University of Regensburg

Martin Gmitra , Denis Kochan, Petra Högl and Jaroslav Fabian

Electronic structure of grapheneon transition-metal dichalcogenides

Oct. 05.-07. 2015internal SFB-workshop in Abbey Frauenwörth

Frauenchiemsee

DFG SFB 689

University of Regensburg

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Transition metal dichalcogenides essentialsMX2 :: [M = metal atom (Mo, W, …) ; X = chalcogen atom (S, Se, Te)]

Space Group: P 63/mmc

atomically thin semiconductors

K.F. Mak et al., PRL 105, 136805 (2010)Molybdenite (MoS2)

University of Regensburg Transition metal dichalcogenides essentialsMX2 :: [M = metal atom (Mo, W, …) ; X = chalcogen atom (S, Se, Te)]

Space Group: P 63/mmc

review: A. Kormányos et al., 2D materials 2, 022001 (2015)

bulk single layer (no inversion)

d-character dominates optical edges

spin-orbit coupling emerges in optics

University of Regensburg

University of Regensburg Optical properties of TMDChelicity resolves ...

● valley polarization H. Zeng et al., Nat. Nanotech. 7, 490 (2012)

● coupled spin and valleys (valleytronics) P. Xiao et al., PRL 108, 196802 (2012) ● spin, valley and layer pseudospin coupling

(intra/inter layer trions) X. Xu et al., Nat. Phys. 10, 343 (2014)

University of Regensburg Graphene on TMDCheterostructure

www.quantum-espresso.org

Method used :: Density Functional Theory (DFT) calculations

University of Regensburg Band structure of TMDC/graphene heterostructuresproximity orbital effects

M. Gmitra et al., arXiv: 1510.00166

University of Regensburg Trivial and inverted Dirac bandsproximity spin-orbit coupling effect

M. Gmitra et al., arXiv: 1510.00166

University of Regensburg Model for low energy bandsdefinition & low energy model fit

M. Gmitra, J. Fabian, arXiv: 1506.08954, PRB in pressM. Gmitra et al., arXiv: 1510.00166

University of Regensburg Graphene zigzag nanoribbon on WSe2quantum spin Hall effect

● inside the gap – topological helical edge states● outside the gap – half-topological states

University of Regensburg Effect of transverse electric field on band offsetDirac massless electrons coupled with conventional 2d electrons

University of Regensburg

All optical detection of spin tunneling and accumulation using magneto-optical Kerr effect.

Graphene on TMDC :: platform for optospintronics

Optical spin injection scheme employing Hanle effect.

M. Gmitra, J. Fabian, arXiv: 1506.08954, PRB in press

University of Regensburg Concluding remarks

ACKNOWLEDGMENTS:

DFG SFB 689

graphene on TMDC serves as● a platform for optospintronics● coupled system of Dirac massless and 2D conventional electrons● new “half” topological states at single edge channel● robust quantum spin Hall effect

M. Gmitra, J. Fabian, Graphene on transition-metal dichalcogenides: a platform for proximity spin-orbit physics and optospintronics arXiv: 1506.08954, PRB in press

M. Gmitra, D. Kochan, P. Högl, J. Fabian,Trivial and inverted Dirac bands, and emergence of quantum spin Hall states in graphene on transition-metal dichalcogenidesarXiv: 1510.00166

University of Regensburg