Transport evidence of strain-induced pseudo magnetic field in graphene

The pseudo magnetic field (B_ps) is a strain-induced gauge field that breaks valley degeneracy in graphene. It enables exploration of novel quantum transport behaviors unattainable via real magnetic field, such as valley-polarization, pseudo-Landau levels, and edge states. However, creating controlled B_ps is challenging in experiment because it requires transport-compatible architecture for precise strain gradient engineering.

Here, we show a patternable strain-engineering architecture that enables experimental transport study of B_ps. By depositing a high-stress MgO thin film on graphene, we create a strain gradient of 0.8%/um, quantified by spatially resolved Raman spectroscopy. This gradient induces a global B_ps of 0.5±0.1 T, as verified in transport experiments. We observe secondary oscillations emerging around each primary Landau level, which disperse linearly with applied magnetic field. These secondary oscillations are attributed to valley-split pseudo-Landau levels caused by the strain-induced B_ps. At zero magnetic field, we find periodic oscillations in resistance as a function of carrier density, indicating quantized pseudo-Landau levels. Furthermore, we report magnetic field anisotropy along opposite edges, suggesting a valley-polarized edge current induced by this B_ps.

This work provides experimental evidence of B_ps induced valley transport phenomenon, helping us understand how symmetry breaking alters the electrical transport properties of graphene. It extends the scope of B_ps study from atomic-scale observations via scanning tunneling microscope to device-scale transport study. This investigation offers new opportunities for manipulating valley carriers, providing a path for valleytronics application.