Anand Sharma

Additional carrier-mediated ferromagnetism in GdN

The mechanism behind ferromagnetic exchange interaction in GdN is not well understood. It has been argued that it can be due to fourth order cross process of d-f mixing and d-f exchange. An alternative explanation suggests an antiferromagnetic interaction between Gd d and N p induced moments on the rock salt structure which aligns the nearest neighbor Gd f moments ferromagnetically through the d-f exchange. In this paper we present results of Curie temperature in GdN as a function of carrier density calculated within our multiband modified RKKYlike exchange interaction. It includes realistic bandstructure of the 5d conduction band as an input for single particle energies. We analyze the possibility of carriermediated ferromagnetism in GdN and also demonstrate a simple phenomenological model which justifies the role of charge carriers.

Effect of uniaxial strain on ferromagnetic instability and formation of localized magnetic states on adatoms in graphene

We investigate the effect of an applied uniaxial strain on the ferromagnetic instability due to long-range Coulomb interaction between Dirac fermions in graphene. In the case of undeformed graphene the ferromagnetic exchange instability occurs at sufficiently strong interaction within the Hartree-Fock approximation. In this work we show that using the same theoretical framework but with an additional applied uniaxial strain, the transition can occur for much weaker interaction, within the range in suspended graphene. We also study the consequence of strain on the formation of localized magnetic states on adatoms in graphene. We systematically analyze the interplay between the anisotropic (strain-induced) nature of the Dirac fermions in graphene, onsite Hubbard interaction at the impurity, and the hybridization between the graphene and impurity electrons. The polarization of the electrons in the localized orbital is numerically calculated within the mean-field self-consistent scheme. We obtain a complete phase diagram containing nonmagnetic as well as magnetic regions, and our results can find prospective application in the field of carbon-based spintronics.

Multi-logarithmic velocity renormalization in graphene

We reexamine the effect of long-range Coulomb interactions on the quasiparticle velocity in graphene. Using a nonperturbative functional renormalization group approach with partial bosonization in the forward scattering channel and momentum transfer cutoff scheme, we calculate the quasiparticle velocity,

Van der Waals forces and electron-electron interactions in two strained graphene layers

v (k)

Excitonic mass gap in uniaxially strained graphene

, and the quasiparticle residue,

Non-perturbative renormalization group calculation of the quasi-particle velocity and the dielectric function of graphene.

Z

Ferromagnetism in the multiband Kondo lattice model

, with frequency-dependent polarization. One of our most striking results is that

Spin dynamics in the diluted ferromagnetic Kondo lattice model

v ( k ) \propto \ln [ C_k (\alpha) / k ]

Temperature dependent electronic correlation effects in GdN

where the momentum- and interaction-dependent cutoff scale

Summing parquet diagrams using the functional renormalization group: X-ray problem revisited

C_k (\alpha)