Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session L17: Graphene: Optical Properties |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Hua Chen, University of Texas at Austin Room: 102AB |
Wednesday, March 4, 2015 8:00AM - 8:12AM |
L17.00001: Graphene in Ultrafast and Ultrastrong Laser Pulses Hamed Koochaki Kelardeh, Vadym Apalkov, Mark Stockman We have shown that graphene subjected to an ultrafast (near-single-oscillation pulse) and strong (F $\sim$ 1-3 V/{\AA}) pulse exhibits fundamental behavior dramatically different from both insulators and metals. In such an ultrafast and ultrastrong field, the electron dynamics is coherent, in contrast to relatively long pulses ($\tau $\textgreater 100 fs) where the electron's dephasing becomes important leading to incoherent dynamics. Electron transfer from the valence band (VB) to the conduction band (CB) is deeply irreversible i.e., non-adiabatic, in which the residual CB population (after pulse ends) is close to the maximum one. The residual CB population as a function of wave vector is nonuniform with a few strongly localized spots near the Dirac points, at which the CB population is almost 100{\%}. Furthermore, it is shown the direction of charge transfer depends on the pulse amplitude. Namely, at small pulse amplitude, $\le $1V/{\AA}, the charge is transferred in the direction of the pulse maximum (positive transferred charge), while at large amplitude, $\ge $1 V/{\AA}, it is in opposite direction of the pulse maximum (negative transferred charge). Consequently, in terms of charge transport, graphene at small pulse intensities behaves as a dielectric while at large intensities acts as a metal. These femtosecond currents and charge transfer in graphene may provide fundamental basis for detection and calibration of ultrashort intense laser pulses and are promising for petahertz information processing. [Preview Abstract] |
Wednesday, March 4, 2015 8:12AM - 8:24AM |
L17.00002: Giant mid-infrared Kerr enhancement from films on SiC Alok Mukherjee, M. Murat Arik, Chase T. Ellis, Payam Taheri, Andreas V. Stier, Myoung Hwan Kim, Hao Zeng, John Cerne, Joseph G. Tischler, Evan R. Glaser, Rachel L. Myers Ward, Joseph L. Tedsco, Charles R. Eddy Jr, D. Kurt Gaskill, Yu Liu, Shunchong Wang, Gang Wang We report an enhancement of over an order of magnitude in the complex Kerr angle at photon energies near 121 meV in a variety of films on SiC substrates. The change in the reflected polarization in the presence of an out-of-plane magnetic field (polar magneto-optical Kerr effect, PMOKE) is measured in films ranging from graphene on SiC, aluminum doped SiC and iron oxide deposition on SiC. We model the PMOKE signal using multilayer analysis and find that the main contributor to this enhancement is the index of SiC becoming unity near 121 meV, at the edge of the Reststrahlen band of SiC. This result not only increases our sensitivity to PMOKE in a wide range of materials but also suggests that choice of substrate plays an important role in enhancing Kerr signal. This work is supported by NSF-DMR1006078. [Preview Abstract] |
Wednesday, March 4, 2015 8:24AM - 8:36AM |
L17.00003: Graphene thermal transport studies via radio-frequency, cross-correlated Johnson noise thermometry Jesse Crossno, Xiaomeng Liu, Ke Wang, Achim Harzheim, Kenji Watanabe, Takashi Taniguchi, Thomas Ohki, Kin Chung Fong, Philip Kim The electronic temperature of a dissipative, mesoscale device can be determined by monitoring the Johnson noise power emitted over a wide frequency range. Using radiometry techniques, we have developed a high-frequency, wide bandwidth, cross-correlation Johnson noise thermometer operating from room temperature to cryogenic levels that is compatible with strong magnetic fields. Precisions ranging from 2 to 25 mK are demonstrated over the temperature range of 3 to 300 K with 1 second of integration time. This non-invasive thermometer has enabled us to perform sensitive electronic thermal transport studies in boron nitride encapsulated monolayer graphene over two orders of magnitude in temperature. This versatile technique also enables precision Fano factor measurements as well as studies of correlated noise phenomena, such as those found in layered Van der Waals heterostructures. [Preview Abstract] |
Wednesday, March 4, 2015 8:36AM - 8:48AM |
