– We studied spin-polarized tunneling through a vacuum barrier using spinpolarized scanning tunneling microscopy on Co(0001). By varying the tip-to-sample distance in a controlled way, the tunneling magnetoresistance, i.e., the tunneling current asymmetry for parallel and antiparallel configuration of tip and sample magnetization, was measured as a function of the gap width. At large gap widths...

Tunneling between two 2D electron gases in a weak magnetic field is of resonance character, and involves a long lifetime excitonic state of an electron and hole uniformly spread over cyclotron orbits. The tunneling gap is linear in the field, in agreement with the experiment, and is anomalously sensitive to the electron density mismatch in the wells. The spatial coherence of tunneling along the...

We experimentally implement the Harper Hamiltonian for neutral particles in optical lattices using laser-assisted tunneling and a potential energy gradient provided by gravity or magnetic field gradients. This Hamiltonian describes the motion of charged particles in strong magnetic fields. Laser-assisted tunneling processes are characterized by studying the expansion of the atoms in the lattice...

The Josephson effect is generally described as Cooper-pair tunneling but it can also be understood in a more general context. The dc Josephson effect is the pseudo-Goldstone boson of two coupled systems with a broken continuous Abelian U 1 symmetry. Hence, an analog should exist for systems with broken continuous nonAbelian symmetries. To exhibit the generality of the phenomenon and make predic...

We study the time-dependent dynamics of a Bose-Einstein condensate trapped in an optical lattice. Modeling the system as a Bose-Hubbard model, we show how applying a periodic driving field can induce coherent destruction of tunneling. In the low-frequency regime, we obtain the novel result that the destruction of tunneling displays extremely sharp peaks when the driving frequency is resonant wi...