Evidence for internal field in graphite: a conduction electron spin-resonance study

Sercheli, M. S.; Kopelevich, Y.; Silva, Robson R. da; Torres, J. H. S.; Rettori, C.

doi:10.1016/s0038-1098(01)00465-3

Cited by 53 publications

(44 citation statements)

References 26 publications

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“…Recently, a similar MIT driven by a magnetic field applied perpendicular to basal planes has been reported for graphite [2,3,4,5]. The quasi-particles (QP) in graphite behave as massless Dirac fermions (DF) with a linear dispersion relation, similar to the QP near the gap nodes in high-temperature superconductors.…”

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confidence: 69%

Reentrant Metallic Behavior of Graphite in the Quantum Limit

et al. 2003

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Magnetotransport measurements performed on several well-characterized highly oriented pyrolitic graphite and single crystalline Kish graphite samples reveal a reentrant metallic behavior in the basal-plane resistance at high magnetic fields, when only the lowest Landau levels are occupied. The results suggest that the quantum Hall effect and Landau-level-quantization-induced superconducting correlations are relevant to understand the metalliclike state(s) in graphite in the quantum limit.PACS numbers: 71.30.+h, 72.20.My, 74.10.+v Conduction processes in two-dimensional (2D) electron (hole) systems, in particular the apparent metal-insulator transition (MIT) which takes place either varying the carrier concentration or applying a magnetic field H, have attracted a broad research interest [1]. Recently, a similar MIT driven by a magnetic field applied perpendicular to basal planes has been reported for graphite [2,3,4,5]. The quasi-particles (QP) in graphite behave as massless Dirac fermions (DF) with a linear dispersion relation, similar to the QP near the gap nodes in high-temperature superconductors. Theoretical analysis [6,7,8] suggests that the MIT in graphite is the condensed-matter realization of the magnetic catalysis (MC) phenomenon [9] known in relativistic theories of (2 + 1)-dimensional DF. According to this theory [6,7,8], the magnetic field H opens an insulating gap in the spectrum of DF of graphene, associated with the electron-hole (e-h) pairing, below a transition temperature T ce (H) which is an increasing function of field. However, at higher fields and at temperatures T < T max (H) an insulator-metal transition (IMT) occurs [2] indicating that additional physical processes may operate approaching the field H QL that pulls carriers into the lowest Landau level. The occurrence of superconducting correlations in the quantum limit (QL) [10,11] and below the temperature T max (H) has been proposed for graphite in Ref. [2]. On the other hand, authors of Ref. [8] argued that at high enough carrier concentration, the basal-plane resistance R b (H, T ) can decrease decreasing temperature below the e-h pairing temperature, and identified T max (H) with T ce (H). Other theoretical works predict the occurrence of the field-induced Luttinger liquid [12] and the integral quantum Hall effect (IQHE) [13] in graphite. All these indicate that understanding of the magnetic-field-induced insulating and metallic states in graphite is of importance and has an interdisciplinary interest. The aim of this Letter is to provide a fresh insight on the magnetotransport properties of graphite in the QL. We show that the IMT is generic to graphite with a sample-dependent

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confidence: 69%

Reentrant Metallic Behavior of Graphite in the Quantum Limit

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“…However, we stress that the relative change in the resistivity with field depends on the sample characteristics. Experimental data from different graphite samples show a change at low temperatures between ∼ 20% up to more than one order of magnitude for a field of the order of 1 kOe [3,4,5,19]. Qualitatively speaking, the transition is similar for all samples studied.…”

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confidence: 87%

“…Our results demonstrate the two-dimensionality of the electron system in ideal graphite samples. Recent experimental and theoretical studies of graphite have renewed the interest in this system [1,2,3,4,5,6,7,8,9,10]. Experimental results show that, contrary to the common belief, the transport and magnetic properties of graphite cannot be accounted for by semiclassical models.…”

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confidence: 99%

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Absence of metal–insulator transition and coherent interlayer transport in oriented graphite in parallel magnetic fields

