Superconductivity in Heavy Alkaline-Earth Intercalated Graphites

Kim, J. S.; Boeri, Lilia; O’Brien, Justin; Razavi, F. S.; Kremer, Reinhard K.

doi:10.1103/physrevlett.99.027001

Cited by 78 publications

(84 citation statements)

References 26 publications

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“…In this work a prediction was made of the superconducting transition temperatures of TC=3 K and 0.2K for SrC6 and BaC6 respectively. Following this prediction, as detailed earlier [28] the TC for SrC6 was found to be 1.65 K. In the case of BaC6 no transition was observed, indeed in [61] no superconducting transition was found down to 80 mK. However, the CDW state, seen in figure 1.7, was not at all predicted by any DFT studies.…”

Section: Theoretical Studies Of Superconductivity In Gicssupporting

confidence: 71%

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Superconductivity in graphite intercalation compounds

Smith

Weller

Howard

et al. 2015

Physica C: Superconductivity and its Applications

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The field of superconductivity in the class of materials known as graphite intercalation compounds has a history dating back to the 1960s [1,2]. This paper recontextualizes the field in light of the discovery of superconductivity in CaC6 and YbC6 in 2005. In what follows, we outline the crystal structure and electronic structure of these and related compounds. We go on to experiments addressing the superconducting energy gap, lattice dynamics, pressure dependence, and how this relates to theoretical studies. The bulk of the evidence strongly supports a BCS superconducting state. However, important questions remain regarding which electronic states and phonon modes are most important for superconductivity and whether current theoretical techniques can fully describe the dependence of the superconducting transition temperature on pressure and chemical composition.Corresponding author. Tel: +44 (0)7792954220 fax: +44 (0)20 7679 7145 e-mail address: mark.ellerby@ucl.ac.uk (Mark Ellerby).

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Section: Theoretical Studies Of Superconductivity In Gicssupporting

confidence: 71%

“…and BaC6 has been shown to be possible via vapour transport on single crystal flakes [50,28] P a g e | 7…”

Section: Reframing Of Superconductivity In Graphite Intercalatesmentioning

confidence: 99%

Superconductivity in graphite intercalation compounds

Smith

Weller

Howard

et al. 2015

Physica C: Superconductivity and its Applications

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“…The properties of the GIC family have been studied extensively using a variety of different experimental techniques (21)(22)(23)(24)(25). Especially, the discovery of superconductivity in CaC 6 at the enhanced transition temperature (11.5 K) (26,27) excited intense research interest in GICs experimentally (28,29). The C-C bond length in phase IV is 1.4672 Å at 105.8 GPa, which is slightly longer than that (1.42 Å) in graphite.…”

