We present magnetization measurements of mesoscopic superconducting niobium loops containing a ferromagnetic (PdNi) pi junction. The loops are prepared on top of the active area of a micro-Hall sensor based on high mobility GaAs/AlGaAs heterostructures. We observe asymmetric switching of the loop between different magnetization states when reversing the sweep direction of the magnetic field. This provides evidence for a spontaneous current induced by the intrinsic phase shift of the pi junction. In addition, the presence of the spontaneous current near zero applied field is directly revealed by an increase of the magnetic moment with decreasing temperature, which results in half integer flux quantization in the loop at low temperatures.

The scanning metallic tip of a scanning force microscope was coupled capacitively to electrons confined in a lithographically defined gate-tunable quantum dot at a temperature of 300 mK. Single electrons were made to hop on or off the dot by moving the tip or by changing the tip bias voltage owing to the Coulomb-blockade effect. Spatial images of conductance resonances map the interaction potential between the tip and individual electronic quantum dot states. Under certain conditions this interaction is found to contain a tip-voltage induced and a tip-voltage-independent contribution.

We present measurements of the fourth and fifth cumulants of the distribution of transmitted charge in a tunable quantum dot. We investigate how the measured statistics is influenced by the finite bandwidth of the detector and by the finite measurement time. By including the detector when modeling the system, we use the theory of full counting statistics to calculate the noise levels for the combined system. The predictions of the finite-bandwidth model are in good agreement with measured data. PACS numbers:Current fluctuations in mesoscopic systems have been extensively studied due to the extra information they give in comparison to measurements of the mean current [1]. The focus has traditionally been on investigations of the shot-noise, which for classical systems arises due to the discreteness of the electron charge. The theory of full counting statistics (FCS) was introduced as a new way of examining current fluctuations [2]. With the FCS, fluctuations are studied by counting the number of electrons that pass through a conductor within a fixed period of time. This gives direct access to the probability distribution function p t0 (N ), which is the probability that N electrons are transferred within a time interval of length t 0 . From the distribution function, not only the shot noise but also correlations of higher order can be calculated.The third moment of a tunneling current has been shown to be independent of the thermal noise [3,4], thus making it a potential tool for investigating electronelectron interactions even at elevated temperatures. Higher order moments in strongly interacting systems are predicted to depend heavily on both the conductance [5] and on the internal level structure [6] of the system. Determining higher order moments may therefore give a more complete characterization of the electron transport process. This can be of importance for realizing measurements of electron correlation and entanglement effects in quantum dots [7,8].Experimentally, the third moment of the current distribution function has been measured for a tunnel junction [9] as well as for a single quantum dot (QD) [10,11] and a double QD [3]. In quantum optics, higher order moments are routinely measured in order to study entanglement and coherence effects of the electromagnetic field [12]. Here, we set out to measure the fourth and fifth cumulant of the distribution function for charge transport * Electronic address: simongus@phys.ethz.ch through a QD.In general, experimental measurements of FCS for electrons are difficult to achieve due to the need of a sensitive, high-bandwidth detector capable of resolving individual electrons [13,14,15]. However, a more fundamental complication with the measurements is that most forms of the FCS theory assume the existence of (1) a detector with infinite bandwidth and (2) infinitely long data traces. Since no physical detector can fulfill these requirements, every experimental realization of the FCS will measure a distribution which is influenced by the properties of the detector....

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To understand quantum mechanical transport in a ferromagnetic semiconductor, the knowledge of basic material properties such as the phase coherence length and corresponding dephasing mechanism are indispensable ingredients. The lack of observable quantum phenomena has prevented experimental access to these quantities so far. Here we report the observations of universal conductance fluctuations in ferromagnetic (Ga,Mn)As. The analysis of the length and temperature dependence of the fluctuations reveals a T(-1) dependence of the dephasing time.