Resistivity anisotropy and charge density wave in 1 T -TiSe2
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ORIGINAL PAPER
Resistivity anisotropy and charge density wave in 1T-TiSe2 A Nader1* and A LeBlanc2 1
Department of Physics, Atomic Energy Commission of Syria, P.O. Box 6091, Damascus, Syria
2
Institut des Mate´riaux Jean Rouxel (IMN), Universite´ de Nantes, CNRS, 2 rue de la Houssinie`re, BP 32229, 44322 Nantes cedex 3, France Received: 25 September 2012 / Accepted: 08 November 2012 / Published online: 1 December 2012
Abstract: The in-plane and out-of-plane resistivities of 1T-TiSe2 are determined precisely down to 14 K. Both of them show the so-called broadened peak, though, the slope of qc becomes negative for T 200 K.On the other hand, the resistivity anisotropy has at least two slope changes at 150 and 250 K, and its values are much less than other transition metal dichalcogenides such as 2H- NbSe2. Keywords:
Resistivity anisotropy; Dichalcogenides; Layered compounds; Charge density wave
PACS Nos.: 72.15.Eb; 71.45.Lr
1. Introduction Layered transition metal dichalcogenides have attracted a widespread interest because of their unique electronic properties. Originally they were discovered as the prototypical 2D charge density wave (CDW) compounds [1–3]. However, later on the discovery of the superconductivity at low temperature made them subject to an intense study. Their general formula is TX2, where T stands for the transition metal (usually Nb, Ti or Ta) and X for the chalcogenide (S, Se or Te). Their structure consists of three-layer packets, inside which the layers are ordered in the X-T-X sequence with covalent binding between them, whereas the packets are bound by weak van der Waals coupling. Due to this weak coupling, adjacent packets may be oriented in different ways relative one to another and as a consequence there is possibility of polytypism in this family. Polytypes are referred as 1T, 2H and 3R. The starting number in this notation denotes the number of X-T-X sandwiches perpendicular to the plane in the unit cell, the T, H, R distinguish respectively the trigonal, hexagonal or rhombohedral symmetry of the structure. Among this family, 1T-TiSe2 turns out to be an interesting and enigmatic material.
*Corresponding author, E-mail: [email protected]
At the critical temperature of Tc 200 K, the system undergoes a second-order phase transition, characterized notably by a peak in the resistivity[4–6] and a phonon softening at Tc [7]. The explanation of the CDW is not completely settled yet and accepts controversial explanations. Indeed, the 1T-TiSe2 Fermi-surface topology does not favor nesting since no large parallel portions of Fermi surface (FS) are present [8]. A band Jahn–Teller effect has been proposed [9] as an alternative mechanism, relying on the fact that at the transition a periodic lattice distortion develops, which results in a tendency of the system to pass from the 1T octahedral environment of the transition atom to the 2H prismatic environment polytype. A third explanation that is developed in [10] is the exciton condensate phase. In this work, the in-plane and out-of-pla
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