Magnetic excitations of a new pressure-induced Kondo lattice superconductor in a magnetic field

In unconventional superconductors the superconductivity is believed to be mediated by spin fluctuations, rather than the electron-phonon pairing mechanism of BCS theory. However, the microscopic mechanisms of spin-fluctuation mediated superconductivity are not yet determined, and there is a lack of understanding as to which types of spin fluctuations are favourable for forming unconventional Cooper pairs. CeSb2 is a heavy-fermion antiferromagnet that becomes superconducting under pressure after magnetic order is suppressed, with highly unusual behaviour of the upper critical field. We recently performed inelastic neutron scattering and mapped the spin-waves in the antiferromagnetic state of CeSb2. Our results suggest unusual magnetism, but determining the magnetic exchange interactions is challenging due to a large number of parameters and the complex antiferromagnetic ground state. To determine these magnetic exchange interactions, we propose to probe the spin-waves in the field-induced ferromagnetic state when a 4T magnetic field is applied, where the simple spin structure makes modelling the spin excitations much easier. Since these magnetic interactions give rise to both the ordered magnetic state at ambient pressure, and the unconventional, possibly spin-triplet, heavy fermion superconductivity under pressure, our study can provide important information about the characteristics of spin fluctuations giving rise to unconventional superconductivity.