arXiv subjects

Stefan Hartl

Publications and source records attributed to Stefan Hartl.

3 recordsLinked to original sources

arXiv2025

Anomalous conductance steps in three-dimensional topological insulator HgTe-based quantum point contacts

We explore electrical transport through a point contact in strained HgTe, a three-dimensional topological insulator. In the absence of a magnetic field $B$, there is no quantization. However, under higher magnetic fields, we observe distinct non-integer conductance steps. Based on numerical tight-binding calculations and a phenomenological Landauer-Büttiker approach, we attribute these atypical, non-integer quantized plateaus to significant scattering effects at the point contact.

cond-mat.mes-hall↗

arXiv2025

Spin injection and detection in all-van der Waals 2D devices

In this work we report efficient out-of-plane spin injection and detection in an all-van der Waals based heterostructure using only exfoliated 2D materials. We demonstrate spin injection by measuring spin-valve and Hanle signals in non-local transport in a stack of Fe$_3$GeTe$_2$ (FGT), hexagonal boron nitride (hBN) and graphene layers. FGT flakes form the spin aligning electrodes necessary to inject and detect spins in the graphene channel. The hBN tunnel barrier provides a high-quality interface between the ferromagnetic electrodes and graphene, eliminating the conductivity mismatch problem, thus ensuring efficient spin injection and detection with spin injection efficiencies of up to $P=40$\%. Our results demonstrate that FGT/hBN/graphene heterostructures form a promising platform for realizing 2D van der Waals spintronic devices.

cond-mat.mes-hall↗

arXiv2018

Measuring anisotropic spin relaxation in graphene

We compare different methods to measure the anisotropy of the spin-lifetime in graphene. In addition to out-of-plane rotation of the ferromagnetic electrodes and oblique spin precession, we present a Hanle experiment where the electron spins precess around either a magnetic field perpendicular to the graphene plane or around an in-plane field. In the latter case, electrons are subject to both in-plane and out-of-plane spin relaxation. To fit the data, we use a numerical simulation that can calculate precession with anisotropies in the spin-lifetimes under magnetic fields in any direction. Our data show a small, but distinct anisotropy that can be explained by the combined action of isotropic mechanisms, such as relaxation by the contacts and resonant scattering by magnetic impurities, and an anisotropic Rashba spin-orbit based mechanism. We also assess potential sources of error in all three types of experiment and conclude that the in-plane/out-of-plane Hanle method is most reliable.

cond-mat.mes-hall↗