Coulomb blockade in an open quantum dot.

We report the observation of Coulomb blockade in a quantum dot contacted by two quantum point contacts each with a single fully transmitting mode, a system thought to be well described without invoking Coulomb interactions. Below 50 mK we observe a periodic oscillation in the conductance of the dot with gate voltage, corresponding to a residual quantization of charge. From the temperature and magnetic field dependence, we infer the oscillations are mesoscopic Coulomb blockade, a type of Coulomb blockade caused by electron interference in an otherwise open system.

Universal scaling in nonequilibrium transport through a single channel Kondo dot.

Scaling laws and universality play an important role in our understanding of critical phenomena and the Kondo effect. We present measurements of nonequilibrium transport through a single-channel Kondo quantum dot at low temperature and bias. We find that the low-energy Kondo conductance is consistent with universality between temperature and bias and is characterized by a quadratic scaling exponent, as expected for the spin-1/2 Kondo effect.

Observation of the two-channel Kondo effect.

Some of the most intriguing problems in solid-state physics arise when the motion of one electron dramatically affects the motion of surrounding electrons. Traditionally, such highly correlated electron systems have been studied mainly in materials with complex transition metal chemistry. Over the past decade, researchers have learned to confine one or a few electrons within a nanometre-scale semiconductor 'artificial atom', and to understand and control this simple system in detail(3).

Experimental realization of a quantum spin pump.

We demonstrate the operation of a quantum spin pump based on cyclic radio-frequency excitation of a GaAs quantum dot, including the ability to pump pure spin without pumping charge. The device takes advantage of bidirectional mesoscopic fluctuations of pumped current, made spin dependent by the application of an in-plane Zeeman field. Spin currents are measured by placing the pump in a focusing geometry with a spin-selective collector.

Spin and polarized current from Coulomb blockaded quantum dots.

We report measurements of spin transitions for GaAs quantum dots in the Coulomb blockade regime and compare ground and excited state transport spectroscopy to direct measurements of the spin polarization of emitted current. Transport spectroscopy reveals both spin-increasing and spin-decreasing transitions, as well as higher-spin ground states, and allows g factors to be measured down to a single electron. The spin of emitted current in the Coulomb blockade regime, measured using spin-sensitive electron focusing, is found to be polarized along the direction of the applied magnetic field regardless of the ground state spin transition.

A gate-controlled bidirectional spin filter using quantum coherence.

We demonstrate a quantum coherent electron spin filter by directly measuring the spin polarization of emitted current. The spin filter consists of an open quantum dot in an in-plane magnetic field; the in-plane field gives the two spin directions different Fermi wavelengths resulting in spin-dependent quantum interference of transport through the device. The gate voltage is used to select the preferentially transmitted spin, thus setting the polarity of the filter.

Detecting spin-polarized currents in ballistic nanostructures.

We demonstrate a mesoscopic spin polarizer/analyzer system that allows the spin polarization of current from a quantum point contact in a large in-plane magnetic field to be measured. A transverse electron focusing geometry is used to couple current from an emitter point contact into a collector point contact. At large in-plane fields, with the point contacts biased to transmit only a single spin (g View Article and Find Full Text PDF

Spin-glass freezing and RKKY interactions near the metal-insulator transition in amorphous Gd-Si alloys.

Magnetization measurements of giant negative magnetoresistive amorphous GdxSi1-x ( 0.04 View Article and Find Full Text PDF