Recent advances in graphene and other 2D materials

The isolation of the first two-dimensional material, graphene-a monolayer of carbon atoms arranged in a hexagonal lattice-opened new exciting opportunities in the field of condensed matter physics and materials. Its isolation and subsequent studies demonstrated that it was possible to obtain sheets of atomically thin crystals and that these were stable, and they also began to show its outstanding properties, thus opening the door to a whole new family of materials, known as two-dimensional materials or 2D materials. The great interest in different 2D materials is motivated by the variety of properties they show, being candidates for numerous applications.Additionally, the combination of 2D crystals allows the assembly of composite, on-demand materials, known as van der Waals heterostructures, which take advantage of the properties of those materials to create functionalities that otherwise would not be accessible. For example, the combination of 2D materials, which can be done with high precision, is opening up opportunities for the study of new challenges in fundamental physics and novel applications. Here we review the latest fundamental discoveries in the area of 2D materials and offer a perspective on the future of the field.

Valleytronics in transition metal dichalcogenides materials

Valley degree of freedom in the first Brillouin zone of Bloch electrons offers an innovative approach to information storage and quantum computation.Broken inversion symmetry together with the presence of time-reversal symmetry endows Bloch electrons non-zero Berry curvature and orbital magnetic moment,which contribute to the valley Hall effect and optical selection rules in valleytronics.Furthermore,the emerging transition metal dichalcogenides(TMDs)materials naturally become the ideal candidates for valleytronics research attributable to their novel structural,photonic and electronic properties,especially the direct bandgap and broken inversion symmetry in the monolayer.However,the mechanism of inter-valley relaxation remains ambiguous and the complicated manipulation of valley predominantly incumbers the realization of valleytronic devices.In this review,we systematically demonstrate the fundamental properties and tuning strategies(optical,electrical,magnetic and mechanical tuning)of valley degree of freedom,summarize the recent progress of TMD-based valleytronic devices.We also highlight the conclusion of present challenges as well as the perspective on the further investigations in valleytronics.