Alladi Ramakrishnan Hall

New Surprises in Quantum Oscillations

Hridis Pal

IIT Bombay

It is well known that, in a magnetic field, electron energy levels quantize into Landau levels. In metals, as the field is changed, Landau levels cross the Fermi level periodically giving rise to oscillations in physical observables, called
quantum oscillations. Because these oscillations arise from the Fermi level, they are considered to be a proof of the existence of an underlying Fermi surface and form the basis for experiments aimed at mapping the Fermi surface in metals. In recent years, however, quantum oscillations have been observed experimentally in certain insulators where, by definition, a Fermi
surface does not exist. A fresh look into the theory of quantum oscillations is warranted. In this talk, I will discuss new
ideas that have emerged as a result which show that the conventional understanding is, indeed, incomplete: in certain
situations, quantum oscillations can arise from inside the Fermi sea and can show up in certain insulators. These unconventional quantum oscillations show a rich phenomenology, different from that found in metals. Such new insights have opened the door to the possibility of using quantum oscillations to study features in systems traditionally thought to be
outside the scope of this technique--I will discuss some of these possibilities.