Interacting line-node semimetal: Proximity effect and spontaneous symmetry breaking

Effects of short-range electronic interactions in a three-dimensional line-node semimetal that supports linearly dispersing quasiparticles around an isolated loop in the Brillouin zone will be presented. I will argue that due to the vanishing density of states ( ρ(E) ~ |E|) various orderings in the bulk of the system, such as the antiferromagnet and charge-density-wave, set in for sufficiently strong onsite (U) and nearest-neighbor (V) repulsions, respectively. While onset of these two orderings from the semimetallic phase takes place through continuous quantum phase transitions, a first-order transition separates two ordered phases. I will demosntrate that topologically protected drumhead shaped surface states, on the other hand, can undergo charge or spin orderings, depending on relative strength of U and V, even when they are sufficiently weak. Such surface orderings as well as weak long-range Coulomb interaction can be conducive to spontaneous symmetry breaking in the bulk for weaker interactions. I will present numerical results supporting the scenario of proximity effect driven spontaneous symmetry breaking in the bulk for subcritical strength of interactions due to flat surface band.