7 research outputs found
Pressure induced electronic topological transition in Sb2S3
Pressure induced electronic topological transitions in the wide band gap
semiconductor Sb2S3 (Eg = 1.7-1.8 eV) with similar crystal symmetry (SG: Pnma)
to its illustrious analog, Sb2Se3, has been studied using Raman spectroscopy,
resistivity and the available literature on the x-ray diffraction studies. In
this report, the vibrational and the transport properties of Sb2S3 have been
studied up to 22 GPa and 11 GPa, respectively. We observed the softening of
phonon modes Ag(2), Ag(3) and B2g and a sharp anomaly in their line widths at 4
GPa. The resistivity studies also shows an anomaly around this pressure. The
changes in resistivity as well as Raman line widths can be ascribed to the
changes in the topology of the Fermi surface which induces the electron-phonon
and the strong phonon-phonon coupling, indicating a clear evidence of the
electronic topological transition (ETT) in Sb2S3. The pressure dependence of
a/c ratio plot obtained from the literature showed a minimum at ~ 5 GPa, which
is consistent with our high pressure Raman and resistivity results. Finally, we
give the plausible reasons for the non-existence of a non-trivial topological
state in Sb2S3 at high pressures.Comment: 24 pages, 6 Figures, 2 tables submitted for publicatio
Pressure-induced superconductivity in weak topological insulator BiSe
Quasi-two-dimensional layered BiSe, a natural super-lattice with
Bi2Se3-Bi2-Bi2Se3 units, has recently been predicted to be a dual topological
insulator, simultaneously weak topological insulator as well as topological
crystalline insulator. Here using structural, transport, spectroscopic
measurements and density functional theory calculations, we show that BiSe
exhibits rich phase diagram with the emergence of superconductivity with Tc ~8K
under pressure. Sequential structural transitions into SnSe-type energetically
tangled orthorhombic and CsCl-type cubic structures having distinct
superconducting properties are identified at 8 GPa and 13 GPa respectively. Our
observation of weak-antilocalization in magneto-conductivity suggests that
spin-orbit coupling (SOC) plays a significant role in retaining non-trivial
band topology in the trigonal phase with possible realization of 2D topological
superconductivity. Theoretical analysis reveals that SOC significantly enhances
superconducting Tc of the high-pressure cubic phase through an increase in
electron-phonon coupling strength. Simultaneous emergence of Dirac-like surface
states suggests cubic BiSe as a suitable candidate for the 3D-topological
superconductor.Comment: 15 pages, 5 figures with Supplementary page
Pressure tuning of bond-directional exchange interactions and magnetic frustration in the hyperhoneycomb iridate
We explore the response of Ir 5d orbitals to pressure in −LiIrO, a hyperhoneycomb iridate in proximity to a Kitaev quantum spin-liquid (QSL) ground state. X-ray absorption spectroscopy reveals a reconstruction of the electronic ground state below 2 GPa, the same pressure range where x-ray magnetic circular dichroism shows an apparent collapse of magnetic order. The electronic reconstruction, which manifests a reduction in the effective spin-orbit interaction in 5d orbitals, pushes −LiIrO further away from the pure = 1/2 limit. Although lattice symmetry is preserved across the electronic transition, x-ray diffraction shows a highly anisotropic compression of the hyperhoneycomb lattice which affects the balance of bond-directional Ir-Ir exchange interactions driven by spin-orbit coupling at Ir sites. An enhancement of symmetric anisotropic exchange over Kitaev and Heisenberg exchange interactions seen in theoretical calculations that use precisely this anisotropic Ir-Ir bond compression provides one possible route to the realization of a QSL state in this hyperhoneycomb iridate at high pressures