Abstract Body

The Sarma state is a superconducting state which exists at a high magnetic field and has electronic structure more similar to a normal metal^[1]. Although normally suffering from thermodynamic instability, the Sarma state has been predicted to occur in multiband superconductors with sufficient gap anisotropy^[2]. In this work, we explore a different route to the Sarma state in nonsymmorphic superconductors. The nonsymmorphic structure allows the coexistence of two types of electrons – strongly spin-coupled electrons with weak Zeeman effect for a magnetic field^[3] and weakly spin-coupled electrons with a normal magnitude of the Zeeman effect. The different strengths of the Zeeman effect on the two Fermi surfaces allow the Sarma state to occur.

The aim of this project is to use mean-field theory to obtain the magnetic field-temperature phase diagram for a superconductor with such a structure and to determine the existence of the Sarma state.  Furthermore, we study the variation of thermodynamic quantities such as specific heat, magnetization and susceptibility across the phase diagram.

References

[1] G. Sarma. On the influence of a uniform exchange field acting on the spins of the conduction electrons in a superconductor. Journal of Physics and Chemistry of Solids, 24(8):1029–1032, August 1963.
[2] Victor Barzykin and L. P. Gor’kov. Gapless Fermi Surfaces of Anisotropic Multiband Superconductors in a Magnetic Field. Physical Review Letters, 98(8):087004, February 2007.
[3] D. C. Cavanagh, T. Shishidou, M. Weinert, P. M. R. Brydon, and Daniel F. Agterberg. Nonsymmorphic symmetry and field-driven odd-parity pairing in CeRh2As2. Physical Review B, 105(2):L020505, January 2022