Ferromagnetism-induced Kondo effect in graphene with a magnetic impurity

Li, Gao-Yang; Fang, Tie-Feng; Guo, Aimin; Sun, Qing-Feng

doi:10.1103/physrevb.100.115115

Cited by 11 publications

(8 citation statements)

References 95 publications

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“…This is quite different from that obtained in Ref. [60] in the context of magnetic graphene, in which Γ ↑ (ω) and Γ ↓ (ω) vanish at different energies, rendering a full polarization of the hybridization function. Here, full polarization is absent and is indeed very small.…”

Section: Numerical Resultscontrasting

confidence: 99%

Kondo screening regimes in multi-Dirac and Weyl systems

Pedrosa,

Silva,

Vernek

2021

Preprint

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We have investigated the Kondo physics of a single magnetic impurity embedded in multi-Dirac (Weyl) node fermionic systems. By using a generic effective model for the host material and employing a numerical renormalization group approach we access the low temperature behavior of the system, identifying the existence of Kondo screening in single-, double-, and triple-Dirac (Weyl) node models. We find that in any multi-Dirac node systems the low-energy regime lies within one of the known classes of pseudogap Kondo problem, extensively studied in the literature. Kondo screening is also observed for time reversal symmetry broken Weyl systems. This is, however, possible only in the particle-hole symmetry broken regime obtained for finite chemical potential µ. Although weakly, breaking time-reversal symmetry suppresses the Kondo resonance, especially in the single-node Weyl semimetals. More interesting Kondo screening regimes are obtained for inversion symmetry broken multi-Weyl fermions. In these systems the Kondo regimes of double-and triple-Weyl node models are much richer than in the single-Weyl node model. While in the single-Weyl node model the Kondo temperature increases monotonically with |µ| regardless the value of the inversion symmetry breaking parameter Q 0 , in double-and triple-Weyl node models there are two distinct regimes: (i) For Q 0 < |µ| the Kondo temperature depends strongly on µ, while (ii) for Q 0 > |µ| the Kondo temperature depends very weakly on µ, resembling the flat-band single impurity Anderson model.

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Section: Numerical Resultscontrasting

confidence: 99%

Kondo screening regimes in multi-Dirac and Weyl systems

Pedrosa,

Silva,

Vernek

2021

Preprint

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“…This is quite different from that obtained in Ref. (LI et al, 2019) in the context of magnetic graphene, in which Γ ↑ (ω) and Γ ↓ (ω) vanish at different energies, rendering a full polarization of the hybridization function. Here, full polarization should be absent and is indeed very small.…”

Section: Multi-dirac Node Fermionscontrasting

confidence: 99%

“…It is worth mentioning that along with the specific values of the set of parameters together with V = 0.12625 we reproduced Fig. 1 of (LI et al, 2019). We first established the particle-hole parameters U and ε d and then tuned the coupling strength until we reach the referred case of the article.…”

Section: Numerical Resultsmentioning

confidence: 94%

Kondo effect in multi-dirac and weyl fermions

Pedrosa¹

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First of all, I would like to thank Capes for the scholarship you trusted me with. Without it, it would be impossible for me to accomplish this work, no doubt about it. I also would like to thank the opportunity Professor Edson Vernek gave me to work beside him, learning how to be a good researcher, learning the state of art of articles and figures in python. I know we talked about aesthetics a lot. You won, I am convinced that beautiful figures and an organized text is an important step to be a good researcher. Not only for that but all your teachings, that extends beyond supervisor-student relation, I am sincerely grateful.My sincere acknowledgments to a great friend, Dr. Joelson Fernandes, one of the biggest minds I have the privilege to know. I am sure that this work is concluded thanks to his contribution as well. My gratitude for your effort to teach me the Kondo effect and propagators. The valuable lessons I will take with me from our conversations is not about physics only, it is about ethics, morality and the faith in an entity that mysteriously allow you to be a great father and husband, and also a great friend. I also would like to thank my dear fraternity brothers that are always there for me, creating and discussing nonsense ideas, living together as a family allowing a healthy environment that was crucial for me to write this work. The Saturday afternoon barbecues will be always remembered with a smile in my face.I would also like to thank my family members, my parents and my two younger brothers. They are always so happy to see me accomplish my goals and cheering for me, motivating me to carry on, no matter how hard life is. It is good to know you have a place to rest your head, a place where you are welcome at any time. I know I can count on each of you guys, thank you very much, I love you all.

