30 research outputs found
Microwave saturation of the Rydberg states of electrons on helium
We present measurements of the resonant microwave excitation of the Rydberg
energy levels of surface state electrons on superfluid helium. The temperature
dependent linewidth agrees well with theoretical predictions and is very small
below 300 mK. Absorption saturation and power broadening were observed as the
fraction of electrons in the first excited state was increased to 0.49, close
to the thermal excitation limit of 0.5. The Rabi frequency was determined as a
function of microwave power. The high values of the ratio of the Rabi frequency
to linewidth confirm this system as an excellent candidate for creating qubits.Comment: 4 pages, 4 figure
Origin of the peaks in the Nernst coefficient of bismuth in strong magnetic fields
We explain the origin of most of the peaks in the Nernst coefficient that
were recently observed at magnetic fields directed along the trigonal axis and
the bisectrix direction in bismuth. Additional experiments are discussed that
enable one to verify our explanation.Comment: Submitted to Physical Review B. 4 pages, 5 figure
Metal-Insulator-Like Behavior in Semimetallic Bismuth and Graphite
When high quality bismuth or graphite crystals are placed in a magnetic field
directed along the c-axis (trigonal axis for bismuth) and the temperature is
lowered, the resistance increases as it does in an insulator but then
saturates. We show that the combination of unusual features specific to
semimetals, i.e., low carrier density, small effective mass, high purity, and
an equal number of electrons and holes (compensation), gives rise to a unique
ordering and spacing of three characteristic energy scales, which not only is
specific to semimetals but which concomitantly provides a wide window for the
observation of apparent field induced metal-insulator behavior. Using
magnetotransport and Hall measurements, the details of this unusual behavior
are captured with a conventional multi-band model, thus confirming the
occupation by semimetals of a unique niche between conventional metals and
semiconductors.Comment: 4 pages, 4 figs, data and discussion on bismuth added, final
published versio
Low-Temperature Mobility of Surface Electrons and Ripplon-Phonon Interaction in Liquid Helium
The low-temperature dc mobility of the two-dimensional electron system
localized above the surface of superfluid helium is determined by the slowest
stage of the longitudinal momentum transfer to the bulk liquid, namely, by the
interaction of surface and volume excitations of liquid helium, which rapidly
decreases with temperature. Thus, the temperature dependence of the
low-frequency mobility is \mu_{dc} = 8.4x10^{-11}n_e T^{-20/3} cm^4 K^{20/3}/(V
s), where n_e is the surface electron density. The relation
T^{20/3}E_\perp^{-3} << 2x10^{-7} between the pressing electric field (in
kV/cm) and temperature (in K) and the value \omega < 10^8 T^5 K^{-5}s^{-1} of
the driving-field frequency have been obtained, at which the above effect can
be observed. In particular, E_\perp = 1 kV/cm corresponds to T < 70 mK and
\omega/2\pi < 30 Hz.Comment: 4 pages, 1 figur
Oscillations of the Nernst coefficient in bismuth
We calculate the magnetic-field dependence (oscillations) of the Nernst
coefficient in bismuth at low temperatures for the case when the magnetic field
is directed along the trigonal axis of the crystal. In the calculations we take
into account the scattering of the electrons and holes in bismuth on impurities
and the dependence of this scattering on the magnetic field. The results of
these calculations are compared with the experimental data recently published
Investigation of the spectrum of surface states in bismuth by scanning tunneling spectroscopy
Microwave absorption saturation and decay heating of surface electrons on liquid helium
The microwave (MW) resonance absorption and decay heating of surface electrons (SEs) on liquid ā“He
are theoretically studied for the vapor atom scattering regime. The decay heating is shown to be an essential
occurrence of a MW resonance experiment appearing even at low excitation rates. It strongly affects the occupancies
of surface levels and the broadening of resonance lines long before the absorption suturation condition
is reached. Contrary to the model of cold SEs usually used for description of the MW resonance, the
new theory leads to MW absorption saturation when only a very small fraction of electrons (less than 10%) is
left on the ground and the first excited levels