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Canali, Carlo M.
Publications (10 of 77) Show all publications
Pournaghavi, N., Holmqvist, C., Pertsova, A. & Canali, C. M. (2018). Quantum Transport by Spin‐Polarized Edge States in Graphene Nanoribbons in the Quantum Spin Hall and Quantum Anomalous Hall Regimes [Letter to the editor]. Physica Status Solidi. Rapid Research Letters, 12(11, Special Issue), Article ID 1800210.
Open this publication in new window or tab >>Quantum Transport by Spin‐Polarized Edge States in Graphene Nanoribbons in the Quantum Spin Hall and Quantum Anomalous Hall Regimes
2018 (English)In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 12, no 11, Special Issue, article id 1800210Article in journal, Letter (Refereed) Published
Abstract [en]

Using the non-equilibrium Green’s function method and the Keldysh formalism, we study the effects of spin–orbit interactions and time-reversal symmetry breaking exchange fields on non-equilibrium quantum transport in graphene armchair nanoribbons. We identify signatures of the quantum spin Hall (QSH) and the quantum anomalous Hall (QAH) phases in nonequilibrium edge transport by calculating the spin-resolved real space charge density and local currents at the nanoribbon edges. We find that the QSH phase, which is realized in a system with intrinsic spin–orbit coupling, is characterized by chiral counter-propagating local spin currents summing up to a net charge flow with opposite spin polarization at the edges. In the QAH phase, emerging in the presence of Rashba spin–orbit coupling and a ferromagnetic exchange field, two chiral edge channels with opposite spins propagate in the same direction at each edge, generating an unpolarized charge current and a quantized Hall conductance  . Increasing the intrinsic spin–orbit coupling causes a transition from the QAH to the QSH phase, evinced by characteristic changes in the non-equilibrium edge transport. In contrast, an antiferromagnetic exchange field can coexist with a QSH phase, but can never induce a QAH phase due to a symmetry that combines time-reversal and sublattice translational symmetry.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2018
Keywords
graphene nanoribbons, quantum anomalous Hall effect, quantum spin Hall effect, topological insulators
National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-76947 (URN)10.1002/pssr.201800210 (DOI)000450130300007 ()
Funder
Carl Tryggers foundation , CTS 14:178Swedish Research Council, 621‐2014‐4785
Available from: 2018-07-19 Created: 2018-07-19 Last updated: 2018-12-06Bibliographically approved
Islam, F., Canali, C. M., Pertsova, A., Balatsky, A., Mahatha, S. K., Carbone, C., . . . Sessi, P. (2018). Systematics of electronic and magnetic properties in the transition metal doped Sb2Te3 quantum anomalous Hall platform. Physical Review B, 97(15), Article ID 155429.
Open this publication in new window or tab >>Systematics of electronic and magnetic properties in the transition metal doped Sb2Te3 quantum anomalous Hall platform
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 15, article id 155429Article in journal (Refereed) Published
Abstract [en]

The quantum anomalous Hall effect (QAHE) has recently been reported to emerge in magnetically doped topological insulators. Although its general phenomenology is well established, the microscopic origin is far from being properly understood and controlled. Here, we report on a detailed and systematic investigation of transition metal (TM) doped Sb2Te3. By combining density functional theory calculations with complementary experimental techniques, i.e., scanning tunneling microscopy, resonant photoemission, and x-raymagnetic circular dichroism, we provide a complete spectroscopic characterization of both electronic and magnetic properties. Our results reveal that the TM dopants not only affect the magnetic state of the host material, but also significantly alter the electronic structure by generating impurity-derived energy bands. Our findings demonstrate the existence of a delicate interplay between electronic and magnetic properties in TM doped topological insulators. In particular, we find that the fate of the topological surface states critically depends on the specific character of the TM impurity: while V-and Fe-doped Sb2Te3 display resonant impurity states in the vicinity of the Dirac point, Cr and Mn impurities leave the energy gap unaffected. The single-ion magnetic anisotropy energy and easy axis, which control the magnetic gap opening and its stability, are also found to be strongly TM impurity dependent and can vary from in plane to out of plane depending on the impurity and its distance from the surface. Overall, our results provide general guidelines for the realization of a robust QAHE in TM doped Sb2Te3 in the ferromagnetic state.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-75724 (URN)10.1103/PhysRevB.97.155429 (DOI)000430545100010 ()
Available from: 2018-06-13 Created: 2018-06-13 Last updated: 2018-07-11Bibliographically approved
Sadowski, J., Kret, S., Siusys, A., Wojciechowski, T., Gas, K., Islam, F., . . . Sawicki, M. (2017). Wurtzite (Ga,Mn)As nanowire shells with ferromagnetic properties. Nanoscale, 9(6), 2129-2137
Open this publication in new window or tab >>Wurtzite (Ga,Mn)As nanowire shells with ferromagnetic properties
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2017 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 9, no 6, p. 2129-2137Article in journal (Refereed) Published
Abstract [en]

