arXiv subjects

Christian Riha

Publications and source records attributed to Christian Riha.

4 recordsLinked to original sources

arXiv2024

Low-temperature magnetoresistance hysteresis in Vanadium-doped Bi$_{2}$Te$_{2.4}$Se$_{0.6}$ bulk topological insulators

Bi$_{2}$Te$_{2.4}$Se$_{0.6}$ single crystals show gapless topological surface states and doping ($x$) with Vanadium allows to shift the chemical potential in the bulk band gap. Accordingly, the resistivity, carrier density, and mobility are constant below 10 K and the magnetoresistance shows weak antilocalization as expected for low-temperature transport properties dominated by gapless surface states of so-called three-dimensional topological "insulators". However, the magnetoresistance also shows a hysteresis depending on the sweep rate and the magnetic field direction. Here, we provide evidence that such magnetoresistance hysteresis is enhanced if both three-dimensional bulk states and quasi-two-dimensional topological states contribute to the transport ($x$ = 0 and 0.03), and it is mostly suppressed if the topological states govern transport ($x$ = 0.015). The results are discussed in terms of spin-dependent scattering between the different available states

cond-mat.mes-hall↗

arXiv2019

Excess noise in Al${}_\text{x}$Ga${}_\text{1-x}$As/GaAs based quantum rings

Cross-correlated noise measurements are performed in etched Al${}_\text{x}$Ga${}_\text{1-x}$As/GaAs based quantum rings in equilibrium at bath temperature of $T_\text{bath}=4.2\text{ K}$. The measured white noise exceeds the thermal (Johnson-Nyquist) noise expected from the measured electron temperature $T_\text{e}$ and the electrical resistance $R$. This excess part of the white noise decreases as $T_\text{bath}$ increases and vanishes for $T_\text{bath}\geq 12\text{ K}$. Excess noise is neither observed if one arm of a quantum ring is depleted of electrons nor in 1D-constrictions that have a length and width comparable to the quantum rings. A model is presented that suggests that the excess noise originates from the correlation of noise sources, mediated by phase-coherent propagation of electrons.

cond-mat.mes-hall↗

arXiv2016

2D layered transport properties from topological insulator Bi$_2$Se$_3$ single crystals and micro flakes

Low-field magnetotransport measurements of topological insulators such as Bi$_2$Se$_3$ are important for revealing the nature of topological surface states by quantum corrections to the conductivity, such as weak-antilocalization. Recently, a rich variety of high-field magnetotransport properties in the regime of high electron densities ($\sim10^{19}$ cm$^{-3}$) were reported, which can be related to additional two-dimensional layered conductivity, hampering the identification of the topological surface states. Here, we report that quantum corrections to the electronic conduction are dominated by the surface states for a semiconducting case, which can be analyzed by the Hikami-Larkin-Nagaoka model for two coupled surfaces in the case of strong spin-orbit interaction. However, in the metallic-like case this analysis fails and additional two-dimensional contributions need to be accounted for. Shubnikov-de Haas oscillations and quantized Hall resistance prove as strong indications for the two-dimensional layered metallic behavior. Temperature-dependent magnetotransport properties of high-quality Bi$_2$Se$_3$ single crystalline exfoliated macro and micro flakes are combined with high resolution transmission electron microscopy and energy-dispersive x-ray spectroscopy, confirming the structure and stoichiometry. Angle-resolved photoemission spectroscopy proves a single-Dirac-cone surface state and a well-defined bulk band gap in topological insulating state. Spatially resolved core-level photoelectron microscopy demonstrates the surface stability.

cond-mat.mtrl-sci↗

arXiv2015

Mode-selected heat flow through a one-dimensional waveguide network

Cross-correlated measurements of thermal noise are performed to determine the electron temperature in nanopatterned channels of a GaAs/AlGaAs heterostructure at 4.2 K. Two-dimensional (2D) electron reservoirs are connected via an extended one-dimensional (1D) electron waveguide network. Hot electrons are produced using a current $I_{\text{h}}$ in a source 2D reservoir, are transmitted through the ballistic 1D waveguide and relax in a drain 2D reservoir. We find that the electron temperature increase $ΔT_{\text{e}}$ in the drain is proportional to the square of the heating current $I_{\text{h}}$, as expected from Joule's law. No temperature increase is observed in the drain when the 1D waveguide does not transmit electrons. Therefore, we conclude that electron-phonon interaction is negligible for heat transport between 2D reservoirs at temperatures below 4.2 K. Furthermore, mode control of the 1D electron waveguide by application of a top-gate voltage reveals that $ΔT_{\text{e}}$ is not proportional to the number of populated subbands $N$, as previously observed in single 1D conductors. This can be explained with the splitting of the heat flow in the 1D waveguide network.

cond-mat.mes-hall↗