17 research outputs found
Direct detection of molecular intermediates from first-passage times
All natural phenomena are governed by energy landscapes. However, the direct measurement of this fundamen-tal quantity remains challenging, particularly in complex systems involving intermediate states. Here, we uncover key details of the energy landscapes that underpin a range of experimental systems through quantitative analysis of first-passage time distributions. By combined study of colloidal dynamics in confinement, transport through a biological pore, and the folding kinetics of DNA hairpins, we demonstrate conclusively how a short-time, power-law regime of the first-passage time distribution reflects the number of intermediate states associated with each of these processes, despite their differing length scales, time scales, and interactions. We thereby establish a powerful method for investigating the underlying mechanisms of complex molecular processes
Conductance and persistent current of a quantum ring coupled to a quantum wire under external fields
The electronic transport of a noninteracting quantum ring side-coupled to a
quantum wire is studied via a single-band tunneling tight-binding Hamiltonian.
We found that the system develops an oscillating band with antiresonances and
resonances arising from the hybridization of the quasibound levels of the ring
and the coupling to the quantum wire. The positions of the antiresonances
correspond exactly to the electronic spectrum of the isolated ring. Moreover,
for a uniform quantum ring the conductance and the persistent current density
were found to exhibit a particular odd-even parity related with the ring-order.
The effects of an in-plane electric field was also studied. This field shifts
the electronic spectrum and damps the amplitude of the persistent current
density. These features may be used to control externally the energy spectra
and the amplitude of the persistent current.Comment: Revised version, 7 pages and 9 figures. To appear in Phys. Rev.
Persistent Currents in Small, Imperfect Hubbard Rings
We have done a study with small, imperfect Hubbard rings with exact
diagonalization. The results for few-electron rings show, that the
imperfection, whether localized or not, nearly always decrease, but can also
\emph{increase} the persistent current, depending on the character of the
imperfection and the on-site interaction. The calculations are generally in
agreement with more specialized studies. In most cases the electron spin plays
an important role.Comment: 6 pages, 4 figure
Phase state dependent current fluctuations in pure lipid membranes
Current fluctuations in pure lipid membranes have been shown to occur under
the influence of transmembrane electric fields (electroporation) as well as a
result from structural rearrangements of the lipid bilayer during phase
transition (soft perforation). We demonstrate that the ion permeability during
lipid phase transition exhibits the same qualitative temperature dependence as
the macroscopic heat capacity of a D15PC/DOPC vesicle suspension. Microscopic
current fluctuations show distinct characteristics for each individual phase
state. While current fluctuations in the fluid phase show spike-like behaviour
of short time scales (~ 2ms) with a narrow amplitude distribution, the current
fluctuations during lipid phase transition appear in distinct steps with time
scales in the order of ~ 20ms. 1 We propose a theoretical explanation for the
origin of time scales and permeability based on a linear relationship between
lipid membrane susceptibilities and relaxation times in the vicinity of the
phase transition.Comment: 22 pages including 6 figure
Site-controlled quantum dots fabricated using an atomic-force microscope assisted technique
An atomic-force microscope assisted technique is developed to control the position and size of self-assembled semiconductor quantum dots (QDs). Presently, the site precision is as good as ± 1.5 nm and the size fluctuation is within ± 5% with the minimum controllable lateral diameter of 20 nm. With the ability of producing tightly packed and differently sized QDs, sophisticated QD arrays can be controllably fabricated for the application in quantum computing. The optical quality of such site-controlled QDs is found comparable to some conventionally self-assembled semiconductor QDs. The single dot photoluminescence of site-controlled InAs/InP QDs is studied in detail, presenting the prospect to utilize them in quantum communication as precisely controlled single photon emitters working at telecommunication bands
Nanomachining of mesoscopic electronic devices using an atomic force microscope
An atomic force microscope (AFM) is used to locally deplete the two-dimensional electron gas (2DEG) of a GaAs/AlGaAs heterostructure. The depletion is induced by repeated mechanical scribing of the surface layers of the heterostructure using the AFM tip. Measuring the room-temperature resistance across the scribed lines during fabrication provides in situ control of the depletion of the 2DEG. Variation of the room-temperature resistance of such lines tunes their low-temperature characteristics from tunneling up to insulating behavior. Using this technique, an in-plane-gate transistor and a single-electron transistor were fabricated. © 1999 American Institute of Physics