ISSN:0031-9228    

DOI:10.1063/1.2808925

出版商:AIP    

年代:1993

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808926

出版商:AIP    

年代:1993

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808927

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Researchers in Germany and France have bound neutral atoms in regular two‐ and three‐dimensional lattices induced by the interference patterns of several laser beams. The work builds on the techniques of magnetooptical trapping and sub‐Doppler laser cooling and on previous work in which atoms were bound in onedimensional standing waves of light. The fields of light in these techniques are called optical molasses, because atoms within them experience viscous forces, which cool the atoms to temperatures on the order of microkelvins. In the new, “crystalline” molasses, the standing waves produce a stable, regular array of potential wells—a microscopic “egg carton”— and the atoms become localized at the bottoms of the wells.

ISSN:0031-9228    

DOI:10.1063/1.2808928

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

During the last decade semiconductor technology has continued to make impressive advances in miniaturization. It is now possible to fabricate artificial structures whose chemical compositions and shapes are controlled with a nanometer accuracy—comparable to interatomic distances. These man‐made systems are too small to behave like the bulk parent compounds and too big to behave like atoms or molecules. We know from the basic principles of quantum mechanics that when the size of a system becomes comparable to the characteristic length scale that determines the coherence of the wavefunctions, quantum size effects occur. The properties then become size and shape dependent. The ability of modern technologies to actually make solid‐state systems in which these conditions are realized opens new opportunities for investigation of condensed matter that has two, one or zero dimensions. Furthermore, because we can tailor some of the properties of these systems for specific purposes, nanostructures have the potential for revolutionary applications in electronics and optoelectronics. Feasibility demonstrations of some of these applications have already been performed, and implementations in actual devices have been achieved.

ISSN:0031-9228    

DOI:10.1063/1.881351

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Semiconductor nanostructures in which mobile electrons reside in a specific spatial region, such as a thin quantum well formed by heterojunction layers on the order of 100 Å in thickness, constitute a particularly striking physical system. The mobile electrons in such a system form a “two‐dimensional electron gas.” In a uniform semiconductor electrons scatter off the ionized donor dopants, but in a two‐dimensional electron gas the electrons can be separate from the dopants and enjoy extraordinarily long mean free paths (many micrometers) at cryogenic temperatures. In the past dozen years or so, this unique property has provided an enormously rich field for the study of electron transport phenomena, ranging from ballistic motion in small device structures to many‐electron correlations in strong magnetic fields

ISSN:0031-9228    

DOI:10.1063/1.881352

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Conduction electrons in real crystalline solids behave very much like electrons in free space, moving in straight lines between collisions when subject to an electric field. But in an ideal (although cold) world, free from scattering by impurities, imperfections and thermal vibrations of the lattice, how would conduction electrons behave? That question, answered in principle long ago in light of the then newly developed quantum mechanics, was purely academic until recently.

ISSN:0031-9228    

DOI:10.1063/1.881353

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Nonlinear optical effects arise when one applies to a material system optical fields that are on the order of or larger than the atomic fields that exist within the system. Quantum size effects appear when the dimensions of a system become comparable to or even smaller than the natural length scale governing its quantum mechanics. Much recent progress has resulted from the combination of these two very productive areas of physics. Because of advances in semiconductor and laser technologies, it is now possible to apply very intense, ultrashort pulses of light to nanometer‐scale semiconductor heterostructures. These conditions produce many new and exciting effects. This article aims to give the reader a flavor of the status of this quickly evolving field of research, with a special emphasis on the most novel and unexpected results.

ISSN:0031-9228    

DOI:10.1063/1.881354

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

For three decades individual transistors in integrated semiconductor circuits have been getting smaller and smaller. Soon they will be approaching the 100‐nanometer regime, where the classical description of diffusive electron motion breaks down and quantum concepts become important, bringing about fundamental changes in electronic and optical properties. Already in the widely used siliconMOSFETtransistors, the interface between the semiconductor and the oxide layer serves as a potential well less than 10 nm wide. While electrons remain free to wander in the plane of the interface, their motion in the perpendicular direction is quantized by this very narrow well. Such two‐dimensional electron systems, best realized in high‐mobility modulation‐doped semiconductor heterostructures, have been found over the years to exhibit new and quite unexpected quantum phenomena, like the integral and fractional quantum Hall effects.

ISSN:0031-9228    

DOI:10.1063/1.881355

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Studies of optical microresonators with dimensions between 0.1 and 10 microns are now under way in a wide variety of condensed matter systems. Ideally, one can isolate a single mode of the optical field in a cube a halfwavelength on a side with perfectly reflecting walls. Liquid droplets, polymer spheres and semiconductor Fabry‐Perot microcavities with dielectric mirrors are examples of microresonators with which one can approach this ideal limit and nearly isolate a few modes of the electromagnetic field from the continuum of surrounding free‐space modes.

ISSN:0031-9228    

DOI:10.1063/1.881356

出版商:AIP    

年代:1993

数据来源: AIP