Compact localized boundary states in a quasi-1D electronic diamond-necklace chain.

Zero-energy modes localized at the ends of one-dimensional (1D) wires hold great potential as qubits for fault-tolerant quantum computing. However, all the candidates known to date exhibit a wave function that decays exponentially into the bulk and hybridizes with other nearby zero-modes, thus hampering their use for braiding operations. Here, we show that a quasi-1D diamond-necklace chain exhibits an unforeseen type of robust boundary state, namely compact localized zero-energy modes that do not decay into the bulk. We find that this state emerges due to the presence of a latent symmetry in the system. We experimentally realize the diamond-necklace chain in an electronic quantum simulator setup.

The effect of anti-TNF on renal function in patients with ankylosing spondylitis: a prospective cohort study.

BACKGROUND: Biologicals, such as anti-tumor necrosis factor (anti-TNF), reduce cardiovascular disease (CVD) in patients with inflammatory rheumatic diseases. Impaired renal function is a known predictor of CVD and elevated in ankylosing spondylitis (AS). OBJECTIVE: To assess the effect of anti-TNF on renal function in patients with AS and whether anti-TNF use is safe in AS patients with pre-existing risk factors for renal decline. METHOD: Biological-naïve consecutive AS patients treated with etanercept or adalimumab were prospectively followed from 2005 to 2014. Renal function was determined by calculation of the estimated glomerular filtration rate (eGFR), estimated with the abbreviated modification of diet in renal disease (MDRD) formula. The effect of anti-TNF on eGFR was analyzed using mixed model analysis. RESULTS: 211 AS patients were followed for a median of 156 (36-286) weeks. Overall mixed model analyses showed a significant decrease of eGFR over time (ß = - 0.040, p = 0.000), although this association did not remain significant after adjustment for responding to anti-TNF, alcohol use, disease duration, body mass index (BMI), C-reactive protein (CRP), and disease activity (ß = - 0.018, p = 0.094). However, patients with pre-existing risk factors for renal decline did have a significant change in eGFR over time (ß = - 0.029, p = 0.006). CONCLUSIONS: We found a significant change in eGFR over time, although this small decrease was not clinically relevant. This study further demonstrates that anti-TNF does not affect renal function in AS patients with and without existing risk factors for renal decline, which means that use of anti-TNF is safe concerning renal function in patients with AS. Key Points • Previous studies showed that biologicals, such as anti-tumor necrosis factor (anti-TNF), reduce cardiovascular disease (CVD) in patients with inflammatory rheumatic diseases, such as ankylosing spondylitis (AS). • Impaired renal function is a known predictor of CVD, and also a known concern for many AS patients. • Use of anti-TNF is safe with regard to renal function in patients with AS. • The effect of anti-TNF on CVD in AS patients does not seem to be mediated by changes in renal function.

Edge-Dependent Topology in Kekulé Lattices.

The boundary states of topological insulators are thought not to depend on the precise atomic structure of the boundary. A recent theoretical study showed that, for topological crystalline insulators with given bond strengths, topological states should only emerge for certain edge geometries. We experimentally probe this effect by creating artificial Kekulé lattices with different atomically well-defined edge geometries and hopping ratios in a scanning tunneling microscope. Topological edge modes are found to only appear for specific combinations of edge geometry and hopping ratio.

Robust zero-energy modes in an electronic higher-order topological insulator.

Quantum simulators are essential tools for understanding complex quantum materials. Platforms based on ultracold atoms in optical lattices and photonic devices have led the field so far, but the basis for electronic quantum simulators is now being developed. Here, we experimentally realize an electronic higher-order topological insulator (HOTI). We create a breathing kagome lattice by manipulating carbon monoxide molecules on a Cu(111) surface using a scanning tunnelling microscope. We engineer alternating weak and strong bonds to show that a topological state emerges at the corner of the non-trivial configuration, but is absent in the trivial one. Different from conventional topological insulators, the topological state has two dimensions less than the bulk, denoting a HOTI. The corner mode is protected by a generalized chiral symmetry, which leads to a particular robustness against perturbations. Our versatile approach to designing artificial lattices holds promise for revealing unexpected quantum phases of matter.

Design and characterization of electrons in a fractal geometry.

The dimensionality of an electronic quantum system is decisive for its properties. In one dimension electrons form a Luttinger liquid and in two dimensions they exhibit the quantum Hall effect. However, very little is known about the behavior of electrons in non-integer, or fractional dimensions1. Here, we show how arrays of artificial atoms can be defined by controlled positioning of CO molecules on a Cu (111) surface2-4, and how these sites couple to form electronic Sierpinski fractals. We characterize the electron wave functions at different energies with scanning tunneling microscopy and spectroscopy and show that they inherit the fractional dimension. Wave functions delocalized over the Sierpinski structure decompose into self-similar parts at higher energy, and this scale invariance can also be retrieved in reciprocal space. Our results show that electronic quantum fractals can be artificially created by atomic manipulation in a scanning tunneling microscope. The same methodology will allow future study to address fundamental questions about the effects of spin-orbit interaction and a magnetic field on electrons in non-integer dimensions. Moreover, the rational concept of artificial atoms can readily be transferred to planar semiconductor electronics, allowing for the exploration of electrons in a well-defined fractal geometry, including interactions and external fields.

