Showing papers by "Kostya S. Novoselov published in 2004"

Electric Field Effect in Atomically Thin Carbon Films

Abstract: We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions, metallic, and of remarkably high quality. The films are found to be a two-dimensional semimetal with a tiny overlap between valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in concentrations up to 10 13 per square centimeter and with room-temperature mobilities of ∼10,000 square centimeters per volt-second can be induced by applying gate voltage.

Long-range nonlocal flow of vortices in narrow superconducting channels.

Abstract: We report a new nonlocal effect in vortex matter, where an electric current confined to a small region of a long and sufficiently narrow superconducting wire causes vortex flow at distances hundreds of intervortex separations away. The observed remote traffic of vortices is attributed to a very efficient transfer of a local strain through the one-dimensional vortex lattice (VL), even in the presence of disorder. We also observe mesoscopic fluctuations in the nonlocal vortex flow, which arise due to "traffic jams" when vortex arrangements do not match a local geometry of a superconducting channel.

Microscopic view on a single domain wall moving through ups and downs of an atomic washboard potential

Abstract: Propagation of ferromagnetic domain walls on sub-atomic scale was measured in a thin uniaxial garnet film by using ballistic Hall magnetometry. Domain walls are found to move by equidistant steps, which correspond to the crystal lattice constant in this material. Our results are in good agreement with the theory of intrinsic pinning of a domain wall in the Peierls potential. We have also measured AC susceptibility of a domain wall moving inside a Peierls valley. The observed nonlinear behavior of the AC susceptibility can be understood within the framework of kinks and breathers nucleating and spreading along the domain wall.

Metallic and Semiconductor Hall Microprobes for Wide Temperature Range Applications

Abstract: We report on mesoscopic Hall sensors allowing accurate magnetization studies of submicron or nanometer-sized samples over a wide temperature range. Even at 300 K, the probes can reliably resolve local changes in dc field of ≈ 1 G with spatial resolution of ≈ 1 μm, which corresponds to a flux sensitivity of less than 0.1 ϕ0 (ϕ0=h/e is a flux quantum). The resolution increases 100 times at temperatures below 80 K. The capabilities of new micromagnetometers are demonstrated by measuring nm-scale movements of individual domain walls in a ferromagnet.

Coercivity of single pinning center measured by hall micromagnetometry

Abstract: Nanometer-scale movements of domain walls in uniaxial garnet films have been studied by means of micromagnetization measurements using miniature gold and semiconductor Hall probes. At helium temperatures the domain walls are found to move by discrete jumps, which we attribute to pinning on isolated defects, and we were able to measure local hysteresis loops associated with pinning on individual pinning centers. The temperature dependence of the coercive field of a single pinning center allowed us to evaluate the characteristic energy and characteristic volume of the pinning center.