Inverse indirect magnetic exchange

Schwabe, Andrej; Titvinidze, Irakli; Potthoff, Michael

doi:10.1103/physrevb.88.121107

Cited by 25 publications

(45 citation statements)

References 36 publications

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“…To ensure that galaxies and Lyman-α clouds form, the Jeans length should be smaller than about 20 kpc. This happens to coincide with the constraint (66), which expresses that the background pressure is negligible up to redshift z eq , see also Eqs. (27) and (29).…”

Section: Gravitational Instabilitysupporting

confidence: 59%

Impact of kinetic and potential self-interactions on scalar dark matter

2019

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We consider models of scalar dark matter with a generic interaction potential and non-canonical kinetic terms of the K-essence type that are subleading with respect to the canonical term. We analyze the low-energy regime and derive, in the nonrelativistic limit, the effective equations of motions. In the fluid approximation they reduce to the conservation of matter and to the Euler equation for the velocity field. We focus on the case where the scalar field mass 10 −21 ≪ m 10 −4 eV is much larger than for fuzzy dark matter, so that the quantum pressure is negligible on cosmological and galactic scales, while the self-interaction potential and non-canonical kinetic terms generate a significant repulsive pressure. At the level of cosmological perturbations, this provides a dark-matter density-dependent speed of sound. At the nonlinear level, the hydrostatic equilibrium obtained by balancing the gravitational and scalar interactions imply that virialized structures have a solitonic core of finite size depending on the speed of sound of the dark matter fluid. For the most relevant potential in λ4φ 4 /4 or K-essence with a (∂φ) 4 interaction, the size of such stable cores cannot exceed 60 kpc. Structures with a density contrast larger than 10 6 can be accommodated with a speed of sound cs 10 −6 . We also consider the case of a cosine self-interaction, as an example of bounded nonpolynomial self-interaction. This gives similar results in low-mass and low-density halos whereas solitonic cores are shown to be absent in massive halos.

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Section: Gravitational Instabilitysupporting

confidence: 59%

Impact of kinetic and potential self-interactions on scalar dark matter

2019

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“…One may explicitly derive the effective low-energy Hamiltonian by using strong-coupling degenerate perturbation theory, where hopping to and off a local Kondo singlet is treated as a weak perturbation. The resulting effective IIME Hamiltonian excludes the (high-energy) local Kondo singlets at i 2 and i L−1 and operates on the remaining conduction-electron degrees of freedom only [10,19]. Up to fourth order in t/J, for impurity distances d ≥ 2, and disregarding unimportant constant energy shifts, one obtains…”

Section: Two-impurity Model In the Strong-coupling Limitmentioning

confidence: 99%

“…The purpose of the present paper is to demonstrate that quantum confinement effects resulting from strong J in a spin-diluted system can effectively result in a weak indirect magnetic RKKY [7][8][9] interaction. This is achieved by exploiting the characteristics of a novel "inverse" indirect magnetic exchange (IIME) mechanism that has been proposed recently [10]. We study the distance dependence of the effective IIME coupling in a one-dimensional prototypical two-impurity model by means of strong-coupling perturbation theory and density-matrix renormalization group (DMRG).…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, these local moments are coupled magnetically by virtual excitations of the magnetically inert Kondo singlets. This constitutes an "inverse" indirect magnetic exchange (IIME) [10] where the roles of the conduction electrons and of the impurity spins are essentially interchanged.…”

Section: Introductionmentioning

confidence: 99%

“…Although the Kondo effect quenches the impurity spins for J t, it has been realized that it may also help to generate magnetism in the case of systems with diluted impurity spins [10], or, more generally, diluted correlated impurity sites [19]. Namely, almost local Kondo singlets can result in an efficient additional confinement of the itinerant electrons.…”

Section: Introductionmentioning

confidence: 99%

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Cooperation of different exchange mechanisms in confined magnetic systems

2014

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The diluted Kondo lattice model is investigated at strong antiferromagnetic local exchange couplings J, where almost local Kondo clouds drastically restrict the motion of conduction electrons, giving rise to the possibility of quantum localization of conduction electrons for certain geometries of impurity spins. This localization may lead to the formation of local magnetic moments in the conduction-electron system, and the inverse indirect magnetic exchange (IIME), provided by virtual excitations of the Kondo singlets, couples those local moments to the remaining electrons. Exemplarily, we study the one-dimensional two-impurity Kondo model with impurity spins near the chain ends, which supports the formation of conduction-electron magnetic moments at the edges of the chain for sufficiently strong J. Employing degenerate perturbation theory as well as analyzing spin gaps numerically by means of the density-matrix renormalization group, it is shown that the low-energy physics of the model can be well captured within an effective antiferromagnetic RKKYlike two-spin model ("RKKY from IIME") or within an effective central-spin model, depending on edge-spin distance and system size.

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