Unconventional Superconductivity in Semimetallic Rhombohedral Graphene

Abstract

Rhombohedral graphene, a metastable stacking configuration of graphene, provides aclean platform for the study of correlated electron physics, hosting a rich set of symmetry-broken phases. Its characteristic staggered structure produces a large low-energy density of states, with wavefunctions predominantly localized on the outer crystal surfaces. This surface-localized density of states is further enhanced with increasing layer number and displacement field, providing a natural route to strong electronic correlations. Against this backdrop, the first part of this thesis explores the semimetallic state of rhombohedral graphene, in which valence and conduction band Fermi pockets reside on opposite crystal surfaces. Within this charge-delocalized regime, we identify multiple superconducting phases that appear at approximately constant conduction band filling. The most prominent of these phases expands dramatically with in-plane magnetic field, spanning a wide region of the phase diagram. It persists to fields far beyond the Pauli limit, consistent with spin triplet superconductivity. In addition to electrostatic control, pressure provides a complementary tuning parameter by directly modifying interlayer coupling and the resulting electronic structure. The second part of this thesis presents a robust approach for high-pressure transport measurements of two-dimensional heterostructures using a piston-cylinder cell. By replacing failure-prone wiring schemes with a compact, scalable design, this method establishes pressure as a practical tuning parameter for studying correlated phases in rhombohedral graphene