Scanning tunneling microscope operating as a spin diode

Abstract

We theoretically investigate spin-polarized transport in a system composed of a ferromagnetic scanningtunneling-microscope (STM) tip coupled to an adsorbed atom (adatom) on a host surface. Electrons can tunnel directly from the tip to the surface or via the adatom. Since the tip is ferromagnetic and the host surface (metal or semiconductor) is nonmagnetic we obtain a spin-diode effect when the adatom is in the regime of single occupancy. This effect leads to an unpolarized current for direct bias (V > 0) and polarized current for reverse (V < 0) bias voltages, if the tip is nearby the adatom. Within the nonequilibrium Keldysh technique we analyze the interplay between the lateral displacement of the tip and the intra adatom Coulomb interaction on the spin-diode effect. As the tip moves away from the adatom the spin-diode effect vanishes and the currents become polarized for both V > 0 and V < 0. We also find an imbalance between the up and down spin populations in the adatom, which can be tuned by the tip position and the bias. Finally, due to the presence of the adsorbate on the surface, we observe spin-resolved Friedel oscillations in the current, which reflects the oscillations in the calculated local density of states (LDOS) of the subsystem surface + adatom.

Graphene sheet versus two-dimensional electron gas: A relativistic Fano spin filter via STM and AFM tips

“…[34][35][36][37][38] Additionally, in the emerging field of spintronics, the presence of spin-polarized hosts gives rise to interesting new features. [39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55] For these cases, the splitting of the Kondo peak in the conductance characterizes the fingerprint of itinerant magnetism in the host. 39,40 A spin-polarized tip and a nonmagnetic host also lead to a spin-dependent STM setup.…”

“…Particularly, the aforementioned system behaves either as a spin filter in the Kondo regime or as a spin diode away from it. [41][42][43] Moreover, a Fano spin filter can in principle be realized even in the absence of ferromagnetism 56,57 and the Kondo effect. This can be achieved in the side-coupled geometry of a quantum wire hybridized with a quantum dot (QD) where spin degeneracy is lifted by the external magnetic field applied at the QD region.…”

“…A spinpolarized tip and a nonmagnetic host also lead to a spindependent STM setup. Particulary, the aforementioned system behaves either as a spin-filter in the Kondo regime or as a spin-diode away from it [43][44][45] . Moreover, a Fano spin-filter can in principle be realized even in the absence of ferromagnetism and Kondo effect.…”

A theoretical analysis of the spin dynamics of magnetic adatoms traced by time-resolved scanning tunneling spectroscopy

“…This method is, in essence, a perturbative formalism and hence requires a separate justification for each of the considered experimental configurations. The non-equilibrium Green's function approach has a potential to systematically take into account many-body effects; however, the transition rates are often introduced as adjustable parameters [13]. In the present method, we focus on the description of the tunneling starting from a model Hamiltonian including the magnetic anisotropy, the exchange coupling and the coupling to the external magnetic field.…”

Dimensionality effects in the local density of states of ferromagnetic hosts probed via STM: Spin-polarized quantum beats and spin filtering

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Away from the Kondo regime, a spin diode emerges. 24 In the condensed-matter literature on scanning microscopy, there is a profusion of work discussing spin-dependent phenomena employing ferromagnetic leads coupled to quantum dots or adatoms in the Kondo regime. 4,6,7,[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] Here, we mention those with metallic samples and buried impurities in which the anisotropy of the Fermi surface plays an important role in electron tunneling.…”