Nonsymmorphic-symmetry-protected hourglass Dirac loop, nodal line, and Dirac point in bulk and monolayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>X</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>SiTe</mml:mi><mml:mn>6</mml:mn></mml:msub></mml:mrow></mml:math> ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>X</mml:mi></mml:math> = Ta, Nb)
Nonsymmorphic-symmetry-protected hourglass Dirac loop, nodal line, and Dirac point in bulk and monolayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>X</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>SiTe</mml:mi><mml:mn>6</mml:mn></mml:msub></mml:mrow></mml:math> ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>X</mml:mi></mml:math> = Ta, Nb)
Nonsymmorphic space group symmetries can generate exotic band crossings in topological metals and semimetals. Here, based on symmetry analysis and first-principles calculations, we reveal rich band-crossing features in the existing layered compounds ${\mathrm{Ta}}_{3}{\mathrm{SiTe}}_{6}$ and ${\mathrm{Nb}}_{3}{\mathrm{SiTe}}_{6}$, enabled by nonsymmorphic symmetries. We show that in the absence of spin-orbit coupling (SOC), these …