NMR Investigation of Field-Induced Energy Gap in Topological Node-Line Semimetal ZrGeSe*

The discovery of topological semimetals provides opportunities to explore the exotic properties of relativistic fermions in condensed matter. Among those materials, the nodal-line semimetal represents a new type of topological quantum state which displays Dirac cones along a one-dimensional line or a closed circle protected by combined symmetry of inversion and time-reversal, in contrast with the Dirac or Weyl semimetals with discrete Dirac or Weyl cones. Here we report NMR investigation of field-induced energy gap in topological nodal-line semimetals of ZrGeSe single crystals, with high magnetic field up to 16 T and high hydrostatic pressure up to 50 GPa. We found that the opening of the energy gap is driven by the magnetic field-induced anti-ferromagnetic (AFM) order, and the gap opening is highly restricted under high pressure.