Control of Surface Plasmon Propagation and Terahertz Near-Field Waveforms in a Scanning Tunneling Microscope.

Coupling subcycle THz pulses to a scanning tunneling microscope (STM) enables ultrafast spectroscopy at the atomic scale. This technique critically depends on the shape of the THz near-field waveform in the tunnel junction. We characterize the THz electric field waveform in the STM junction by electro-optic sampling of tip-scattered THz light (-EOS) and pulse correlation using the THz-induced current.

Terahertz spectroscopy of collective charge density wave dynamics at the atomic scale.

Charge density waves are wave-like modulations of a material's electron density that display collective amplitude and phase dynamics. The interaction with atomic impurities induces strong spatial heterogeneity of the charge-ordered phase. Direct real-space observation of phase excitation dynamics of such defect-induced charge modulation is absent.

An Atomic-Scale Vector Network Analyzer.

Electronic devices have been ever-shrinking toward atomic dimensions and have reached operation frequencies in the GHz range, thereby outperforming most conventional test equipment, such as vector network analyzers (VNA). Here the capabilities of a VNA on the atomic scale in a scanning tunneling microscope are implemented. Nonlinearities present in the voltage-current characteristic of atoms and nanostructures for phase-resolved microwave spectroscopy with unprecedented spatial resolution at GHz frequencies are exploited.

Imaging the Breakdown of Ohmic Transport in Graphene.

Ohm's law describes the proportionality of the current density and electric field. In solid-state conductors, Ohm's law emerges due to electron scattering processes that relax the electrical current. Here, we use nitrogen-vacancy center magnetometry to directly image the local breakdown of Ohm's law in a narrow constriction fabricated in a high mobility graphene monolayer.

Quantum stochastic resonance of individual Fe atoms.

Stochastic resonance, where noise synchronizes a system's response to an external drive, is a wide-reaching phenomenon found in noisy systems spanning from the dynamics of neurons to the periodicity of ice ages. Quantum tunneling can extend stochastic resonance to the quantum realm. We demonstrate quantum stochastic resonance for magnetic transitions in atoms by inelastic electron tunneling with a scanning tunneling microscope.

Generation of constant-amplitude radio-frequency sweeps at a tunnel junction for spin resonance STM.

We describe the measurement and successful compensation of the radio-frequency transfer function of a scanning tunneling microscope over a wide frequency range (15.5-35.5 GHz) and with high dynamic range (>50 dB).

Electron paramagnetic resonance of individual atoms on a surface.

We combined the high-energy resolution of conventional spin resonance (here ~10 nano-electron volts) with scanning tunneling microscopy to measure electron paramagnetic resonance of individual iron (Fe) atoms placed on a magnesium oxide film. We drove the spin resonance with an oscillating electric field (20 to 30 gigahertz) between tip and sample. The readout of the Fe atom's quantum state was performed by spin-polarized detection of the atomic-scale tunneling magnetoresistance.

Pasteur's Experiment Performed at the Nanoscale: Manual Separation of Chiral Molecules, One by One.

Understanding the principles of molecular recognition is a difficult task and calls for investigation of appropriate model systems. Using the manipulation capabilities of scanning tunneling microscopy (STM) we analyzed the chiral recognition in self-assembled dimers of helical hydrocarbons at the single molecule level. After manual separation of the two molecules of a dimer with a molecule-terminated STM tip on a Cu(111) surface, their handedness was subsequently determined with a metal atom-terminated tip.

Reaching the magnetic anisotropy limit of a 3d metal atom.

Designing systems with large magnetic anisotropy is critical to realize nanoscopic magnets. Thus far, the magnetic anisotropy energy per atom in single-molecule magnets and ferromagnetic films remains typically one to two orders of magnitude below the theoretical limit imposed by the atomic spin-orbit interaction. We realized the maximum magnetic anisotropy for a 3d transition metal atom by coordinating a single Co atom to the O site of an MgO(100) surface.

Measuring the three-dimensional structure of ultrathin insulating films at the atomic scale.

The increasing technological importance of thin insulating layers calls for a thorough understanding of their structure. Here we apply scanning probe methods to investigate the structure of ultrathin magnesium oxide (MgO) which is the insulating material of choice in spintronic applications. A combination of force and current measurements gives high spatial resolution maps of the local three-dimensional insulator structure.

Obesity - a promoter of allergy?

The prevalence of both obesity and allergy has been increasing throughout the world, leading to the hypothesis that the two are linked to one another. This overview summarizes the results of 34 studies from 2002 to 2012 that investigated a possible contributing effect of increasing body mass on the development and prevalence of various atopic diseases. Obesity was found to clearly affect bronchial asthma.

Bistability in atomic-scale antiferromagnets.

Control of magnetism on the atomic scale is becoming essential as data storage devices are miniaturized. We show that antiferromagnetic nanostructures, composed of just a few Fe atoms on a surface, exhibit two magnetic states, the Néel states, that are stable for hours at low temperature. For the smallest structures, we observed transitions between Néel states due to quantum tunneling of magnetization.

Reduced reactivity and enhanced negative feedback sensitivity of the hypothalamus-pituitary-adrenal axis in chronic whiplash-associated disorder.

Dysregulations of the hypothalamus-pituitary-adrenal (HPA) axis have been discussed as a physiological substrate of chronic pain and fatigue. The aim of the study was to investigate possible dysregulations of the HPA axis in chronic whiplash-associated disorder (WAD). In 20 patients with chronic WAD and 20 healthy controls, awakening cortisol responses as well as a short circadian free cortisol profile were assessed before and after administration of 0.