Kempa

Semmelhack

Esquinazi

et al. 2003

Solid State Communications

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Measurements of the magnetoresistivity of graphite with a high degree of control of the angle between the sample and magnetic field indicate that the metal-insulator transition (MIT), shown to be induced by a magnetic field applied perpendicular to the layers, does not appear in parallel field orientation. Furthermore, we show that interlayer transport is coherent in less ordered samples and high magnetic fields, whereas appears to be incoherent in less disordered samples. Our results demonstrate the two-dimensionality of the electron system in ideal graphite samples. Recent experimental and theoretical studies of graphite have renewed the interest in this system [1,2,3,4,5,6,7,8,9,10]. Experimental results show that, contrary to the common belief, the transport and magnetic properties of graphite cannot be accounted for by semiclassical models. Experiment and theory raise a number of questions concerning the coupling between the graphite layers. The understanding of the transport properties is of primary interest and can provide a fundamental contribution to the physics of two-dimensional (2D) systems in general. In this letter we deal with two important open questions: 1. A MIT appears both in the in-plane [1,3,4] and out-of-plane [5] resistivity induced by a magnetic field B applied perpendicular to the graphite layers, i.e. B||c-axis. Based on magnetization data [2] and the found 2D scaling similar to that in the MIT of Si-MOSFETs (metal-oxide-semiconductor field-effecttransitor) [11], and Bi-films [13], the MIT in graphite has been

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“…Taking into account this fact and that upon defect concentration in the crystals and their influence on the effective carrier density λ D,m 1 µm, we expect that size effects might be seen at relatively large sample or constriction size. This should be in principle possible also because the electron mean free path L e ≃ m ⋆ v F µ/e 1 µm in HOPG, taking into account a mobility µ ∼ 10 6 cm 2 /Vs measured in samples of low mosaicity [18], a value much larger than those found in typical FLG. All these numbers already suggest a situation very different from that found in metals, where size effects in the magnetoresistance may start to be seen when the sample size reduces to ∼ 20 nm or less.…”

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Sample-Size Effects in the Magnetoresistance of Graphite

Muñoz

Garcı́a

et al. 2007

Phys. Rev. Lett.

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We present a study of the magnetoresistance of highly oriented pyrolytic graphite (HOPG) as a function of the sample size. Our results show unequivocally that the magnetoresistance reduces with the sample size even for samples of hundreds of micrometers size. This sample size effect is due the large mean free path and Fermi wavelength of carriers in graphite and may explain the observed practically absence of magnetoresistance in micrometer confined small graphene samples where quantum effects should be at hand. These were not taken into account in the literature yet and ask for a revision of experimental and theoretical work on graphite.PACS numbers: 81.05. Uw,72.80.Cw Graphitic systems are nowadays a field of intensive activity [1]. There have been observations of quantum Hall effect in HOPG [2,3] as well as very large anisotropy in the electrical conductance (ratio between current parallel to perpendicular to the graphene planes) larger than 10 4 at room temperature [1]. Graphite looks as a good conductor in plane and an insulator between planes leading to a weak screening to external electric fields [4]. This means that an external electric field penetrates by tens of nanometers in graphite, in contrast to a normal metal where the field is screened in the first atomic layers. In fact the dielectric constant of graphite at optical frequencies is positive, insulator like (ǫ plane = 5.6 + i7.0, ǫ c = 2.25) [5,6]. Electric field microscopy [7] detects that regions of graphite are more insulating than others upon the interconnections of graphite planes produced by defects and their overall density that influences the density of states and the Fermi level. The material exhibits a huge magnetic field driven metal-insulator transition [1,8]. Its band structure and interband transitions with electron and hole carriers manifest in a huge ordinary magnetoresistance (OMR) [2,9]. All these effects happen in macroscopic size samples of the order of millimeters.A large research activity has been recently started on a few graphene layers (FLG) [10] with typical size of a few microns. Strikingly, the OMR in FLG samples is practically suppressed even at T < 4 K, in contrast to bulk HOPG or Kish graphite where the OMR is 1000% at B 0.5 T at low temperatures [1]. Earlier work with graphite samples in the micrometer range showed similar behavior [11,12]. However, the question on what happens when the graphite sample size is reduced has not been correctly addressed and the experimental data may need a new interpretation. The size of the sample is very important for defining the properties of the system because the de-Broglie wavelength for massless Dirac6 m/s is the Fermi velocity and a typical Fermi energy k B E F 100 K) or for massive carriers with effective mass m ⋆ 0.01m, λ m = h/ √ 2m ⋆ E F , as well as the Fermi wavelength λ F ∼ 2πn −1/2 are of the order of microns or larger due to the low density of Dirac and massive fermions. Moreover, one can show that in such micron size systems new quantum mechanical oscillations ap...

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Evidence for internal field in graphite: a conduction electron spin-resonance study

Cited by 53 publications

References 26 publications

Reentrant Metallic Behavior of Graphite in the Quantum Limit

Reentrant Metallic Behavior of Graphite in the Quantum Limit

Absence of metal–insulator transition and coherent interlayer transport in oriented graphite in parallel magnetic fields

Sample-Size Effects in the Magnetoresistance of Graphite

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