Study of carrier dynamics in strained graphene with giant pseudo-magnetic fields

Since it was first discovered in 2004, graphene has emerged as one of the most promising materials due to its outstanding physical, electrical, and optical properties. Among the surprising properties is its exceptional mechanical strength, which has accelerated research activity on graphene-based strain engineering. Approximately a decade ago, the creation of pseudo-magnetic fields in strained graphene attracted a lot of attention as a potential route to study interesting physical phenomena that would be unachievable with laboratory superconducting magnets. Although the giant pseudo-magnetic fields observed in highly strained graphene can substantially alter the optical properties of graphene beyond what is feasible with external magnetic fields, experimental characterization of the effects of such pseudo-magnetic fields has yet to be demonstrated. Here, we present an experimental observation of the effect of pseudo-magnetic fields on hot carrier relaxation processes. Our periodic strain engineering platform allows the formation of a non-uniform strain distribution with a maximum strain field of ~3.5% that is the largest value for sustainable strain in graphene. The maximum pseudomagnetic field at the edges of the nanopillar structure is calculated to be ~100 T via rigorous tight-binding simulations combined with the elasticity theory. Using time-resolved infrared pump-probe spectroscopy, we experimentally demonstrate that the hot carrier relaxation process in our strained graphene system is decelerated by more than an order of magnitude by the pseudo-magnetic fields. Our finding presents unforeseen opportunities for harnessing the new physics of graphene enabled by pseudo-magnetic fields for optoelectronics and condensed matter physics.