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Trend of the magnetic anisotropy for individual Mn dopants near the (110) GaAs surface
Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE). (Condensed Matter Physics Group)ORCID-id: 0000-0002-7831-7214
Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).ORCID-id: 0000-0003-4489-7561
2014 (engelsk)Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 26, nr 39, s. Article ID: 394006-Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Using a microscopic finite-cluster tight-binding model, we investigate the trend of the magnetic anisotropy energy as a function of the cluster size for an individual Mn impurity positioned in the vicinity of the (1 1 0) GaAs surface. We present results of calculations for large cluster sizes containing approximately 104 atoms, which have not been investigated so far. Our calculations demonstrate that the anisotropy energy of a Mn dopant in bulk GaAs, found to be non-zero in previous tight-binding calculations, is purely a finite size effect that vanishes with inverse cluster size. In contrast to this, we find that the splitting of the three in-gap Mn acceptor energy levels converges to a finite value in the limit of the infinite cluster size. For a Mn in bulk GaAs this feature is related to the nature of the mean-field treatment of the coupling between the impurity and its nearest neighbor atoms. We also calculate the trend of the anisotropy energy in the sublayers as the Mn dopant is moved away from the surface towards the center of the cluster. Here the use of large cluster sizes allows us to position the impurity in deeper sublayers below the surface, compared to previous calculations. In particular, we show that the anisotropy energy increases up to the fifth sublayer and then decreases as the impurity is moved further away from the surface, approaching its bulk value. The present study provides important insights for experimental control and manipulation of the electronic and magnetic properties of individual Mn dopants at the semiconductor surface by means of advanced scanning tunneling microscopy techniques.

sted, utgiver, år, opplag, sider
Institute of Physics (IOP), 2014. Vol. 26, nr 39, s. Article ID: 394006-
Emneord [en]
Soft matter; liquids and polymers; Condensed matter; electrical; magnetic and optical; Semiconductors; Surfaces; interfaces and thin films
HSV kategori
Forskningsprogram
Fysik, Kondenserade materians fysik
Identifikatorer
URN: urn:nbn:se:lnu:diva-33302DOI: 10.1088/0953-8984/26/39/394006ISI: 000343313400008Scopus ID: 2-s2.0-84907203371OAI: oai:DiVA.org:lnu-33302DiVA, id: diva2:707955
Forskningsfinansiär
Swedish Research Council, 621-2010-3761
Merknad

Övriga finansiärer:

NordForsk research network 'Nanospintronics: theory and simulations' 080134

Faculty of Technology at Linnaeus University

Tilgjengelig fra: 2014-03-26 Laget: 2014-03-26 Sist oppdatert: 2017-12-05bibliografisk kontrollert
Inngår i avhandling
1. Magnetic solotronics near the surface of a semiconductor and a topological insulator
Åpne denne publikasjonen i ny fane eller vindu >>Magnetic solotronics near the surface of a semiconductor and a topological insulator
2015 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Technology where a solitary dopant acts as the active component of an opto-electronic device is an emerging  field known as solotronics, and bears the promise to revolutionize the way in which information is stored, processed and transmitted. Magnetic doped semiconductors and in particular (Ga, Mn)As, the archetype of dilute magnetic semiconductors, and topological insulators (TIs), a new phase of quantum matter with unconventional characteristics, are two classes of quantum materials that have the potential to advance spin-electronics technology. The quest to understand and control, at the atomic level, how a few magnetic atoms precisely positioned in a complex environment respond to external stimuli, is the red thread that connects these two quantum materials in the research presented here.

The goal of the thesis is in part to elucidate the properties of transition metal (TM) impurities near the surface of GaAs semiconductors with focus on their response to local magnetic and electric fields, as well as to investigate the real-time dynamics of their localized spins. Our theoretical analysis, based on density functional theory (DFT) and using tight-binding (TB) models, addresses the mid-gap electronic structure, the local density of states (LDOS) and the magnetic anisotropy energy of individual Mn and Fe impurities near the (110) surface of GaAs. We investigate the effect of a magnetic field on the Mn acceptor LDOS measured in cross-sectional scanning tunneling microscopy, and provide an explanation of why the experimental LDOS images depend weakly on the field direction despite the strongly anisotropic nature of the Mn acceptor wavefunction. We also investigate the effects of a local electrostatic field generated by nearby charged As vacancies, on individual and pairs of ferromagnetically coupled magnetic dopants near the surface of GaAs, providing a means to control electrically the exchange interaction of Mn pairs. Finally, using the mixed quantum-classical scheme for spin dynamics, we calculate explicitly the time evolution of the Mn spin and its bound acceptor, and analyze the dynamic interaction between pairs of ferromagnetically coupled magnetic impurities in a nanoscaled semiconductor.

The second part of the thesis deals with the theoretical investigation of a single substitutional Mn impurity and its associated acceptor state on the (111) surface of Bi2Se3 TI, using an approach that combines DFT and TB calculations. Our analysis clarifies the crucial role played by the spatial overlap and the quasi-resonant coupling between the Mn-acceptor and the topological surface states inside the Bi2Se3 band gap, in the opening of a gap at the Dirac point. Strong electronic correlations are also found to contribute significantly to the mechanism leading to the gap, since they control the hybridization between the p orbitals of nearest-neighbor Se atoms and the acceptor spin-polarization. Our results explain the effects of inversion-symmetry and time-reversal symmetry breaking on the electronic states in the vicinity of the Dirac point, and contribute to clarifying the origin of surface-ferromagnetism in TIs. The promising potential of magnetic-doped TIs accentuates the importance of our contribution to the understanding of the interplay between magnetic order and topological protected surface states.

sted, utgiver, år, opplag, sider
Linnaeus University Press, 2015. s. 251
Serie
Linnaeus University Dissertations ; 211/2015
Emneord
Magnetic solotronics, Transition metal dopants, Dilute magnetism in semiconductors and topological insulators, Atomistic tight-binding models, DFT, Spin dynamics, Magnetic anisotropy, Scanning tunneling microscope.
HSV kategori
Forskningsprogram
Fysik, Kondenserade materians fysik
Identifikatorer
urn:nbn:se:lnu:diva-40398 (URN)978-91-87925-49-8 (ISBN)
Disputas
2015-03-27, Ny227, Kalmar Nyckel, Kalmar, 13:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2015-02-25 Laget: 2015-02-25 Sist oppdatert: 2016-11-01bibliografisk kontrollert

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