5,823 research outputs found
Charge Transfer and Charge Transport on the Double Helix
We present a short review of various experiments that measure charge transfer
and charge transport in DNA. Some general comments are made on the possible
connection between 'chemistry-style' charge transfer experiments that probe
fluorescence quenching and remote oxidative damage and 'physics-style'
measurements that measure transport properties as defined typically in the
solid-state. We then describe measurements performed by our group on the
millimeter wave response of DNA. By measuring over a wide range of humidity
conditions and comparing the response of single strand DNA and double strand
DNA, we show that the appreciable AC conductivity of DNA is not due to photon
assisted hopping between localized states, but instead due to dissipation from
dipole motion in the surrounding water helix.Comment: 7 pages, 3 figure
A broadband microwave Corbino spectrometer at He temperatures and high magnetic fields
We present the technical details of a broadband microwave spectrometer for
measuring the complex conductance of thin films covering the range from 50 MHz
up to 16 GHz in the temperature range 300 mK to 6 K and at applied magnetic
fields up to 8 Tesla. We measure the complex reflection from a sample
terminating a coaxial transmission line and calibrate the signals with three
standards with known reflection coefficients. Thermal isolation of the heat
load from the inner conductor is accomplished by including a section of NbTi
superconducting cable (transition temperature around 8 9 K) and hermetic
seal glass bead adapters. This enables us to stabilize the base temperature of
the sample stage at 300 mK. However, the inclusion of this superconducting
cable complicates the calibration procedure. We document the effects of the
superconducting cable on our calibration procedure and the effects of applied
magnetic fields and how we control the temperature with great repeatability for
each measurement. We have successfully extracted reliable data in this
frequency, temperature and field range for thin superconducting films and
highly resistive graphene samples
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