Abstract Primary cilia are sensory organelles present in many cell types, partaking in various signaling processes. Primary cilia of pancreatic beta cells play pivotal roles in paracrine signaling and their dysfunction is linked to diabetes. Yet, the structural basis for their functions is unclear. We present three-dimensional reconstructions of beta cell primary cilia by electron and expansion microscopy. These cilia are spatially confined within deep ciliary pockets or narrow spaces between cells, lack motility components and display an unstructured axoneme organization. Furthermore, we observe a plethora of beta cell cilia-cilia and cilia-cell interactions with other islet and non-islet cells. Most remarkably, we have identified and characterized axo-ciliary synapses between beta cell cilia and the cholinergic islet innervation. These findings highlight the beta cell cilia’s role in islet connectivity, pointing at their function in integrating islet intrinsic and extrinsic signals and contribute to understanding their significance in health and diabetes.

Chemical synapses between axons and dendrites mediate neuronal intercellular communication. Here, we describe a synapse between axons and primary cilia: the axo-ciliary synapse. Using enhanced focused ion beam-scanning electron microscopy on samples with optimally preserved ultrastructure, we discovered synapses between brainstem serotonergic axons and the primary cilia of hippocampal CA1 pyramidal neurons. Functionally, these cilia are enriched in a ciliary-restricted serotonin receptor, the 5-hydroxytryptamine receptor 6 (5-HTR6). Using a cilia-targeted serotonin sensor, we show that opto- and chemogenetic stimulation of serotonergic axons releases serotonin onto cilia. Ciliary 5-HTR6 stimulation activates a non-canonical Gαq/11-RhoA pathway, which modulates nuclear actin and increases histone acetylation and chromatin accessibility. Ablation of this pathway reduces chromatin accessibility in CA1 pyramidal neurons. As a signaling apparatus with proximity to the nucleus, axo-ciliary synapses short circuit neurotransmission to alter the postsynaptic neuron's epigenetic state.

Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) generates 3D datasets optimally suited for segmentation of cell ultrastructure and automated connectome tracing but is limited to small fields of view and is therefore incompatible with the new generation of ultrafast multibeam SEMs. In contrast, section-based techniques are multibeam-compatible but are limited in z-resolution making automatic segmentation of cellular ultrastructure difficult. Here we demonstrate a novel 3D electron microscopy technique, Gas Cluster Ion Beam SEM (GCIB-SEM), in which top-down, wide-area ion milling is performed on a series of thick sections, acquiring < 10 nm isotropic datasets of each which are then stitched together to span the full sectioned volume. Based on our results, incorporating GCIB-SEM into existing single beam and multibeam SEM workflows should be straightforward and should dramatically increase reliability while simultaneously improving z-resolution by a factor of 3 or more.

The endoplasmic reticulum (ER) is an expansive, membrane-enclosed organelle that plays crucial roles in numerous cellular functions. We used emerging superresolution imaging technologies to clarify the morphology and dynamics of the peripheral ER, which contacts and modulates most other intracellular organelles. Peripheral components of the ER have classically been described as comprising both tubules and flat sheets. We show that this system consists almost exclusively of tubules at varying densities, including structures that we term ER matrices. Conventional optical imaging technologies had led to misidentification of these structures as sheets because of the dense clustering of tubular junctions and a previously uncharacterized rapid form of ER motion. The existence of ER matrices explains previous confounding evidence that had indicated the occurrence of ER "sheet" proliferation after overexpression of tubular junction-forming proteins.

It is demonstrated theoretically and experimentally that the low energy density of states N(E) is described by a singular V-shape form N(E)=N(0)(H)+alpha|E|+O(E2) for all clean superconductors in a vortex state, irrespective of the underlying gap structure. The linear term alpha|E| which has not been recognized so far is obtained by exactly evaluating the vortex contribution. Based on microscopic Eilenberger theory N(E) is evaluated for the isotropic gap, line, and point-node gaps to yield a V-shape N(E). Scanning tunneling spectroscopy-STM experiments on NbSe2 and YNi2B2C give direct evidence for this. We provide arguments on the significance of this finding and on the relevance to other experiments.

