Cotunneling and nonequilibrium magnetization in magnetic molecular monolayers

Elste, Florian; Timm, Carsten

doi:10.1103/physrevb.75.195341

Cited by 68 publications

(72 citation statements)

References 48 publications

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“…From the formal point of view our results are in agreement with previous works based on a truncation of the T matrix to second order in the coupling Hamiltonian. [35][36][37][38] Our approach permits us to obtain an effective cotunneling Hamiltonian that can be compared with effective Kondo-like Hamiltonians proposed in most theoretical analysis of IETS experiments. [14][15][16][17][18][19][20][21][22] We have also explored the origin of the experimentally observed asymmetry with respect to bias inversion in the dI/dV curves.…”

Section: Discussionmentioning

confidence: 99%

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Cotunneling theory of atomic spin inelastic electron tunneling spectroscopy

Delgado

Fernández-Rossier

2011

Phys. Rev. B

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We propose cotunneling as the microscopic mechanism that makes possible inelastic electron tunneling spectroscopy of magnetic atoms in surfaces for a wide range of systems, including single magnetic adatoms, molecules, and molecular stacks. We describe electronic transport between the scanning tip and the conducting surface through the magnetic system (MS) with a generalized Anderson model, without making use of effective spin models. Transport and spin dynamics are described with an effective cotunneling Hamiltonian in which the correlations in the magnetic system are calculated exactly and the coupling to the electrodes is included up to second order in the tip MS and MS substrate. In the adequate limit our approach is equivalent to the phenomenological Kondo exchange model that successfully describes the experiments. We apply our method to study in detail inelastic transport in two systems, stacks of cobalt phthalocyanines and a single Mn atom on Cu 2 N. Our method accounts for both the large contribution of the inelastic spin exchange events to the conductance and the observed conductance asymmetry.

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Section: Discussionmentioning

confidence: 99%

“…[35][36][37][38][39] For instance, in Refs. 35-38 they compute the cotunneling scattering rates by truncating the T matrix down to second order in the electrode coupling.…”

Section: Comparison With Other Cotunneling Theoriesmentioning

confidence: 99%

Cotunneling theory of atomic spin inelastic electron tunneling spectroscopy

Delgado

Fernández-Rossier

2011

Phys. Rev. B

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“…[13][14][15][16] Additional gate-voltage dependent transport resonances have been found inside the Coulomb-blockade regime 25 and discussed theoretically. 26,27 These resonances are due to sequential tunneling events starting from states excited by inelastic cotunneling processes ͑"heating the molecule"͒, which are called cotunneling-assisted sequential tunneling ͑COSET͒. It was recently suggested 28 that these resonances can be used to experimentally estimate the decay rate of vibrational excitations due to a coupling to a dissipative environment.…”

Section: Introductionmentioning

confidence: 99%

Kinetic equations for transport through single-molecule transistors

2008

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We present explicit kinetic equations for quantum transport through a general molecular quantum dot, accounting for all contributions up to fourth order perturbation theory in the tunneling Hamiltonian and the complete molecular density matrix. Such a full treatment describes not only sequential, cotunneling, and pair tunneling, but also contains terms contributing to renormalization of the molecular resonances as well as their broadening. Due to the latter all terms in the perturbation expansion are automatically well defined for any set of system parameters: no divergences occur and no by-hand regularization is required. Additionally we show that, in contrast to second order perturbation theory, in fourth order it is essential to account for quantum coherence between nondegenerate states, entering the theory through the nondiagonal elements of the density matrix. As a first application, we study a single-molecule transistor coupled to a localized vibrational mode ͑Anderson-Holstein model͒. We find that cotunneling-assisted sequential tunneling processes involving the vibration give rise to current peaks, i.e., negative differential conductance in the Coulomb-blockade regime. Such peaks occur in the crossover to strong electron-vibration coupling, where inelastic cotunneling competes with Franck-Condon suppressed sequential tunneling, and thereby indicate the strength of the electronvibration coupling. The peaks depend sensitively on the coupling to a dissipative bath, thus providing also an experimental probe of the Q factor of the vibrational motion.

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“…25,[35][36][37][38][39][40][41][42][43][44][45][46] The systems studied include magnetic grains, 39,47 semiconductor 37 and Mn-doped quantum dots, 35,44 and molecular magnets and magnetic molecules. [40][41][42][43]48 Here we can model the current driven dynamics of a quantum spin whose Hamiltonian parameters are accurately known from experiments, 11 making it possible to compare successfully theory and experiment.…”

Section: Introductionmentioning

confidence: 99%

Spin dynamics of current-driven single magnetic adatoms and molecules

2010

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A scanning tunneling microscope can probe the inelastic spin excitations of a single magnetic atom in a surface via spin-flip assisted tunneling in which transport electrons exchange spin and energy with the atomic spin. If the inelastic transport time, defined as the average time elapsed between two inelastic spin flip events, is shorter than the atom spin-relaxation time, the scanning tunnel microscope ͑STM͒ current can drive the spin out of equilibrium. Here we model this process using rate equations and a model Hamiltonian that describes successfully spin-flip-assisted tunneling experiments, including a single Mn atom, a Mn dimer, and Fe Phthalocyanine molecules. When the STM current is not spin polarized, the nonequilibrium spin dynamics of the magnetic atom results in nonmonotonic dI / dV curves. In the case of spin-polarized STM current, the spin orientation of the magnetic atom can be controlled parallel or antiparallel to the magnetic moment of the tip. Thus, spin-polarized STM tips can be used both to probe and to control the magnetic moment of a single atom.

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Cotunneling and nonequilibrium magnetization in magnetic molecular monolayers

Cited by 68 publications

References 48 publications

Cotunneling theory of atomic spin inelastic electron tunneling spectroscopy

Cotunneling theory of atomic spin inelastic electron tunneling spectroscopy

Kinetic equations for transport through single-molecule transistors

Spin dynamics of current-driven single magnetic adatoms and molecules

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