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Register a new userNon-monotonic magnetoresistance of two-dimensional electron systems in the ballistic regime
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Alexander Kuntsevich
Publication date
2009
fields
Physics
and research's language is
English
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We report experimental observations of a novel magnetoresistance (MR) behavior of two-dimensional electron systems in perpendicular magnetic field in the ballistic regime, for k_BTtau/hbar>1. The MR grows with field and exhibits a maximum at fields B>1/mu, where mu is the electron mobility. As temperature increases the magnitude of the maximum grows and its position moves to higher fields. This effect is universal: it is observed in various Si- and GaAs- based two-dimensional electron systems. We compared our data with recent theory based on the Kohn anomaly modification in magnetic field, and found qualitative similarities and discrepancies.
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In ultra-high quality two-dimensional (2D) materials the mean free paths of phonons and electrons relative to all mechanisms of scattering can be much greater than a size of a sample. In this case the most intensive type of scattering of particles is their collisions with sample edges and the ballistic regime of heat and charge transport is realized. We study the ballistic transport of classical interacting 2D particles in a long narrow sample. We show that the inter-particle scattering conserving momentum leads to a positive hydrodynamic correction to the ballistic conductance, which is a precursor of the viscous Poiseuille flow. We examine the effect of weak magnetic field on the electron ballistic conductance and predict a novel classical ballistic mechanism for negative magnetoresistance. Our analysis demonstrates that, apparently, such mechanism explains the temperature-independent part of the giant negative magnetoresistance recently observed in the ultra-high mobility GaAs quantum wells.
Negative longitudinal magnetoresistance (NLMR) has been reported in a variety of materials and has attracted extensive attention as an electrotransport hallmark of topological Weyl semimetals. However, its origin is still under debate. Here, we demonstrate that the NLMR in a two dimensional electron gas can be influenced by the measurement current. While the NLMR persists up to 130 K, its magnitude and magnetic field response become dependent on the applied current below 60 K. The tunable NLMR at low and high currents can be best attributed to quantum interference and disorder scattering effects, respectively. This work uncovers non-Ohmic NLMR in a non-Weyl material and highlights potential effects of the measurement current in elucidating electrotransport phenomena. We also demonstrate that NLMRs can be a valuable phenomenon in revealing the origins of other properties, such as negative MRs in perpendicular magnetic fields.
We study the characterization and realization of higher-order topological Anderson insulator (HOTAI) in non-Hermitian systems, where the non-Hermitian mechanism ensures extra symmetries as well as gain and loss disorder.We illuminate that the quadrupole moment $Q_{xy}$ can be used as the real space topological invariant of non-Hermitian higher-order topological insulator (HOTI). Based on the biorthogonal bases and non-Hermitian symmetries, we prove that $Q_{xy}$ can be quantized to $0$ or $0.5$. Considering the disorder effect, we find the disorder-induced phase transition from normal insulator to non-Hermitian HOTAI. Furthermore, we elucidate that the real space topological invariant $Q_{xy}$ is also applicable for systems with the non-Hermitian skin effect. Our work enlightens the study of the combination of disorder and non-Hermitian HOTI.
We study the dependence of the glassy properties of strongly localized indium-oxide films on the sample lateral dimensions. Characteristic mesoscopic effects such as reproducible conductance fluctuations (CF) are readily observable in gated structures for sample size smaller than 100 microns measured at 4K, and the relative amplitude of the CF decreases with the sample volume as does the flicker noise. By contrast, down to sample size of few microns, the non-equilibrium features that are attributed to the electron-glass are indistinguishable from those observed in macroscopic samples, and in particular, the relaxation dynamics is independent of sample size down to 2 microns. In addition, The usual features that characterize the electron-glass including slow-relaxation, memory effects, and full-aging behavior are all observed in the `mesoscopic regime, and they appear to be independent of the conductance fluctuations.
Recently, negative longitudinal and positive in-plane transverse magnetoresistance have been observed in most topological Dirac/Weyl semimetals, and some other topological materials. Here we present a quantum theory of intrinsic magnetoresistance for three-dimensional Dirac fermions at a finite and uniform magnetic field B. In a semiclassical regime, it is shown that the longitudinal magnetoresistance is negative and quadratic of a weak field B while the in-plane transverse magnetoresistance is positive and quadratic of B. The relative magnetoresistance is inversely quartic of the Fermi wave vector and only determined by the density of charge carriers, irrelevant to the external scatterings in the weak scattering limit. This intrinsic anisotropic magnetoresistance is measurable in systems with lower carrier density and high mobility. In the quantum oscillation regime a formula for the phase shift in Shubnikov-de Hass oscillation is present as a function of the mobility and the magnetic field, which is useful for experimental data analysis.
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