exploit them for applications have inspired a great deal of investigations. A large portion of the mystery has been unveiled over the past decade of intense research; however, many questions remain open and require further explorations. This review is concerned with investigations on structural and electronic evolution of TMDCs driven by electrochemically controlled intercalations. Herein, we aim to survey the recent advances and experimental platforms for monitoring the intercalation processes in situ by utilizing nanodevices. In addition, several inquiries and prospects are outlined in a broader context for future avenues of studies. [ABSTRACT FROM AUTHOR]

Novel physical properties appear when the size of a superconductor is reduced to the nanoscale, in the range of its superconducting coherence length (ξ0). Such nanosuperconductors are being investigated for potential applications in nanoelectronics and quantum computing. The design of three-dimensional nanosuperconductors allows one to conceive novel schemes for such applications. Here, we report for the first time the use of a He+ focused-ion-beam-microscope in combination with the W(CO)6 precursor to grow three-dimensional superconducting hollow nanowires as small as 32 nm in diameter and with an aspect ratio (length/diameter) of as much as 200. Such extreme resolution is achieved by using a small He+ beam spot of 1 nm for the growth of the nanowires. As shown by transmission electron microscopy, they display grains of large size fitting with face-centered cubic WC1-x phase. The nanowires, which are grown vertically to the substrate, are felled on the substrate by means of a nanomanipulator for their electrical characterization. They become superconducting at 6.4 K and show large critical magnetic field and critical current density resulting from their quasi-one-dimensional superconducting character. These results pave the way for future nanoelectronic devices based on three-dimensional nanosuperconductors. [ABSTRACT FROM AUTHOR]

Topological insulators (TIs) are the promising materials for next-generation technology due to their exotic features such as spin momentum locking, conducting surface states, etc. However, the high-quality growth of TIs by sputtering technique, which is one of the foremost industrial requirements, is extremely challenging. Also, the demonstration of simple investigation protocols to characterize topological properties of TIs using electron-transport methods is highly desirable. Here, we report the quantitative investigation of non-trivial parameters employing magnetotransport measurements on a prototypical highly textured Bi 2 Te 3 TI thin film prepared by sputtering. Through the systematic analyses of the temperature and magnetic field dependent resistivity, all topological parameters associated with TIs, such as coherency factorα, Berry phase (ΦB), mass term ( m ), the dephasing parameter ( p ), slope of temperature dependent conductivity correction (κ) and the surface state penetration depth ( λ ) are estimated by using the modified 'Hikami-Larkin-Nagaoka', 'Lu-Shen' and 'Altshuler-Aronov' models. The obtained values of topological parameters are well comparable to those reported on molecular beam epitaxy grown TIs. The epitaxial growth of Bi 2 Te 3 film using sputtering, and investigation of the non-trivial topological states from its electron-transport behavior are important for their fundamental understanding and technological applications., (© 2023 IOP Publishing Ltd.)

An archetypical layered topological insulator Bi _2 Se _3 becomes superconductive upon doping with Sr, Nb or Cu. Superconducting properties of these materials in the presence of in-plane magnetic field demonstrate spontaneous symmetry breaking: 180 ^◦ -rotation symmetry of superconductivity versus 120 ^◦ -rotation symmetry of the crystal. Such behavior brilliantly confirms nematic topological superconductivity. To what extent this nematicity is due to superconducting pairing in these materials, rather than due to crystal structure distortions? This question remains unanswered, because so far no visible deviations from the 3-fold crystal symmetry were resolved in these materials. To address this question we grow high quality single crystals of Sr _x Bi _2 Se _3 , perform detailed x-ray diffraction and magnetotransport studies and reveal that the observed superconducting nematicity direction correlates with the direction of small structural distortions in these samples (∼0.02% elongation in one crystallographic direction). Additional anisotropy comes from orientation of the crystallite axes. 2-fold symmetry of magnetoresistance observed in the most uniform crystals well above the critical temperature demonstrates that these structural distortions are nevertheless strong enough. Our data in combination with strong sample-to-sample variation of the superconductive anisotropy parameter are indicative for significance of the structural factor in the apparent nematic superconductivity in Sr _x Bi _2 Se _3 .