(Ga,Mn)As having a wurtzite crystal structure was coherently grown by molecular beam epitaxy on the 1100 side facets of wurtzite (Ga,In)As nanowires and further encapsulated by (Ga,Al)As and low temperature GaAs. For the first time, a truly long-range ferromagnetic magnetic order is observed in non-planar (Ga,Mn)As, which is attributed to a more effective hole confinement in the shell containing Mn by the proper selection/choice of both the core and outer shell materials. © The Royal Society of Chemistry.

Keywords
Crystal structure; Ferromagnetic materials; Ferromagnetism; Gallium; Molecular beam epitaxy; Nanowires; Temperature; Zinc sulfide, Ferromagnetic properties; Hole confinement; Low-temperature GaAs; Magnetic orders; Outer shells; Wurtzite crystal structure; Wurtzites, Manganese
National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-61167 (URN)10.1039/c6nr08070g (DOI)000395626600004 ()2-s2.0-85012111095 (Scopus ID)
Available from: 2017-03-08 Created: 2017-03-08 Last updated: 2018-05-17Bibliographically approved
Sjöqvist, E., Mousolou, V. A. & Canali, C. M. (2016). Conceptual aspects of geometric quantum computation. Quantum Information Processing, 15(10), 3995-4011
Open this publication in new window or tab >>Conceptual aspects of geometric quantum computation
2016 (English)In: Quantum Information Processing, ISSN 1570-0755, E-ISSN 1573-1332, Vol. 15, no 10, p. 3995-4011Article in journal (Refereed) Published
Abstract [en]

Geometric quantum computation is the idea that geometric phases can be used to implement quantum gates, i.e., the basic elements of the Boolean network that forms a quantum computer. Although originally thought to be limited to adiabatic evolution, controlled by slowly changing parameters, this form of quantum computation can as well be realized at high speed by using nonadiabatic schemes. Recent advances in quantum gate technology have allowed for experimental demonstrations of different types of geometric gates in adiabatic and nonadiabatic evolution. Here, we address some conceptual issues that arise in the realizations of geometric gates. We examine the appearance of dynamical phases in quantum evolution and point out that not all dynamical phases need to be compensated for in geometric quantum computation. We delineate the relation between Abelian and non-Abelian geometric gates and find an explicit physical example where the two types of gates coincide. We identify differences and similarities between adiabatic and nonadiabatic realizations of quantum computation based on non-Abelian geometric phases.

Keywords
Geometric phase, Quantum computation, Quantum gates
National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-57651 (URN)10.1007/s11128-016-1381-1 (DOI)000383587100004 ()2-s2.0-84978033590 (Scopus ID)
Available from: 2016-10-27 Created: 2016-10-27 Last updated: 2017-11-29Bibliographically approved
Gooth, J., Zierold, R., Sergelius, P., Hamdou, B., Garcia, J., Damm, C., . . . Nielsch, K. (2016). Local Magnetic Suppression of Topological Surface States in Bi2Te3 Nanowires. ACS Nano, 10(7), 7180-7188
Open this publication in new window or tab >>Local Magnetic Suppression of Topological Surface States in Bi2Te3 Nanowires
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2016 (English)In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 10, no 7, p. 7180-7188Article in journal (Refereed) Published
Abstract [en]

Locally induced, magnetic order on the surface of a topological insulator nanowire could enable room-temperature topological quantum devices. Here we report on the realization of selective magnetic control over topological surface states on a single facet of a rectangular Bi2Te3 nanowire via a magnetic insulating Fe3O4 substrate. Low-temperature magnetotransport studies provide evidence for local time-reversal symmetry breaking and for enhanced gapping of the interfacial 1D energy spectrum by perpendicular magnetic-field components, leaving the remaining nanowire facets unaffected. Our results open up great opportunities for development of dissipation-less electronics and spintronics.

