2012 Moseley medal and prize

Dr Suchitra Sebastian, University of Cambridge.

For her important discoveries in frustrated quantum magnets, heavy fermion systems and high temperature semiconductors.

Suchitra Sebastian has made exciting experimental discoveries in the field of interacting electron systems. Her success is due to her insights and talent in combining materials synthesis with thermodynamic and transport measurements at low temperature, high magnetic field and high pressure.

In the field of frustrated quantum magnets, she discovered an unexpected and striking phenomenon known as “dimensional reduction” in BaCuSi2O6 in which the effective dimension of the magnetic lattice decreases with decreasing temperature. In a related system, SrCu2(BO3)2, she observed a remarkably rich structure consisting of sharp plateaus in the magnetisation versus applied magnetic field. This behaviour, reminiscent of the fractional quantum Hall effect, poses a new challenge to the theory of magnetic insulators. In the field of heavy fermion systems she discovered an unusual quantum phase transition in the f-electron antiferromagnet, CeIn3, associated with a change in the topology of the Fermi surface as a function of magnetic field at low temperatures. This phenomenon, known as the Lifshitz transition, occurs at a critical magnetic field unexpectedly well below the critical field at which anti-ferromagnetism is suppressed. Her findings are leading to a re-examination of the conventional description of the heavy fermion state in this and related materials.

In the field of high temperature superconductivity she has made three important contributions. First, she demonstrated the possibility of attaining high temperature superconductivity via pressure tuning alone, starting from a magnetic but non-superconducting state at ambient pressure in SrFe2As2 and BaFe2As2. Second, she observed via the evolution of the Fermi surface, a continuous quantum phase transition in an under-doped copper oxide superconductor YBa2Cu3Oy. Third, she discovered new components in the spectrum of quantum oscillations in underdoped YBa2Cu3O3 in high magnetic fields, which combined with other findings is leading to a realistic model of the Fermi surface for this important material.