Journal Article

Emergence of coherence in the charge-density wave state of 2H-NbSe2

Norman, M. R., Di Capua, R., Trivedi, N., Malliakas, C. D., Claus, H., Campuzano, J. C., Osborn, R., Iavarone, M., Ruff, J. P. C., Kanatzidis, M. G., Karapetrov, G., Castellan, J. P., Randeria, M., Weber, F., van Wezel, J., Rosenkranz, S., Chatterjee, U., Zhao, J.

2015

Overview

A charge-density wave (CDW) state has a broken symmetry described by a complex order parameter with an amplitude and a phase. The conventional view, based on clean, weak-coupling systems, is that a finite amplitude and long-range phase coherence set in simultaneously at the CDW transition temperature T cdw . Here we investigate, using photoemission, X-ray scattering and scanning tunnelling microscopy, the canonical CDW compound 2 H -NbSe 2 intercalated with Mn and Co, and show that the conventional view is untenable. We find that, either at high temperature or at large intercalation, CDW order becomes short-ranged with a well-defined amplitude, which has impacts on the electronic dispersion, giving rise to an energy gap. The phase transition at T cdw marks the onset of long-range order with global phase coherence, leading to sharp electronic excitations. Our observations emphasize the importance of phase fluctuations in strongly coupled CDW systems and provide insights into the significance of phase incoherence in ‘pseudogap’ states. Charge density waves are described by a complex order parameter whose amplitude is expected to vanish at the transition temperature. This study shows that the transition in 2 H -NbSe 2 is driven by fluctuations of the phase of the order parameter, with a finite amplitude surviving in the disordered state.

• Publisher: Nature Publishing Group UK,Nature Publishing Group,Nature Pub. Group
• Subject: 140/146 / 639/301/119/2795 / 639/766/483 / catalysis (heterogeneous) / CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY / defects / energy storage (including batteries and capacitors) / High temperature / Humanities and Social Sciences / hydrogen and fuel cells / materials and chemistry by design / MATERIALS SCIENCE / mechanical behavior / multidisciplinary / Science / Science (multidisciplinary) / solar (photovoltaic) / synthesis (novel materials) / Transition temperatures