We report electron-hole conduction asymmetry in monolayer graphene. Previously, it has been claimed that electron-hole conduction asymmetry is due to imbalanced carrier injection from metallic electrodes. Here, we show that metallic contacts have negligible impact on asymmetric conduction and may be either sample or device-dependent phenomena. Electrical measurements show that monolayer graphene based devices exhibit suppressed electron conduction compared to hole conduction due to presence of donor impurities which scatter electrons more efficiently. This can be explained by the relativistic nature of charge carriers in graphene monolayer and can be reconciled with the fact that in a relativistic quantum system transport cross section does depend on the sign of scattering potential in contrast to a non-relativistic quantum system. There has been much progress in the understanding of fabrication and technology of graphene based devices [1-3]. However, there are several issues to be addressed to exploit the high mobility exhibited by mono-layer graphene (MLG) [4]. One such important issue is electron-hole (e-h) conduction asymmetry which has been attributed to imbalanced charge injection from the metal electrodes [5, 6]. It has been claimed [5] that metallic electrodes in graphene based devices create misalign-ment of neutrality points between electrode and channel, resulting in e-h conduction asymmetry. Whereas other groups [7-9] have claimed that metallic contact-induced electrostatic potential fluctuations is responsible for the e-h conduction asymmetry in graphene devices. In these reports, it has been claimed that e-h conduction asymmetry is entirely of extrinsic origin. However, there are several reports which showed metallic contact induced doping in graphene without e-h asymmetry [9-12]. All these findings have been either interpreted with opposite conclusions or claimed extrinsic mechanism as origin behind e-h asymmetry. In view of these results it appears that there are three issues to be resolved: (i) whether metal contacts are responsible for e-h conduction asymmetry , (ii) whether it is due to metal induced doping or, (iii) whether e-h conduction asymmetry is extrinsic or intrinsic. The objectives laid down in this communication are twofold. The first objective is to investigate the effect of metallic contacts on asymmetric conduction in MLG based field effect transistors (FETs). We have chosen different metallic electrodes (source/drain) for MLG based devices. In contrast to previous findings , no significant difference in the conduction asymmetry has been observed in our devices with three different metallic electrodes. Hence, the second objective is to probe the factor responsible for asymmetric conduction. We have used two types of graphene monolayers for this study: undoped almost-prestine graphene (type I), and doped graphene (type II). Transfer characteristics, i.e. variation of current between source and drain with gate voltage, in type I MLG based FET always shows symmetry around the Dirac p...

We report studies of the magnetospectroscopy of graphite into a new regime of high energies and ultrahigh magnetic fields which allows us to perform the first spectroscopic studies of the interlayer split-off bands, E1 and E2. These bands can be well described by an asymmetric bilayer model and have only a small interlayer band gap asymmetry. We show that all of the properties of the electrons and holes can be described by a simple relativistic behavior determined by γ0 and γ1.

Current opportunities and recent examples for research in magnetic fields well above 100 T using single-turn coils are discussed. After a general introduction into basic principles and technical constraints associated with the generation of Megagauss fields we discuss data obtained at the LNCMI Toulouse, where such fields are routinely used for scientific applications.

A magneto-optical study of the 1.4 eV Ni color center in boron-free synthetic diamond, grown at high pressure and high temperature, has been performed in magnetic fields up to 56 T. The data is interpreted using the effective spin Hamiltonian of Nazaré, Nevers and Davies [Phys. Rev. B 43, 14196 (1991)] for interstitial Ni + with the electronic configuration 3d 9 and effective spin S = 1/2. Our results unequivocally demonstrate the trigonal symmetry of the defect which preferentially aligns along the [111] growth direction on the (111) face, but reveal the shortcomings of the crystal field model for this particular defect.