Electronic Band Structure and Structural Properties of Zircon Nitride Chloride

Unconventional superconductivity in electron-doped layered metal nitride halides MNX (M= Ti, Zr, Hf; X= Cl, Br, I)

“…When the incident angle (θ) is small, and hence electric-field vector is close to in-plane configuration, the intensity is stronger at the absorption edge for both compounds, demonstrating that the wave function at the conduction band bottom consists of the orbitals that are strongly hybridized with N p x and p y while hybridization with p z is small. This result clearly indicates the highly anisotropic electronic states, and is in good accord with the prediction of the band calculations [11][12][13][14][15].…”

“…Since the discovery of superconductivity in Li-doped β-HfNCl and β-ZrNCl [6,7], several groups have thus far performed band calculations [11][12][13][14][15] to elucidate the basic electronic structure. All the calculation results indicate very similar band structures, and the band diagram calculated for Na 0.…”

“…In the standard BCS theory, T c ∝ Z −α (Z represents the atomic mass) and α = 0.5 are obtained. The Nisotope effect, replacing 14 N to 15 N, has been investigated for Li x ZrNCl and Li x (THF) y HfNCl [41,42]. and Li x (THF) y HfNCl, which is much smaller than α = 0.5.…”

“…Kuroki [61] introduced a two-band tightbinding model that reproduces the band structure near the Fermi level obtained in the first-principles calculations [11,12,14,15]. In real space, this corresponds to considering both the M (Zr or Hf) and the nitrogen sites on the honeycomb lattice.…”

Unconventional pairing in doped band insulators on a honeycomb lattice: the role of the disconnected Fermi surface and a possible application to superconducting β-MNCl (M=Hf, Zr)

“…Although β-MNCl has a bilayer honeycomb lattice, we find that the two bands closest to the Fermi level, obtained in the first principles calculation [8,10,20,21], can roughly be reproduced by a single layer honeycomb lattice model consisting of alternating 'M' and 'N' orbitals with a level offset as shown in figure 8. Here we take t = 1.2 eV, /t = 2.7, and t /t = 0.35.…”