Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session V33: 2D Materials in Magnetic Fields |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Zhaoli Gao, University of Pennsylvania Room: 296 |
Thursday, March 16, 2017 2:30PM - 2:42PM |
V33.00001: Magnetic quantization in monolayer bismuthene Szu-Chao Chen, Chih-Wei Chiu, Hui-Chi Lin, Ming-Fa Lin The magnetic quantization in monolayer bismuthene is investigated by the generalized tight-binding model. The quite large Hamiltonian matrix is built from the tight-binding functions of the various sublattices, atomic orbitals and spin states. Due to the strong spin orbital coupling and sp$^{\mathrm{3}}$ bonding, monolayer bismuthene has the diverse low-lying energy bands such as the parabolic, linear and oscillating energy bands. The main features of band structures are further reflected in the rich magnetic quantization. Under a uniform perpendicular magnetic field (B$_{\mathrm{z}})$, three groups of Landau levels (LLs) with distinct features are revealed near the Fermi level. Their B$_{\mathrm{z}}$-dependent energy spectra display the linear, square-root and non-monotonous dependences, respectively. These LLs are dominated by the combinations of the 6p$_{\mathrm{z}}$ orbital and (6p$_{\mathrm{x}}$,6p$_{\mathrm{y}})$ orbitals as a result of strong sp$^{\mathrm{3}}$ bonding. Specifically, the LL anti-crossings only occur between LLs originating from the oscillating energy band. [Preview Abstract] |
Thursday, March 16, 2017 2:42PM - 2:54PM |
V33.00002: Expectations for photo-excitation-induced oscillatory magnetoresistance in graphene Ramesh Mani Microwave/mm-wave/terahertz photoexcitation of high quality quasi-2D electron systems based on GaAs/AlGaAs heterostructures results in large amplitude ``1/4 cycle shifted'' magnetoresistance oscillations.[1] Most remarkably, at the lowest temperatures under modest photo-excitation, the deepest resistance minima saturate into zero-resistance states in the vicinity of 4/[(4j$+$1)B$_{f}$] with j $=$1,2,3,\textellipsis of the characteristic field B$_{f} \quad =$ 2$\pi $ f \quad m*/e, where f is the electromagnetic-wave frequency, m* is the effective mass ratio, and e is the electronic charge.[1] Analogous photo-excited magnetoresistance studies of atomic layer 2D systems such as monolayer and bilayer graphene could potentially unveil new science and applications. However, the theoretical device response for these materials is not known and such phenomena have not been observed thus far in the graphene system. Thus, we examine here the possible response of monolayer and AB-bilayer graphene arising from the (a) linear and quadratic dispersion laws at the K(K$\prime $ ) symmetry points, respectively, and (b) dissimilar magnetic Landau level dispersions in a quantizing magnetic field B \textgreater 0. [1] R. G. Mani et al., Nature 420, 646 (2002). [Preview Abstract] |
Thursday, March 16, 2017 2:54PM - 3:06PM |
V33.00003: Transport of Andreev pairs via quantum-Hall edge states in graphene Geon-Hyoung Park, Minsoo Kim, Kenji Watanabe, Takashi Taniguchi, Hu-Jong Lee Andreev reflection (AR), retro reflection of an incident electron as a hole and vice versa at a superconductor-normal metal interface, leads to the formation of an Andreev edge state (AES) that consists of a coherent pair of an electron and a hole in a strong magnetic field. The resulting incoming electrons and outgoing holes act as Andreev pairs, giving the zero-bias conductance enhancement along the AES. The coexistence of AR and quantum-Hall (QH) effect in semiconducting two-dimensional electron systems has been confirmed in two-terminal conductance measurement configurations where both bulk and longitudinal contributions are bound to be contained. Here we report signature of the AES formed in mono- and bi-layer graphene devices with a three-terminal measurement configuration. A graphene layer, encapsulated by hexagonal boron nitride crystals, was in proximity contact with a Nb electrode having a high upper critical magnetic field ($H_{c2}$(0) \textasciitilde 3.3 T). The high carrier mobility of our graphene layers allowed the formation of QH edge states in perpendicular magnetic fields as low as \textasciitilde 1 T. The signature of AR was clearly visible in the bias spectroscopy as a conductance enhancement near zero-bias in both up and down stream of QH edge states corresponding to high filling factors. [Preview Abstract] |
Thursday, March 16, 2017 3:06PM - 3:18PM |
