Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session L16: Black Phosphorus Device PhysicsFocus
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Sponsoring Units: DMP Chair: Yuanbo Zhang, Fudan University, China Room: 315 |
Wednesday, March 16, 2016 11:15AM - 11:51AM |
L16.00001: Black Phosphorus Optoelectronics and Electronics Invited Speaker: Fengnian Xia Black phosphorus recently emerged as a promising new 2D material due to its widely tunable and direct bandgap, high carrier mobility and remarkable in-plane anisotropic electrical, optical and phonon properties. It serendipitously bridges the zero-gap graphene and the relatively large-bandgap transition metal dichalcogenides such as molybdenum disulfide (MoS$_{\mathrm{2}})$. In this talk, I will first cover the basic properties of few-layer and thin-film black phosphorus, followed by a discussion of recent observation of highly anisotropic robust excitons in monolayer black phosphorus. Finally I will present a few potential applications of black phosphorus such as radio-frequency transistors and wideband photodetectors. [Preview Abstract] |
Wednesday, March 16, 2016 11:51AM - 12:03PM |
L16.00002: Anisotropic Raman Spectroscopy of Few-Layer Phosphorene Yuchen Du, Wangran Wu, Jesse Maassen, Zhe Luo, Mark Lundstrom, Xianfan Xu, Peide Ye Much recent research of black phosphorus (BP) and phosphorene has been focused on their unique anisotropy of this novel 2D material in terms of electrical, optical and thermal properties. Here we report the emerging Raman spectroscopy measurements of BP with respect to its isolation from bulk BP down to single layer phosphorene. The found frequency shift of BP in Raman spectra is to be correlated with atomic motion of modes, which can be explained by applying classical model of coupled harmonic oscillators. Raman intensity of different modes has also been included in our studies, which is confirmed as a solid strategy to quickly determine BP layer thickness. In addition, more information of their mechanical properties can also be obtained from Raman spectroscopy. [Preview Abstract] |
Wednesday, March 16, 2016 12:03PM - 12:15PM |
L16.00003: Interlayer Interaction that is Decisive in the Energy Gap of a Few Layer Phosphorene Yuki Sugihara, Atsushi Oshiyama We report on our first-principles calculations that clarify the microscopic origin of the band-gap variation in a few-layer phosphorene (i.e. layered phosphorous) and also rectify a prevailed picture of the electronic structure of this new layered material [1]. Calculations have been done either using GGA with inclusion of van der Waals correction in the density-functional theory or GW approximation in the self-energy. We unequivocally reveal that the interlayer interaction causes the bonding-antibonding splitting of the highest valence band state, thus reducing the fundamental energy gap. This is due to the highest state consists mainly of $p$ orbitals along the direction perpendicular to the layers. It was predicted that phosphorene has four polytypes named $\alpha$ (black), $\beta$ (blue), $\gamma$ and $\delta$ and all these polytypes exhibit common feature of the band-gap variation [2]. Especially, $\gamma$ phosphorene is proposed to show the metal-insulator transition from the semiconductor mono-layer to the metal bi-layer. We reveal that this transition takes place in thicker region. [1]L. Li, Y. Yu, G. J. Ye, Q. Ge, X. ou, H. Wu, D. Feng, X. H. Chen, and Y. Zhang, Nat. Nanotechnol. $\bf{9}$, 372 (2014), [2] J. Guan, Z. Zhu, and D. Tomanek, PRL, $\bf{113}$, 046804 (2014) [Preview Abstract] |
Wednesday, March 16, 2016 12:15PM - 12:27PM |
L16.00004: Quantum Hall Effect in Black Phosphorus Two-dimensional Electron System Likai Li, Fangyuan Yang, Guo Jun Ye, Zuocheng Zhang, Zengwei Zhu, Wenkai Lou, Xiaoying Zhou, Liang Li, Kenji Watanabe, Takashi Taniguchi, Kai Chang, Yayu Wang, Xian Hui Chen, Yuanbo Zhang The recent advent of black phosphorus has greatly enriched the material base of two-dimensional electron systems (2DES). In this work, we reached a milestone in black phosphorus research – the observation of integer quantum Hall (QH) effect in high quality black phosphorus 2DES. We achieved high carrier mobility by embedding the black phosphorus 2DES in a van der Waals heterostructure close to a graphite back gate; the graphite gate screens the impurity potential in the 2DES, and brings the Hall mobility up to 6000 cm2/Vs. The exceptional mobility enabled us, for the first time, to observe QH effect, and to gain important information on the energetics of the spin-split Landau levels in black phosphorus. Our results set the stage for further study on quantum transport and device application in the ultrahigh mobility regime. [Preview Abstract] |
