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@@ -1294,8 +1294,8 @@ <h3 id="main-problem-and-dependencies">Main Problem and Dependencies</h3>
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<h3id="subproblems">Subproblems</h3>
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<p><strong>1.1 Write a Haldane model Hamiltonian on a hexagonal lattice, given the following parameters: wavevector components <spanclass="arithmatex">\(k_x\)</span> and <spanclass="arithmatex">\(k_y\)</span> (momentum) in the x and y directions, lattice spacing <spanclass="arithmatex">\(a\)</span>, nearest-neighbor coupling constant <spanclass="arithmatex">\(t_1\)</span>, next-nearest-neighbor coupling constant <spanclass="arithmatex">\(t_2\)</span>, phase <spanclass="arithmatex">\(\phi\)</span> for the next-nearest-neighbor hopping, and the on-site energy <spanclass="arithmatex">\(m\)</span>.</strong></p>
Source: Haldane, F. D. M. (1988). Model for a quantum Hall effect without Landau levels: Condensed-matter realization of the" parity anomaly". Physical review letters, 61(18).</p>
<p>Source: Haldane, F. D. M. (1988). Model for a quantum Hall effect without Landau levels: Condensed-matter realization of the" parity anomaly". Physical review letters, 61(18).</p>
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<p>We denote <spanclass="arithmatex">\(\{\mathbf{a}_i\}\)</span> are the vectors from a B site to its three nearest-neighbor A sites, and <spanclass="arithmatex">\(\{\mathbf{b}_i\}\)</span> are next-nearest-neighbor distance vectors, then we have</p>
<strong>1.2 Calculate the Chern number using the Haldane Hamiltonian, given the grid size <spanclass="arithmatex">\(\delta\)</span> for discretizing the Brillouin zone in the <spanclass="arithmatex">\(k_x\)</span> and <spanclass="arithmatex">\(k_y\)</span> directions (assuming the grid sizes are the same in both directions), the lattice spacing <spanclass="arithmatex">\(a\)</span>, the nearest-neighbor coupling constant <spanclass="arithmatex">\(t_1\)</span>, the next-nearest-neighbor coupling constant <spanclass="arithmatex">\(t_2\)</span>, the phase <spanclass="arithmatex">\(\phi\)</span> for the next-nearest-neighbor hopping, and the on-site energy <spanclass="arithmatex">\(m\)</span>.</strong></p>
Source: Fukui, Takahiro, Yasuhiro Hatsugai, and Hiroshi Suzuki. "Chern numbers in discretized Brillouin zone: efficient method of computing (spin) Hall conductances." Journal of the Physical Society of Japan 74.6 (2005): 1674-1677.</p>
<p>Source: Fukui, Takahiro, Yasuhiro Hatsugai, and Hiroshi Suzuki. "Chern numbers in discretized Brillouin zone: efficient method of computing (spin) Hall conductances." Journal of the Physical Society of Japan 74.6 (2005): 1674-1677.</p>
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<p>Here we can discretize the two-dimensional Brillouin zone into grids with step <spanclass="arithmatex">\(\delta {k_x} = \delta {k_y} = \delta\)</span>. If we define the U(1) gauge field on the links of the lattice as <spanclass="arithmatex">\(U_\mu (\mathbf{k}_l) := \frac{\left\langle n(\mathbf{k}_l)\middle|n(\mathbf{k}_l + \hat{\mu})\right\rangle}{\left|\left\langle n(\mathbf{k}_l)\middle|n(\mathbf{k}_l + \hat{\mu})\right\rangle\right|}\)</span>, where <spanclass="arithmatex">\(\left|n(\mathbf{k}_l)\right\rangle\)</span> is the eigenvector of Hamiltonian at <spanclass="arithmatex">\(\mathbf{k}_l\)</span>, <spanclass="arithmatex">\(\hat{\mu}\)</span> is a small displacement vector in the direction <spanclass="arithmatex">\(\mu\)</span> with magnitude <spanclass="arithmatex">\(\delta\)</span>, and <spanclass="arithmatex">\(\mathbf{k}_l\)</span> is one of the momentum space lattice points <spanclass="arithmatex">\(l\)</span>. The corresponding curvature (flux) becomes</p>
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