We investigate experimentally transport through ring-shaped devices etched in graphene and observe clear Aharonov-Bohm conductance oscillations. The temperature dependence of the oscillation amplitude indicates that below 1 K, the phase coherence length is comparable to or larger than the size of the ring. An increase in the amplitude is observed at high magnetic field, when the cyclotron diameter becomes comparable to the width of the arms of the ring. By measuring the dependence on gate voltage, we find that the Aharonov-Bohm effect vanishes at the charge neutrality point, and we observe an unexpected linear dependence of the oscillation amplitude on the ring conductance. DOI: 10.1103/PhysRevB.77.085413 PACS number͑s͒: 73.23.Ϫb, 73.20.Ϫr, 73.22.Ϫf, 73.61.Wp The investigation of transport phenomena originating from quantum interference of electronic waves has proven to be a very effective probe of the electronic properties of conducting materials. Recent work has shown that this is also the case for graphene, a novel material consisting of an individual layer of carbon atoms, in which the electron dynamics is governed by the Dirac equation.1 The anomalous behavior of the weak-localization correction to the conductivity that is observed in the experiments, 2 for instance, is directly related to the presence of two independent valleys in the band structure of graphene 3,4 and can be used to extract the intervalley scattering time.5 Another example is provided by the observation of a Josephson supercurrent in graphene superconducting junctions, which permits to conclude that transport through graphene is phase coherent even when the material is biased at the charge neutrality point ͑i.e., where nominally no charge carriers are present͒. 6 Possibly, the phenomenon that most directly illustrates electronic interference in solid-state devices is the occurrence of periodic oscillations in the conductance of ringshaped devices, measured as a function of magnetic field. 7 This phenomenon, which is a direct consequence of the Aharonov-Bohm ͑AB͒ effect, has been investigated extensively in the past in rings made with metallic films or with semiconducting heterostructures, and its study has contributed significantly to our understanding of mesoscopic physics. For example, the analysis of h/e and h/2e AB conductance oscillations has clarified the difference between sample-specific and ensemble-averaged phenomena.7 The investigation of the temperature and magnetic field dependences of the oscillation amplitudes has been used to investigate processes leading to decoherence of electron waves, such as electron-electron interaction, 7,8 or the interaction with magnetic impurities. 9 In graphene, however, no experimental observation of AB conductance oscillations has been reported so far, although there is an emerging interest in the problem from the theoretical side. 10,11 In the course of recent experiments, we have observed AB conductance oscillations experimentally in several rings fabricated on few-layer graphene. In thi...

Quenching thermoelectric effects in graphene leads to an extraordinary increase of the linear dynamic range in photodetectors.

We present the first systematic study of the stability of the structure and electrical properties of FeCl3 intercalated few-layer graphene to high levels of humidity and high temperature. Complementary experimental techniques such as electrical transport, high resolution transmission electron microscopy and Raman spectroscopy conclusively demonstrate the unforseen stability of this transparent conductor to a relative humidity up to 100% at room temperature for 25 days, to a temperature up to 150°C in atmosphere and to a temperature as high as 620°C in vacuum, that is more than twice higher than the temperature at which the intercalation is conducted. The stability of FeCl3 intercalated few-layer graphene together with its unique values of low square resistance and high optical transparency, makes this material an attractive transparent conductor in future flexible electronic applications.

We determine and analyze the photocurrent J ph in polymer solar cells under conditions where, no, one, or two different charge carriers can be injected by choosing appropriate electrodes and compare the experimental results to simulations based on a drift-diffusion device model that accounts for photogeneration and Langevin recombination of electrons and holes. We demonstrate that accounting for the series resistance of the device is essential to determine J ph . Without such correction, the results are, even qualitatively, incorrect. We show that in solar cells with forward bias applied J ph is reduced by recombination of photogenerated charge carriers with injected charge carriers. Self-selective contacts or band bending are not necessary to explain the effects. Without injecting contacts J ph is symmetric around the compensation voltage. A simple analytical model shows that under high forward bias J ph scales inversely with 1 + ξγ pre , in which γ pre represents the extent of Langevin recombination and ξ is a positive constant. Under conditions where Langevin recombination is very low or when electron and hole mobility are a very different, photogenerated charge carriers can affect the space-charge field and modify the injection of charge carriers. We show by simulations and experimentally that under such conditions the photocurrent can exceed that charge generation such that, effectively, photocurrent multiplication occurs.

The high flexibility, impermeability and strength of graphene membranes are key properties that can enable the next generation of nanomechanical sensors. However, for capacitive pressure sensors, the sensitivity offered by a single suspended graphene membrane is too small to compete with commercial sensors. Here, we realize highly sensitive capacitive pressure sensors consisting of arrays of nearly ten thousand small, freestanding double-layer graphene membranes. We fabricate large arrays of small-diameter membranes using a procedure that maintains the superior material and mechanical properties of graphene, even after high-temperature annealing. These sensors are readout using a low-cost battery-powered circuit board, with a responsivity of up to $$47.8$$ 47.8  aF Pa−1 mm−2, thereby outperforming the commercial sensors.