Wednesday, March 16, 2016 12:27PM - 12:39PM |
L16.00005: \textbf{Nanoscopy Reveals Surface-Metallic Black Phosphorus}. Yohannes Abate \textbf{Nanolayer and two-dimensional (2D) materials.............}$^{\mathrm{\mathbf{1}}}$\textbf{ such as graphene...}$^{\mathrm{\mathbf{2,3}}}$\textbf{, boron nitride...}$^{\mathrm{\mathbf{1,4}}}$\textbf{, transition metal dichalcogenides...}$^{\mathrm{\mathbf{1,5-8}}}$\textbf{ (TMDCs), and black phosphorus (BP)...}$^{\mathrm{\mathbf{1,9-13}}}$\textbf{ have intriguing fundamental physical properties and bear promise of important applications in electronics and optics...}$^{\mathrm{\mathbf{9,14,15}}}$\textbf{. Of them, BP...}$^{\mathrm{\mathbf{11,12,16}}}$\textbf{ is a novel layered material that has been theoretically predicted...}$^{\mathrm{\mathbf{10}}}$\textbf{ to acquire plasmonic behavior for frequencies below \textasciitilde 0.4 eV when highly doped. The electronic properties of BP are unique due to its anisotropic structure}\textbf{. }\textbf{Advantages of BP as a material for nanoelectronics and nanooptics are due to the fact that, in contrast to metals, the free carrier density in it can be dynamically controlled by chemical or electrostatic gating, which has been demonstrated by its use in field-effect transistors....}$^{\mathrm{\mathbf{9,14,15}}}$\textbf{ Despite all the interest that BP attracts, near-field and plasmonic properties of BP have not yet been investigated experimentally. Here we report the first observation of nanoscopic near-field properties of BP. We have discovered near-field patterns of outside bright fringes and high surface polarizability of nanofilm BP consistent with its surface-metallic, plasmonic behavior at mid-infrared (mid-IR) frequencies below critical frequency }$\mathbf{\omega }_{\mathbf{m}} \mathbf{\approx 1176}$\textbf{ cm}$^{\mathrm{\mathbf{-1}}}$\textbf{. This has allowed us to estimate plasma frequency }$\mathbf{\omega }_{\mathbf{p}} \mathbf{\approx }\mathbf{0.4}$\textbf{ eV, carrier density }$\mathbf{n}\approx {\rm {\bf 1}}.{\rm {\bf 1}}\times {\rm {\bf 10}}^{{\rm {\bf 11}}} {\rm {\bf cm}}^{-{\rm {\bf 1}}}$\textbf{ and the thickness of the surface metallic layer of }${\rm {\bf \sim }}\mathbf{1 nm}$\textbf{. We have also observed similar behavior in other nanolayer semiconductors such as TMDC MoS}$_{\mathrm{\mathbf{2}}}$\textbf{ and topological insulator Bi}$_{\mathrm{\mathbf{2}}}$\textbf{Te}$_{\mathrm{\mathbf{3}}}$\textbf{ but not in insulators such as boron nitride. This new phenomenon is attributed to surface band-bending and charging of the semiconductor nanofilms. The surface plasmonic behavior has been found for 10-40 nm BP thickness but absent for 4 nm BP thickness. This discovery opens up a new field of research and potential applications in nanoelectronics, plasmonics, and optoelectronics.} [Preview Abstract] |
Wednesday, March 16, 2016 12:39PM - 12:51PM |
L16.00006: Near-field optical microscopy and spectroscopy of few-layer black phosphorous A. J. Frenzel, S. Tran, J. P. Hinton, A. J. Sternbach, J. Yang, N. Gillgren, C. N. Lau, D. N. Basov Few-layer black phosphorous is a recent addition to the family of two-dimensional (2D) materials which exhibits strongly anisotropic transport and optical properties due to its puckered honeycomb structure. It was recently predicted that this intrinsic anisotropy should manifest in the plasmon dispersion. Additionally, tuning layer number and carrier density can control the dispersion of these collective modes. Scanning near-field optical microscopy (SNOM) has been demonstrated as a powerful method to probe electronic properties, including propagating collective modes, in layered 2D materials. We used SNOM to investigate anisotropic carrier response in few-layer black phosphorous encapsulated by hexagonal boron nitride. In addition to exploring gate-voltage tunability of the electronic response, we demonstrate effective modulation of the near-field signal by ultrafast photoexcitation. [Preview Abstract] |