Electronic components embedded in a single graphene nanoribbon.

The use of graphene in electronic devices requires a band gap, which can be achieved by creating nanostructures such as graphene nanoribbons. A wide variety of atomically precise graphene nanoribbons can be prepared through on-surface synthesis, bringing the concept of graphene nanoribbon electronics closer to reality. For future applications it is beneficial to integrate contacts and more functionality directly into single ribbons by using heterostructures. Here, we use the on-surface synthesis approach to fabricate a metal-semiconductor junction and a tunnel barrier in a single graphene nanoribbon consisting of 5- and 7-atom wide segments. We characterize the atomic scale geometry and electronic structure by combined atomic force microscopy, scanning tunneling microscopy, and conductance measurements complemented by density functional theory and transport calculations. These junctions are relevant for developing contacts in all-graphene nanoribbon devices and creating diodes and transistors, and act as a first step toward complete electronic devices built into a single graphene nanoribbon.Adding functional electronic components to graphene nanoribbons requires precise control over their atomic structure. Here, the authors use a bottom-up approach to build a metal-semiconductor junction and a tunnel barrier directly into a single graphene nanoribbon, an exciting development for graphene-based electronic devices.

Long-range orientation and atomic attachment of nanocrystals in 2D honeycomb superlattices.

Oriented attachment of synthetic semiconductor nanocrystals is emerging as a route for obtaining new semiconductors that can have Dirac-type electronic bands such as graphene, but also strong spin-orbit coupling. The two-dimensional (2D) assembly geometry will require both atomic coherence and long-range periodicity of the superlattices. We show how the interfacial self-assembly and oriented attachment of nanocrystals results in 2D metal chalcogenide semiconductors with a honeycomb superlattice. We present an extensive atomic and nanoscale characterization of these systems using direct imaging and wave scattering methods. The honeycomb superlattices are atomically coherent and have an octahedral symmetry that is buckled; the nanocrystals occupy two parallel planes. Considerable necking and large-scale atomic motion occurred during the attachment process.

Controlling the orbital sequence in individual Cu-phthalocyanine molecules.

We report on the controlled change of the energetic ordering of molecular orbitals. Negatively charged copper(II)phthalocyanine on NaCl/Cu(100) undergoes a Jahn-Teller distortion that lifts the degeneracy of two frontier orbitals. The energetic order of the levels can be controlled by Au and Ag atoms in the vicinity of the molecule. As only one of the states is occupied, the control of the energetic order is accompanied by bistable changes of the charge distribution inside the molecule, rendering it a bistable switch.

Hypothalamic NPY, AGRP, and POMC mRNA responses to leptin and refeeding in mice.

Food deprivation (FD) increases hypothalamic neuropeptide Y (NPY) and agouti-related protein (AGRP) mRNA levels and decreases proopiomelanocortin (POMC) mRNA levels; refeeding restores these levels. We determined the time course of changes in hypothalamic NPY, AGRP, and POMC mRNA levels on refeeding after 24 h FD in C57BL mice by in situ hybridization. After 24 h deprivation, mice were refed with either chow or a palatable mash containing no calories or were injected with murine leptin (100 microg) without food. Mice were perfused 2 or 6 h after treatment. Food deprivation increased hypothalamic NPY mRNA (108 +/- 6%) and AGRP mRNA (78 +/- 7%) and decreased hypothalamic POMC mRNA (-15 +/- 1%). Refeeding for 6 h, but not 2 h, was sufficient to reduce (but not restore) NPY mRNA, did not affect AGRP mRNA, and restored POMC mRNA levels to ad libitum control levels. Intake of the noncaloric mash had no effect on mRNA levels, and leptin administration after deprivation (at a dose sufficient to reduce refeeding in FD mice) was not sufficient to affect mRNA levels. These results suggest that gradual postabsorptive events subsequent to refeeding are required for the restoration of peptide mRNA to baseline levels after food deprivation in mice.

The effect of food deprivation and experimental diabetes on orexin and NPY mRNA levels.

Although exogenous orexin can induce feeding, reports of increased orexin gene expression after caloric manipulations have been inconsistent. We hypothesized that orexin gene expression is increased only by extreme negative energy balance challenges. We measured hypothalamic orexin and NPY mRNA by in situ hybridization and orexin-A immunoreactivity in rats after food deprivation, streptozotocin-induced diabetes, and combined deprivation and diabetes. Neither food deprivation, nor diabetes, nor the combination affected orexin mRNA levels, although orexin-A immunoreactivity was increased by diabetes. NPY mRNA levels were increased by either treatment. These results suggest that increased orexin gene expression is not a consistent correlate of negative energy balance challenges.