We introduce a method to fabricate high-performance field-effect transistors on the surface of freestanding organic single crystals. The transistors are constructed by laminating a monolithic elastomeric transistor stamp against the surface of a crystal. This method, which eliminates exposure of the fragile organic surface to the hazards of conventional processing, enables fabrication of rubrene transistors with charge carrier mobilities as high as approximately 15 cm2/V.s and subthreshold slopes as low as 2nF.V/decade.cm2. Multiple relamination of the transistor stamp against the same crystal does not affect the transistor characteristics; we exploit this reversibility to reveal anisotropic charge transport at the basal plane of rubrene.

An even-denominator rational quantum number has been observed in the Hall resistance of a twodimensional electron system. At partial filling of the second Landau level v=2+ y = y and at temperatures below 100 mK, a fractional Hall plateau develops at p xy =(h/e 2 )/y defined to better than 0.5%. Equivalent even-denominator quantization is absent in the lowest Landau level under comparable conditions.

We describe a patterning technique that uses self-assembled monolayers and other surface chemistries for guiding the transfer of material from relief features on a stamp to a substrate. This purely additive contact printing technique is capable of nanometer resolution. Pattern transfer is fast and it occurs at ambient conditions. We illustrate the versatility of this method by printing single-layer metal patterns with feature sizes from a few tens of microns to a few tens of nanometers. We also demonstrate its use for patterning, in a single step, metal/dielectric/metal multilayers for functional thin film capacitors on plastic substrates.

We report the first direct observation of the cyclotron motion of new quasiparticles in a 2D electron system near y filling factor. Just as electrons in a metal geometrically resonate with a sound wave when a magnetic field is applied perpendicular to the sound propagation direction, near j filling factor we observe resonance of a surface sound wave with cyclotron orbits of charge carriers. The presence of a Fermi surface and geometric resonance of a sound wave with Chern-Simons gauge transformed fermions were explicitly predicted in a recent theory of the half filled Landau level. PACS numbers: 73.20.Dx, 73.40.Kp, 73.50.Jt The two dimensional electron system (2DES) in low disorder GaAs/AlGaAs heterostructures has produced a wealth of experimental results that are changing our understanding of lower dimensional physics. When a large magnetic field is applied to a 2DES containing little disorder, the electron-electron interaction will become manifest at low temperatures. Our understanding of these interactions has been limited largely to what has been gleaned by examining the dominant finding in simple dc transport measurements, the fractional quantum Hall effect (FQHE) [1]. Yet because the interactions are present at more than the odd denominator filling factors of the FQHE, our comprehension of the underlying physics in the electron system is lacking. A picture describing the entire filling factor spectrum is a goal of both theory and experiment. Such a theoretical picture has recently been developed [2], as we outline below. Experimentally it is important to examine the electron-electron interactions throughout the spectrum with a technique that does not destructively perturb the interaction. We have accomplished this and have explored the 2DES in a previously unreachable small length scale regime. In doing so we have revealed a remarkable phenomenon new to the 2DES, and have critically tested this new theory.A useful approach to the problem of the interacting 2D electron system is that of the field theoretic construction. In this method a singular gauge transformation converts the electrons to a system of particles interacting with a "fictitious" or Chern-Simons gauge field. A flux tube containing an integer number n of quanta of Chern-Simons magnetic field is attached to each particle. If n is an odd integer, the transformed particles obey Bose statistics, and if n is even they obey Fermi statistics. In the 2DES the motivation for such a construction is that in a simple Hartree approximation for some choice of n at various rational filling factors the resulting ground state is nondegenerate and as such has a chance of being an approximation to the system's true ground state. While these statistical transmutations have provided a new means of examining the correlated 2DES in an abstract sense, they have not in general presented explicit new properties that are experimentally testable.Recently, however, Halperin, Lee, and Read [2] (HLR) have used the fermion Chern-Simons method to examine the properties of a...

A standing problem in low-dimensional electron systems is the nature of the 5/2 fractional quantum Hall (FQH) state: Its elementary excitations are a focus for both elucidating the state's properties and as candidates in methods to perform topological quantum computation. Interferometric devices may be used to manipulate and measure quantum Hall edge excitations. Here we use a small-area edge state interferometer designed to observe quasiparticle interference effects. Oscillations consistent in detail with the Aharonov-Bohm effect are observed for integer quantum Hall and FQH states (filling factors ‫؍‬ 2, 5/3, and 7/3) with periods corresponding to their respective charges and magnetic field positions. With these factors as charge calibrations, periodic transmission through the device consistent with quasiparticle charge e/4 is observed at ‫؍‬ 5/2 and at lowest temperatures. The principal finding of this work is that, in addition to these e/4 oscillations, periodic structures corresponding to e/2 are also observed at 5/2 and at lowest temperatures. Properties of the e/4 and e/2 oscillations are examined with the device sensitivity sufficient to observe temperature evolution of the 5/2 quasiparticle interference. In the model of quasiparticle interference, this presence of an effective e/2 period may empirically reflect an e/2 quasiparticle charge or may reflect multiple passes of the e/4 quasiparticle around the interferometer. These results are discussed within a picture of e/4 quasiparticle excitations potentially possessing non-Abelian statistics. These studies demonstrate the capacity to perform interferometry on 5/2 excitations and reveal properties important for understanding this state and its excitations.5/2 fractional quantum Hall effect ͉ fractional quantum Hall effect ͉ non-Abelian statistics ͉ topological quantum computation E xperimentally, the fractional quantum Hall (FQH) state at 5/2 ϭ filling factor is anomalous in that it occurs at an even denominator quantum number (1). The state is fragile: It displays a weak quantum Hall effect, requiring temperatures for observation substantially lower than the principal odd denominator states at ϭ 1/3 and 2/3. It has been proposed as either a spin polarized [Moore-Read Pfaffian (2)] or non-spin polarized [Haldane-Rezayi (3)] paired composite fermion state. The fundamental quasiparticle excitations are expected to be charged e/4, and for the Pfaffian state these quasiparticles are to obey non-Abelian statistics. These nonAbelian states may display utility in topological quantum computational schemes (4) To the end of determining the charge, and more importantly the statistics of the quasiparticles, interference devices and their function in displaying the Aharonov-Bohm (A-B) effect at 5/2 have been described theoretically (5-9). Interference devices are typically constructed with nominally 2 adjacent quantum point contacts (qpcs), each able to variably transmit current, and a confinement area between the qpcs (see schematic in Fig. 1). By splitting the cur...