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“…The second system, which we believe to be a feasible experimental realization of the model just described, is based on a QI strongly coupled to an armchair graphene nanoribbon (AGNR), which is in an externally induced insulating phase 18 , and weakly coupled, through a small coupling Γ tip , to a scanning tunneling microscope (STM) tip (modeled as a metallic-like band). This AGNR+QI+STM system is particularly attractive, as Kondo physics in carbon-based materials, mainly in bulk samples, has attracted a great deal of attention in the last few years [19][20][21][22][23][24][25][26][27][28] . The Kondo physics in graphene results from localized magnetic moments formed at vacancy sites [29][30][31][32] or through the surface deposition of magnetic atoms 33,34 , in which the local density of states may be modified by either disorder 35,36 or by ripples induced by the underlying substrate 34 .…”

Section: Introductionmentioning

confidence: 99%

Reentrant Kondo effect for a quantum impurity coupled to a metal-semiconductor hybrid contact

2020

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Using the Numerical Renormalization Group (NRG) and Anderson's poor man's scaling, we show that a system containing a quantum impurity (QI), strongly coupled to a semiconductor (with gap 2∆) and weakly coupled to a metal, displays a reentrant Kondo stage as one gradually lowers the temperature T. The NRG analysis of the corresponding Single Impurity Anderson Model (SIAM), through the impurity's thermodynamic and spectral properties, shows that the reentrant stage is characterized by a second sequence of SIAM fixed points, viz., free orbital (FO) → local moment (LM) → strong coupling (SC). In the higher temperature stage, the SC fixed point (with a Kondo temperature T K1 ) is unstable, while the lower temperature Kondo screening exhibits a much lower Kondo temperature T K2 , associated to a stable SC fixed point. The results clearly indicate that the reentrant Kondo screening is associated to an effective SIAM, with an effective Hubbard repulsion U eff , whose value is clearly identifiable in the impurity's local density of states. This low temperature effective SIAM, which we dub as reentrant SIAM, behaves as a replica of the high temperature (bare) SIAM. The second stage RG flow (obtained through NRG), whose FO fixed point emerges for T ≈ ∆ < T K1 , takes over once the RG flows away from the unstable first stage SC fixed point. The intuitive picture that emerges from our analysis is that the first Kondo state develops through impurity screening by semiconducting electrons, while the second Kondo state involves screening by metallic electrons, once the semiconducting electrons are out of reach to thermal excitations (T < ∆) and only the metallic (low) spectral weight inside the gap is available for impurity screening. This switch implies that the first Kondo cloud is much smaller than the second, since the NRG results show that, for all parameter ranges analyzed, T K2 T K1 . Last, but not least, we analyze a hybrid system formed by a QI 'sandwiched' between an armchair graphene nanoribbon (AGNR) and a scanning tunneling microscope (STM) tip (an AGNR+QI+STM system), with respective couplings set to reproduce the generic model described above. The energy gap (2∆) in the AGNR can be externally tuned by an electric-field-induced Rashba spin-orbit interaction. We analyzed this system for realistic parameter values, using NRG, and concluded that the reentrant SIAM, with its associated second stage Kondo, is worthy of experimental investigation.

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Ferromagnetism-induced Kondo effect in graphene with a magnetic impurity

Cited by 11 publications

References 95 publications

Kondo screening regimes in multi-Dirac and Weyl systems

Kondo screening regimes in multi-Dirac and Weyl systems

Kondo effect in multi-dirac and weyl fermions

Reentrant Kondo effect for a quantum impurity coupled to a metal-semiconductor hybrid contact

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