Laser pulses create topological state in graphene

December 02, 2019

Discovering ways to control the topological aspects of quantum materials is an important research frontier because it can lead to desirable electrical and spin transport properties for future device technologies. Now MPSD scientists have discovered a pioneering laser-driven approach to generate a topological state in graphene. Their work has just been published in Nature Physics.

Topological quantum states in graphene induced by light

In topological materials, electrons experience a twisted world. Instead of simply moving straight ahead when feeling a force, they may be pushed sideways. In such a material current actually flows orthogonally to an applied voltage.

The basic model describing the effect was developed by Duncan Haldane in the late 1980s, but even its inventor was skeptical that it could ever be implemented in a real material. Nevertheless, elaborate chemical synthesis eventually allowed for very similar effects to be observed, sparking a technological revolution - and eventually earning Haldane the 2016 Nobel Prize in Physics.

Topological transport is usually induced in materials by applying strong magnetic fields or by crafting compounds with strong spin-orbit coupling. Researchers in Andrea Cavalleri’s group at the MPSD have now demonstrated that a coherent interaction with circularly polarized light can also induce topological electrical currents in the material graphene. 

The team’s radically different approach consists of illuminating graphene with a strong, circularly polarized laser pulse, whose electric field drives electrons in loops. When the material is illuminated, it suddenly behaves like a topological material. It returns to its normal state once the pulse is gone.

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