Reversible doping and fine-tuning of the Dirac point position in the topological crystalline insulator Pb Sn Se sputtering and annealing process.

In this study, we utilize scanning tunneling microscopy and spectroscopy to detail a sputter- and annealing methodology for preparing atomically clean Pb Sn Se(001) surfaces. We examine the impact these processes have on the surface quality, the composition, and the electronic properties. Our findings demonstrate that annealing temperatures between 250 °C and 280 °C produce smooth surfaces while maintaining the topological properties of Pb Sn Se.

Spin Spiral State at a Ferromagnetic Gd Vacuum Interface.

Centrosymmetric bulk magnets made of layered Gd intermetallics had been discovered recently to exhibit helical spin spirals with a wavelength of ≈2  nm that transform into skyrmion lattices at certain magnetic fields. Here we report on the observation of a spin spiral state at the Gd(0001) surface. Spin-polarized scanning tunneling microscopy images show striped regions with a periodicity of about 2 nm.

Diboraperylene Diborinic Acid Self-Assembly on Ag(111)-Kagome Flat Band Localized States Imaged by Scanning Tunneling Microscopy and Spectroscopy.

Replacement of sp-hybridized carbon in polycyclic aromatic hydrocarbons (PAHs) by boron affords electron-deficient π-scaffolds due to the vacant p-orbital of three-coordinate boron with the potential for pronounced electronic interactions with electron-rich metal surfaces. Using a diboraperylene diborinic acid derivative as precursor and a controlled on-surface non-covalent synthesis approach, we report on a self-assembled chiral supramolecular kagome network on an Ag(111) surface stabilized by intermolecular hydrogen-bonding interactions at low temperature. Scanning tunneling microscopy (STM) and spectroscopy (STS) reveal a flat band at ca.

Probing Spin-Dependent Ballistic Charge Transport at Single-Nanometer Length Scales.

The coherent transport of charge and spin is a key requirement of future devices for quantum computing and communication. Scattering at defects or impurities may significantly reduce the coherence of quantum-mechanical states, thereby affecting the device functionality. While numerous methods exist to experimentally assess charge transport, the real-space detection of a material's ballistic spin transport properties with nanometer resolution remains a challenge.

Anisotropic coupling of individual vibrational modes to a Cu(110) substrate.

We present a study on the excitation of individual vibrational modes with ballistic charge carriers propagating along the Cu(110) surface. By means of the molecular nanoprobe technique, where the reversible switching of a molecule-in this case tautomerization of porphycene-is utilized to detect excitation events, we reveal anisotropic coupling of two distinct vibrational modes to the substrate. The N-H bending mode, excited below || ≈ 376 meV, exhibits maxima perpendicular to the rows of the Cu(110) substrate and minima along the rows.

Interaction Effects in a 1D Flat Band at a Topological Crystalline Step Edge.

Step edges of topological crystalline insulators can be viewed as predecessors of higher-order topology, as they embody one-dimensional edge channels embedded in an effective three-dimensional electronic vacuum emanating from the topological crystalline insulator. Using scanning tunneling microscopy and spectroscopy, we investigate the behavior of such edge channels in PbSnSe under doping. Once the energy position of the step edge is brought close to the Fermi level, we observe the opening of a correlation gap.

Real-space resolved surface reactions: deprotonation and metalation of phthalocyanine.

Upon deposition on a surface, molecules can undergo a plethora of changes, such as reactions with adsorbates and surface atoms and catalytic decomposition. Since different reaction pathways may coexist, spatially averaging techniques can be insufficient for the characterization and distinction of all on-surface products. Here, we present a study of single phthalocyanine molecules on a Cu(111) surface which was performed using high-resolution low-temperature STM.

Controlled Formation of Porous 2D Lattices from C -symmetric Ph -Me-Tribenzotriquinacene-OAc.

The on-surface self-assembly of molecules to form holey nanographenes is a promising approach to control the properties of the resulting 2D lattice. Usually, planar molecules are utilized to prepare flat, structurally confined molecular layers, with only a few recent examples of warped precursors. However, control of the superstructures is limited thus far.

Brain proteome profiling implicates the complement and coagulation cascade in multiple system atrophy brain pathology.

Background: Multiple system atrophy (MSA) is a rare, progressive, neurodegenerative disorder presenting glia pathology. Still, disease etiology and pathophysiology are unknown, but neuro-inflammation and vascular disruption may be contributing factors to the disease progression. Here, we performed an ex vivo deep proteome profiling of the prefrontal cortex of MSA patients to reveal disease-relevant molecular neuropathological processes.

Systematic Investigation of the Coupling between One-Dimensional Edge States of a Topological Crystalline Insulator.

The interaction of spin-polarized one-dimensional (1D) topological edge modes localized along single-atomic steps of the topological crystalline insulator Pb_{0.7}Sn_{0.3}Se(001) has been studied systematically by scanning tunneling spectroscopy.

Anisotropic Ballistic Transport Revealed by Molecular Nanoprobe Experiments.

Atomic-scale charge transport properties are not only of significant fundamental interest but also highly relevant for numerous technical applications. However, experimental methods that are capable of detecting charge transport at the relevant single-digit nanometer length scale are scarce. Here we report on molecular nanoprobe experiments on Pd(110), where we use the charge carrier-driven switching of a single cis-2-butene molecule to detect ballistic transport properties over length scales of a few nanometers.

Epigenetic modulation of AREL1 and increased HLA expression in brains of multiple system atrophy patients.

Multiple system atrophy (MSA) is a rare disease with a fatal outcome. To date, little is known about the molecular processes underlying disease development. Its clinical overlap with related neurodegenerative movement disorders underlines the importance for expanding the knowledge of pathological brain processes in MSA patients to improve distinction from similar diseases.

