arXiv subjects

Giulio Cocco

Publications and source records attributed to Giulio Cocco.

4 recordsLinked to original sources

arXiv2015

Tunability of the Berry phase in gapped graphene

When a gap of tunable size opens at the conic band intersections of graphene, the Berry phase does not vanish abruptly, but progressively decreases as the gap increases. The phase depends on the reciprocal-space path radius, i.e., for a doped system, the Fermi wave vector. The phase and its observable consequences can thus be tuned continuously via gap opening --by a modulating potential induced by strain, epitaxy, or nanostructuration-- and doping adjustment.

cond-mat.mes-hall↗

arXiv2015

Vibrational stability of graphene under combined shear and axial strains

We study the vibrational properties of graphene under combined shear and uniaxial tensile strain using density-functional perturbation theory. Shear strain always causes rippling instabilities with strain-dependent direction and wavelength; armchair strain contrasts this instability, enabling graphene stability in a large range of combined strains. A complementary description based on membrane elasticity theory nicely clarifies the competition of shear-induced instability and uniaxial tension. We also report the large strain-induced shifts of the split components of the G optical phonon line, which may serve as a shear diagnostic. As to the electronic properties, we find that conical intersections move away from the Brillouin zone border under strain, and they tend to coalesce at large strains, making the opening of gaps difficult to assess. By a detailed search, we find that even at large strains, only small gaps in the tens-of-meV range open at the former Dirac points.

cond-mat.mtrl-sci↗

arXiv2010

Reply to "Comment on Gap opening in graphene by shear strain''

In reply to the Comment by Ramasubramaniam regarding our article [Phys. Rev. B {\bf 81}, 241412(R) (2010)] we clarify that our results are indeed valid provided that out-of-plane atomic relaxations are inhibited, as it may occur in the technologically relevant case of supported graphene sheets. We argue that the Comment, while overall interesting, is addressed to the different case of a free standing graphene monolayer and, therefore, does not invalidate our conclusions. We also remark that the rippled configuration discussed in the Comment is most likely affected by major size effects and that, contrary to what suggested, our conclusions are not in contrast with the recent work by Pereira {\it et al.} [Phys. Rev. B {\bf 80}, 045401 (2009)].

cond-mat.mes-hall↗

arXiv2010

Gap opening in graphene by shear strain

We exploit the concept of strain-induced band structure engineering in graphene through the calculation of its electronic properties under uniaxial, shear, and combined uniaxial-shear deformations. We show that by combining shear deformations to uniaxial strains it is possible modulate the graphene energy gap value from zero up to $0.9$ eV. Interestingly enough, the use of a shear component allows for a gap opening at moderate absolute deformation, safely smaller than the graphene failure strain.

cond-mat.mes-hall↗