title: Multiferroic behavior in elemental selenium below 40 K: effect of electronic topology.
abstract: The quasi-one-dimensional, chiral crystal structure of Selenium has fascinating implications: we report simultaneous magnetic and ferroelectric order in single crystalline Se microtubes below ≈40 K. This is accompanied by a structural transition involving a partial fragmentation of the infinite chains without losing overall crystalline order. Raman spectral data indicate a coupling of magnons with phonons and electric field, while the dielectric constant shows a strong dependence on magnetic field. Our first-principles theoretical analysis reveals that this unexpected multiferroic behavior originates from Selenium being a weak topological insulator. It thus exhibits stable electronic states at its surface, and magnetism emerges from their spin polarization. Consequently, the broken two-fold rotational symmetry permits switchable polarization along its helical axis. We explain the observed magnetoelectric couplings using a Landau theory based on the coupling of phonons with spin and electric field. Our work opens up a new class of topological surface-multiferroics with chiral bulk structure.
authors.affiliation: Department of Condensed Matter Physics & Materials Science, Tata Institute of Fundamental Research, Mumbai 400005, India.
authors.forename: Anirban
authors.initials: A
authors.lastname: Pal
authors.forename: Sharmila N
authors.initials: SN
authors.lastname: Shirodkar
authors.forename: Smita
authors.initials: S
authors.lastname: Gohil
authors.forename: Shankar
authors.initials: S
authors.lastname: Ghosh
authors.forename: Umesh V
authors.initials: UV
authors.lastname: Waghmare
authors.forename: Pushan
authors.initials: P
authors.lastname: Ayyub