Multiwalled carbon nanotubes as ultrasensitive electrometers

We show that it is possible to construct low-noise single-electron transistors (SETs) using free-standing multiwalled carbon nanotubes. The 1/fα -noise of our devices, 6×10 exp −6 e/√Hz at 45 Hz, is close in the performance to the best metallic SETs of today.Peer reviewe

Manipulation of Ag nanoparticles utilizing noncontact atomic force microscopy

We have developed a scheme to manipulate metallic aerosol particles on silicon dioxide substrates using an atomic force microscope. The method utilizes the noncontact mode both for locating and moving nanoparticles of size 10–100 nm. The main advantage of our technique is the possibility of “seeing” the moving particle in real time. Our method avoids well sticking problems that typically hamper the manipulation in the contact mode.Peer reviewe

Noise of a single electron transistor on a Si3N4 membrane

We have investigated the influence of electron-beam writing on the creation of charge trapping centers which cause 1/f noise in single electron transistors (SET). Two Al/AlOx/Al devices were compared: one where the SET is on a {100} silicon wafer covered by a 120-nm-thick layer of Si3N4, and another one in which the Si was etched away from below the nitride membrane before patterning the SET. The background charge noise was found to be 1×10 exp −3 e/√Hz at 10 Hz in both devices, independent of the substrate thickness.Peer reviewe

Using multiple imputation and intervention-based scenarios to project the mobility of older adults

Background: Projections of the development of mobility limitations of older adults are needed for evidence-based policy making. The aim of this study was to generate projections of mobility limitations among older people in the United States, England, and Finland. Methods: We applied multiple imputation modelling with bootstrapping to generate projections of stair climbing and walking limitations until 2026. A physical activity intervention producing a beneficial effect on self-reported activities of daily living measures was identified in a comprehensive literature search and incorporated in the scenarios used in the projections. We utilised the harmonised longitudinal survey data from the Ageing Trajectories of Health – Longitudinal Opportunities and Synergies (ATHLOS) project (N = 24,982). Results: Based on the scenarios from 2012 to 2026, the prevalence of walking limitations will decrease from 9.4 to 6.4%. A physical activity intervention would decrease the prevalence of stair climbing limitations compared with no intervention from 28.9 to 18.9% between 2012 and 2026. Conclusions: A physical activity intervention implemented on older population seems to have a positive effect on maintaining mobility in the future. Our method provides an interesting option for generating projections by incorporating intervention-based scenarios

Band offsets at the GaInP/GaAs heterojunction

We have measured current–voltage curves and the temperature dependence of the zero bias conductance for a p -type Be-doped GaInP/GaAs heterojunction grown by the molecular beam epitaxy method. We have determined the valence band offset ΔEν from both measurements and find it to be 310 meV within 5% of accuracy. Similarly, we find for an n -type Si-doped sample that the conduction band offset ΔEC is 95 meV. First-principles calculations have been carried out for the atomic and electronic structures of the interfaces. For the thermodynamically favored interfaces, the valence band offset is found not to be sensitive to atomic relaxations at the interface. The calculated values are in good agreement with the experiments.Peer reviewe

Particle-Hole Symmetry and the Effect of Disorder on the Mott-Hubbard Insulator

Recent experiments have emphasized that our understanding of the interplay of electron correlations and randomness in solids is still incomplete. We address this important issue and demonstrate that particle-hole (ph) symmetry plays a crucial role in determining the effects of disorder on the transport and thermodynamic properties of the half-filled Hubbard Hamiltonian. We show that the low-temperature conductivity decreases with increasing disorder when ph-symmetry is preserved, and shows the opposite behavior, i.e. conductivity increases with increasing disorder, when ph-symmetry is broken. The Mott insulating gap is insensitive to weak disorder when there is ph-symmetry, whereas in its absence the gap diminishes with increasing disorder.Comment: 4 pages, 4 figure

Magnetoresistance of composite fermions at \nu=1/2

We have studied temperature dependence of both diagonal and Hall resistivity in the vicinity of $\nu=1/2$. Magnetoresistance was found to be positive and almost independent of temperature: temperature enters resistivity as a logarithmic correction. At the same time, no measurable corrections to the Hall resistivity has been found. Neither of these results can be explained within the mean-field theory of composite fermions by an analogy with conventional low-field interaction theory. There is an indication that interactions of composite fermions with fluctuations of the gauge field may reconcile the theory and experiment.Comment: 9 pages, 4 figure

Anderson-Mott transition as a quantum glass problem

We combine a recent mapping of the Anderson-Mott metal-insulator transition on a random-field problem with scaling concepts for random-field magnets to argue that disordered electrons near an Anderson-Mott transition show glass-like behavior. We first discuss attempts to interpret experimental results in terms of a conventional scaling picture, and argue that some of the difficulties encountered point towards a glassy nature of the electrons. We then develop a general scaling theory for a quantum glass, and discuss critical properties of both thermodynamic and transport variables in terms of it. Our most important conclusions are that for a correct interpretation of experiments one must distinguish between self-averaging and non-self averaging observables, and that dynamical or temperature scaling is not of power-law type but rather activated, i.e. given by a generalized Vogel-Fulcher law. Recent mutually contradicting experimental results on Si:P are discussed in the light of this, and new experiments are proposed to test the predictions of our quantum glass scaling theory.Comment: 25pp, REVTeX, 5 ps figs, final version as publishe

Typical-Medium Theory of Mott-Anderson Localization

The Mott and the Anderson routes to localization have long been recognized as the two basic processes that can drive the metal-insulator transition (MIT). Theories separately describing each of these mechanisms were discussed long ago, but an accepted approach that can include both has remained elusive. The lack of any obvious static symmetry distinguishing the metal from the insulator poses another fundamental problem, since an appropriate static order parameter cannot be easily found. More recent work, however, has revisited the original arguments of Anderson and Mott, which stressed that the key diference between the metal end the insulator lies in the dynamics of the electron. This physical picture has suggested that the "typical" (geometrically averaged) escape rate from a given lattice site should be regarded as the proper dynamical order parameter for the MIT, one that can naturally describe both the Anderson and the Mott mechanism for localization. This article provides an overview of the recent results obtained from the corresponding Typical-Medium Theory, which provided new insight into the the two-fluid character of the Mott-Anderson transition.Comment: to be published in "Fifty Years of Anderson localization", edited by E. Abrahams (World Scientific, Singapore, 2010); 29 pages, 22 figures

Multiwalled carbon nanotube: Luttinger liquid or not?

We have measured IV-curves of multiwalled carbon nanotubes using end contacts. At low voltages, the tunneling conductance obeys non-Ohmic power law, which is predicted both by the Luttinger liquid and the environment-quantum-fluctuation theories. However, at higher voltages we observe a crossover to Ohm's law with a Coulomb-blockade offset, which agrees with the environment-quantum-fluctuation theory, but cannot be explained by the Luttinger-liquid theory. From the high-voltage tunneling conductance we determine the transmission line parameters of the nanotubes.Comment: RevTeX, 4 pages, 2 EPS-figures, submitted to Phys. Rev. Let