L17.00004: Valley polarized transport through irradiated graphene Arijit Kundu, Herb Fertig, Babak Seradjeh Graphene under the application of circularly polarized light can go through Floquet topological transitions between various topological phases. With a drive protocol that breaks the valley symmetry, such transitions can occur at different points in the drive parameter space for different valleys. This may lead to valley polarized transport. We apply this concept to propose geometries for valleytronics devices like valves and transistors, which we theoretically analyze. [Preview Abstract] |
Wednesday, March 4, 2015 8:48AM - 9:00AM |
L17.00005: Interaction of Dirac Fermion excitons and biexciton-exciton cascade in graphene quantum dots Isil Ozfidan, Marek Korkusinski, Pawel Hawrylak We present a microscopic theory of interacting Dirac quasi-electrons and quasi-holes confined in graphene quantum dots. The single particle states of quantum dots are described using a tight binding model and screened direct, exchange, and scattering Coulomb matrix elements are computed using Slater $p_z$ orbitals. The many-body ground and excited states are expanded in a finite number of electron-hole pair excitations from the Hartree-Fock ground state and computed using exact diagonalization techniques. The resulting exciton and bi-exciton spectrum reflects the degeneracy of the top of the valence and bottom of the conduction band characteristic of graphene quantum dots with C3 symmetry. We study the interaction of multi-electron and hole complexes as a function of quantum dot size, shape and strength of Coulomb interactions. We identify two degenerate bright exciton (X) states and a corresponding biexciton (XX) state as XX-X cascade candidates, a source of entangled photon pairs. We next calculate the exciton to bi-exciton transitions detected in transient absorption experiments to extract the strength of exciton-exciton interactions and biexciton binding energies. We further explore the possibility of excitonic instability. [Preview Abstract] |
Wednesday, March 4, 2015 9:00AM - 9:12AM |
L17.00006: Optical limiting and nonlinear optical properties of gold-decorated graphene nanocomposites Ramakrishna Podila, Prabin Pradhan, Muralikrishna Molli, Adarsh Kaniyoor, Sai Muthukumar V, S. Siva Sankara Sai, S. Ramaprabhu, Apparao Rao Although metal nanoparticle-decorated nanomaterials exhibit excellent optical limiting (OL) performance at a relatively higher fluence (\textgreater 9 J/cm$^{2})$, there is a dearth of OL materials for protecting low damage threshold (\textless 1 J/cm$^{2})$ photonic devices. The rehybridization of some metal $d$-orbitals and graphene $p$-orbitals often leads to undesirable changes in graphene's electronic structure, which adversely affects OL. Here, we demonstrate that $d$-orbitals of Au nanoparticles exhibit little or no rehybridization with graphene, and result in an enhanced OL behavior even at a low fluence of $\sim$ 0.4 J/cm$^{2}$ due to the excellent photo-absorption of Au combined with rapid carrier thermalization by graphene. [Preview Abstract] |
Wednesday, March 4, 2015 9:12AM - 9:24AM |
L17.00007: Background-Free Ultrafast Pump-Probe Transmission Spectroscopy of Graphene Joseph R. Murphy, Tianmu Zhang, Tim Thomay, Alexander N. Cartwright, Saima Husaini, Robert G. Bedford Graphene and graphene-related materials exhibit properties of interest for optical applications. Time-resolved pump-probe spectroscopy has been proven an effective tool to measure the time scales of carrier dynamics of materials with adequate absorption. Ultrafast measurements are challenging to conduct due to graphene's low absorption of 2.3\% per layer and time scales of the carrier dynamics in the sub-picosecond range. To perform these experiments, laser pulses with a duration of 200 fs from the 800 nm beam from an amplified Ti:sapphire laser system with a repetition rate of 250 kHz were used with energy densities as low as 4 $\mu$J/cm$^{2}$. The difficulty of the detection of the low absorption in this single-color experiment is further exacerbated by the need to distinguish the signal in the probe beam from the noise present in the two beams used. We present the results from a background-free technique used in our ultrafast pump-probe measurements; these results reveal the presence of electronic processes with time scales on the order of 500 to 700 fs in multilayer graphene. This background-free technique uses optical chopping to modulate the pump and probe beams at different frequencies and we have found that this method significantly improves the signal to noise ratio. [Preview Abstract] |
