Topological insulators under pressure
Researchers using the XSD 11-BM-B and HP-CAT 16-ID-B beamlines at the APS are exploring the structural phase transitions in Bi2Se3 under high pressure to gain a better understanding of structural evolutions of topological insulators.
Topological insulators (TIs) are electronic materials that have a bulk band gap like ordinary insulators, but feature conducting states on their surface. Besides the importance of theoretical investigation in condensed matter physics, TIs also have various actual applications in the fields of spintronics, quantum computation and thermoelectric energy conversion.
Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm).
Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3 crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculations favor the viewpoint that the I4/mmm phase Bi2Se3 can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi2Se3 from this work (two independent runs) are still Raman active up to ~35 GPa. It is worthy to note that the disordered BCC phase at 27.8 GPa is not observed here. The remarkable difference in atomic radii of Bi and Se in Bi2Se3 may explain why Bi2Se3 shows different structural behavior than isocompounds Bi2Te3 and Sb2Te3.
Zhenhai Yu, Lin Wang, Qingyang Hu, Jinggeng Zhao, Shuai Yan, Ke Yang, Stanislav Sinogeikin, Genda Gu and Ho-kwang Mao, “Structural Phase Transitions in Bi2Se3 under High Pressure,” Scientific Reports 5, Article Number: 15939 (2015). DOI:10.1038/srep15939. Published Online November 2, 2015.