Fig. 1
Schematic crystal structure and the experimental scheme of the neutron scattering measurements. a Schematic of the hexagonal crystal structure of Sr0.1Bi2Se3. The dopant Sr ions are believed to be intercalated in the van der Waals gaps between the quintuple layers consisting of Bi and Se ions39. The dashed lines denote a unit cell, while the shades denote the octahedra formed by the Se ions, with Bi ions in the centre. b Brillouin zones in the (H0L) plane defined by two orthogonal axes [100] and [001] in the reciprocal space, constructed based on the hexagonal notation illustrated in (a). The two long arrows point to (1, 0, −5) and (0, 0, −15), the two strongest Bragg peaks available around which we measure the phonons. Arrows on (1, 0, −5) and (0, 0, −15) represent the directions along which we plot the phonon dispersions in Fig. 2. The letters a–d correspond to panels a–d in Fig. 2. Dashed lines illustrate the Brillouin zone boundaries, and the shades represent the two measured Brillouin zones. Dots represent high-symmetry points, with \({\mathrm{\Gamma }}\), Z, F, and L in the measured Brillouin zones being labelled. The wave vector Q is expressed as (H, K, L) reciprocal lattice unit (rlu) of \(\left( {a^ \ast ,b^ \ast ,c^ \ast } \right) = \left( {4\pi /\sqrt 3 a,4\pi /\sqrt 3 b,2\pi /c} \right)\), with \(a = b = 4.14\,{\mathrm{{\AA}}}\), and \(c = 28.6\,{\mathrm{{\AA}}}\)