Wednesday, March 4, 2015 9:24AM - 9:36AM |
L17.00008: Photocurrent Generation in the Fractional Quantum Hall Regime of Graphene Sanfeng Wu, Lei Wang, You Lai, Grant Aivazian, Helin Cao, Cory Dean, James Hone, Zhiqiang Li, Xiaodong Xu Significant understanding toward fractional quantum Hall effects has been made through probing the quantum transport of carriers at the Fermi surface. However, little is known about the non-equilibrium behavior of the carriers that are excited above the Fermi Sea. In this talk, we will discuss the transport phenomena of photo-excited carriers in the quantum Hall regime of graphene. By probing the photocurrent generation through the edge channels of a graphene field effect transistor under high magnetic field and low temperature, we observe chiral edge transport of photo-excited carriers. The observed photocurrent can directly resolve both integer and fractional quantum Hall states. Our measurements may provide a new experimental approach to uncover the rich and exotic physics related to fractional quantum Hall effects. [Preview Abstract] |
Wednesday, March 4, 2015 9:36AM - 9:48AM |
L17.00009: Study of photocurrent response in bilayer graphene Long Ju, Lei Wang, James Hone, Feng Wang Bilayer graphene is a unique system where the electronic band structure can be controlled by external electric field. The transition between semimetal to semiconductor with a bandgap up to 250 meV can be achieved by applying voltages on top and bottom gates. In this talk I'll show our photocurrent measurement in dual-gated bilayer graphene devices. Different mechanisms of photocurrent generation will be discussed. I'll also talk about its implications for potential opto-electronic applications of bilayer graphene. [Preview Abstract] |
Wednesday, March 4, 2015 9:48AM - 10:00AM |
L17.00010: Photoresponse in Graphene Boron Nitride Vertical Heterostructures Trond Andersen, Qiong Ma, Chun-Hung Lui, Nityan Nair, Nathaniel Gabor, Andrea Young, Wenjing Fang, Kenji Watanabe, Takashi Taniguchi, Jing Kong, Nuh Gedik, Pablo Jarillo-Herrero Combining two-dimensional materials into vertical heterostructures reveals diverse, intriguing phenomena and provides a novel way of engineering materials with desired electronic properties. Placing graphene on hexagonal boron nitride (hBN) has given particularly interesting results, including enhanced mobility, opening of a band gap, and highly controllable photo-induced doping. We explore the photoresponse of vertical graphene-hBN-graphene heterostructures in a high electronic temperature regime where thermionic emission dominates. Near the charge neutral point, we observe a pronounced conductance peak, which we attribute to a cooling bottleneck that appears at low carrier density, thus suggesting hot carrier enhanced thermionic emission. To further investigate the mechanism by which current is generated, we conduct two-pulse correlation measurements and study the temporal dynamics of the system. We observe a positive correlation, implying that the hot carriers thermalize before crossing the hBN barrier. Finally, we propose an advanced, modified two-temperature model, which allows for numerical simulations that are consistent with our measurements. [Preview Abstract] |
Wednesday, March 4, 2015 10:00AM - 10:12AM |
L17.00011: Scanning photocurrent microscopy in Graphene mediated by photo-Nernst effect Zaiyao Fei, Helin Cao, Grant Aivazian, Jason Ross, David Cobden, Xiaodong Xu We have performed scanning photocurrent microscopy on monolayer graphene devices in a perpendicular magnetic field of up to 7 T. At zero field we observe photocurrent generated only near the contacts, but for a finite magnetic field an additional edge magneto-photocurrent contribution appears far from the contacts which is odd in magnetic field. The edge photocurrent also has opposite polarities for opposite edges. At low field this contribution can be well explained by the photo-Nernst effect combined with the nonlocal current generation mechanism described by Son and Levitov (ref. Phys. Rev. B 90, 075415, 2014). The effect persists to room temperature. At higher fields Landau quantization effects are seen along with oscillations of the magneto-photocurrent. The theory remains inadequate to explain all the features in this regime. [Preview Abstract] |
