Electron Transport in Metallic Grains

We discuss electron transport in individual nanometer-scale metallic grainsat dilution refrigerator temperatures. In the weak coupling regime, the grainsexhibit Coulomb blockade and discrete energy levels. Electron-electroninteractions lead to clustering and broadening of quasiparticle states.Magnetic field dependences of tunneling resonances directly reveal Kramersdegeneracy and Lande g-factors. In grains of Au, which have strong spin-orbitinteraction, g-factors are strongly suppressed from the free electron value. Wehave recently studied grains in the strong coupling regime. Coulomb blockadepersists in this regime. It leads to a suppression in sample conductance atzero bias voltage at low temperatures. The conductance fluctuates with theapplied magnetic field near zero bias voltage. We present evidence that thefluctuations are induced by electron spin. This paper reviews the evolvingprogress in interpreting these observations.Comment: Since the original submission, we have gathered data in weak coupling regime, showing that our initial speculation - that the conductance dip is due to EE interactions in the Altshuler-Aronov sense - is not correct. Instead, it is caused by the Coulomb Blockade. Conference Proceedings, "Quantum Transport and Quantum Coherence" Localisation 2002, Sophia University, Tokyo, August 16-19, to be published in the supplement of the Journal of the Physical Society of Japa