A maximally particle-hole asymmetric spectrum emanating from a semi-Dirac point

• Published in: Journal of physics. Condensed matter Vol. 30; no. 7; p. 75501
• Main Authors: Quan, Yundi, Pickett, Warren E
• Format: Journal Article
• Language: English
• Published: England IOP Publishing 21.02.2018
• Subjects: Hofstadter; semi-Dirac; topology; semi-Dirac; topology; Hofstadter
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/1361-648X/aaa521

Tight binding models have proven an effective means of revealing Dirac (massless) dispersion, flat bands (infinite mass), and intermediate cases such as the semi-Dirac (sD) dispersion. This approach is extended to a three band model that yields, with chosen parameters in a two-band limit, a closed line with maximally asymmetric particle-hole dispersion: infinite mass holes, zero mass particles. The model retains the sD points for a general set of parameters. Adjacent to this limiting case, hole Fermi surfaces are tiny and needle-like. A pair of large electron Fermi surfaces at low doping merge and collapse at half filling to a flat (zero energy) closed contour with infinite mass along the contour and enclosing no carriers on either side, while the hole Fermi surface has shrunk to a point at zero energy, also containing no carriers. The tight binding model is used to study several characteristics of the dispersion and density of states. The model inspired generalization of sD dispersion to a general  ±kx2n+ky2m form, for which analysis reveals that both n and m must be odd to provide a diabolical point with topological character. Evolution of the Hofstadter spectrum of this three band system with interband coupling strength is presented and discussed.