title: Electronic instability in a zero-gap semiconductor: the charge-density wave in (TaSe4)2I.
abstract: We report a comprehensive study of the paradigmatic quasi-1D compound (TaSe(4))(2)I performed by means of angle-resolved photoemission spectroscopy (ARPES) and first-principles electronic structure calculations. We find it to be a zero-gap semiconductor in the nondistorted structure, with non-negligible interchain coupling. Theory and experiment support a Peierls-like scenario for the charge-density wave formation below T(CDW)=263  K, where the incommensurability is a direct consequence of the finite interchain coupling. The formation of small polarons, strongly suggested by the ARPES data, explains the puzzling semiconductor-to-semiconductor transition observed in transport at T(CDW).
authors.affiliation: Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: C
authors.initials: C
authors.lastname: Tournier-Colletta
authors.affiliation: Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: L
authors.initials: L
authors.lastname: Moreschini
authors.affiliation: Institute of Theoretical Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: G
authors.initials: G
authors.lastname: Autès
authors.affiliation: Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Moser
authors.affiliation: Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Crepaldi
authors.affiliation: Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: H
authors.initials: H
authors.lastname: Berger
authors.affiliation: Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Walter
authors.affiliation: Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: K S
authors.initials: KS
authors.lastname: Kim
authors.affiliation: Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: A
authors.initials: A
authors.lastname: Bostwick
authors.affiliation: Institut Néel, CNRS/Université Joseph Fourier, 38042 Grenoble, France.
authors.forename: P
authors.initials: P
authors.lastname: Monceau
authors.affiliation: Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: E
authors.initials: E
authors.lastname: Rotenberg
authors.affiliation: Institute of Theoretical Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: O V
authors.initials: OV
authors.lastname: Yazyev
authors.affiliation: Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Grioni