Quantum oscillations

In condensed matter physics, quantum oscillations describes a series of related experimental techniques used to map the Fermi surface of a metal in the presence of a strong magnetic field.

In a quantum oscillation experiment, the external magnetic field is varied, which causes the Landau levels to pass over the Fermi surface, which in turn results in oscillations of the electronic density of states at the Fermi level; this produces oscillations in the many material properties which depend on this, including resistance (the Shubnikov–de Haas effect), Hall resistance,[2] and magnetic susceptibility (the de Haas–van Alphen effect).

[1] Studies using these experiments have shown that the ground state of underdoped cuprates behave similar to a Fermi liquid, and display characteristics such as Landau quasiparticles.

When a magnetic field is applied to a system of free charged fermions, their energy states are quantized into the so-called Landau levels, given by[7]

is increased in an isolated system, the Landau levels expand, and eventually "fall off" the Fermi surface.

This leads to oscillations in the observed energy of the highest occupied level, and hence in many physical properties (including Hall conductivity, resistivity, and susceptibility).

[8] Studies of underdoped cuprate compounds such as YBa2Cu3O6+x through probes such as ARPES have indicated that these phases show characteristics of non-Fermi liquids,[9] and in particular, the absence of well-defined Landau quasiparticles.

[10] However, quantum oscillations have been observed in these materials at low temperatures, if their superconductivity is suppressed by a sufficiently high magnetic field,[2] which is evidence for the presence of well-defined quasiparticles with fermionic statistics.