V33.00004: Electrostatically Defined Structure for Novel Fractional Quantum Hall States in Graphene Shaowen Chen, Rebeca Ribeiro-Palau, Takashi Taniguchi, Kenji Watanabe, James Hone, Cory R. Dean The electronic structure of graphene has a four-fold symmetry with spin and valley, which, together with the linear band dispersion is expected to lead to novel fractional quantum hall (FQH) states. Experimental probes of this regime however have remained limited. While compressibility measurement of high quality devices has rapidly progressed, enabling detailed measurement of the FQH bulk response, transport measurement, where the edge modes may be directly assessed, has remained limited. The reason for this is incompletely understood and may be due to a number of contributing effects. Here we report on BN-encapsulated graphene devices where we utilize an electrostatic gate to define the active device region, taking advantage of the properties of the nu$=$0 energy gap. In these structures the sample disorder, as measured by transport, is reduced and the FQH signature is enhanced. As a result, we observed FQH states at magnetic fields as low as 6 T with enhanced energy gaps compared with previous works. We also observed the clear presence of four-flux states from magnetic fields as low as 20 T. Our result provides a proof of principle demonstration that complex structures in the FQHE regime, such as quantum point contacts and quantum interferometers, are now accessible in graphene devices. [Preview Abstract] |
Thursday, March 16, 2017 3:18PM - 3:30PM |
V33.00005: Realization of Quantum Anomalous Hall Effect in Graphene from n-p Codoping Induced Stable Atomic-Adsorption Xinzhou Deng, Shifei Qi, Yulei Han, Kunhua Zhang, Xiaohong Xu, Zhenhua Qiao Using first-principles calculation methods, we study the possibility of realizing quantum anomalous Hall effect in graphene from stable 3d-atomic adsorption via charge-compensated n-p codoping scheme. As concrete examples, we show that long-range ferromagnetism can be established by codoping 3d transition metal and boron atoms, but only the Ni codopants can open up a global bulk gap to harbour the quantum anomalous Hall effect. Our estimated ferromagnetic Curie transition temperature can reach over 10 Kelvin for various codoping concentrations. [Preview Abstract] |
Thursday, March 16, 2017 3:30PM - 3:42PM |
V33.00006: Hot carrier cooling with Landau levels in graphene Xinghan Cai, Sanfeng Wu, You Lai, David Cobden, Zhiqiang Li, Xiaodong Xu Photo-excited hot carriers in homogeneous graphene can give rise to photocurrent under perpendicular magnetic field. In turn, this so-called photo-Nernst effect can be used to probe hot-carrier dynamics as modified by the formation of Landau levels. We have carried out an ultrafast optical pump-probe photocurrent study of hexagonal boron nitride encapsulated graphene devices in the quantum Hall regime. Photocurrent, which exhibits quantum oscillations, is observed when the laser spot is near the free edges of the graphene. The relaxation time of the photo-Nernst current shows a drastic change when the graphene's Fermi energy is tuned across a Landau level. Our observation points to a new means of probing and control of non-equilibrium carrier dynamics in the quantum regime. [Preview Abstract] |
Thursday, March 16, 2017 3:42PM - 3:54PM |
V33.00007: Large magnetoresistance and sharp switching in Fe$_x$TiS$_2$ Jesse Choe, Emilia Morosan Large magnetoresistance materials are suitable for applications in sensors, read heads, and random access memories. Most metals, though having excellent ductility which is important for manufacturing processes, have changes of magnetoresistance on the order of only $\sim 1\%$. Very large magnetoresistances in Fe$_{0.30}$TaS$_2$ [Phys. Rev. B 94 054406 (2016)] ($\sim 140\%$) have been attributed to misalignment of magnetic moments causing spin disorder scattering. We performed measurements of the magnetic field dependence of resistivity and magnetization of Fe$_x$TiS$_2$ single crystals ($x = 0.1-0.5$), which show both the large magnetoresistance, as well as the sharp switching in magnetization as those reported in the Ta analogue. By comparing and contrasting these two materials, we can gain deeper understanding of the underlying physics, allowing us to strategically search for materials with higher transition temperature, lower switching fields, and larger magnetoresistances. [Preview Abstract] |
Thursday, March 16, 2017 3:54PM - 4:06PM |
