Sz. Csonka

Conductance of Pd-H Nanojunctions

Results of an experimental study of palladium nanojunctions in a hydrogen environment are presented. Two new hydrogen-related atomic configurations are found, which have conductances of similar to0.5 and similar to1 quantum unit (2e(2)/h). Phonon spectrum measurements demonstrate that these configurations are situated between electrodes containing dissolved hydrogen. The crucial differences compared to the previously studied Pt-H-2 junctions and the possible microscopic realizations of the new configurations in palladium-hydrogen atomic-sized contacts are discussed.

Atomic size oscillations in conductance histograms for gold nanowires and the influence of work hardening

Nanowires of different natures have been shown to self-assemble as a function of stress at the contact between two macroscopic metallic leads. Here we demonstrate for Au wires that the balance between various metastable nanowire configurations is influenced by the microstructure of the starting materials, and we discover a new set of periodic structures, which we interpret as due to the atomic discreteness of the contact size for the three principal crystal orientations.

Regular atomic narrowing of Ni, Fe, and v nanowires resolved by two-dimensional correlation analysis

We present a novel statistical method for the study of stable atomic configurations in breaking nanowires based on the 2D cross-correlation analysis of conductance versus electrode separation traces. Applying this method, we can clearly resolve the typical evolutions of the conductance staircase in some transition metal nanojunctions (Ni, Fe, V) up to high conductance values. In these metals our analysis demonstrates a very well ordered atomic narrowing of the nanowire, indicating a very regular, stepwise decrease of the number of atoms in the minimal cross section of the junction, in contrast to the majority of the metals. All these features are hidden in traditional conductance histograms.

Huge negative differential conductance in Au- H2 molecular nanojunctions

Experimental results showing huge negative differential conductance in gold-hydrogen molecular nanojunctions are presented. The results are analyzed in terms of two-level system (TLS) models: It is shown that a simple TLS model cannot produce peaklike structures in the differential conductance curves, whereas an asymmetrically coupled TLS model gives perfect fit to the data. Our analysis implies that the excitation of a bound molecule to a large number of energetically similar loosely bound states is responsible for the peaklike structures. Recent experimental studies showing related features are discussed within the framework of our model.

Magnetic Field Tuning and Quantum Interference in a Cooper Pair Splitter.

Cooper pair splitting (CPS) is a process in which the electrons of the naturally occurring spin-singlet pairs in a superconductor are spatially separated using two quantum dots. Here, we investigate the evolution of the conductance correlations in an InAs CPS device in the presence of an external magnetic field. In our experiments the gate dependence of the signal that depends on both quantum dots continuously evolves from a slightly asymmetric Lorentzian to a strongly asymmetric Fano-type resonance with increasing field. These experiments can be understood in a simple three-site model, which shows that the nonlocal CPS leads to symmetric line shapes, while the local transport processes can exhibit an asymmetric shape due to quantum interference. These findings demonstrate that the electrons from a Cooper pair splitter can propagate coherently after their emission from the superconductor and how a magnetic field can be used to optimize the performance of a CPS device. In addition, the model calculations suggest that the estimate of the CPS efficiency in the experiments is a lower bound for the actual efficiency.

Nanoscale spin polarization in the dilute magnetic semiconductor (In,Mn)Sb

Results of point-contact Andreev-reflection experiments on (In,Mn)Sb are presented and analyzed in terms of current models of charge conversion at a superconductor-ferromagnet interface. We investigate the influence of surface transparency, and study the crossover from ballistic to diffusive transport regime as contact size is varied. Application of a Nb tip to a (In,Mn)Sb sample with Curie temperature

Pressure dependence of the spin gap in BaVS 3

{T}_{C}

Wet etch methods for InAs nanowire patterning and self-aligned electrical contacts

of 5.4 K allowed the determination of spin polarization when the ferromagnetic phase-transition temperature is crossed. We find a striking difference between the temperature dependence of the local spin polarization and of the macroscopic magnetization, and demonstrate that nanoscale clusters with magnetization close to the saturated value are present even well above the magnetic phase-transition temperature.

Field and temperature induced effects in the surface modification process

We carried out magnetotransport experiments under hydrostatic pressure in order to study the nature of the metal-insulator transition in

Fractional conductance in hydrogen-embedded gold nanowires

{\mathrm{BaVS}}_{3}.