Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C35: 2D Materials - Phosphorene and h-BN |
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Sponsoring Units: DMP Chair: Wang Yao, University of Hong Kong Room: LACC 409B |
Monday, March 5, 2018 2:30PM - 2:42PM |
C35.00001: Interaction of Phosphorene with Ultrafast Optical Pulse Fatemeh Nematollahi, Vadym Apalkov, Mark Stockman We study theoretically interaction of monolayer black phosphorous, phosphorene, with an ultrafast optical pulse with the duration of a few femtoseconds. For such short pulse the electron dynamics is coherent and can be described by the time-dependent Schrodinger equation. A conduction band population in the reciprocal space shows hot spots near the point, at which the interband dipole coupling is the largest. We show that the interband electron dynamics is irreversible, i.e., the residual conduction band population is comparable to the maximum conduction band population during the pulse. Also, the electron redistribution between the bands generates an electric current and finally causes a charge transfer through the phosphorene during the pulse. The direction of the charge transfer is the same as the direction of the field maximum. |
Monday, March 5, 2018 2:42PM - 2:54PM |
C35.00002: Ultrafast dynamics in atomically thin black phosphorus Vivek Pareek, Bryan Berggren, Takaaki Harada, Christopher Weber, Andrew Winchester, Bala Mariserla, Julien Madéo, Keshav Dani Black Phosphorous (BP) is a new emerging material in the family of two-dimensional van der Waals semiconductors. Unlike transition metal dichalcogenides, BP has direct band gap ranging from bulk to monolayer, significantly higher carrier mobility, and an unusual in-plane anisotropy in its optical response. Despite its importance for potential optoelectronics applications, efforts in understanding carrier dynamics have only been limited to bulk BP due to its rapid photo-oxidation in ambient conditions. Here we report on the ultrafast and nonlinear optical response of mechanically exfoliated bilayer BP. By covering the BP with hBN, or eliminating exposure to air during preparation and measurement, we observe substantial inhibition of its degradation over several days in multiple samples. We study the nonlinear optical response of the bilayer BP for different pump intensities, probe wavelengths, and substrates. |
Monday, March 5, 2018 2:54PM - 3:06PM |
C35.00003: The Layer-Dependence on the Work Function and Degradation Evolution of Black Phosphorus Minju Kim, Han-gyu Kim, Soohyung Park, Jin Sung Kim, Hyoung Joon Choi, Seongil Im, Hyunbok Lee, Taekyeong Kim, Yeonjin Yi Black phosphorus (BP) has been received great attention due to the layer-electronic structure. This layer-dependent electronic structure of BP shows not only the variation of bandgap but also work function (WF) shift. These layer-dependent electronic properties at such interfaces are key parameters to determine interfacial properties, such as Schottky barrier and charge redistribution. Furthermore, the fast degradation of BP is currently a critical obstacle for an application. Since the degradation progress at the interface between BP and O2/H2O molecules in ambient condition, the layer-dependent electronic properties are key parameters to understood the degradation process of BP. |
Monday, March 5, 2018 3:06PM - 3:18PM |
C35.00004: Resonant Raman Scattering in Anisotropic Black Phosphorus Crystals Nannan Mao, Xingzhi Wang, Xi Ling, Jing Kong Black phosphorus (BP), a remarkable elemental layered semiconductor with puckered structure, has attracted significant attentions in the past three years. Due to the in-plane low symmetry, few-layer BP exhibits distinct anisotropic electron-photon and electron-phonon interactions in the visible region, giving rise to significant linear dichroism feature and anisotropic Raman scattering. Previous literature reported that the totally symmetric (Ag) Raman modes of BP show abnormal angle-dependent polarized Raman intensities, which are dependent on the excitation energy, thickness and Raman modes too. Several models have been proposed to explain this abnormal phenomenon from the perspective view of complex Raman tensor, birefringence effect, and interference enhancement. However, the resonant Raman effect, which significantly enhances the Raman intensity has not been taken into consideration. Here we investigated the resonant Raman scattering of BP along armchair and zigzag directions with different excitation wavelengths in the visible range. Our results show that the resonant Raman effect plays a crucial role in observing the abnormal polarized Raman scattering in BP. |
Monday, March 5, 2018 3:18PM - 3:30PM |
C35.00005: Calculations of Second-Order Raman Scattering in Monolayer Black Phosphorus Felix Antoine Goudreault, Alexandre Favron, Vincent Gosselin, Julien Groulx, Michel Cote, Richard Martel, Richard Leonelli Ab initio electronic and phonons band structure calculations were performed on a monolayer of Black Phosphorus to simulate and identify the origin of bulk-forbidden Raman modes in the experimental spectrum. In our previous experimental work, we observed four of these new modes in the Ag1 and Ag2 regions, called the D modes. They are present for the three wavelengths at which they were probed and appear to dominate the Raman spectrum for an excitation wavelength of 633 nm. The laser frequency and layer number dependence of the D modes, that seem linked to the decrease of the peak intensity ratio Ag1/Ag2 with degradation time, suggest that these modes are “defect-induced” second-order Raman scattering. The simulated Raman spectrum adds to this conclusion by identifying them to be due to phonon-defect interactions occurring through intravalley scatterings. This talk will focus on the simulation and theoretical details. Using scattering theory and values obtained from DFT calculations, we identified which electronic states were coupled resonantly by a phonon and a defect. From those states, we extracted the corresponding phonon frequency to build the Raman spectrum. It allowed us to locate the regions of the band structures mostly contributing to the Raman spectrum. |
