Scientist: Neil Harrison <email@example.com>
or (505) 665-3200
The de Haas-van Alphen effect occurs in very clean metallic systems, typically in strong magnetic fields exceeding several tesla. These oscillations in the magnetization result from a phenomenon known as ``Landau quantization" whereby the electrons in a metal exist only as a series of orbitally quantized states in a magnetic field. Because the number of occupied Landau levels changes with the magnetic field, on sweeping the magnetic field one observes oscillations in the magnetization which are periodic in an inverse magnetic field.
While de Haas-van Alphen measurements are more often measured in static magnetic field using sensitive ac modulation techniques, the use of pulsed magnetic fields enables one to investigate specific phenomena that might take place in exceptionally strong magnetic fields of order 30 tesla and above. However, because metals that most readily yield de Haas-van Alphen oscillations are usually very good metals, samples need to be made very small in order to avoid the effects of eddy current heating.
The de Haas van Alphen
pulsed magnetic field set-up in Los Alamos has been engineered to accommodate
samples that can fit within a 400 micrometer hole, and measurements can
be conducted in nearly all the magnets. This is the dimension of the inner
bore of a concentrically wound pair of detection coils that are used to
measure the oscillatory induced voltage during a pulse. The small size
together with concentric geometry also helps combat problems associated
with vibrational and/or electrical noise during the pulse. By using 10
micrometer thick insulated copper wire, approximately 500 pick-up coil
windings paked-in within 200 micrometers of the inner bore. By using a
custom built amplifier, we can both compensate-out the background remnant
magnetic field in addition to amplifying the induced voltages by gains
of up to 50,000.