Metal-Insulator-Like Behavior in Semimetallic Bismuth and Graphite

Du, Xu; Tsai, Shan-Wen; Maslov, Dmitrii L.; Hebard, A. F.

doi:10.1103/physrevlett.94.166601

Cited by 210 publications

(203 citation statements)

References 13 publications

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“…We note that Bi, as graphite, has a low density, low effective mass of carriers and huge values of the electron mean free path [24,25]. It shows a very similar magnetic field induced metal-insulator transition and also has a very low resistivity [21]. We may speculate that a similar superconductivity phenomenon may play a role.…”

Section: Figurementioning

confidence: 99%

Sample size effects on the transport characteristics of mesoscopic graphite samples

Barzola‐Quiquia

Yao

Rödiger

et al. 2008

Physica Status Solidi (a)

144

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In this work we investigated correlations between the internal microstructure and sample size (lateral as well as thickness) of mesoscopic, tens of nanometer thick graphite (multigraphene) samples and the temperature (T ) and field (B) dependence of their electrical resistivity ρ(T, B). Low energy transmission electron microscopy reveals that the original highly oriented pyrolytic graphite material -from which the multigraphene samples were obtained by exfoliation -is composed of a stack of ∼ 50 nm thick and micrometer long crystalline regions separated by interfaces running parallel to the graphene planes. We found a qualitative and quantitative change in the behavior of ρ(T, B) upon thickness of the multigraphene samples, indicating that their internal microstructure is important.The overall results indicate that the metallic-like behavior of ρ(T ) at zero field measured for bulk graphite samples is not intrinsic of ideal graphite. The results suggest that the interfaces between crystalline regions may be responsible for the superconducting-like properties observed in graphite. Our transport measurements also show that reducing the sample lateral size as well as the length between voltage electrodes decreases the magnetoresistance, in agreement with recently published results. The magnetoresistance of the multigraphene samples shows a scaling of the form ((R(B) − R(0))/R(0))/T α = f (B/T ) with a sample dependent exponent α ∼ 1, which applies in the whole temperature 2 K ≤ T ≤ 270 K and magnetic field range B ≤ 8 T.

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Section: Figurementioning

confidence: 99%

Sample size effects on the transport characteristics of mesoscopic graphite samples

Barzola‐Quiquia

Yao

Rödiger

et al. 2008

Physica Status Solidi (a)

144

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“…The residual resistivity 0 is observed to be 4:5 cm by extrapolating the zero field curve, corresponding to a residual resistivity ratio of 16. The magnetoresistance (MR) is comparatively weak in C 6 Yb, only 15% by 0.1 T at 6 K, compared to a factor of 80 increase at the same field in pure graphite at T 5 K [16]. From the magnitude of 0 , we estimate the electronic mean-free path to be 1000 Å at low temperatures in zero field, assuming k F 0:5 A ÿ1 [11].…”

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confidence: 97%

“…Second, pure graphite is characterized by an extremely strong magnetoresistance, which arises from the fact that it undergoes a field-tuned metal-insulator-like transition. At a field of only 0.15 T along the c axis, for instance, the in-plane resistivity of graphite has been observed to increase 100-fold at low temperatures [16], whereas for a good metal like C 6 Yb, we would expect a negligible MR in comparable fields. The observation of a 10% positive MR in the normal state of our sample, at a field of only 0.1 T and at temperatures well above T c and away from the paraconductivity regime, is therefore almost certainly due to a small amount of graphite, at the 10% or so volume level.…”

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confidence: 99%

Bulk Evidence for Single-Gaps-Wave Superconductivity in the Intercalated Graphite SuperconductorC6Yb

et al. 2007

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We report measurements of the in-plane electrical resistivity and thermal conductivity of the intercalated graphite superconductor C 6 Yb down to temperatures as low as T c =100. When a field is applied along the c axis, the residual electronic linear term 0 =T evolves in an exponential manner for H c1 < H < H c2 =2. This activated behavior is compelling evidence for an s-wave order parameter, and is a strong argument against the possible existence of multigap superconductivity. DOI: 10.1103/PhysRevLett.98.067003 PACS numbers: 74.70.Wz, 74.25.Fy, 74.25.Op Carbon is a remarkably versatile element -in its pure form it may exist as an electronic insulator, semiconductor, or semimetal depending on its bonding arrangement. When dopant atoms are introduced, superconductivity may be added to this list, observed in graphite [1,2], fullerenes [3], and even diamond [4]. Superconductivity in doped carbon was first discovered in the graphite intercalate compounds (GICs), materials composed of sheets of carbon separated by layers of intercalant atoms. The first of these compounds contained alkali atoms, and had modest transition temperatures of 0.13-0.5 K [1]. The recent discovery of T c 's two orders of magnitude higher than this in C 6 Yb [5] and C 6 Ca [5,6] has, however, refocused attention on this intriguing family of compounds.The effects of the intercalant atoms in the GICs are twofold: they dramatically change the electronic properties of the host graphite lattice by both increasing the separation of the carbon sheets, as well as contributing charge carriers. This causes the two-dimensional graphite bands to dip below the Fermi level. The graphite interlayer band, previously unoccupied, also crosses the new Fermi level, contributing three-dimensional, free-electron-like states located between the carbon sheets. This new interlayer band hybridizes strongly with the bands, and its occupation appears to be linked with the occurrence of superconductivity in the GICs [7].There are still several fundamental questions remaining about superconductivity in the GICs, especially in C 6 Yb and C 6 Ca, where little experimental data exist. The pairing mechanism is unresolved, with speculation ranging from a conventional route involving the intercalant phonons [8][9][10] to superconductivity via acoustic plasmons [7].Early theoretical studies motivated by the alkali-metal GICs [11,12] emphasized a two-gap model for the superconducting state, where gaps of different magnitudes exist on different sheets of the Fermi surface. Such a scenario is plausible, as there are notable similarities between the GICs and MgB 2 [7,13], a known multigap superconductor. Indeed, some aspects of graphite intercalate superconductivity can be understood by this two-gap phenomenology; however, there is little direct evidence to support this picture, and recent band structure calculations suggest this scenario is unlikely [14].A necessary starting point is to establish the superconducting order parameter, but in C 6 Yb, this task is complicated as th...

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“…This results in a π band with a small number of holes and a π * band with a small number of electrons. In fact the number of holes and electrons are very similar and this leads to some interesting properties such as a large magnetoresistance [15,16]. [17, 18, 19, 20, 21, 22 ,23].…”

Section: Electronic Structurementioning

confidence: 99%

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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Metal-Insulator-Like Behavior in Semimetallic Bismuth and Graphite

Cited by 210 publications

References 13 publications

Sample size effects on the transport characteristics of mesoscopic graphite samples

Sample size effects on the transport characteristics of mesoscopic graphite samples

Bulk Evidence for Single-Gaps-Wave Superconductivity in the Intercalated Graphite SuperconductorC6Yb

Superconductivity in graphite intercalation compounds

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