Ophir M. Auslaender

Experimental evidence for resonant tunneling in a luttinger liquid.

We have measured the low-temperature conductance of a one-dimensional island embedded in a single mode quantum wire. The quantum wire is fabricated using the cleaved edge overgrowth technique and the tunneling is through a single state of the island. Our results show that while the resonance line shape fits the derivative of the Fermi function the intrinsic linewidth decreases in a power law fashion as the temperature is reduced. This behavior agrees quantitatively with Furusakis model for resonant tunneling in a Luttinger liquid.

Mechanics of Individual, Isolated Vortices in a Cuprate Superconductor

The ability to wiggle and stretch individual superconducting vortices with nanoscale precision enables unprecedented insight into their dynamics and the properties of the superconductor that supports them. Superconductors often contain quantized microscopic whirlpools of electrons, called vortices, that can be modelled as one-dimensional elastic objects1. Vortices are a diverse area of study for condensed matter because of the interplay between thermal fluctuations, vortex–vortex interactions and the interaction of the vortex core with the three-dimensional disorder landscape2,3,4,5. Although vortex matter has been studied extensively1,6,7, the static and dynamic properties of an individual vortex have not. Here, we use magnetic force microscopy (MFM) to image and manipulate individual vortices in a detwinned YBa2Cu3O6.991 single crystal, directly measuring the interaction of a moving vortex with the local disorder potential. We find an unexpected and marked enhancement of the response of a vortex to pulling when we wiggle it transversely. In addition, we find enhanced vortex pinning anisotropy that suggests clustering of oxygen vacancies in our sample and demonstrates the power of MFM to probe vortex structure and microscopic defects that cause pinning.

Local Measurement of the Superfluid Density in the Pnictide Superconductor Ba ( Fe 1 − x Co x ) 2 As 2 across the Superconducting Dome

We measure the penetration depth λab(T) in Ba(Fe(1-x)Co(x))(2)As(2) using local techniques that do not average over the sample. The superfluid density ρs(T) ≡ 1/λab(T)2 has three main features. First, ρs (T = 0) falls sharply on the underdoped side of the dome. Second, λab(T) is flat at low T at optimal doping, indicating fully gapped superconductivity, but varies more strongly in underdoped and overdoped samples, consistent with either a power law or a small second gap. Third, ρs (T) varies steeply near Tc for optimal and underdoping. These observations are consistent with an interplay between magnetic and superconducting phases.

Finite-Size Effects in Tunneling between Parallel Quantum Wires

We present theoretical calculations and experimental measurements which reveal finite-size effects in the tunneling between two parallel quantum wires, fabricated at the cleaved edge of a GaAs/AlGaAs bilayer heterostructure. Observed oscillations in the differential conductance, as a function of bias voltage and applied magnetic field, provide direct information on the shape of the confining potential. Superimposed modulations indicate the existence of two distinct excitation velocities, as expected from spin-charge separation.

Controlled Manipulation of Individual Vortices in a Superconductor

We report controlled local manipulation of single vortices by low temperature magnetic force microscopy in a thin film of superconducting Nb. We are able to position the vortices in arbitrary configurations and to measure the distribution of local depinning forces. This technique opens up possibilities for the characterization and use of vortices in superconductors.

Interference and zero-bias anomaly in tunneling between Luttinger-liquid wires

We present theoretical calculations and experimental measurements which reveal the Luttinger-liquid (LL) nature of elementary excitations in a system consisting of two quantum wires connected by a long narrow tunnel junction at the edge of a GaAs/AlGaAs bilayer heterostructure. The boundaries of the wires are important and lead to a characteristic interference pattern in measurements on short junctions. We show that the experimentally observed modulation of the conductance oscillation amplitude as a function of the voltage bias can be accounted for by spin-charge separation of the elementary excitations in the interacting wires. Furthermore, boundaries affect the LL exponents of the voltage and temperature dependence of the tunneling conductance at low energies. We show that the measured temperature dependence of the conductance zero-bias dip as well as the voltage modulation of the conductance oscillation pattern can be used to extract the electron interaction parameters in the wires.

Localization Transition in a Ballistic Quantum Wire

The many-body wave function of localized states in one dimension is probed by measuring the tunneling conductance between two parallel wires, fabricated in a

Local characterization of superconductivity inBaFe2(As1−xPx)2

\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}

Single-vortex pinning and penetration depth in superconducting NdFeAsO1−xFx

heterostructure. Tunneling conductance in the presence of a magnetic field perpendicular to the plane of the wires serves as probe of the momentum space wave function of the wires. One of the two wires is driven into the localized regime using a density tuning gate, whereas the other wire, still in the regime of extended electronic states, serves as a momentum spectrometer. As the electron density is lowered to a critical value, the state at the Fermi level abruptly changes from an extended state with a well-defined momentum to a localized state with a wide range of momentum components. The signature of the localized states appears as discrete tunneling features at resonant gate voltages, corresponding to the depletion of single electrons and showing Coulomb-Blockade behavior. Typically 5--10 such features appear, where the one-electron state has a single-lobed momentum distribution, and the few-electron states have double-lobed distributions with peaks at

Disorder-induced power-law response of a superconducting vortex on a plane

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