We study hot electron transport in short-channel suspended multilayer graphene devices created by a distinct experimental approach. For devices with semi-transparent contact barriers, a dip of differential conductance (dI/dV) has been observed at source drain bias Vd = 0, along with anomalies at higher Vd likely induced by optical phonon scattering. For devices with low contact barriers, only the dI/dV dip at Vd = 0 is observed, and we find a well-fit logarithmic dependence of dI/dV on both the bias Vd and the temperature T. The logarithmic Vd dependence is explained with the hot electron effect and the logarithmic T dependence could be attributed to the weak-localization in two-dimensions

We report a distinct experimental approach to point-contact Andreev reflection spectroscopy with diagnostic capability via a unique design of nano-scale normal metal/superconductor devices with excellent thermo-mechanical stability, and have employed this method to unveil the existence of two superconducting energy gaps in iron chalcogenide Fe 1+y Te 1-x Se x which is crucial for understanding its pairing mechanism.This work opens up new opportunities to study gap structures in superconductors and elemental excitations in solids.

We report the synthesis of AB-stacked multilayer graphene via ambient pressure chemical vapor deposition on Cu foils, and demonstrate a method to construct suspended multilayer graphene devices. In four-terminal geometry, such devices were characterized by hot carrier transport at temperatures down to 240 mK and in magnetic fields up to 14 T. The differential conductance (dI/dV) shows a characteristic dip at longitudinal voltage bias V=0 at low temperatures, indicating the presence of hot electron effect due to a weak electron-phonon coupling. Under magnetic fields, the magnitude of the dI/dV dip diminishes through the enhanced intra-Landau level cyclotron phonon scattering. Our results provide new perspectives in obtaining and understanding AB-stacked multilayer graphene, important for future graphene-based applications.

We study hot carrier transport under magnetic fields up to 15 T in suspended graphitic multilayers through differential conductance (dI/dV) spectroscopy. Distinct high-energy dI/dV anomalies have been observed and shown to be related to intrinsic phonon-emission processes in graphite. The evolution of such dI/dV anomalies under magnetic fields is further understood as a consequence of inter-Landau level cyclotronphonon resonance scattering. The observed magneto-phonon effects not only shed light on the physical mechanisms responsible for high-current transport in graphitic systems, but also offer new perspectives for optimizing performance in graphitic nano-electronic devices.Description: Figure 1S shows the phonon dispersion and phonon density of states (ph-DOS) of graphite calculated using the Density Functional Perturbation Theory (DFTP) [1] as implemented in the CASTEP code.[2] The first-principles energy calculations were done within the generalized-gradient approximation (GGA) with Perdew-Burke-Ernzerhof (PBE) exchangecorrelation functional [3] using the norm-conserved pseudopotential plane-wave method . The non-bonding interaction between graphene planes were accounted for by dispersion corrections of the form C 6 R -6 included in the DFT formalism by using Tkathcenko and Scheffer scheme. [4] We used a graphite crystal structure obtained from the experimental one by energy minimization and convergence tolerances 1.8 × 10 −7 eV/atom for energy, 2.0 × 10 −7 eV/Å for forces, 0.009 GPa for stresses, and 4.7 × 10 −10 Å for displacements. The phonon dispersion and ph-DOS were calculated over 23 × 23 × 8 Monkhorst-Pack grid in the k-space along the lines connecting the high symmetry points in the Brillouin zone.

We report a tunable magnetoresistance (MR) behavior in suspended graphitic multilayers through point defect engineering by ion implantation. We find that ion implantation drastically changes the MR behavior: the linear positive MR in pure graphitic multilayers transforms into a negative MR after introducing significant short-range disorders (implanted boron or carbon atoms), consistent with recent non-Markovian transport theory. Our experiments suggest the important role of the non-Markovian process in the intriguing MR behavior for graphitic systems, and open a new window for understanding transport phenomena beyond the Drude-Boltzmann approach and tailoring the electronic properties of graphitic layers. Supplementary Materials for:Tunable magnetoresistance behavior in suspended graphitic multilayers through ion implantation