Correlation-driven transport asymmetries through coupled spins in a tunnel junction

Abstract

Spin–spin correlations can be the driving force that favours certain ground states and are key in numerous models that describe the behaviour of strongly correlated materials. While the sum of collective correlations usually lead to a macroscopically measurable change in properties, a direct quantification of correlations in atomic scale systems is difficult. Here we determine the correlations between a strongly hybridized spin impurity on the tip of a scanning tunnelling microscope and its electron bath by varying the coupling to a second spin impurity weakly hybridized to the sample surface. Electronic transport through these coupled spins reveals an asymmetry in the differential conductance reminiscent of spin-polarized transport in a magnetic field. We show that at zero field, this asymmetry can be controlled by the coupling strength and is related to either ferromagnetic or antiferromagnetic spin–spin correlations in the tip.

Probing magnetic excitations and correlations in single and coupled spin systems with scanning tunneling spectroscopy

“…Note, that the two spins can be coupled also vertically by having one spin center adsorbed to the tip apex and the second one onto the substrate surface. In this situation, the antiferromagnetic exchange coupling has been found to be proportional to the tunneling coupling which depends exponentially on the distance between the two spins on tip and sample [198,168]. Building a similar structure as discussed in this section with a S = 1 spin adsorbed on the sample and a strongly correlated half-integer spin on the tip lead to the observation of bias direction dependent step asymmetries at the energetically outer steps (blue dashed lines in Fig.…”

“…17d). These asymmetries enable to directly determine the correlation strength between the half-integer spin and the supporting electron bath [168].…”

Spin-driven electrical power generation at room temperature

“…In general, compared to low-temperature transport across wellcharacterized quantum objects (e.g. from single atoms and dimers to molecules and atomic clusters [43][44][45][46][47][48][49] ) thanks to a scanning tunneling microscope (STM), it is thus far difficult to assemble and ascertain the effective nanotransport path 50 in a solid state device, especially for the oxides used as MTJ barriers. Here, uncontrolled imperfections such as oxygen vacancies in the MgO tunnel barrier can concentrate electronic tunneling transport across a macrojunction onto a nanotransport path 50,51 , such that the device operates due to a rare tunneling event 52 .…”

“…To achieve routine experimental reproducibility, we propose that all spintronic selector tracks be attempted (see introduction), noting that, in addition to the two published reports 1,2 , similar effects were observed at low temperature on MTJs with manganite half metals 57 . In all cases, control over the spatial position and density of the barrier's PM centers will be required with a precision that, at this time, remains the domain of model STMassembled junctions [43][44][45][46][47][48][49] . Considering that all reports involved microscale devices, this suggests reducing the junction's lateral size from the micro-to the nano-scale.…”

Encoding Information on the Excited State of a Molecular Spin Chain

“…Inelastic excitations can cause a large increase in the current flowing across a set of coupled electron spins by inducing electronic transitions in the spin chain from its quantum ground state to an excited state. [ 1–13 ] Due to the conservation of spin angular momentum and transition rules, [ 14 ] this spin‐flip process causes minority spin electrons from the electrode to transport as majority electrons. The converse scenario is forbidden.…”