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Nossa, Javier
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Publications (9 of 9) Show all publications
Nossa, J. & Canali, C. M. (2014). Cotunneling signatures of Spin-Electric coupling in frustrated triangularmolecular magnets. Physical Review B. Condensed Matter and Materials Physics, 89(23), Article ID: 235435
Open this publication in new window or tab >>Cotunneling signatures of Spin-Electric coupling in frustrated triangularmolecular magnets
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 23, p. Article ID: 235435-Article in journal (Refereed) Published
Abstract [en]

The ground state of frustrated (antiferromagnetic) triangular molecular magnets is characterized by two total-spin S = 1/2 doublets with opposite chirality. According to a group theory analysis [M. Trif et al., Phys. Rev. Lett. 101, 217201 (2008)] an external electric field can efficiently couple these two chiral spin states, even when the spin-orbit interaction (SOI) is absent. The strength of this coupling, d, is determined by an off-diagonal matrix element of the dipole operator, which can be calculated by ab-initio methods [M. F. Islam et al., Phys. Rev. B 82, 155446 (2010)]. In this work we propose that Coulomb-blockade transport experiments in the cotunneling regime can provide a direct way to determine the spin-electric coupling strength. Indeed, an electric field generates a d-dependent splitting of the ground state manifold, which can be detected in the inelastic cotunneling conductance. Our theoretical analysis is supported by master-equation calculations of quantum transport in the cotunneling regime. We employ a Hubbard-model approach to elucidate the relationship between the Hubbard parameters t and U, and the spin-electric coupling constant d. This allows us to predict the regime in which the coupling constant d can be extracted from experiment.

 

National Category
Physical Sciences
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-34400 (URN)10.1103/PhysRevB.89.235435 (DOI)000339049700004 ()2-s2.0-84903732948 (Scopus ID)
Available from: 2014-05-26 Created: 2014-05-26 Last updated: 2017-12-05Bibliographically approved
Nossa, J. & Canali, C. M. (2013). Cotunneling signatures of spin-electric coupling in frustrated triangularmolecular magnets. In: APS MARCH MEETING 2013: . Paper presented at APS MARCH MEETING 2013.
Open this publication in new window or tab >>Cotunneling signatures of spin-electric coupling in frustrated triangularmolecular magnets
2013 (English)In: APS MARCH MEETING 2013, 2013Conference paper, Oral presentation with published abstract (Refereed)
National Category
Condensed Matter Physics
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-27946 (URN)
Conference
APS MARCH MEETING 2013
Available from: 2013-08-07 Created: 2013-08-07 Last updated: 2018-08-17Bibliographically approved
Nossa, J., Islam, F., Canali, C. M. & Pederson, M. R. (2013). Electric control of a {Fe4} single-molecule magnet in a single-electron transistor. Physical Review B. Condensed Matter and Materials Physics, 88(22), Article ID: 224423
Open this publication in new window or tab >>Electric control of a {Fe4} single-molecule magnet in a single-electron transistor
2013 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 22, p. Article ID: 224423-Article in journal (Refereed) Published
Abstract [en]

Using first-principles methods, we study theoretically the properties of an individual {Fe-4} single-molecule magnet (SMM) attached to metallic leads in a single-electron transistor geometry. We show that the conductive leads do not affect the spin ordering and magnetic anisotropy of the neutral SMM. On the other hand, the leads have a strong effect on the anisotropy of the charged states of the molecule, which are probed in Coulomb blockade transport. Furthermore, we demonstrate that an external electric potential, modeling a gate electrode, can be used to manipulate the magnetic properties of the system. For a charged molecule, by localizing the extra charge with the gate voltage closer to the magnetic core, the anisotropy magnitude and spin ordering converges to the values found for the isolated {Fe-4} SMM. We compare these findings with the results of recent quantum transport experiments in three-terminal devices.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-33310 (URN)10.1103/PhysRevB.88.224423 (DOI)000331753300006 ()2-s2.0-84892423956 (Scopus ID)
Available from: 2014-03-26 Created: 2014-03-26 Last updated: 2017-12-05Bibliographically approved
Nossa, J., Islam, F., Canali, C. M. & Pederson, M. (2012). DFT calculations of the charged states of N@C60 and {\{}Fe4{\}} single molecule magnets investigated in tunneling spectroscopy. In: : . Paper presented at American Physical Society March Meeting 2012.
Open this publication in new window or tab >>DFT calculations of the charged states of N@C60 and {\{}Fe4{\}} single molecule magnets investigated in tunneling spectroscopy
2012 (English)Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