Monday, March 5, 2018 3:30PM - 3:42PM |
C35.00006: Dynamical Anisotropic Response of Black Phosphorus under Magnetic Field Wei Lu, Xuefeng Liu, Xiaoying Zhou, Yang Zhou, Chenglong Zhang, Jiawei Lai, Shaofeng Ge, M. Chandra Sekhar, Shuang Jia, Kai Chang, Dong Sun Black phosphorus (BP) has emerged as a promising material candidate for next generation electronic and optoelectronic devices due to its high mobility, tunable band gap and highly anisotropic properties. In this work, polarization resolved ultrafast mid-infrared transient reflection spectroscopy measurements are performed to study the dynamical anisotropic optical properties of BP under magnetic fields up to 9 T. The relaxation dynamics of photoexcited carrier is found to be insensitive to the applied magnetic field due to the broadening of the Landau levels and large effective mass of carriers. While the anisotropic optical response of BP decreases with increasing magnetic field, its enhancement due to the excitation of hot carriers is similar to that without magnetic field. These experimental results can be well interpreted by the magneto-optical conductivity of the Landau levels of BP thin film, based on an effective k●p Hamiltonian and linear response theory. These findings suggest attractive possibilities of multi-dimensional controls of anisotropic response (AR) of BP with light, electric and magnetic field, which further introduces BP to the fantastic magnetic field sensitive applications. |
Monday, March 5, 2018 3:42PM - 3:54PM |
C35.00007: Engineering Kondo State in Two-dimensional Semiconducting Phosphorene Rohit Babar, Mukul Kabir Correlated interaction between dilute localized electrons with the itinerant conduction electrons gives rise to Kondo effect below sufficiently low temperature. Beyond the conventional impurity in a metal systems, many artificial Kondo systems have been discovered in the last two decades. In sharp contrast to the artificial Kondo systems, we report an intrinsic, robust and high-temperature Kondo state in two-dimensional semiconducting phosphorene based on density functional theory calculations at different levels of approximations. While absorbed at a thermodynamically stable lattice defect, Cr impurity triggers an electronic phase transition in phosphorene to provide conduction electrons, which strongly interact with the localized moment generated at the Cr site. This manifests in an intrinsic Kondo state, where a multi-stage quenching of the impurity moment occurs in the temperature range 40-200 K. Further, along with a significantly small extension of Kondo cloud, the predicted Kondo state is shown to be robust under uniaxial strain and layer thickness, which greatly simplifies its future experimental realization. Our findings will broaden the current understanding of Kondo physics in two-dimensional materials. |
Monday, March 5, 2018 3:54PM - 4:06PM |
C35.00008: Symmetry-Protected Dirac Semimetal Phase in Surface-Doped Black Phosphorus Jimin Kim, Seung Su Baik, SungWon Jung, Yeongsup Sohn, Sae Hee Ryu, Hyoung Joon Choi, Bohm-Jung Yang, Keun Su Kim Two-dimensional (2D) black phosphorus has attracted growing interest owing to its tunable band structure with external parameters such as field and strain. In particular, the effect of strong vertical electric field can be induced by in-situ surface doping of alkali metal atoms on the surface of black phosphorus, leading to the widely tunable band gap. In this study, we experimentally demonstrate the giant band inversion in the surface of black phosphorus by means of angle-resolved photoemission spectroscopy (ARPES). Our ARPES spectra reveal that the band-inverted state of black phosphorus has a pair of Dirac cones that are separated along the zigzag direction. Unlike graphene, the Dirac points of black phosphorus are stable even in the presence of spin-orbit coupling owing to space-time inversion symmetry, a combination of glide-mirror symmetry and time-reversal symmetry. |
Monday, March 5, 2018 4:06PM - 4:18PM |
C35.00009: Superfluidity of dipolar excitons in a black phosphorene double layer Roman Kezerashvili, Oleg Berman, Godfrey Gumbs The formation of dipolar excitons and their superfluidity in a black phosphorene double layer was studied [1]. It is predicted that a dilute weakly interacting Bose gas of dipolar excitons in a black phosphorene double layer exhibits superfluidity, caused by the dipole-dipole repulsion between dipolar excitons. In calculations the Keldysh and Coulomb potentials for the interaction between the electron and hole are employed to analyze the influence of the screening effects on the single-particle and collective properties of dipolar excitons. A critical velocity of superfluidity, spectrum of collective excitations, concentrations of the superfluid and normal components, and mean |
Monday, March 5, 2018 4:18PM - 4:30PM |
