Quantum transport in graphene in presence of strain-induced pseudo-Landau levels

Abstract

We report on mesoscopic transport fingerprints in disordered graphene caused by strain-field induced pseudomagnetic Landau levels (pLLs). Efficient numerical real space calculations of the Kubo formula are performed for an ordered network of nanobubbles in graphene, creating pseudomagnetic fields up to several hundreds of Tesla, values inaccessible by real magnetic fields. Strain-induced pLLs yield enhanced scattering effects across the energy spectrum resulting in lower mean free path and enhanced localization effects. In the vicinity of the zeroth order pLL, we demonstrate an anomalous transport regime, where the mean free paths increases with disorder. We attribute this puzzling behavior to the low-energy sub-lattice polarization induced by the zeroth order pLL, which is unique to pseudomagnetic fields preserving time-reversal symmetry. These results, combined with the experimental feasibility of reversible deformation fields, open the way to tailor a metal-insulator transition driven by pseudomagnetic fields.Inhomogeneous lattice deformations in graphene generate an effective gauge field modulating the electronic spectrum 1-3 . However, compared to a real magnetic field, the formation of a pseudomagnetic field preserves time reversal symmetry, having an opposite sign in the two inequivalent K and K' valleys 4-6 . This leads to different behavior than for real magnetic field especially when introducing disorder. Experimentally, scanning-tunneling measurements on graphene nanobubbles have revealed an electronic spectrum consisting of pseudo-Landau levels (pLL), including a zero-energy peak, showing that moderate spatial deformations can introduce pseudomagnetic field values reaching hundreds of Tesla 7-9 . Pseudomagnetic fields (PMF) have also been analyzed in deformed crystals by an atomically controlled arrangement of CO molecules on a gold surface 10 , graphene on Ir with intercalated Pb monolayer islands 11 , or have been harnessed for designing innovative electronic and photonic graphene devices 12-17 .However, the intrinsic quantum transport fingerprints of graphene in presence of pseudomagnetic fields still needs investigation, especially in disordered systems. In particular, random strain fluctuations are believed to be the dominating disorder source in high-quality onsubstrate graphene devices 18,19 . A signature of the pseudomagnetic n = 0 pLL state has been predicted for stretched graphene ribbons in the form of a quadruplet low-energy conductance resonance split by edge-induced valley mixing16 , but its experimental confirmation remains challenging, and the variable range of transport features in deformed graphene still require further indepth exploration.Here we study the effect of pLLs, generated by an ordered network of graphene nanobubbles (or pseudomagnetic dots), using an efficient real space Kubo quantum transport methodology. We consider samples containing electron-hole puddles caused by substrate interactions where the presence of pLLs leads to several anomalous transport features resultin...

Magnetic phases in periodically rippled graphene

“…The effective fields generated by non uniform strain can interfere with externally applied magnetic fields giving rise to new physical effects [23][24][25]. Also the existence of pseudo magnetic fields could produce anomalous effects in the electronic quantum transport [26].…”

Topological phase-diagram of time-periodically rippled zigzag graphene nanoribbons

“…Therefore, we analyze the topological properties of a 1D slice of the system, in other words, we study our system for a fixed k x . Once that we have fixed k x , the topological properties can be obtained from the winding of the unit vector h eff that appears in the effective Hamiltonian equation (19), since a non-vanishing winding number is a signature of non-trivial topological properties. If h eff , for fixed k x , has a non-vanishing winding number around the origin, then the 1D slice has non-trivial topological properties and the whole 2D system is topologically weak [85][86][87].…”

Low-energy theory for strained graphene: an approach up to second-order in the strain tensor

“…11,12 Nowadays, the transport signatures of the such fictitious fields are actively investigated. [13][14][15][16][17][18][19][20] Moreover, from a view point of basic research, strained graphene opens an opportunity to explore mixed Dirac-Schrödinger Hamtiltonian, 21 fractal spectrum, 22 superconducting states, 23 magnetic phase transitions, 24 metal-insulator transition, 25 among others exotic behaviours.…”