Wednesday, March 16, 2016 12:51PM - 1:03PM |
L16.00007: Resonant optical third-harmonic generation in few-layer black phosphorus Christiano J. S. de Matos, Manuel J. L. F. Rodrigues, Rafael E. P. de Oliveira, H\'elder X. P. Peixoto, Hsin-Yu Wu, Ho Y. Wei, Antonio H. Castro Neto, Jos\'e C. Viana-Gomes Black phosphorus (BP), a layered monoatomic anisotropic crystal, has recently re-emerged due to demonstrations of its exfoliation down to few-layer thicknesses. It has been shown that BP remains a direct bandgap semiconductor from the bulk to the monolayer, which has triggered interest in its optoelectronic applications. However, optical characterization has been largely restricted to the linear regime, with nonlinear characterization limited to z-scan and saturable absorption measurements. In this work, we show optical third-harmonic generation measurements in bulk and few-layer BP. Results indicate a resonant increase in the generation efficiency of the latter, with signal intensities reaching values three orders of magnitude higher then those of graphene. The mechanisms leading to the resonant increase will be discussed. [Preview Abstract] |
Wednesday, March 16, 2016 1:03PM - 1:15PM |
L16.00008: Transmission pump-probe spectroscopy on multilayer black phosphorus Ryan J. Suess, Mohammad M. Jadidi, Thomas E. Murphy, Martin Mittendorff Black phosphorus is a two-dimensional material that has recently attracted interest due to its high mobility and direct bandgap. In this work we examine the pump-induced change in optical transmission of mechanically exfoliated black phosphorus flakes using a two-color optical pump-probe measurement. The time-resolved data reveal a fast pump-induced transparency accompanied by a slower absorption that we attribute to Pauli blocking and free-carrier absorption, respectively. Polarization studies show that these effects are also highly anisotropic - underscoring the importance of crystal orientation in the design of optical devices based on this material. Ongoing work suggests that exploring the carrier density dependence of the pump-probe signals, which can be accessed experimentally via electrostatic gating, may allow for improved understanding of the optical response and carrier dynamics in the material. [Preview Abstract] |
Wednesday, March 16, 2016 1:15PM - 1:27PM |
L16.00009: Electronic Structure and Optical Properties of Twisted Bilayer Black Phosphorus Ting Cao, Zhenglu Li, Diana Y. Qiu, Steven G. Louie Using first-principles calculations, we find that the electronic structure and optical properties of bilayer black phosphorus can be modified significantly through changing the interlayer twist angle. We demonstrate the origin of these twist angle dependent effects, and connect our predicted results to experimental measurements. [Preview Abstract] |
Wednesday, March 16, 2016 1:27PM - 1:39PM |
L16.00010: Phosphorene Nanoribbons: Electronic Structure and Electric Field Modulation Sina Soleimanikahnoj, Irena Knezevic Phosphorene, a newcomer among the 2D van der Waals materials, has attracted the attention of many scientists due to its promising electronic properties. Monolayer phosphorene has a direct band gap of 2 eV located at the Gamma point of the Brillouin zone. Increasing the number of layers reduces the bandgap due to the van der Waals interaction. The direct nature of the bandgap makes phosphorene particularly favorable for electronic transport and optoelectronic applications. While multilayer phosphorene sheets have been studied, the electronic properties of their 1D counterparts are still unexplored. An accurate tight-binding model was recently proposed for multilayer phosphorene nanoribbons. Employing this model along with the non-equilibrium Green’s function method, we calculate the band structure and electronic properties of phosphorene nanoribbons. We show that, depending on the edge termination, phosphorene nanoribbons can be metallic or semiconducting. Our analysis also shows that the electronic properties of phosphorene nanoribbons are highly tunable by in-plane and out-of-plane electric fields. In metallic ribbons, the conductance can be switched off by a threshold electric field, similar to field effect devices. [Preview Abstract] |