C35.00010: Reliable nonvolatile memory black phosphorus ferroelectric field effect transistors with van der Waals buffer Shili Yan, Hai Huang, Zhijian Xie, Guo Ye, Xiaoxi Li, Takashi Taniguchi, Kenji Watanabe, Zheng Han, Xianhui Chen, Jianlu Wang, Jianhao Chen Two dimensional materials based ferroelectric field effect transistors (2D-FeFETs) have attracted much attention due to the prospect of low power consumption information storage with alleviated short channel effect and fast processing speed. However, an often-observed and hard-to-control anti-hysteresis response of 2D-FeFETs, e.g., a hysteretic switching of the resistance states of the devices which is opposite to that of the actual polarization of the ferroelectric dielectric, represent a major issue in the industrial applications of such devices. Here, we demonstrate a van der Waals buffer layer technique that eliminates anti-hysteresis in 2D-FeFETs and restores their intrinsic hysteretic behavior. Our modified 2D-FeFETs showed outstanding performance including high room temperature carrier mobility, robust bi-stable states with fast response to gate, large on/off ratio at zero gate voltage, large and considerably more stable memory window, and a long retention time. During repeated gate operation, the memory window of the buffered device is ~7000 times more stable than the unbuffered device. |
Monday, March 5, 2018 4:30PM - 4:42PM |
C35.00011: Work functions of two-dimensional black phosphorus from first principles Han-gyu Kim, Hyoung Joon Choi We performed first-principles calculations to investigate the work function of two-dimensional black phosphorus (BP) as a function of the number of layers. First, we considered pristine BP layers using the density-functional theory (DFT) and GW approximation. The work function of pristine BP obtained from DFT tends to increase slightly as the number of BP layers decreases from four-layer to monolayer. In our GW calculation of pristine BP layers, the work function is increased, compared with DFT results. The increase of the work function depends very weakly on the number of layers. Second, we also investigated the effect of the metal substrate on the work function of BP layers. In this case, we performed DFT calculations. The presence of metal substrate increases the work function of BP and makes it depend more strongly on the number of layers than the pristine case. |
Monday, March 5, 2018 4:42PM - 4:54PM |
C35.00012: Tailoring electronic properties of low-dimensional P-based systems by utilizing phosphorene reactivity Oleksandr Malyi, Kostiantyn Sopiha, Clas Persson Phosphorene is a direct or close direct band gap semiconductor with the gap energy of about 1.2-2.0 eV, which makes it very attractive for various semiconductor applications. However, owing to its high chemical reactivity, electronic properties of phosphorene change drastically upon interaction with an environment. Motivated by this, we develop the concept for tailoring electronic properties of P-based systems using phosphorene reactivity.[1, 2] Combining screening by first-principles calculations and Born-Oppenheimer molecular dynamics simulations, we fully reconsider phosphorene oxidation and formation of low-dimensional phosphorus oxides (PxOy). We show that P-O interaction can result in the formation of highly stable 0d-PxOy and 2d-PxOy structures. Herein, the formation of amorphous 2d-PxOy structures and their unique electronic properties are also studied in detail.[2] Finally, we also show the possibility of using phosphorene reactivity for controlling thickness dependence of electronic properties as well as to design other P-based 2d materials. |
Monday, March 5, 2018 4:54PM - 5:06PM |
C35.00013: Monolayer to bulk properties of hexagonal boron nitride Darshana Wickramaratne, Leigh Weston, Chris Van de Walle Hexagonal boron nitride (h-BN) has attracted a lot of attention as a layered material in which the layers are weakly bound by van der Waals interactions. h-BN is being explored as a host for single-photon emitters and as a dielectric in heterostructures comprised of two-dimensional materials. For these applications an accurate description of the evolution of the electronic structure of h-BN as a function of the number of layers is required. We will present hybrid functional calculations of the electronic structure of h-BN as a function of the number of layers, starting from a monolayer, which has a direct band gap. Above a monolayer the band gap becomes indirect. We find that, with respect to the vacuum level, the conduction band at M decreases as the number of layers increases which leads to the direct-to-indirect cross over. These findings are analyzed in terms of the orbital composition and effective masses at the band edges at various high-symmetry points in the Brillouin zone. |
Monday, March 5, 2018 5:06PM - 5:18PM |
C35.00014: First-Principles Study of Stacking Type Influences on the Nature of the Band Gap for 2D and 3D h-BN Structures Kelsey Mengle, Emmanouil Kioupakis Various interesting electronic and optical properties can be derived through manipulation of the stacking type of layered materials. In particular, h-BN is of interest because the two-atom-type structure reduces its crystal symmetry compared to graphene and opens up a sizable gap. By engineering the stacking type of h-BN structures, the nature and magnitude of the band gap can be adjusted. Differences in the stacking layers shift the locations of the valence band maximum and conduction band minimum, which may lead to a direct or indirect band gap. We used first-principles calculations based on density functional theory and many-body perturbation theory to investigate the influence of different stacking sequences on the nature and magnitude of the band gap in bulk and few-layer structures of h-BN, including both ordered and randomly-stacked layered structures. Our results establish the connection between the microscopic atomic structure to the character and magnitude of the gap. |
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