Enhancement of the Bulk Photovoltaic Effect in Topological Insulators

We investigate the shift current bulk photovoltaic response of materials close to a band inversion topological phase transition. We find that the bulk photocurrent reverses direction across the band inversion transition, and that its magnitude is enhanced in the vicinity of the phase transition. These results are demonstrated with first principles density functional theory calculations of BiTeI and ${\mathrm{CsPbI}}_3$ under hydrostatic pressure, and explained with an analytical model, suggesting that this phenomenon remains robust across disparate material systems.

Figure 1

Structure of BiTeI displayed in top view (a), and side view (b). Grey: Bi, purple: Te, orange: I. Panels (c)–(e): Evolution of band structure across the topological phase transition, from the normal insulator phase (lattice constant $a=4.42\AA$) (c), to the band inversion transition ($a=4.18\AA$) (d), to the topological insulator phase ($a=4.05\AA$) (e). Colors represent the projection of the wave functions to Bi $6p$ orbitals. The band character changes rapidly at the band inversion transition (d).

Figure 2

Shift current bulk photovoltaic response of BiTeI (a) and ${\mathrm{CsPbI}}_3$ (b). In each panel, spectra are given for a range of lattice constants, specified in Å.

Figure 3

Spectral parameters of the shift current response for BiTeI. Absolute value of the peak shift current is shown in (a) as a function of different band gap energies, corresponding to different applied pressures and lattice constants. Full width at half maximum of the shift current peak is shown in (b) as a function of different band gap energies, corresponding to different lattice constants. Dashed lines show the prediction of the model developed in Eq. (7), using dipole matrix elements fitted to the normal insulator (NI) phase.

Figure 4

Low energy band structure of BiTeI (a) and ${\mathrm{CsPbI}}_3$ (b) near the band inversion transitions. Energy difference between the lowest conduction band and highest valence band is shown at $a=7.90\AA$ for BiTeI (a) and at $a=6.075\AA$ for ${\mathrm{CsPbI}}_3$ (b).