For device applications of single molecule magnets (SMMs) in high-density information storage and quantum-state control it is essential that the magnetic properties of the molecules remain stable under the influence of metallic contacts or surface environment. Recent tunneling experiments [1, 2] on N@C60 and {\{}Fe4{\}} SMM have shown that these molecules preserve their magnetic characteristics when they are used as the central island of single-electron transistors. Although quantum spin models have been used extensively to study theoretically tunneling spectroscopy of SMMs, it has been shown recently that the orbital degrees of freedom, which is absent in spin models, can significantly affect the tunneling conductance [3]. In this work we present first-principles calculations of the neutral and charged states of N@C60 and {\{}Fe4{\}} SMMs, and discuss a strategy to include their properties into a theory of quantum transport. We also present results of the magnetic anisotropy for the different charge states of Fe4 and discuss their relevance for experiments [2] in the sequential tunneling and cotunnelling regimes.

National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-27945 (URN)
Conference
American Physical Society March Meeting 2012
Available from: 2013-08-07 Created: 2013-08-07 Last updated: 2018-08-17Bibliographically approved
Nossa, J., Islam, F., Canali, C. M. & Pederson, M. (2012). First-principles studies of spin-orbit and Dzyaloshinskii-Moriya interactions in the {Cu3} single-molecule magnet. Physical Review B. Condensed Matter and Materials Physics, 85(8), 085427-1-085427-10
Open this publication in new window or tab >>First-principles studies of spin-orbit and Dzyaloshinskii-Moriya interactions in the {Cu3} single-molecule magnet
2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 8, p. 085427-1-085427-10Article in journal (Refereed) Published
Abstract [en]

Frustrated triangular molecule magnets such as {Cu3} are characterized by two degenerate S = 1/2 ground states with opposite chirality. Recently, it has been proposed theoretically [M. Trif et al., Phys. Rev. Lett. 101, 217201 (2008)] and verified by ab initio calculations [M. F. Islam et al., Phys. Rev. B 82, 155446 (2010)] that an external electric field can efficiently couple these two chiral spin states, even in the absence of spin-orbit interaction (SOI). The SOI is, nevertheless, important since it introduces a splitting in the ground-state manifold via the Dzyaloshinskii-Moriya (DM) interaction. In this paper, we present a theoretical study of the effect of the SOI on the chiral states within spin-density functional theory. We employ a recently introduced Hubbard-model approach to elucidate the connection between the SOI and the Dzyaloshinskii-Moriya interaction. This allows us to express the Dzyaloshinskii-Moriya interaction constant D in terms of the microscopic Hubbard-model parameters, which we calculate from first principles. The small splitting that we find for the {Cu3} chiral state energies (≈ 0.02 meV) is consistent with experimental results. The one-band Hubbard-model approach adopted and analyzed here also yields a better estimate of the isotropic exchange constant than the ones obtained by comparing total energies of different spin configurations. The method used here for calculating the DM interaction unmasks its simple fundamental origin, which is the off-diagonal spin-orbit interaction between the generally multireference vacuum state and single-electron excitations out of those states.

