Vibron-assisted spin excitation in a magnetically anisotropic molecule

Abstract

The ability to electrically-drive spin excitations in molecules with magnetic anisotropy is key for high-density storage and quantum-information technology. Electrons, however, also tunnel via the vibrational excitations unique to a molecule. The interplay of spin and vibrational excitations offers novel routes to study and, ultimately, electrically manipulate molecular magnetism. Here we use a scanning tunneling microscope to electrically induce spin and vibrational excitations in a single molecule consisting of a nickelocene magnetically coupled to a Ni atom. We evidence a vibron-assisted spin excitation at an energy one order of magnitude higher compared to the usual spin excitations of nickelocene and explain it using first-principles calculations that include electron correlations. Furthermore, we observe that spin excitations can be quenched by modifying the Ni-nickelocene coupling. Our study suggests that nickelocene-based complexes constitute a model playground for exploring the interaction of spin and vibrations in the electron transport through single magnetic molecules.Magnetic molecules are potential candidates for information-storing technology [1], molecular spintronics [2] and quantum computing [3], provided that their axial magnetic anisotropy DS 2 z ensures a magnetic bistability among longlived magnetic states. But molecules also vibrate. In particular, in magnetic molecules the interplay of vibrational modes, or vibrons, with the spin degrees of freedom is known to impact the spin lifetime [4][5][6]. Since vibrational modes can couple to the electric charge, producing vibron-assisted electron excitations in transport [7][8][9], expectations are that similar effects should be also observed with the electronic spin [10,11].Concerning this last point, experimental work has predominantly focused on a well-known spin-related manybody effect, the Kondo effect. The electron-vibron interaction in Kondo molecules was shown to produce satellite Kondo resonances in the differential conductance spectra at the bias of the vibron's excitation energy [12][13][14]. These resonances were ascribed to tunneling electrons that have their spin flipped when elastically scattering off the molecular spin, but with sufficient energy to activate a vibrational mode in the molecule [15]. The question arises whether a similar mechanism is also possible with other spin scattering mechanisms that magnetically excite a molecule such as inelastic scattering involving magnetic anisotropy [16]. These so-called spin excitations show great potential in view of an all-electrical manipulation of the molecular spin [17,18].Here, we use scanning tunneling microscopy (STM) to demonstrate the presence of a combined vibrational-spin excitation in a single nickelocene molecule [Ni(C 5 H 5 ) 2 , see Fig. 1(d); noted Nc hereafter] coupled to a Ni atom. Nickelocene is a spin S = 1 molecule of the metallocene family with magnetic anisotropy, where spin excitations produce a sizable increase of the electronic transport [19]. We show that the o...

Superconducting Scanning Tunneling Microscope Tip to Reveal Sub-millielectronvolt Magnetic Energy Variations on Surfaces

“…3 (c) emerges. As in previous studies, 39,47,48 we find a combination of vertical (with the molecular axis perpendicular to the surface) and horizontal (parallel to the surface) Nc resulting from a T-shaped vdW interaction. 45 The new pattern…”

Molecular templates of spin textures on superconducting surfaces

“…These peaks correspond to the inelastic electron tunneling spectra (IETS) of the Nc magnetic excitation on a superconductor [31]. Indeed, these peaks match the excitation energy of the molecular spin from the S z = 0 ground state to the S z = ±1 excited states [20][21][22][23] with excitation energy D = 6.4 ± 0.2 − 2.6 = 3.8 ± 0.2 meV shifted by 2∆ due to the presence of the tip and substrate superconducting gaps [31].…”

“…1 (a) shows that Nc is composed by two cyclopentadienyl rings (C 5 H 5 ) and a Ni atoms in between. It is a S = 1 spin with sizeable hard-axis longitudinal magnetic anisotropy perpendicular to the cyclopentadienyl rings ranging from D = 3.4 to 4.0 meV depending on the substrate [20][21][22][23]. Studies on copper surfaces [20,21,23,24] show that vertical Nc molecules are intercalating with horizontal ones to form the molecular assembly.…”

“…It is a S = 1 spin with sizeable hard-axis longitudinal magnetic anisotropy perpendicular to the cyclopentadienyl rings ranging from D = 3.4 to 4.0 meV depending on the substrate [20][21][22][23]. Studies on copper surfaces [20,21,23,24] show that vertical Nc molecules are intercalating with horizontal ones to form the molecular assembly. Due to the molecular magnetic anisotropy, such an assembly has the potential for producing a complex spin texture.…”

“…2 (d) emerges. As in previous studies [23,24,32] a combination of vertical (with the molecular axis perpendicular to the surface) and horizontal (parallel to the surface) Nc has to be considered. The new pattern consists of two vertical molecules and two horizontal molecules.…”