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Register a new userMnSi-nanostructures obtained from thin films: magnetotransport and Hall effect
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D. Schroeter
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We present a comparative study of the (magneto)transport properties, including Hall effect, of bulk, thin film and nanostructured MnSi. In order to set our results in relation to published data we extensively characterize our materials, this way establishing a comparatively good sample quality. Our analysis reveals that in particular for thin film and nanostructured material, there are extrinsic and intrinsic contributions to the electronic transport properties, which by modeling the data we separate out. Finally, we discuss our Hall effect data of nanostructured MnSi under consideration of the extrinsic contributions and with respect to the question of the detection of a topological Hall effect in a skyrmionic phase.
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Bismuth chalcogenides are the most studied 3D topological insulators. As a rule, at low temperatures thin films of these materials demonstrate positive magnetoresistance due to weak antilocalization. Weak antilocalization should lead to resistivity decrease at low temperatures; in experiments, however, resistivity grows as temperature decreases. From transport measurements for several thin films (with various carrier density, thickness, and carrier mobility), and by using purely phenomenological approach, with no microscopic theory, we show that the low temperature growth of the resistivity is accompanied by growth of the Hall coefficient, in agreement with diffusive electron-electron interaction correction mechanism. Our data reasonably explain the low-temperature resistivity upturn.
The magnetic structure of the in-plane skyrmions in epitaxial MnSi/Si(111) thin films is probed in three dimensions by the combination of polarized neutron reflectometry (PNR) and small angle neutron scattering (SANS). We demonstrate that skyrmions exist in a region of the phase diagram above at temperature of 10 K. PNR shows the skyrmions are confined to the middle of the film due to the potential well formed by the surface twists. However, SANS shows that there is considerable disorder within the plane indicating that the magnetic structure is a 2D skyrmion glass.
We show that a thin film of a three-dimensional topological insulator (3DTI) with an exchange field is a realization of the famous Haldane model for quantum Hall effect (QHE) without Landau levels. The exchange field plays the role of staggered fluxes on the honeycomb lattice, and the hybridization gap of the surface states is equivalent to alternating on-site energies on the AB sublattices. A peculiar phase diagram for the QHE is predicted in 3DTI thin films under an applied magnetic field, which is quite different from that either in traditional QHE systems or in graphene.
A wide variation in the disorder strength, as inferred from an order of magnitude variation in the longitudinal resistivity of Co2FeSi (CFS) Huesler alloy thin films of fixed (50 nm) thickness, has been achieved by growing these films on Si(111) substrates at substrate temperatures ranging from room temperature (RT) to 600 C. An in-depth study of the influence of disorder on anomalous Hall resistivity,longitudinal resistivity(LR) and magnetoresistance, enabled by this approach, reveals the following. The side-jump mechanism gives a dominant contribution to anomalous Hall resistivity (AHR) in the CFS thin films, regardless of the degree of disorder present. A new and novel contribution to both LR and AHR characterized by the logarithmic temperature dependence at temperatures below the minimum, exclusive to the amorphous CFS films, originates from the scattering of conduction electrons from the diffusive hydrodynamic modes associated with the longitudinal component of magnetization, called diffusons. In these amorphous CFS films, the electron-diffuson, e d, scattering and weak localization (WL) mechanisms compete with that arising from the inelastic electron magnon, e m, scattering to produce the minimum in longitudinal resistivity, whereas the minimum in AHR is caused by the competing contributions from the e d and e m scattering, as WL does not make any contribution to AHR. In sharp contrast, in crystalline films, enhanced electron electron Coulomb interaction (EEI), which is basically responsible for the resistivity minimum, makes no contribution to AHR with the result that AHR does not exhibit a minimum.
We report the first electrical manipulation and detection of the mesoscopic intrinsic spin-Hall effect (ISHE) in semiconductors through non-local electrical measurement in nano-scale H-shaped structures built on high mobility HgTe/HgCdTe quantum wells. By controlling the strength of the spin-orbit splittings and the n-type to p-type transition by a top-gate, we observe a large non-local resistance signal due to the ISHE in the p-regime, of the order of kOhms, which is several orders of magnitude larger than in metals. In the n-regime, as predicted by theory, the signal is at least an order of magnitude smaller. We verify our experimental observation by quantum transport calculations which show quantitative agreement with the experiments.
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