This comprehensive study aims to investigate the change of the flux pinning mechanism, electrical and superconducting properties of the inorganic solid Bi-2212 materials with the La inclusions inserted in the crystal structure by means of magnetotransport measurements exerted in the applied magnetic field range of 0—7 T. Crucial characteristics as regards critical transition temperatures ( T c onset and T c offset ), room temperature resistivities ( ρ 300K ), residual resistivities ( ρ 0 ), residual resistivity ratios ( RRR ), irreversibility fields ( μ 0 H irr ), upper critical fields ( μ 0 H c 2 ), thermodynamic critical fields ( μ 0 H c ), activation energies ( U 0 ), penetration depths ( λ ) and coherence lengths ( ξ ) are evaluated from the experimental magnetoresistivity curves and available theoretical approaches. All the properties obtained above confirm the considerable degradation in the pinning of 2D pancake vortices with the increment of the La individuals randomly distributed in the Bi-2212 superconducting system. Thus, the improved recoupling linelike nature among the consecutively stacked layers leads to decoupling of the adjacent layers and suppression of the interlayer Josephson coupling length as a result of the enhancement in the thermal fluctuations of flattened pancake vortices. The long and short of it is that the La impurities undermine the elasticity of the vortex lattice. For example, the T c offset and T c onset values are found to be about 84.5 K and 85.7 K for the best (pure) sample while the material exposed to the La content level of x = 0.2 obtains the values of 82.2 K and 15.1 K, respectively at zero applied magnetic field. In the case of the applied magnetic field of 7 T, the T c offset value reduces considerably towards the lower temperature values of 72.6 K for the former compound. However, the values belonging to the worst sample (La4) cannot be determined at higher external magnetic field value such as 1 T due to the hybridization of La-3/states with the Cu3d–O2p states in the Cu–O 2 layers (dissipation). This is attributed to the existence of the pair-breaking mechanism in Bi-site La substituted Bi-2212 systems. Moreover, the flux pinning energy values calculated from thermally activated flux flow (TAFF) model decrease dramatically with the enhancement of both the La content level and external magnetic fields. Numerically, the activation energy value is calculated to be about 5173 K (1077 K) for the pure sample at the field value of 0 T (7 T) whereas the values pertaining to the compound substituted by the La concentration level of x = 0.15 are found to be in a range of 1196–281 K. The lack of the experimental evidences does not enable us to find the energy values belonging to the La4 sample at higher applied field. As for the critical field parameters ( μ 0 H c 1 , μ 0 H c , μ 0 H irr , μ 0 H c 2 and μ 0 H c 3 ) and the extracted values ( λ , ξ and κ ), the changes in the parameters given also verify the degradation of the flux pinning ability (random distribution of the artificial pinning centers) with the La concentration as a result of the Cooper pair-breaking mechanism. To sum up, the La impurities are unfavorable for the potential applications of these materials in the commercial sector at high temperatures and magnetic fields. [ABSTRACT FROM AUTHOR]

Magnetoresistivity performance of the polycrystalline YBaCuGdO (Y123) superconductors is discussed by the change of the flux pinning mechanism using magnetotransport measurements performed in the magnetic field range from 0 to 7 T. The critical transition temperatures, irreversibility fields ( μ H), upper critical fields ( μ H), penetration depths ( λ) and coherence lengths ( ξ) of the Y123 materials are deduced from the magnetoresistivity curves. Further, activation (flux pinning) energies belonging to the samples are determined from thermally activated flux creep (TAFC) model. The results obtained display that the flux pinning energies reduce with enhancing the applied magnetic field. This may be attributed to the fact that Gd nanoparticles inserted in the Y123 superconducting core lead to exhibit much weaker flux pinning, lesser crystallinity and connectivity between grains as compared to the pure sample due to the presence of stronger pair-breaking mechanism. [ABSTRACT FROM AUTHOR]

Abstract: The behaviour of an InP/InGaAs heterojunction bipolar transistor stack in a magnetic field is described here with reference to various surface modifications. These include surface passivation with sulphur-based species, surface amorphisation with plasma-induced ion bombardment and inclusion of three-dimensional ferromagnetic thin-film structures on the surface of the device. The structure, fabrication and modelling of the device is described in brief, followed by the results of transport and transduction experiments on the hybrid ferromagnet-bipolar transistor device. The results clearly show the important role played by surface conditions on surface and near-surface electron interactions brought about by Lorentz deflection of transport current in bipolar transistors and the potential for using these effects to measure the strength of magnetic fields. A new type of compound semiconductor integrated ferromagnet-bipolar transistor magnetic field sensor, based on these processes, is presented. [Copyright &y& Elsevier]

Abstract: The results of surface modification induced effects on InP/InGaAs single heterojunction bipolar transistors, as revealed by magnetotransport experiments, are described here. The surface treatments included both sulphur-based surface passivation and ion bombardment-induced surface damage. The former is known to improve device characteristics and the latter to degrade device operation. In this work the aim was to assess these techniques for tailoring device performance for surface sensing applications. Device characteristics were found to be sensitive to surface preparation prior to measurements. Measurements revealed that surface treatments that improve device performance also reduce sensitivity to external magnetic fields while treatments that degrade performance make devices more sensitive to externally applied magnetic fields. [Copyright &y& Elsevier]

Novel physical properties appear when the size of a superconductor is reduced to the nanoscale, in the range of its superconducting coherence length (ξ 0 ). Such nanosuperconductors are being investigated for potential applications in nanoelectronics and quantum computing. The design of three-dimensional nanosuperconductors allows one to conceive novel schemes for such applications. Here, we report for the first time the use of a He + focused-ion-beam-microscope in combination with the W(CO) 6 precursor to grow three-dimensional superconducting hollow nanowires as small as 32 nm in diameter and with an aspect ratio (length/diameter) of as much as 200. Such extreme resolution is achieved by using a small He + beam spot of 1 nm for the growth of the nanowires. As shown by transmission electron microscopy, they display grains of large size fitting with face-centered cubic WC 1-x phase. The nanowires, which are grown vertically to the substrate, are felled on the substrate by means of a nanomanipulator for their electrical characterization. They become superconducting at 6.4 K and show large critical magnetic field and critical current density resulting from their quasi-one-dimensional superconducting character. These results pave the way for future nanoelectronic devices based on three-dimensional nanosuperconductors.