Lukasz Plucinski

Van der Waals (vdW) heterostructures allow the engineering of magnetic and electronic properties via interfacial orbital hybridization and charge transfer. The resulting electric fields can give rise to Rashba spin-orbit coupling and Dzyaloshinskii-Moriya interactions, which may stabilize novel two-dimensional magnetic phases. While such emergent magnetic ‘interphases’ may offer a promising platform for spin-based electronics, direct spectroscopic evidence for them is still lacking. Here, we report electric-field tunable Zeeman effects with Landé g -factors up to ≈ 230 at the interface of graphene and the vdW ferromagnet Fe ₃ GeTe ₂ . They arise from an interplay of local-moment canting and the itinerant orbital moments of Fe ₃ GeTe ₂ , producing a giant asymmetric level splitting. Exploiting the inelastic phonon gap of graphene, scanning tunneling spectroscopy allows us to access the buried interface properties, and quantify Faraday-like screening. Our findings provide new insights and opportunities for electrically controlled interface magnetism, e.g. for spintronics and orbitronics devices.

Magnetic kagome metals host complex electronic states and real-space magnetic textures, but their small and temperature-dependent magnetic domains make experimental access difficult. Here we show that micro-focused circular-dichroic photoemission spectroscopy enables spectroscopic access to individual magnetic domains in the kagome metal DyMn ₆ Sn ₆ at low temperature. By tuning to element-specific electronic states, we image domain contrast associated with Dy 4 f levels and detect corresponding signatures from Mn core states. The energy dependence of the dichroic response is consistent with modeling and indicates ferrimagnetic alignment between Dy and Mn local moments. Measurements of Mn 3 d -derived valence bands, supported by first-principles calculations, reveal features related to orbital magnetization. These results establish element- and orbital-resolved spectroscopy of single magnetic domains and enable studies of magnetic textures and electronic structure in complex magnetic quantum materials.

We visualize the topological ladder and band inversions in PtTe 2 using spin-polarized photoemission spectroscopy augmented by three-dimensional momentum imaging. This approach enables the detection of spin polarization in dispersive bands and provides access to topological properties beyond the reach of conventional methods. Extensive mapping of spin-momentum space reveals distinct topological surface states, including a surface Dirac cone at a binding energy E B ∼ 2.3 eV and additional states at E B ∼ 1.6 eV , E B ∼ 1.0 eV , and near the Fermi level. The electronic structure analysis demonstrates strong hybridization between Pt and Te atomic orbitals, confirming the nontrivial topology of these surface states. Furthermore, by comparison to one-step model photoemission calculations, we identify a robust correlation between the initial-state and measured spin polarizations while revealing asymmetries in specific experimental spin textures. These asymmetries, absent in the initial states due to symmetry constraints, arise from the breaking of time-reversal symmetry during the photoemission process, emphasizing the crucial influence of symmetries on experimental signatures of topology. A phase analysis of ladder states in real space suggests a route to probe them using photoemission, paving the way towards spectroscopic access to the quantum geometric tensor.

Recent years have witnessed a steady progress towards blending two-dimensional quantum materials into technology, with future applications often rooted in the electronic structure. Since crossings and inversions of electronic bands with different orbital characters determine intrinsic quantum transport properties, knowledge of the orbital character is essential. Here, we benchmark angle-resolved photoelectron emission spectroscopy (ARPES) as a tool to experimentally derive orbital characters. For this purpose we study the valence electronic structure of two technologically relevant quantum materials, graphene and WSe 2 , and focus on circular dichroism that is believed to provide sensitivity to the orbital angular momentum. We analyze the contributions related to angular atomic photoionization profiles, interatomic interference, and multiple scattering. Regimes in which initial-state properties could be disentangled from the ARPES maps are critically discussed and the potential of using circular dichroic ARPES as a tool to investigate the spin polarization of initial bands is explored. For the purpose of generalization, results from two additional materials, GdMn 6 Sn 6 and PtTe 2 , are presented in addition. This research demonstrates rich complexity of the underlying physics of circular dichroic ARPES, providing insights that will shape the interpretation of both past and future circular-dichroic ARPES studies.

Recent years have witnessed a steady progress towards blending 2D quantum materials into technology, with future applications often rooted in the electronic structure. Since crossings and inversions of electronic bands with different orbital characters determine intrinsic quantum transport properties, knowledge of the orbital character is essential. Here, we benchmark angle-resolved photoelectron emission spectroscopy (ARPES) as a tool to experimentally derive orbital characters. For this purpose we study the valence electronic structure of two technologically relevant quantum materials, graphene and WSe$_2$, and focus on circular dichroism that is believed to provide sensitivity to the orbital angular momentum. We analyze the contributions related to angular atomic photoionization profiles, interatomic interference, and multiple scattering. Regimes in which initial-state properties could be disentangled from the ARPES maps are critically discussed and the potential of using circular-dichroic ARPES as a tool to investigate the spin polarization of initial bands is explored. For the purpose of generalization, results from two additional materials, GdMn$_6$Sn$_6$ and PtTe$_2$ are presented in addition. This research demonstrates rich complexity of the underlying physics of circular-dichroic ARPES, providing new insights that will shape the interpretation of both past and future circular-dichroic ARPES studies.

Over the past three decades, the growth of Bi thin films has been extensively explored due to their potential applications in various fields such as thermoelectrics, ferroelectrics, and recently for topological and neuromorphic applications, too. Despite significant research efforts in these areas, achieving reliable and controllable growth of high-quality Bi thin-film allotropes has remained a challenge. Previous studies have reported the growth of trigonal and orthorhombic phases on various substrates yielding low-quality epilayers characterized by surface morphology. In this study, we present a systematic growth investigation, enabling the high-quality growth of Bi epilayers on Bi-terminated Si (111) 1 × 1 surfaces using molecular beam epitaxy. Our work yields a phase map that demonstrates the realization of trigonal, orthorhombic, and pseudocubic thin-film allotropes of Bi. In-depth characterization through X-ray diffraction (XRD) techniques and scanning transmission electron microscopy (STEM) analysis provides a comprehensive understanding of phase segregation, phase stability, phase transformation, and phase-dependent thickness limitations in various Bi thin-film allotropes. Our study provides recipes for the realization of high-quality Bi thin films with desired phases, offering opportunities for the scalable refinement of Bi into quantum and neuromorphic devices and for revisiting technological proposals for this versatile material platform from the past 30 years.