We show that the wavefunctions form caustics in circular graphene p-n junctions which in the framework of geometrical optics can be interpreted with negative refractive index.

We study an accumulation mode Si/SiGe double quantum dot (DQD) containing a single electron that is dipole coupled to microwave photons in a superconducting cavity. Measurements of the cavity transmission reveal dispersive features due to the DQD valley states in Si. The occupation of the valley states can be increased by raising the temperature or applying a finite source-drain bias across the DQD, resulting in an increased signal. Using the cavity input-output theory and a four-level model of the DQD, it is possible to efficiently extract valley splittings and the inter- and intravalley tunnel couplings.

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We derive the boundary conditions for MoS2 and similar transition-metal dichalcogenide honeycomb (2H polytype) monolayers with the same type of k ·p Hamiltonian within the continuum model around the K points. In an effective 2-band description, the electron-hole symmetry breaking quadratic terms are also taken into account. We model the effect of the edges with a linear edge constraint method that has been applied previously to graphene. Focusing mainly on zigzag edges, we find that different reconstruction geometries with different edge-atoms can generally be described with one scalar parameter varying between 0 and 2π. We analyze the edge states and their dispersion relation in MoS2 in particular, and we find good agreement with the results of previous density functional theory calculations for various edge types. √ 3 2 N d a, where the lattice constant in MoS2 is a = |a1| = |a2| = 3.1565Å. 29 arXiv:1509.00184v2 [cond-mat.mes-hall]

We propose an implementation of a valley selective electronic Veselago lens in bilayer graphene. We demonstrate that in the presence of an appropriately oriented potential step, low-energy electrons radiating from a point source can be re-focused coherently within the same band. The phenomenon is due to the trigonal warping of the band structure that leads to a negative refraction index. We show that the interference pattern can be controlled by an external mechanical strain.