51 research outputs found
Simple mechanisms that impede the Berry phase identification from magneto-oscillations
The phase of quantum magneto-oscillations is often associated with the Berry
phase and is widely used to argue in favor of topological nontriviality of the
system (Berry phase ). Nevertheless, the experimentally determined
value may deviate from arbitrarily, therefore more care should be
made analyzing the phase of magneto-oscillations to distinguish trivial systems
from nontrivial. In this paper we suggest two simple mechanisms dramatically
affecting the experimentally observed value of the phase in three-dimensional
topological insulators: (i) magnetic field dependence of the chemical
potential, and (ii) possible nonuniformity of the system. These mechanisms are
not limited to topological insulators and can be extended to other
topologically trivial and non-trivial systems.Comment: 9 pages, 4 figures, in published version the title was change
Laser-pump-resistive-probe technique to study nanosecond-scale relaxation processes
Standard optical pump-probe techniques allow to study a temporal response of
a system to a laser pulse starting from the sub-femtoseconds to several
nanoseconds, limited by the length of the optical delay line. Resistance is a
sensitive detector of a plethora of phenomena in solid state, nanostructure
physics, chemistry, and biology. However, resistance measurements are typically
rather slow (> microsecond) because they require stabilization of current or
voltage and analog-to-digital conversion. Here we develop a time-resolved
pump-probe technique, where the "Pump" is an optical pulse from the laser and
the "Probe" is a rectangular electrical pulse passing through the sample under
study. Transmission of the probe pulse through the sample is measured in the 50
Ohm matched circuit with the digital oscilloscope. The delay can be
electrically driven from nanoseconds to seconds. We demonstrate the usability
of the technique to study heat-induced changes in a thin amorphous VO film
and carrier relaxation in a CdS photoresistor. The technique could be further
explored to study heat transfer, biochemical reactions, and slow electronic
transformations
- …