Keywords
1D confinement, magnetism, nanowire, surface, topological insulator
National Category
Condensed Matter Physics Atom and Molecular Physics and Optics
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-56093 (URN)10.1021/acsnano.6b03537 (DOI)000380576600085 ()27351276 (PubMedID)2-s2.0-84979873036 (Scopus ID)
Available from: 2016-09-16 Created: 2016-08-31 Last updated: 2017-11-21Bibliographically approved
Pertsova, A., Canali, C. M. & MacDonald, A. H. (2016). Quantum Hall edge states in topological insulator nanoribbons. Physical Review B, 94(12), Article ID 121409.
Open this publication in new window or tab >>Quantum Hall edge states in topological insulator nanoribbons
2016 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 12, article id 121409Article in journal (Refereed) Published
Abstract [en]

We present a microscopic theory of the chiral one-dimensional electron gas system localized on the sidewalls of magnetically doped Bi2Se3-family topological insulator nanoribbons in the quantum anomalous Hall effect (QAHE) regime. Our theory is based on a simple continuum model of sidewall states whose parameters are extracted from detailed ribbon and film geometry tight-binding model calculations. In contrast to the familiar case of the quantum Hall effect in semiconductor quantum wells, the number of microscopic chiral channels depends simply and systematically on the ribbon thickness and on the position of the Fermi level within the surface state gap. We use our theory to interpret recent transport experiments that exhibit nonzero longitudinal resistance in samples with accurately quantized Hall conductances.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-57610 (URN)10.1103/PhysRevB.94.121409 (DOI)000384070000003 ()2-s2.0-84990882880 (Scopus ID)
Available from: 2016-10-27 Created: 2016-10-25 Last updated: 2017-11-29Bibliographically approved
Azimi Mousolou, V., Canali, C. M. & Sjöqvist, E. (2016). Spin-electric Berry phase shift in triangular molecular magnets. Physical Review B, 94(23), Article ID 235423.
Open this publication in new window or tab >>Spin-electric Berry phase shift in triangular molecular magnets
2016 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 23, article id 235423Article in journal (Refereed) Published
Abstract [en]

We propose a Berry phase effect on the chiral degrees of freedom of a triangular magnetic molecule. The phase is induced by adiabatically varying an external electric field in the plane of the molecule via a spin-electric coupling mechanism present in these frustrated magnetic molecules. The Berry phase effect depends on spin-orbit interaction splitting and on the electric dipole moment. By varying the amplitude of the applied electric field, the Berry phase difference between the two spin states can take any arbitrary value between zero and π, which can be measured as a phase shift between the two chiral states by using spin-echo techniques. Our result can be used to realize an electric-field-induced geometric phase-shift gate acting on a chiral qubit encoded in the ground-state manifold of the triangular magnetic molecule.

National Category
Other Physics Topics
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-61166 (URN)10.1103/PhysRevB.94.235423 (DOI)000394546100004 ()2-s2.0-85007574217 (Scopus ID)
Available from: 2017-03-08 Created: 2017-03-08 Last updated: 2018-10-22Bibliographically approved
Pertsova, A., Canali, C. M., Pederson, M. R., Rungger, I. & Sanvito, S. (2015). Chapter Three: Electronic Transport as a Driver for Self-Interaction-Corrected Methods. In: Ennio Arimondo, Chun C. Lin and Susanne F. Yelin (Ed.), Advances In Atomic, Molecular, and Optical Physics: Volume 64 (pp. 29-86). Academic Press, 64
Open this publication in new window or tab >>Chapter Three: Electronic Transport as a Driver for Self-Interaction-Corrected Methods
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2015 (English)In: Advances In Atomic, Molecular, and Optical Physics: Volume 64 / [ed] Ennio Arimondo, Chun C. Lin and Susanne F. Yelin, Academic Press, 2015, Vol. 64, p. 29-86Chapter in book (Refereed)
Abstract [en]

While spintronics often investigates striking collective spin e ects in large systems, a very important research direction deals with spin-dependent phenomena in nanostructures, reaching the extreme of a single spin conned in a quantum dot, in a molecule, or localized on an impurity or dopant. The issue considered in this chapter involves taking this extreme to the nanoscale and the quest to use rst-principles methods to predict and control the behavior of a few \spins" (down to 1 spin) when they are placed in an interesting environment. Particular interest is on environments for which addressing these systems with external elds and/or electric or spin currents is possible. The realization of such systems, including those that consist of a core of a few transition-metal (TM) atoms carrying a spin, connected and exchanged-coupled through bridging oxo-ligands has been due to work by many experimental researchers at the interface of atomic, molecular and condensed matter physics. This chapter addresses computational problems associated with understanding the behaviors of nanoand molecular-scale spin systems and reports on how the computational complexity increases when such systems are used for elements of electron transport devices. Especially for cases where these elements are attached to substrates with electronegativities that are very di erent than the molecule, or for coulomb blockade systems, or for cases where the spin-ordering within the molecules is weakly antiferromagnetic, the delocalization error in DFT is particularly problematic and one which requires solutions, such as self-interaction corrections, to move forward. We highlight the intersecting elds of spin-ordered nanoscale molecular magnets, electron transport, and coulomb blockade and highlight cases where self-interaction corrected methodologies can improve our predictive power in this emerging field.

