Spin transfer torque induced paramagnetic resonance

Shakirov, Alexey M.; Rubtsov, A. N.; Ribeiro, Pedro

doi:10.1103/physrevb.99.054434

Cited by 16 publications

(26 citation statements)

References 28 publications

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“…Reproducible EPR-STM experiments require the use of a magnetic tip (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12), which further complicates the modeling of the STM junction. Several EPR-STM excitation and detection mechanisms have been proposed (19)(20)(21)(22)(23)(24)(25)(26), including modulation of the tunneling barrier by the rf electric field (23), breathing of the density of states mediated by spin-orbit coupling (19), spin torque due to tunneling electrons (24), and piezoelectric coupling (PEC) of the rf electric field to the magnetic adatom (22). In the PEC mechanism, the oscillating electric field couples to the electric dipole of the EPR species and induces vibrations in the inhomogeneous magnetic field of the nearby magnetic STM tip leading to an effective oscillating magnetic field that drives the EPR transitions.…”

Section: Introductionmentioning

confidence: 99%

Longitudinal and transverse electron paramagnetic resonance in a scanning tunneling microscope

et al. 2020

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Electron paramagnetic resonance (EPR) spectroscopy is widely used to characterize paramagnetic complexes. Recently, EPR combined with scanning tunneling microscopy (STM) achieved single-spin sensitivity with sub-angstrom spatial resolution. The excitation mechanism of EPR in STM, however, is broadly debated, raising concerns about widespread application of this technique. We present an extensive experimental study and modeling of EPR-STM of Fe and hydrogenated Ti atoms on a MgO surface. Our results support a piezoelectric coupling mechanism, in which the EPR species oscillate adiabatically in the inhomogeneous magnetic field of the STM tip. An analysis based on Bloch equations combined with atomic-multiplet calculations identifies different EPR driving forces. Specifically, transverse magnetic field gradients drive the spin-1/2 hydrogenated Ti, whereas longitudinal magnetic field gradients drive the spin-2 Fe. Also, our results highlight the potential of piezoelectric coupling to induce electric dipole moments, thereby broadening the scope of EPR-STM to nonpolar species and nonlinear excitation schemes.

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Section: Introductionmentioning

confidence: 99%

Longitudinal and transverse electron paramagnetic resonance in a scanning tunneling microscope

et al. 2020

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“…A direct comparison of the predictions of the cotunneling mechanism with other theoretical proposals [1,[13][14][15] reveals the strengths of this theory. For instance, the ubiquity of the STM-ESR for transition-metal atoms and the weak dependence on the chemical species is difficult to conciliate with the strict symmetry arguments in Baumann et al [1].…”

Section: Discussionmentioning

confidence: 66%

“…Finally, the nonlinear coupling between the magnetic moment and the spin-polarized current in Ref. [15] predicts a quadratic dependence of the resonant current peak on the driving voltage V ac , with an important current dependence. In addition, we notice that our calculations indicate a minor role of the spin-transfer torque, with no qualitative difference between the small [1] and the large [4] current regimes.…”

Section: Discussionmentioning

confidence: 92%

“…The most prominent question is how a magnetic moment can respond resonantly to an ac electric field. Several theoretical proposals have been formulated [1,[13][14][15]. Baumann et al conjecture [1] that the ac electric field induces an adiabatic mechanical oscillation of the adatom, leading to a modulation of the crystal field which, together with the spin orbit, originates spin transitions under very particular symmetry constrains.…”

Section: Introductionmentioning

confidence: 99%

“…An alternative scenario that does not rely on the coupling to the orbital (and symmetry-dependent) degrees of freedom was introduced by Shakirov et al [15], who defended that the ESR signal appears as a consequence of the nonlinearity of the coupling between the magnetic moment and the spinpolarized current, which should yield a strong current dependence, again, contrary to the experimental observations [4].…”

Section: Introductionmentioning

confidence: 99%

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Cotunneling mechanism for all-electrical electron spin resonance of single adsorbed atoms

et al. 2019

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The recent development of all-electrical electron spin resonance (ESR) in a scanning tunneling microscope (STM) setup has opened the door to vast applications. Despite the fast-growing number of experimental works on STM-ESR, the fundamental principles remain unclear. By using a cotunneling picture, we show that the spin resonance signal can be explained as a time-dependent variation of the tunnel barrier induced by the alternating electric driving field. We demonstrate how this variation translates into the resonant frequency response of the direct current. Our cotunneling theory explains the main experimental findings. Namely, the linear dependence of the Rabi flop rate with the alternating bias amplitude, the absence of resonant response for spin-unpolarized currents, and the weak dependence on the actual atomic species.

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Harnessing the Quantum Behavior of Spins on Surfaces

2022

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out via microwave photons. [4] Spins in solid-state materials constitute another family of individual quantum systems where spin states with naturally quantized energy levels can be manipulated via magnetic fields. Physical realizations of solidstate spin systems include gate-defined quantum dots, single dopants in semiconductors such as phosphorus donors in silicon, and single defects in insulators such as nitrogen-vacancy centers in diamond. [5][6][7] Harnessing quantum resources at the nanoscale gives birth to the discipline of quantum-coherent nanoscience that may bring forth useful quantum nanodevices "at the bottom." [8,9] In this review, we focus on a new class of quantum spin systems, individual atomic and molecular spins on surfaces, which has the potential to produce quantum functionalities at the atomic scale. An STM is used to access this tiny length scale, where a sharp metallic tip is positioned in nanometer proximity to spin carriers on a surface to probe their properties through tunneling electrons. [10] Experiments with single atomic spins on material surfaces date back to the early days of low-temperature STM, when Yu-Shiba-Rusinov states and a Kondo resonance were measured in individual magnetic atoms on bulk superconductors [11] and noble metals, [12,13] respectively. STM has also been extensively used on single molecular spins to characterize molecular structures, [14][15][16] probe and modify their electronic and magnetic properties, [17][18][19] and investigate their classical and quantum applications. [19][20][21] Following early STM experiments on single spins, the desire to further control and magnetically image individual spins has prompted the developments of new local probe techniques such as spinpolarized STM, [22] inelastic-tunneling-based spin-flip spectroscopy, [23] electrical pump-probe measurements, [24] and various innovative forms of force and magnetic microscopy. [25][26][27][28] An exciting development in recent years is the incorporation of coherent spin control in atomic-scale microscopy. The need to coherently manipulate and measure individual spins at this length scale necessitates all-electrical protocols with Angstrom precision. These stringent requirements are met by drawing on powerful methodologies from material and quantum sciences, that is, STM's abilities to build nanostructures atom-by-atom and selectively sense individual spin-carrying atoms, as well as electron spin resonance's (ESR's) ability to coherently control electron spin states via electromagnetic waves. This unique combination has so far enabled the quantum control of single electron spins of atoms [29][30][31][32][33] and molecules, [34] as well as the manipulation of single nuclear spins through hyperfine interactions. [35] Quantum coherence can be increased using singlet-triplet The desire to control and measure individual quantum systems such as atoms and ions in a vacuum has led to significant scientific and engineering developments in the past decades that form the basis of today's quantum infor...

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Spin transfer torque induced paramagnetic resonance

Cited by 16 publications

References 28 publications

Longitudinal and transverse electron paramagnetic resonance in a scanning tunneling microscope

Longitudinal and transverse electron paramagnetic resonance in a scanning tunneling microscope

Cotunneling mechanism for all-electrical electron spin resonance of single adsorbed atoms

Harnessing the Quantum Behavior of Spins on Surfaces

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