Pressure-induced phase transitions and superconductivity in a quasi–1-dimensional topological crystalline insulator α-Bi ₄ Br ₄

Abstract

Great progress has been achieved in the research field of topological states of matter during the past decade. Recently, a quasi–1-dimensional bismuth bromide, Bi4Br4, has been predicted to be a rotational symmetry-protected topological crystalline insulator; it would also exhibit more exotic topological properties under pressure. Here, we report a thorough study of phase transitions and superconductivity in a quasihydrostatically pressurized α-Bi4Br4 crystal by performing detailed measurements of electrical resistance, alternating current magnetic susceptibility, and in situ high-pressure single-crystal X-ray diffraction together with first principles calculations. We find a pressure-induced insulator–metal transition between ∼3.0 and 3.8 GPa where valence and conduction bands cross the Fermi level to form a set of small pockets of holes and electrons. With further increase of pressure, 2 superconductive transitions emerge. One shows a sharp resistance drop to 0 near 6.8 K at 3.8 GPa; the transition temperature gradually lowers with increasing pressure and completely vanishes above 12.0 GPa. Another transition sets in around 9.0 K at 5.5 GPa and persists up to the highest pressure of 45.0 GPa studied in this work. Intriguingly, we find that the first superconducting phase might coexist with a nontrivial rotational symmetry-protected topology in the pressure range of ∼3.8 to 4.3 GPa; the second one is associated with a structural phase transition from monoclinic C2/m to triclinic P-1 symmetry.

High-Pressure Modification of BiI3

“…The anisotropy is shown in Figure 3. [17] curves are shown in red ([100]: a0 = 434 pm, B0 = 85.78(5) GPa and B0' = 8.085(6); [010]: b0 = 1400 pm, B0 = 31.82(2) GPa, B0' = 18.721(6); [001]: c0 = 1062 pm, B0 = 23.42(2) GPa, B0' = 17.057 (7). Please note the pronounced hardening upon pressure increase in direction [010] and [001], causing the distinct curvature.…”

“…Please note the pronounced hardening upon pressure increase in direction [010] and [001], causing the distinct curvature. .057 (7). Please note the pronounced hardening upon pressure increase in direction [010] and [001], causing the distinct curvature.…”

“…Bismuth compounds and especially halides are in special focus as their atomic arrangements often exhibit low-symmetry patterns caused by the stereochemical activity of lone pairs [3][4][5][6]. Moreover, their structural and physical properties can be substantially modified by application of hydrostatic pressure [7][8][9][10].…”

“…Lattice parameters a, b and c (from left to right) of the high-pressure phase (oS16) BiI 3 at pressures between ambient and 40 GPa. Blue symbols indicate experimental data and the fitted equations of state [17] curves are shown in red ([100]: a 0 = 434 pm, B 0 = 85.78(5) GPa and B 0 = 8.085(6); [010]: b 0 = 1400 pm, B 0 = 31.82(2) GPa, B 0 = 18.721(6); [001]: c 0 = 1062 pm, B 0 = 23.42(2) GPa, B 0 = 17.057(7). Please note the pronounced hardening upon pressure increase in direction [010] and [001], causing the distinct curvature.…”

Optical Response from Charge-Density Waves in Weyl Semimetals

“…Recent progress in the search for topological materials has revealed topological insulators and semimetals with local magnetic order, as well as highlighted the link between phonon-driven structural distortions and changes in electronic topology. One particularly illustrative material class is the bismuth halides Bi 4 X 4 [1][2][3][4][5], where a structural phase transition drives a band inversion between trivial and weak or higher-order topological insulating phases. Additionally, several topological semimetals such as (TaSe 4 ) 2 I[ [6][7][8][9][10][11], and ZrTe 5 [12] in a magnetic field, TaTe 4 [13], and GdSbTe [14] undergo charge-density wave (CDW) distortions that can drastically change the electronic structure and band topology.…”