Place, publisher, year, edition, pages
Academic Press, 2015
Series
Advances In Atomic, Molecular, and Optical Physics, ISSN 1049-250X ; 64
Keywords
Spin dependent transport; Coulomb blockade; Averaged self-interaction correction; Molecular magnets; Quantum information; Electronic structure
National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-43575 (URN)10.1016/bs.aamop.2015.06.002 (DOI)000370490900004 ()2-s2.0-84937605309 (Scopus ID)978-0-12-802127-9 (ISBN)
Funder
Swedish Research Council
Available from: 2015-06-03 Created: 2015-06-03 Last updated: 2016-11-01Bibliographically approved
Aikebaier, F., Pertsova, A. & Canali, C. M. (2015). Effects of short-range electron-electron interactions in doped graphene. Physical Review B. Condensed Matter and Materials Physics, 92(15), Article ID 155420.
Open this publication in new window or tab >>Effects of short-range electron-electron interactions in doped graphene
2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 15, article id 155420Article in journal (Refereed) Published
Abstract [en]

We study theoretically the effects of short-range electron-electron interactions on the electronic structure of graphene, in the presence of substitutional impurities. Our computational approach is based on the π orbital tight-binding model for graphene, with the electron-electron interactions treated self-consistently at the level of the mean-field Hubbard model. The finite impurity concentration is modeled using the supercell approach. We compare explicitly noninteracting and interacting cases with varying interaction strength and impurity potential strength. We focus in particular on the interaction-induced modifications in the local density of states around the impurity, which is a quantity that can be directly probed by scanning tunneling spectroscopy of doped graphene. We find that the resonant character of the impurity states near the Fermi level is enhanced by the interactions. Furthermore, the size of the energy gap, which opens up at high-symmetry points of the Brillouin zone of the supercell upon doping, is significantly affected by the interactions. The details of this effect depend subtly on the supercell geometry. We use a perturbative model to explain these features and find quantitative agreement with numerical results.

Keywords
graphene, impurities in graphene, electron-electron interactions
National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-39636 (URN)10.1103/PhysRevB.92.155420 (DOI)000362895500003 ()2-s2.0-84944810134 (Scopus ID)
Available from: 2015-02-02 Created: 2015-02-02 Last updated: 2017-12-05Bibliographically approved
Mahani, M. R., MacDonald, A. H. & Canali, C. M. (2015). Electric manipulation of the Mn-acceptor binding energy and the Mn-Mn exchange interaction on the GaAs (110) surface by nearby As vacancies. Physical Review B. Condensed Matter and Materials Physics, 92(4), Article ID 045304.
Open this publication in new window or tab >>Electric manipulation of the Mn-acceptor binding energy and the Mn-Mn exchange interaction on the GaAs (110) surface by nearby As vacancies
2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 4, article id 045304Article in journal (Refereed) Published
Abstract [en]

We investigate theoretically the effect of nearby As (arsenic) vacancies on the magnetic properties of substitutional Mn (manganese) impurities on the GaAs (110) surface, using a microscopic tight-binding model which captures the salient features of the electronic structure of both types of defects in GaAs. The calculations show that the binding energy of the Mn-acceptor is essentially unaffected by the presence of a neutral As vacancy, even at the shortest possible VAs--Mn separation. On the other hand, in contrast to a simple tip-induced-band-bending theory and in agreement with experiment, for a positively charged As vacancy the Mn-acceptor binding energy is significantly reduced as the As vacancy is brought closer to the Mn impurity. For two Mn impurities aligned ferromagnetically, we find that nearby charged As vacancies enhance the energy level splitting of the associated coupled acceptor levels, leading to an increase of the effective exchange interaction. Neutral vacancies leave the exchange splitting unchanged. Since it is experimentally possible to switch reversibly between the two charge states of the vacancy, such a local electric manipulation of the magnetic dopants could result in an efficient real-time control of their exchange interaction.

National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-37824 (URN)10.1103/PhysRevB.92.045304 (DOI)000357857500004 ()2-s2.0-84937934941 (Scopus ID)
Available from: 2014-10-23 Created: 2014-10-23 Last updated: 2017-12-05Bibliographically approved
Projects
Magnetism and nanospintronics in semiconductor nanostructures, topological insulators and molecular magnets [2014-04785_VR]; Linnaeus University
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