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confidence: 99%

Pressure-induced superconductivity in CaC ₂

Luo

Zhang

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Carbon can exist as isolated dumbbell, 1D chain, 2D plane, and 3D network in carbon solids or carbon-based compounds, which attributes to its rich chemical binding way, including sp-, sp 2 -, and sp 3 -hybridized bonds. sp 2 -hybridizing carbon always captures special attention due to its unique physical and chemical property. Here, using an evolutionary algorithm in conjunction with ab initio method, we found that, under compression, dumbbell carbon in CaC 2 can be polymerized first into 1D chain and then into ribbon and further into 2D graphite sheet at higher pressure. The C2/m structure transforms into an orthorhombic Cmcm phase at 0.5 GPa, followed by another orthorhombic Immm phase, which is stabilized in a wide pressure range of 15.2-105.8 GPa and then forced into MgB 2 -type phase with wide range stability up to at least 1 TPa. Strong electron-phonon coupling λ in compressed CaC 2 is found, in particular for Immm phase, which has the highest λ value (0.562-0.564) among them, leading to its high superconducting critical temperature T c (7.9∼9.8 K), which is comparable with the 11.5 K value of CaC 6 . Our results show that calcium not only can stabilize carbon sp 2 hybridization at a larger range of pressure but also can contribute in superconducting behavior, which would further ignite experimental and theoretical interest in alkaline-earth metal carbides to uncover their peculiar physical properties under extreme conditions. high pressure | metallization H igh pressure, as a crucial thermodynamic parameter, has been emerging as a powerful tool to investigate physical and chemical behavior of materials, especially to explore the evolution of planets, and synthesize or design materials with peculiar properties such as superhardness and superconductivity (1-5). Recently, Ca and C, as ordinary elemental solids, have been studied extensively in physical, chemical, and material science fields due to their interesting structural properties when pressure is applied (6-10). These peculiar physical properties of compressed Ca and C solids have motivated our attention on Cabased dicarbide CaC 2 . In CaC 2 (11, 12) at ambient pressure, experimentally, four temperature-induced modifications were reported, which are the well-known tetragonal room temperature modification CaC 2 I (space group I4/mmm, Z = 2), two lowtemperature monoclinic modifications CaC 2 II (C2/c, Z = 4), and CaC 2 III (C2/m, Z = 4), and cubic high-temperature modification CaC 2 IV (Fm-3m, Z = 4) (12). Theoretically, orthorhombic CaC 2 Immm (Z = 2, referred to as Immm-1 below) structure, monoclinic CaC 2 C2/m (Z = 2, referred to as C2/m-1 below) structure, and trigonal CaC 2 R-3m (Z = 1) structure, were predicted by Kulkarni et al. (13) using a global exploration method based on simulated annealing scheme. In all structures reported above, carbon atoms form isolated dumbbells. Because both Ca and C solids tend to form C-atom network structures at ambient and high pressure (6-10), it is reasonable and interesting to investigate pressure-induced possi...

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“…5,6,7 In all these compounds the light elements are arranged in honeycomb layers which are intercalated by alkaline earth atoms. Depending on the elements forming the honeycomb layer, the electron and phonon states involved in the superconducting pairing are quite different.…”

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confidence: 99%

Pressure effects on the superconducting transition innH-CaAlSi

et al. 2008

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We present a combined experimental and theoretical study of the effects of pressure on Tc of the hexagonal layered superconductors nH -CaAlSi (n = 1, 5, 6), where nH labels the different stacking variants that were recently discovered. Experimentally, the pressure dependence of Tc has been investigated by measuring the magnetic susceptibility of single crystals up to 10 kbar. In contrast to previous results on polycrystalline samples, single crystals with different stacking sequences display different pressure dependences of Tc. 1H-CaAlSi shows a decrease of Tc with pressure, whereas 5H and 6H-CaAlSi exhibit an increase of Tc with pressure. Ab-initio calculations for 1H, 5H and 6H -CaAlSi reveal that an ultrasoft phonon branch associated to out-of-plane vibrations of the Al-Si layers softens with pressure, leading to a structural instability at high pressures. For 1H-CaAlSi the softening is not sufficient to cause an increase of Tc, which is consistent with the present experiments, but adverse to previous reports. For 5H and 6H the softening provides the mechanism to understand the observed increase of Tc with pressure. Calculations for hypothetical 2H and 3H stacking variants reveal qualitative and quantitative differences.

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Superconductivity in Heavy Alkaline-Earth Intercalated Graphites

Cited by 78 publications

References 26 publications

Superconductivity in graphite intercalation compounds

Superconductivity in graphite intercalation compounds

Pressure-induced superconductivity in CaC ₂

Pressure effects on the superconducting transition innH-CaAlSi

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Superconductivity in Heavy Alkaline-Earth Intercalated Graphites

Cited by 78 publications

References 26 publications

Superconductivity in graphite intercalation compounds

Superconductivity in graphite intercalation compounds

Pressure-induced superconductivity in CaC 2

Pressure effects on the superconducting transition innH-CaAlSi

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Pressure-induced superconductivity in CaC ₂