arXiv subjects

Maciej Bazarnik

Publications and source records attributed to Maciej Bazarnik.

8 recordsLinked to original sources

arXiv2026

Image-potential states on a 2D Gr-ferromagnet hybrid: enhancing spin and stacking sensing

Spin-resolved scanning tunneling microscopy and spectroscopy studies of image-potential states on Gr/Fe/Ir(111) show their sensitivity to the spatial variation of the Gr-Fe distance, and of the interfacial charge and spin transfer within the moiré unit cell. A stacking contrast between fcc and hcp sites, indistinguishable in the direct tunneling mode, is provided by the image-potential states in both resonant tunneling topography and spectroscopy images. The spin-polarized measurements reveal a site- and energy-dependent spin-polarization of the image-potential states that is mapped across the moiré unit cell with a spin contrast between hcp and fcc sites unobservable in direct tunneling mode. On the on-top sites, the lowest image-potential states are found to exhibit a high spin-polarization, in contrast to the electronic states around the Fermi energy evanescent into vacuum, and attributed to their interfacial character at the respective Gr-Fe distance. Since the physisorbed graphene is only weakly spin-polarized on these sites, image-potential states reflect the spin density at buried interfaces covered by non-magnetic passivation layers. The simultaneous imaging of structural, electronic and magnetic properties, both at the surface and the buried interface will prove invaluable in research of 2D hybrids and heterostructures.

cond-mat.mes-hall↗

arXiv2026

Layer thickness dependent band gap of MBE grown single- to few-layer MoS$_{2}$

In light of the rise of transition metal dichalcogenides as 2D semiconductors for device applications, band engineering becomes very important from an application point of view. In many of these materials, such as the canonical example of MoS$_{2}$, the semiconductor band gap depends on the layer number. It changes from indirect to direct as it evolves from a bulk semiconductor to a monolayer. Interestingly, it was predicted and experimentally confirmed that, by thinning the material from bulk to a bilayer, the indirect transition shows a strong blue-shift. Here, we present the results of scanning tunnelling spectroscopy measurements on MoS$_{2}$ that has been grown \textit{in situ} via molecular beam epitaxy on graphene on Ir(111) at thicknesses ranging from 1 to 5 layers. We find a drastic decrease of the band gap with increasing layer number, to values even below the band gap in bulk. We also observe that the pinning of the conduction band vanishes above 4 layers. Comparing our experimental data with density functional theory and \textit{GW} calculations indicates that an additional screening is introduced by the sample growth conditions.

cond-mat.mtrl-sci↗

arXiv2026

In-plane ferromagnetism-driven topological nodal-point superconductivity with tilted Weyl cones

The potential application of topological superconductivity in quantum transport and quantum information has fueled an intense investigation of hybrid materials with emergent electronic properties, including magnet-superconductor heterostructures. Here, we report evidence of a topological nodal-point superconducting phase in a one-atom-thick in-plane ferromagnet in direct proximity to a conventional $s$-wave superconductor. Low-temperature scanning tunneling spectroscopy data reveal the presence of a double-peak low-energy feature in the local density of states of the hybrid system, which is rationalized via model calculations to be an emergent topological nodal-point superconducting phase with tilted Weyl cones. Our results further establish the combination of in-plane ferromagnetism and conventional superconductivity as a route to design two-dimensional topological quantum phases.

cond-mat.supr-con↗

arXiv2025

Spin filtering on demand via localized states in an atomic-scale resonant tunneling magnetic tunnel junction

Spin filtering and its back-action spin transfer torque (STT) are key ingredients of latest spintronic devices based on magnetic tunnel junctions (MTJs). Resonant tunneling (RT), implemented by design or occurring as parasitic effects, is known to crucially affect macroscopic device performance, but direct experimental access to its individual microscopic processes has remained difficult. Here we apply the RT scheme from MTJs to spin-polarized scanning tunneling microscopy (SP-STM) for ultimate miniaturization obtained by addressing distinct sites on individual nanomagnets. Combined with energy selectivity, our experimental model set-up enables to study the spin filtering capabilities of RT through an individual spin-split vacuum resonance state and of the corresponding STT exerted on the nanomagnet. We find, that the sign and magnitude of the STT follow the effective spin-polarization of the resonance state, which, as we show, can by tailored on demand either by adjusting the applied bias or the current injection point on the nanostructure. We anticipate, that our atomic-scale RT-MTJ approach and the discovery of a versatile tunable spin-filter at smallest scale will prove invaluable for studying and designing next generation MTJs potentially based on recently discovered 2D van-der-Waals magnets or altermagnets.

cond-mat.mes-hall↗

arXiv2023

Preparation and STM study of clean Nb(111) surfaces

Niobium with its highest transition temperature among all elemental superconductors has become a favorable substrate for realizing well-defined low-dimensional magnet-superconductor hybrid systems exhibiting novel types of exotic electronic states such as Majorana zero-energy modes. While a preparation procedure for obtaining atomically clean Nb(110) substrates has previously been reported, a suitable preparation method for clean Nb(111) surfaces is still lacking. Here, we report a recipe for cleaning Nb(111) surfaces based on an atomic hydrogen treatment followed by short flashes to elevated temperatures. The atomic surface structure of clean non-reconstructed Nb(111) is investigated by high-resolution scanning tunneling microscopy (STM), as well as a surface reconstruction with a reduced atom density compared to the (111) plane of a bcc crystal resulting from a surface premelting at high annealing temperatures.

cond-mat.supr-con↗

arXiv2022

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$-$TaS$_2$ 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.

cond-mat.supr-con↗

arXiv2021

Coexistence of Antiferromagnetism and Superconductivity in Mn/Nb(110)

We report on the structural and magnetic properties of single and double atomic layers of Mn on a clean and unreconstructed Nb(110) substrate. Low-temperature scanning tunneling spectroscopy measurements reveal a proximity-induced superconducting state in the Mn thin films, which are found to grow pseudomorphically on the Nb surface. Spin-polarized scanning tunneling microscopy measurements reveal a c(2x2) antiferromagnetic order in the Mn layers, with an out-of-plane spin-orientation. First-principles density functional theory calculations confirm the experimentally observed magnetic state, which is understood as the consequence of a strong intra- and inter-layer nearest-neighbor antiferromagnetic exchange coupling. These results are expected to be of importance for the design and the investigation of novel superconducting antiferromagnetic spintronic systems.

cond-mat.mes-hall↗

arXiv2019

Probing weakly hybridized magnetic molecules by spin-polarized tunneling

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 (SP-STM/STS). 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 moire structure, which determines the level of hybridization between the GR/Fe surface pi-system, the molecular ligand pi-orbitals and the molecular Co-ion d-orbital.

physics.app-ph↗