title: Recent advances inβ-FeSe1-xand related superconductors.
abstract: It has been more than four years since the discovery ofβ-FeSe1-xsuperconductors. Through the efforts of many outstanding research groups, unprecedented advances in the field have been achieved. High-quality single crystals ofβ-FeSe1-xand related compounds have been prepared by various techniques, allowing us to explore in detail the physical properties of this class of materials. Detailed characterizations of the structure and properties of these crystals have helped us to understand the origin of superconductivity inβ-FeSe1-x. The occurrence of superconductivity is associated with the low-temperature structure distortion, which is accompanied by several anomalies. Recent measurements on quasiparticle and acoustic phonon dynamics with respect to the orbital modification inβ-FeSe1-xsuggest the opening of an energy gap below 130-140 K, accompanied by a coincident transfer of optical spectral weight in the visible range and alterations in transport properties. These observations provide convincing evidence that the modification of the electronic structure occurs prior to the lattice distortion. They further suggest that the high-temperature gap and the lattice symmetry breaking are driven by short-range orbital and/or charge orders.
authors.affiliation: Department of Physics, National Dong-Hwa University, Hualien, Taiwan; Institute of Physics, Academia Sinica, Taipei, Taiwan.
authors.forename: Maw-Kuen
authors.initials: MK
authors.lastname: Wu
authors.affiliation: Institute of Physics, Academia Sinica, Taipei, Taiwan; Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan.
authors.forename: Ming-Jye
authors.initials: MJ
authors.lastname: Wang
authors.affiliation: Institute of Physics, Academia Sinica, Taipei, Taiwan.
authors.forename: Kuo-Wei
authors.initials: KW
authors.lastname: Yeh
keywords: 10.14; 20.04; FeSe; high-quality single crystals; structure and properties characterization; superconductors