[MR-guided focused ultrasound for treatment of essential tremor].

Essential tremor can be a debilitating disease. In many cases, medical treatment is ineffective and/or holds significant side effects. Surgical treatment using deep brain stimulation is only possible in few and selected cases.

[Stiff person syndrome: still a difficult and overlooked diagnosis].

We present a case of stiff person syndrome (SPS) with a description of the diagnostic challenges and a discussion of the implication of novel antibodies. SPS is a rare neurological disorder presenting with severe rigidity, muscle spasms and impaired gait function, and diagnosis is often delayed due to low awareness. SPS is classically associated with antibodies directed against glutamic acid decarboxylase or amphiphysin.

Indirect chiral magnetic exchange through Dzyaloshinskii-Moriya-enhanced RKKY interactions in manganese oxide chains on Ir(100).

Localized electron spins can couple magnetically via the Ruderman-Kittel-Kasuya-Yosida interaction even if their wave functions lack direct overlap. Theory predicts that spin-orbit scattering leads to a Dzyaloshinskii-Moriya type enhancement of this indirect exchange interaction, giving rise to chiral exchange terms. Here we present a combined spin-polarized scanning tunneling microscopy, angle-resolved photoemission, and density functional theory study of MnO chains on Ir(100).

A novel PDGFRB sequence variant in a family with a mild form of primary familial brain calcification: a case report and a review of the literature.

Background: Primary familial brain calcification is a rare autosomal dominant or recessive neurodegenerative disease, characterized by bilateral brain calcifications in different areas of the brain. It is a clinically heterogeneous disease and patients are reported to exhibit a wide spectrum of neurological and psychiatric symptoms. Mutations in five genes have been identified so far including SLC20A2, PDGFRB, PDGFB, XPR1, and MYORG.

Jahn-Teller Splitting in Single Adsorbed Molecules Revealed by Isospin-Flip Excitations.

Scanning tunneling spectroscopy measurements of Mn phthalocyanine (MnPc) molecules adsorbed on (sqrt[3]×sqrt[3]) surface alloys show single inelastic steps at exclusively positive or negative bias strongly depending on the tip position. This is in contrast to conventional molecular excitation thresholds, which are independent of the current direction and therefore always occur at both positive and negative bias. This polarity selectivity is found to coincide with the spatial distribution of occupied and empty orbitals.

Imprinting Directionality into Proton Transfer Reactions of an Achiral Molecule.

Directionality is key for the functionality of molecular machines, which is often achieved by built-in structural chiralities. Here, we present a scanning tunneling microscopy study of achiral HPc and HPc molecules that acquire chirality by adsorption onto a Ag(100) surface. The adsorption-geometry-induced chirality is caused by a -29° (+29°) rotation of the molecules with respect to the [011] substrate direction, resulting in tautomerization processes that preferentially occur in a clockwise (counterclockwise) direction.

Magnetic Ground State Stabilized by Three-Site Interactions: Fe/Rh(111).

We report the direct observation of a theoretically predicted magnetic ground state in a monolayer Fe on Rh(111), which is referred to as an up-up-down-down (↑↑↓↓) double-row-wise antiferromagnetic spin structure, using spin-polarized scanning tunneling microscopy. This exotic phase, which exists in three orientational domains, is revealed by experiments with magnetic probe tips performed in external magnetic fields. It is shown that a hitherto unconsidered four-spin-three-site beyond-Heisenberg interaction distinctly contributes to the spin coupling of atoms with S≥1 spins.

Analyzing the Wave Nature of Hot Electrons with a Molecular Nanoprobe.

We report on a novel method, the molecular nanoprobe (MONA) technique, which allows us to measure the nanoscale quasiparticle transport between two arbitrary surface points. In these experiments, hot electrons are injected into the sample surface from the probe tip of a scanning tunneling microscope (STM) and detected by tautomerization switching events of a single deprotonated phthalocyanine (HPc) molecule. By making use of atom-by-atom-engineered interferometers on a Ag(111) surface, we demonstrate that the quantum-mechanical wave nature of hot electrons leads to characteristic oscillations of the molecule tautomerization probability.

Remote Single-Molecule Switching: Identification and Nanoengineering of Hot Electron-Induced Tautomerization.

Molecular electronics where single molecules perform basic functionalities of digital circuits is a fascinating concept that one day may augment or even replace nowadays semiconductor technologies. The tautomerization of molecules, that is, the bistable functional position of hydrogen protons within an organic frame, has recently been intensively discussed as a potential avenue toward nanoscale switches. It has been shown that tautomerization can be triggered locally or nonlocally, that is, by a scanning tunneling microscope (STM) tip positioned directly above or in close vicinity to the molecule.

Breaking Degeneracy of Tautomerization-Metastability from Days to Seconds.

We present a detailed study of the tautomerization, that is, the switching of hydrogen protons, between different sites in the molecular frame of phthalocyanine (HPc) on a Ag(111) substrate by means of scanning tunneling microscopy (STM) and STM-based pump-and-sample techniques. Our data reveal that the symmetry mismatch between the substrate and the molecular frame lifts the energetic degeneracy of the two HPc tautomers. Their energy difference is so large that only one tautomer can be found in the ground state.

Robust spin-polarized midgap states at step edges of topological crystalline insulators.

Topological crystalline insulators are materials in which the crystalline symmetry leads to topologically protected surface states with a chiral spin texture, rendering them potential candidates for spintronics applications. Using scanning tunneling spectroscopy, we uncover the existence of one-dimensional (1D) midgap states at odd-atomic surface step edges of the three-dimensional topological crystalline insulator (Pb,Sn)Se. A minimal toy model and realistic tight-binding calculations identify them as spin-polarized flat bands connecting two Dirac points.