Dresden 2014 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 89: Graphene-Like Materials: Silicene, MoS₂ and Relatives (organized by HL)

TT 89.1: Talk

Thursday, April 3, 2014, 10:00–10:15, POT 081

Many-body effects in 2D hexagonal semimetals and semiconductors — •Tineke Stroucken, Johanna Grönqvist, and Stephan W. Koch — Department of Physics and Material Sciences Center, Philipps University Marburg, Renthof 5, D-35032 Marburg, Germany

Recently, a variety of graphene-analogues materials like h-BN, silicene or transition-metal dichalcogenides have been fabricated. Similar to graphene, these novel material systems display exciting new physical properties, distinct from their bulk counterparts.

Owing to the symmetry of the hexagonal lattice, band edge carriers are described by massive Dirac Fermions. Typically, the Fermi-velocity is in the range of c/300 or below. This yields effective fine structure constants α=e²/єℏ v_F 2/є, implying prominent Coulomb interaction and relativistic effects. Particularly, α 1 indicates an excitonic instability of the noninteracting ground state.

In this presentation, we discuss conditions for strong Coulomb coupling in 2D hexagonal crystals and identify experimentally observable signatures signaling an excitonic ground state. To this end, the gap equations are solved self consistently with the polarization function, which depends on the interacting band structure.

[1] T. Stroucken et al., Phys. Rev. B 84, 205445 (2011)

[2] J. H. Grönqvist et al., EPJ B 85, 12 (2012)

[3] T. Stroucken et al., Phys. Rev. B. 87, 245428(2013)