National Category
Condensed Matter Physics
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-18060 (URN)10.1103/PhysRevB.85.085427 (DOI)2-s2.0-84857778215 (Scopus ID)
Funder
Swedish Research Council, 621-2007-5019 and 621-2010-3761
Available from: 2012-03-19 Created: 2012-03-19 Last updated: 2017-12-07Bibliographically approved
Nossa, J., Islam, F., Canali, C. M. & Pederson, M. (2011). Spin-orbit interaction and magnetic field in antiferromagnetic triangular molecular magnets. In: APS MARCH MEETING 2011: . Paper presented at APS MARCH MEETING 2011.
Open this publication in new window or tab >>Spin-orbit interaction and magnetic field in antiferromagnetic triangular molecular magnets
2011 (English)In: APS MARCH MEETING 2011, 2011Conference paper, Oral presentation with published abstract (Refereed)
National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-27944 (URN)
Conference
APS MARCH MEETING 2011
Available from: 2013-08-07 Created: 2013-08-07 Last updated: 2018-05-31Bibliographically approved
Nossa, J. & Canali, C. M. (2010). Effects of spin-orbit interaction in spin-polarized single-electron transistors.. In: APS MARCH MEETING 2010: . Paper presented at APS MARCH MEETING 2010.
Open this publication in new window or tab >>Effects of spin-orbit interaction in spin-polarized single-electron transistors.
2010 (English)In: APS MARCH MEETING 2010, 2010Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

We consider a model of an artificial atom with interacting electrons having both spin degrees of freedom and orbital degeneracies. The interaction includes both spin and orbital exchange couplings, which favour a spin polarized ground state with nonzero orbital moment. For the two-electron problem with l=1 orbital degeneracy we enumerate all the eigenstates of the system with and without spin-orbit interaction. We then study quantum transport for the case in which the atom is weakly connected to metallic leads, focusing in particular on the effect of the spin-orbit interaction on the tunnelling conductance. We also discuss how spin-orbit interaction and an external magnetic field influence the conductance when the leads are spin-polarized and tunnelling magneto-resistance is expected.

National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-27943 (URN)
Conference
APS MARCH MEETING 2010
Available from: 2013-08-07 Created: 2013-08-07 Last updated: 2018-05-31Bibliographically approved
Islam, F., Nossa, J., Canali, C. M. & Pederson, M. (2010). First-principles study of spin-electric coupling in a {Cu3} single molecular magnet. Physical Review B. Condensed Matter and Materials Physics, 82(15), article number-155446
Open this publication in new window or tab >>First-principles study of spin-electric coupling in a {Cu3} single molecular magnet
2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 15, p. article number-155446Article in journal (Refereed) Published
Abstract [en]

We report on a study of the electronic and magnetic properties of the triangular antiferromagnetic {Cu3} single-molecule magnet, based on spin-density-functional theory. Our calculations show that the low-energy magnetic properties are correctly described by an effective three-site spin s = 1/2 Heisenberg model, with an antiferromagnetic exchange coupling J approximate to 5 meV. The ground-state manifold of the model is composed of two degenerate spin S = 1/2 doublets of opposite chirality. Due to lack of inversion symmetry in the molecule these two states are coupled by an external electric field, even when spin-orbit interaction is absent. The spin-electric coupling can be viewed as originating from a modified exchange constant delta J induced by the electric field. We find that the calculated transition rate between the chiral states yields an effective electric dipole moment d = 3.38 x 10(-33) C m approximate to e10(-4)a, where a is the Cu separation. For external electric fields epsilon approximate to 10(8) V/m this value corresponds to a Rabi time tau approximate to 1 ns and to a delta J on the order of a few mu eV.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-7453 (URN)10.1103/PhysRevB.82.155446 (DOI)2-s2.0-78149273503 (Scopus ID)
Available from: 2010-08-18 Created: 2010-08-18 Last updated: 2017-12-12Bibliographically approved
Nossa, J. & Canali, C. M.Effects of spin-orbit interaction in molecular-magnet single electron transistors.
Open this publication in new window or tab >>Effects of spin-orbit interaction in molecular-magnet single electron transistors
(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics Condensed Matter Physics
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-7464 (URN)
Available from: 2010-08-18 Created: 2010-08-18 Last updated: 2016-11-01Bibliographically approved
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