Much attention has been focused on exotic super- conductors, ranging from high Tc cuprates, Ce and U based heavy Fermion materials, filled skutterdites such as PrOs4Sb12 to cobaltites NaxCoO2� yH2O(1, 2). The identification of the Cooper-pair symmetry consists of two parts; its parity and the gap structure. The former is responsible for the spin structure of a pair which is either singlet or triplet. This can be probed by directly measuring the spin susceptibility through NMR Knight shift experiment under an applied field. The latter gap structure is related to the orbital symmetry of a Cooper pair. This can be probed by thermodynamic measure- ments via a variety of experimental methods, such as temperature (T) dependence of specific heat C(T), ther- mal conductivity �(T) or nuclear relaxation time T1(T) in NMR-NQR experiments. The basic principle of this identification for the gap structure is based on the fact that the energy (E) de- pendence of the density of states (DOS) N(E) near the Fermi level, which characterizes low-lying excitations of a given gap structure. This N(E) gives rise to a specific power law temperature dependence(2). For example, the line (point) node gap yields a C(T)/T ∼ T(T 2) behavior in specific heat, �(T) ∼ T 2 (T 3) for thermal conduc- tivity and T −1 1 ∼ T 3 (T 5) in nuclear relaxation time at lower T region. This comes from the fact that the den- sity of states is described by a specific functional form; N(E) ∝ |E| for line node and N(E) ∝ E2 for point node, through which a simple power counting rule yields spe- cific power law indices in various quantities. Therefore it is decisive to precisely understand the DOS form N(E) in order to identify the gap structure. We have attained a lot of information of the pairing symmetry in various superconductors by this way(2).

Using a single electron transistor mounted on the tip of a scan probe microscope we have imaged the electronic compressibility of a two-dimensional electron gas in the integer quantum Hall regime. The compressibility images show quasi-insulating “incompressible” strips that separate region of electron liquid of near integer filling. The strips follow the contours of constant electron density that match exact occupancy of the Landau levels, and shift accordingly with magnetic field and electron density changes. The surface electrostatic potential distribution has an overall correlation with the compressibility patterns and the density contours marked by them and an abrupt step at the boundaries that provides a direct measure of the energy gap between the Landau levels.

We have imaged the electronic compressibility of a two-dimensional electron gas in the integer quantum Hall regime. The compressibility images show quasi-insulating “incompressible” strips that separate region of electron liquid of near integer filling. The strips follow the contours of constant electron density that match exact occupancy of the Landau levels, and shift accordingly with magnetic field and electron density changes. The surface electrostatic potential distribution has an overall correlation with the compressibility patterns and the density contours marked by them and an abrupt step, at the boundaries, that provides a direct measure of the energy gap between the Landau levels.

The concept of electron localization has long been accepted to be essential to the physics of the quantum Hall effect1,2 in a two-dimensional electron gas. The exact quantization of the Hall resistance and the zero of the diagonal resistance over a range of filling factors close to integral are attributed to the localization of electronic states at the Fermi level in the interior of the gas. As the electron density is changed, charging of the individual localized states may occur by single-electron jumps3,4, causing associated oscillations in the local electrostatic potential. Here we search for such a manifestation of localized states in the quantum Hall regime, using a scanning electrometer probe5,6. We observe localized potential signals, at numerous locations, that oscillate with changing electron density. In general, the corresponding spatial patterns are complex, but well-defined objects are often seen which evidently arise from individual localized states. These objects interact, and at times form a lattice-like arrangement.

Microscopic images of the local electron compressibility, electrostatic potential, and current-induced Hall voltage of a two-dimensional sheet of electrons in the quantum Hall regime are acquired using a single-electron transistor as a scanned probe. Regions identified as differing in quantum state (Landau level) occupancy of the electrons appear in interrelated ways in all of these properties. The compressibility images show quasi-insulating “incompressible” strips, associated with edge states that bound these regions. These strips follow the contours of a constant electron density that match exact occupancy of Landau levels, and shift accordingly with magnetic field and electron density changes. The potential distribution has an overall correlation with the density contours marked by the incompressible strips and a step across the strips that provides a direct measure of the energy gap between Landau levels. The Hall voltage and the inferred current flow patterns are also guided by these strips.

The coulomb blockade effect of a single electron transistor is harnessed to make an electrometer probe capable of imaging electric properties of a sample at 100 nm resolution. The sensitivity is such that it can image individual electrons that have been photoexcited, a sensitivity adequate so that a number of other mesoscopic phenomenon can be directly imaged.

