Finite-size effects and spin texture of hourglass fermions in KHgSb films

Abstract

Recently, nonsymmorphic symmetry was found to be able to protect various exotic surface fermions. One example is the hourglass fermions predicted and realized in the (010) surface of KHgSb. In this work, we investigate the finite-size effects of hourglass fermions in KHgSb (010) thin films by careful first-principles calculations and thorough group analyses. We find that in thin films, although most hourglasses open up a gap due to the finite-size effects, some hourglasses remain intact. The surviving hourglass fermions are protected by certain nonsymmorphic symmetries at certain high-symmetry lines. We propose that a feasible external electric field can recover all the gapless hourglasses. Also, we notice that hourglass fermions can hold a large-scale spin texture featuring Dirac points with the two constituting bands having the same spin polarization. Our findings may pave the way for thickness-engineered manipulation and application of hourglass fermions.