: Electronic instability and extremely strong quasiparticle renormalisation
Introduction
The layered perovskite ruthenates have generated a wealth of novel physics since the discovery of superconductivity in [1]. The superconducting order parameter has been shown to be unconventional [2], and extensive investigations of related compounds such as , , and have revealed a number of novel phase transitions and magnetic states [3], [4], [5], [6], [7]. Among the series, the properties of the bilayer material have presented something of a mystery. Single crystals have been grown by both the flux method [8] and in image furnaces [9]. The measured resistivity shows metallic behaviour at low temperatures with a residual resistivity of in Ref. [9], but flux-grown crystals present a non-metallic temperature dependence [8]. Besides, the electronic specific heat has been reported to have a metallic component that varies considerably, from mol-Ru [9] to mol-Ru [10]. Shubnikov–de Haas oscillations have been seen by both groups, but the only direct comparisons of the specific heat coefficient with the quasiparticle masses gave very poor agreement [11], leaving many open questions about the precise nature of the ground state of the material. In this paper, we describe the growth, in an image furnace, of metallic single crystals of with a residual resistivity one order of magnitude lowerthan the best previously observed value. Using these crystals, we have performed detailed electronic structure studies by means of quantum oscillations and high-resolution angle-resolved photoemission-spectroscopy (ARPES).
Section snippets
Experiment
The crystals were grown by a floating-zone method with -rich feed rods. The optimised feed rods for our image furnace were prepared with a composition of reflecting a heavy evaporation of during the crystal growth. The growth was done at the speed of 7 mm/h and under a pressure of 1 MPa with a flowing gas mixture . Crystals with the typical size of were obtained. The crystals were characterised by X-ray and SEM (scanning electron
Transport properties and electronic structure
The in-plane resistivity of two of the resulting crystals is plotted in Fig. 1 as a function of temperature down to 4 K. The most prominent features are associated with the previously-established Néel and first order structural phase transitions denoted as and [8], [9], [12], [13]. At temperatures above these transitions, is almost linear in T.
Approximately below 30 K, drops dramatically, giving evidence for a strongly metallic temperature dependence. Using these metallic
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Ca3Ru2 O7: Interplay among degrees of freedom and the role of the exchange correlation
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2010, Physica Status Solidi (B) Basic Research
- 1
Present address: National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan.
- 2
Present address: School of Physics and Astronomy, University of St. Andrews, Fife KY16 9SS, UK.