Spontaneous symmetry breakings in graphene subjected to in-plane magnetic field - Condensed Matter > Mesoscale and Nanoscale PhysicsReport as inadecuate




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Abstract: Application of the magnetic field parallel to the plane of the graphene sheetleads to the formation of electron- and hole-like Fermi surfaces. Suchsituation is shown to be unstable with respect to the formation of an excitoniccondensate even for an arbitrary weak magnetic field and interaction strength.At temperatures lower than the mean-field temperature the order parameteramplitude is formed. The order parameter itself is a U2 matrix allowing forthe combined rotations in the spin and valley spaces. These rotations smoothlyinterpolate between site and bond centered spin density waves and spin fluxstates. The trigonal warping, short range interactions, and the three particleUmklapp processes freeze some degrees of freedom at temperatures much smallerthan the mean-field transition temperature and make eitherBerezinskii-Kosterlitz-Thouless driven either by vortices or half-vortices orIsing type transitions possible. Strong logarithmic renormalization for thecoupling constants of these terms by the Coulomb interaction are calculatedwithin one-loop renormalization group. It is found that in the presence of theCoulomb interaction some short range interaction terms become much greater thanone might expect from the naive dimensionality counting.



Author: I.L. Aleiner, D.E. Kharzeev, A.M. Tsvelik

Source: https://arxiv.org/







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