Wednesday, March 16, 2016 1:39PM - 1:51PM |
L16.00011: Two dimensional disorder in black phosphorus and layered monochalcogenides Salvador Barraza-Lopez, Mehrshad Mehboudi, Pradeep Kumar, Edmund O. Harriss, Hugh O. H. Churchill, Alex M. Dorio, Wenjuan Zhu, Arend van der Zande, Alejandro A. Pacheco SanJuan The degeneracies of the structural ground state of materials with a layered orthorhombic structure such as black phosphorus and layered monochalcogenides GeS, GeSe, SnS, and SnSe, lead to an order/disorder transition in two dimensions at finite temperature. This transition has consequences on applications based on these materials requiring a crystalline two-dimensional structure. Details including a Potts model that explains the two-dimensional transition, among other results, will be given in this talk. References: M. Mehboudi, A.M. Dorio, W. Zhu, A. van der Zande, H.O.H. Churchill, A.A. Pacheco Sanjuan, E.O.H. Harris, P. Kumar, and S. Barraza-Lopez. arXiv:1510.09153. [Preview Abstract] |
Wednesday, March 16, 2016 1:51PM - 2:03PM |
L16.00012: \textbf{Two-dimensional massless Dirac fermions, chiral pseudo-spins, and Berry's phase in few-layer black phosphorus} Seung Su Baik, Hyoung Joon Choi Black phosphorus (BP) and its two-dimensional (2D) derivative phosphorene are rapidly emerging nanoelectronic materials with potential applicability to field effect transistors and optoelectronic devices. Unlike the gapless semiconductor graphene, multilayer BP has a substantial band gap of 0.2 eV, and this band-gap size is predicted being sensitive to the external perturbations such as pressure, strain, and electric field. Very recently, a semiconductor-semimetal transition in BP was realized by the surface potassium (K) doping, producing a Dirac semimetal state with a linear dispersion in the armchair direction and a quadratic one in the zigzag direction [1,2]. Here, based on first-principles density functional calculations, we present that beyond the critical K density, 2D massless Dirac fermions emerge in K-doped few-layer BP, and the electronic states around Dirac points have chiral pseudo-spins and Berry's phase. These features are robust with respect to the spin-orbit interaction. The switchable massless Dirac fermions discussed here may open a new way for the development of high performance devices in 2D materials beyond graphene. [1] J. Kim, S. S. Baik, S. H. Ryu, Y. Sohn, S. Park, B. Park, J. Denlinger, Y. Yi, H. J. Choi, and K. S. Kim, Science \textbf{349}, 723-725, (2015). [2] S. S. Baik, K. S. Kim, Y. Yi and H. J. Choi, arXiv:1508.04932. [Preview Abstract] |
Wednesday, March 16, 2016 2:03PM - 2:15PM |
L16.00013: Two-dminensional exciton states in monolayer semiconducting phosphorus alotropes Alexandre R Rocha, Cesar E P Villegas During the last decade, novel two-dimensional (2D) semiconducting materials have been synthesized and characterised. As a result, there have been several theoretical and experimental proposals to incorporate 2D materials for designing next generation electronic and optoelectronics devices. In particular, it has been demonstrated that light absorption in phosphorus-based monolayers can span the whole visible spectrum, suggesting they could be used for optolectronic applications. A key ingredient for optolectronic applications is the presence of excitons and their subsequent diffusion along a donor material. This is influenced by the character of the different excitations taking place, as well as, the exciton binding energy. Therefore, In this work we use accurate many-body corrected density functional theory by means of GW-BSE methodology to elucidate the most important optical transitions, exciton energy spectrum as well as exciton extension in different types of phosphorene materials. In addition, we solve the Schrodinger equation for different 2D screened potentials and estimate the 2D exciton energy levels and radius extension. Finally, in order to assess further studies based on these systems, we provide a simple analityc expression for estimating 2D exciton energy levels. [Preview Abstract] |
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