Wednesday, March 4, 2015 10:12AM - 10:24AM |
L17.00012: Altshuler-Aronov-Spivak Oscillation in Graphene Antidot lattice Ryuta Yagi, Ryoji Sakakibara, Junpei Onishi We have observed the Altshuler-Aronov-Spivac (AAS) oscillation in triangular antidot lattice of single layer graphene. Low temperature magnetoresistance exhibited $h/2e$ periodic oscillations near zero magnetic field, negative magnetoresistance, and $h/e$ periodic (AB-type) oscillations at higher magnetic fields. Phase of the AAS oscillation was the same as those for conventional 2D electrons with negligible spin orbit interaction, showing that inter-valley scattering averaged the Berry phase effect which results in anti-localization. (R. Yagi {\it et al}. J. Phys. Soc. Jpn. {\bf 81}, 064707 (2012).) [Preview Abstract] |
Wednesday, March 4, 2015 10:24AM - 10:36AM |
L17.00013: Low-gate-biased edge-state manipulation for turnable spin-polarized current source in zigzag graphene ribbon Li Chang, Chon-Saar Chu In this work, we investigate the spin transport through a region with inhomogeneous edge-potential generated by split gates in a zigzag graphene ribbon (ZGNR). The split gates (each covers the lower and upper edges of the ribbon) actively modify the coupling between the pair of edge states and electrically generate the tunable edge-sate gap (ESG). With a homogeneous exchange field in the whole background, the ESGs of opposite spins are separated. We utilize these separated gaps to realize the tunable spin-polarized current source. Specifically, the split gates are placed in the middle segment of the ZGNR and we numerically study the spin transport through the potential region. With the exchange field strength of 5 $ meV $ and the on-site energy uncertainty within $ \pm 4\ meV $, we still get nearly $100\% $ spin polarized current. [Preview Abstract] |
Wednesday, March 4, 2015 10:36AM - 10:48AM |
L17.00014: Temperature-dependent Transport Properties of CVD grown Graphene with Pd Functionalization Bochen Zhong, Ahsan Uddin, Amol Singh, Goutam Koley, Richard Webb We have investigated the temperature dependence of carrier density and mobility of CVD grown graphene before and after 2nm Pd deposition by Hall effect measurement. In our samples, Hall mobility increases as temperature increases, indicating that Coulomb scattering is the most important scattering mechanism. The Pd functionalization layer scattering limited carrier mobility is calculated as a function of temperature, and a least-square fit is done. Furthermore, Hall mobility of the Pd-functionalized graphene enhances significantly after exposure to H$_{2}$ and the dominant scattering mechanism switches to thermal excited substrate optical phonon scattering. [Preview Abstract] |
Wednesday, March 4, 2015 10:48AM - 11:00AM |
L17.00015: Toward High Performance Graphene-based Solar Cells: Spectroscopic Study on Doped Graphene Jan-Kai Chang, Chen-Chih Hsu, Wei-Hsiang Lin, Chih-I Wu, Nai-Chang Yeh A polymer-free transfer method with in situ doping process for graphene, aiming at simple and efficient doping of residue-free graphene, has been developed to achieve stacked graphene/dopant intercalation films. The proposed facile strategy led to a tunable work function from 3.25 eV to 5.10 eV, enabling graphene anode and cathode for solar cell devices. Both hybrid and organic photovoltaics using graphene electrodes have been carried out with a series of optimization based on spectroscopic characterizations. Since aging of doped graphene is crucial to the lifetime of graphene-based solar cells, the doping-induced electronic state variation with time has been investigated via X-ray and ultra-violet photoemission spectroscopy analysis to gain insight in its electronic properties and stability. The doping effect developed in graphene has also been studied via Raman spectroscopy, including time evolution of the Raman D, G and 2D bands under normal and humid conditions for up to 30 days. This systematic investigation of aging effect provides better understanding and helps optimize the stacking of doped graphene films for achieving high performance graphene-based devices. [Preview Abstract] |
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