We report direct, high resolution images of the magnetic field above a superconducting wire grid as applied flux penetrates into an initially empty state or into a state with half the plaquettes containing a magnetic quantum. We find two qualitatively different initial approaches to equilibrium: in wide structures for the former, or with long, linear structures for the latter case. In the approach to an empty state, we observe the formation of residual quasi-bound magnetic vortex/anti-vortex pairs.

A spatial distribution of luminescent centers with sharp (<0.1meV), spectrally distinct emission lines are revealed in a GaAs/AlGaAs quantum wells[1] using low temperature nearfield scanning optical microscopy [2], a technique where a subwavelength source and/or detector of light in close proximity (<40nm) to the sample is used to probe with a resolution beyond the diffraction limit. These centers are the energy eigenstate components that comprise the inhomogeneously broadened line shape observed in standard far-field photoluminescence. Measurements as a function of temperature, magnetic field, and well width establish that these centers arise from excitons localized by quantum well thickness fluctuations. For sufficiently narrow wells, virtually all emission originates from such centers. Quantities such as diffusion (both thermal and tunneling), lateral confinement energies, lifetimes, g-factors from magnetic field induced spin splittings, diamagnetic energy coefficients of the luminescent states can now be measured at a site-by-site individual quantum level rather than averaged over a statistical distribution. This information can be used in turn to provide a direct local picture of the interface fluctuations and how they vary under different MBE growth conditions. Near-field microscopy/spectroscopy provides a means to access energies and homogeneous line widths for the individual eigenstates of these centers, and thus allows the luminescent components to be identified and characterized with the extraordinary detail previously limited to the realm of atomic physics.

Luminescent centers with sharp (<0.07 millielectron volt), spectrally distinct emission lines were imaged in a GaAs/AIGaAs quantum well by means of low-temperature near-field scanning optical microscopy. Temperature, magnetic field, and linewidth measurements establish that these centers arise from excitons laterally localized at interface fluctuations. For sufficiently narrow wells, virtually all emission originates from such centers. Near-field microscopy/spectroscopy provides a means to access energies and homogeneous line widths for the individual eigenstates of these centers, and thus opens a rich area of physics involving quantum resolved systems.

Summary form only given. Low temperature near-field scanning optical microscopy/spectroscopy has proven useful in characterization of quantum confined semiconductor structures even to the extent of revealing the individual optically active quantum constituents of such a system. Specifically, sharp (<0.07 meV), spectrally distinct emission lines of a GaAs/AlGaAs quantum well can be imaged at a specific spatial location, or as a spectral evolution image as the probe is scanned along a line across the surface, or as a real space image at a specific luminescence wavelengths. Temperature, magnetic field, and line width measurements establish that these luminescence centers arise from excitons localized at interface fluctuations

A high resolution scanning Hall probe microscope is used to spatially resolve vortices in high temperature superconducting Bi2Sr2CaCu2O8+(delta) crystals. We observe a partially ordered vortex lattice at several different applied magnetic fields and temperatures. At higher temperatures, a limited amount of vortex re-arrangement is observed, but most vortices remain fixed for periods long compared to the imaging time of several hours even at temperatures as high as 75 degree(s)K (the superconducting transition temperature for these crystals is approximately 84 degree(s)K). A measure of these local magnetic penetration depth can be obtained from a fit to the surface field of several neighboring vortices, and has been measured as a function of temperature. In particular, we have measured the zero temperature penetration depth and found it to be 275 +/- 40 nm.

Individual vortices and the Abrikosov flux lattice are imaged with a low temperature scanning tunneling microscope on 2H-NbSe2. The quasiparticle wavefunctions of different energy are highlighted by tunneling at various bias voltages. The sequence of different energy bound states wavefunction images reveal a continuously evolving star shaped pattern. These patterns are consistent with previously acquired spectral evolution data, and may result from the interplay of charge density waves and superconductivity.

We report direct observations of vortices in a square superconducting wire grid imaged using scanning Hall probe microscopy. Real space images of vortex configurations are obtained as a function of the flux per unit cell f by measuring the local magnetic field just above the sample. At f = 1/2 we observe domains of the checkerboard ground state. As f is reduced from 1/2 to 1/3 vacancies first penetrate the grain boundaries and then the checkerboard domains. Near f = 1/3 we observe domains of the 1/3 staircase ground state. Heating the sample close to T(c) produces correlated vortex hopping.