calcQPI: a versatile tool to simulate quasiparticle interference (code)

This is a repository of minimal tight-binding models to demonstrate the capabilities of calcQPI in calculating QPI patterns. The examples are described in the preprint at https://arxiv.org/abs/2507.22137

Homepage: https://wahl.wp.st-andrews.ac.uk/calcqpi

Github: https://github.com/gpwahl/calcqpi-release (version accompanying preprint)

The minimal models test a range of functionalities of calcQPI, including calculation of surface states, Rashba spin splitting, topogically protected surface states, nearest neighbour tight-binding models on square and hexagonal lattices, and calculations of Bogoljubov quasi-particle interference.

The folders are:

1nn nearest neighbour model on a square lattice in 2D
1nn-hex nearest neighbour model on a hexagonal lattice in 2D
1nnz nearest neighbour model on a square lattice with non-negligible out-of-plane coupling
rashba nearest neighbour model with Rashba term (through non-local spin-orbit coupling)
ssh nearest neighbour model where the out of plane coupling is alternating as in an SSH-chain, creating a surface state
topo nearest neighbour model of a topological insulator, again with non-local spin-orbit coupling
1nn-sc nearest neighbour model with a dx2 superconducting gap
1nn-josephson as 1nn-sc, but with configuration files to simulate Josephson current as would be measured with a superconducting tip
sr2ruo4 QPI calculation for Sr2RuO4, as in fig. 12 of the preprint (though with lower resolution and not including the experimental data). In the sub-folder 'wannnierization' we provide an example for how to obtain the tight-binding model and wave function files from DFT calculations
To run the simulations, calcQPI is required, and to generate the figures, an installation of python3 with numpy and matplotlib. The file config.mk contains the path to calcQPI and mkwavefunctions, which are required to run the simulations. All simulations can be run by just typing make

Note that the plotting part requires python 3.9 or later and matplotlib.