Abstract
We demonstrate that the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in graphene can be strongly modified by a time-periodic driving field even in the weak drive regime. This effect is due to the opening of a dynamical band gap at the Dirac points when graphene is exposed to circularly polarized light. Using Keldysh-Floquet Green's functions, we develop a theoretical framework to calculate the time-averaged RKKY coupling under weak periodic drives and show that its magnitude in undoped graphene can be decreased controllably by increasing the driving strength, while mostly maintaining its ferromagnetic or antiferromagnetic character. In doped graphene, we find RKKY oscillations with a period that is tunable by the driving field. When a sufficiently strong drive is turned on that brings the Fermi level completely within the dynamically opened gap, the behavior of the RKKY coupling changes qualitatively from that of doped to undoped irradiated graphene.
Highlights
The Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling is the indirect exchange interaction in a magnetically doped system, in which the coupling between the localized impurity spins is mediated via the conduction electrons of the host material [1,2,3]
This work has presented a formalism for calculating the RKKY interaction in graphene irradiated by a circularly polarized light
By transforming the original Floquet Hamiltonian into a new basis, we arrived at a new Hamiltonian that carries a transparent physical meaning as a tight-bindinglike Hamiltonian in the Floquet space, allowing for a systematic order-by-order inclusion of different photon processes
Summary
The Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling is the indirect exchange interaction in a magnetically doped system, in which the coupling between the localized impurity spins is mediated via the conduction electrons of the host material [1,2,3]. As a function of the impurity separation, it oscillates between positive and negative values indicating ferromagnetic and antiferromagnetic spin couplings with a period determined by the host’s Fermi level [4] The envelope of these oscillations decays in a power law that depends on the dimensionality and the specific band structure of the host material [5,6,7,8,9,10,11,12]. On top of possible short-ranged fluctuations due to the lattice, its RKKY interaction oscillates between ferromagnetic and antiferromagnetic values, with the envelope decreasing as R−2 This makes the RKKY coupling of doped graphene qualitatively similar to that of a 2D system with a parabolic dispersion [8,10].
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