Probing Weakly Hybridized Magnetic Molecules by Single-Atom Magnetometry.

Advances in molecular spintronics rely on the in-depth characterization of the molecular building blocks in terms of their electronic and, more importantly, magnetic properties. For this purpose, inert substrates that interact only weakly with adsorbed molecules are required in order to preserve their electronic states. Here, we investigate the magnetic-field response of a single paramagnetic 5,5'-dibromosalophenatocobalt(II) (CoSal) molecule adsorbed on a weakly interacting magnetic substrate, namely, Fe-intercalated graphene (GR/Fe) grown on Ir(111), by using spin-polarized scanning tunneling microscopy and spectroscopy. We have obtained local magnetization curves, spin-dependent tunneling spectra, and spatial maps of magnetic asymmetry for a single CoSal molecule, revealing its magnetic properties and coupling to the local environment. The distinct magnetic behavior of the Co metal center is found to rely strictly on its position relative to the GR/Fe moiré structure, which determines the level of hybridization between the GR/Fe surface π-system and the molecular orbitals.

Toward Tailored All-Spin Molecular Devices.

Molecular based spintronic devices offer great potential for future energy-efficient information technology as they combine ultimately small size, high-speed operation, and low-power consumption. Recent developments in combining atom-by-atom assembly with spin-sensitive imaging and characterization at the atomic level have led to a first prototype of an all-spin atomic-scale logic device, but the very low working temperature limits its application. Here, we show that a more stable spintronic device could be achieved using tailored Co-Salophene based molecular building blocks, combined with in situ electrospray deposition under ultrahigh vacuum conditions as well as control of the surface-confined molecular assembly at the nanometer scale. In particular, we describe the tools to build a molecular, strongly bonded device structure from paramagnetic molecular building blocks including spin-wires, gates, and tails. Such molecular device concepts offer the advantage of inherent parallel fabrication based on molecular self-assembly as well as an order of magnitude higher operation temperatures due to enhanced energy scales of covalent through-bond linkage of basic molecular units compared to substrate-mediated coupling schemes employing indirect exchange coupling between individual adsorbed magnetic atoms on surfaces.

Mechanism of a molecular photo-switch adsorbed on Si(100).

We present a very compact molecular photoswitch on the technologically important Si(100) surface. Its adsorption configuration is determined by a combined scanning tunneling microscopy (STM) and density functional theory (DFT) study. The mechanisms of the isomerization reactions are discussed in view of DFT calculations and proven by in situ light irradiation.

Antiferromagnetism-driven two-dimensional topological nodal-point superconductivity.

Magnet/superconductor hybrids (MSHs) hold the promise to host emergent topological superconducting phases. Both one-dimensional (1D) and two-dimensional (2D) magnetic systems in proximity to s-wave superconductors have shown evidence of gapped topological superconductivity with zero-energy end states and chiral edge modes. Recently, it was proposed that the bulk transition-metal dichalcogenide 4Hb-TaS2 is a gapless topological nodal-point superconductor (TNPSC). However, there has been no experimental realization of a TNPSC in a MSH system yet. Here we present the discovery of TNPSC in antiferromagnetic (AFM) monolayers on top of an s-wave superconductor. Our calculations show that the topological phase is driven by the AFM order, resulting in the emergence of a gapless time-reversal invariant topological superconducting state. Using low-temperature scanning tunneling microscopy we observe a low-energy edge mode, which separates the topological phase from the trivial one, at the boundaries of antiferromagnetic islands. As predicted by the calculations, we find that the relative spectral weight of the edge mode depends on the edge's atomic configuration. Our results establish the combination of antiferromagnetism and superconductivity as a novel route to design 2D topological quantum phases.

On-Surface Oligomerization of Self-Terminating Molecular Chains for the Design of Spintronic Devices.

Molecular spintronics is currently attracting a lot of attention due to its great advantages over traditional electronics. A variety of self-assembled molecule-based devices are under development, but studies regarding the reliability of the growth process remain rare. Here, we present a method to control the length of molecular spintronic chains and to make their terminations chemically inert, thereby suppressing uncontrolled coupling to surface defects. The temperature evolution of chain formation was followed by X-ray photoelectron spectroscopy to determine optimal growth conditions. The final structures of the chains were then studied, using scanning tunneling microscopy, as a function of oligomerization conditions. We find that short chains are readily synthesized with high yields and that long chains, even exceeding 70mers, can be realized under optimized growth parameters, albeit with reduced yields.

Long-range magnetic coupling between nanoscale organic-metal hybrids mediated by a nanoskyrmion lattice.

The design of nanoscale organic-metal hybrids with tunable magnetic properties as well as the realization of controlled magnetic coupling between them open gateways for novel molecular spintronic devices. Progress in this direction requires a combination of a clever choice of organic and thin-film materials, advanced magnetic characterization techniques with a spatial resolution down to the atomic length scale, and a thorough understanding of magnetic properties based on first-principles calculations. Here, we make use of carbon-based systems of various nanoscale size, such as single coronene molecules and islands of graphene, deposited on a skyrmion lattice of a single atomic layer of iron on an iridium substrate, in order to tune the magnetic characteristics (for example, magnetic moments, magnetic anisotropies and coercive field strengths) of the organic-metal hybrids. Moreover, we demonstrate long-range magnetic coupling between individual organic-metal hybrids via the chiral magnetic skyrmion lattice, thereby offering viable routes towards spin information transmission between magnetically stable states in nanoscale dimensions.

Tailoring molecular self-assembly of magnetic phthalocyanine molecules on Fe- and Co-intercalated graphene.

We investigate molecule-molecule, as well as molecule-substrate, interactions of phthalocyanine molecules deposited on graphene. In particular, we show how to tune the self-assembly of molecular lattices in two dimensions by intercalation of transition metals between graphene and Ir(111): modifying the surface potential of the graphene layer via intercalation leads to the formation of square, honeycomb, or Kagome lattices. Finally, we demonstrate that such surface induced molecular lattices are stable even at room temperature.

Light driven reactions of single physisorbed azobenzenes.

We present a successful attempt of decoupling a dye molecule from a metallic surface via physisorption for enabling direct photoisomerization. Effective switching between the isomers is possible by exposure to UV light via the rotation pathway.