Dr. Siddarth S. Saxena

Dr Saxena's research programme focuses on novel forms of quantum order in metallic and insulating magnets, intercalated compounds, ferroelectric systems and multi-ferroic materials. In particular he has pioneered the study of model materials in which the magnetic and charge ordered states give way to exotic superconductivity and other forms of novel quantum order as a function of applied hydrostatic pressure.

With his co-workers, he discovered the coexistence of a novel form of superconductivity and itinerant-electron ferromagnetism in the f-electron metal UGe₂ (Nature 2000), the first example of its kind. Importantly the magnetic electrons in this material can be described in terms of a spin polarized Fermi surface and thus the magnetic electrons participate in the formation of a spin-triplet superconducting state.

He and collaborators from UCL led a team to the discovery published as cover story in Nature Physics of an unexpectedly robust form of superconductivity in the intercalated graphite compounds C₆Yb and C₆Ca. This discovery motivated numerous theoretical and experimental studies worldwide and has led to a revival of the field of carbon-based superconductivity and a re-examination of electron pairing mechanisms in general. 

Over the last decade he has led an investigation of the insulator to metal transition in the van der Waal compounds of the type MPS₃ where M stands for a transition metal element. These are low-dimensional systems that are magnetic insulators at ambient pressure but are expected to display an unconventional form of superconductivity at very high pressures. He has paved the way to the search for this type of superconductivity via a series of lattice and electronic structure studies up to several hundred thousand atmospheres. These studies that are of wide interest in their own right in a rapidly developing field of magnetic van der Waal materials (magnetic graphene) have just been published in Physical Review Letters (2018) 

His group has also pioneered in particular the study of quantum critical phenomena in displacive ferroelectric materials and of superconductivity on the border of ferroelectric quantum phase transitions. With his students he has carried out a series of high-precision studies as a function of electric field, temperature and pressure that have dramatically confirmed for the first time the applicability of the Larkin-Khmelnitskii-Schneerson theory of the quantum critical state in displacive ferroelectrics and of the Gurevich-Larkin-Firsov-Takada theory of superconductivity in polar materials. This work, published in Nature Physics (2014) & PNAS(2020), constitutes a major advance in the description of the quantum properties of ferroelectrics and opens up new opportunities for the study of exotic normal and superconducting states in polar materials including order-disorder as well as displacive ferroelectrics, ferrielectrics, anti-ferroelectrics and multi-ferroics.