V33.00008: Electronic instabilities of extended Hubbard models on the honeycomb lattice David S\'anchez de la Pe\~na, Julian Lichtenstein, Carsten Honerkamp We investigate the quantum many-body instabilities for electrons on the honeycomb lattice at half-filling with extended interactions[1], as a model for graphene-type systems. We use a recently developed functional Renormalization Group scheme[2] which allows for highly resolved calculations of momentum dependences in the low-energy effective interactions. We find the expected anti-ferromagnetic instability for a pure on-site repulsion term, and charge order with different modulations for pure $n^{\text{th}}$ nearest neighbor repulsive interactions. An interaction induced Quantum Spin Hall state is not realized as a dominant instability in our results, with charge order being favored instead. Novel instabilities towards incommensurate charge density waves take place when non-local density interactions over several bond distances are included simultaneously. We further comment on the effect of realistic Coulomb potentials from ab-initio interaction parameters for graphene, where the semi-metallic state is stabilized due to competition effects between different ordering tendencies. \\ \ [1] D. S\'{a}nchez de la Pe\~{n}a et al., \textit{ArXiv e-prints} (2016),arXiv:1606.01124.\\ \ [2] J. Lichtenstein et al., \textit{ArXiv e-prints} (2016),arXiv:1604.06296. \\ [Preview Abstract] |
Thursday, March 16, 2017 4:06PM - 4:18PM |
V33.00009: Electronic structure of Pb-intercalated graphene on Ir(111): an ab initio study Mikhail Otrokov, Héctor Ochoa, Francisco Guinea, Amadeo L. Vázquez de Parga, Rodolfo Miranda, Evgueni V. Chulkov, Andrés Arnau Extending graphene’s electronic properties beyond those intrinsically inherent to it is a great challenge of the contemporary condensed matter physics. In particular, because of graphene's extremely weak spin-orbit coupling, currently there is an intense research aiming at inducing pronounced spin-orbit effects in it \cite{\1,2,3}. We present the results of our \emph{ab initio} study of the graphene on Ir(111), intercalated by a monolayer of Pb atoms. We discuss system's crystal and electronic structures, as well as spin texture and analyse the influence of the intercalated Pb monolayer on the graphene $\pi$ bands.\\ \\ ${1}$ D. Marchenko et al. Nat. Commun. {\bf 3}, 1232 (2012). \bibitem{2} F. Calleja et al. Nat. Phys. {\bf 11}, 43 (2015). \bibitem{3} A. Varykhalov et al. Nat. Commun. {\bf 6}, 7610 (2015). [Preview Abstract] |
Thursday, March 16, 2017 4:18PM - 4:30PM |
V33.00010: Two-Dimensional Multiferroics in Monolayer Group IV Monochalcogenides Hua Wang, Xiaofeng Qian Low-dimensional multiferroics with strongly coupled ferroic orders are highly valuable for miniaturized transducers, actuators, sensors, photovoltaics, and nonvolatile memories. However, they are very scarce owing to the stringent symmetry and chemistry requirements for practical applications at room temperature. Using first-principles theory, we predict that two-dimensional monolayer Group IV monochalcogenides including GeS, GeSe, SnS, and SnSe are a class of 2D semiconducting multiferroics with giant strongly coupled in-plane spontaneous ferroelectric polarization and spontaneous ferroelastic lattice strain. In addition, they are thermodynamically stable at room temperature, and possess strong anisotropic and excitonic in-plane photoabsorption with visible-spectrum excitonic gaps and large exciton binding energies. The interplay of low domain wall energy, small migration barrier, coupled ferroelastic-ferroelectric order, and anisotropic electronic structures suggest their great potential for tunable multiferroic functional devices by manipulating external electrical, mechanical, and optical field to control the internal responses. (Reference: Hua Wang and Xiaofeng Qian, http://arxiv.org/abs/1606.04522 (2016)) [Preview Abstract] |
Thursday, March 16, 2017 4:30PM - 4:42PM |
V33.00011: Edge pseudo-magnetoplasmons Alessandro Principi, Mikhail Katsnelson, Giovanni Vignale We study the properties of edge plasmons in two-component electron liquids in the presence of pseudomagnetic fields, which have opposite signs for the two different electronic populations and therefore preserve the time-reversal symmetry. The physical realizations of such systems are many. We discuss the case of strained graphene, solving the problem with the Wiener-Hopf technique. We show (i) that two charged counter-propagating acoustic edge modes exist at the boundary and (ii) that, in the limit of large pseudomagnetic fields, each of them involves oscillations of only one of the two electronic components. We suggest that the edge pseudo-magnetoplasmons of graphene can be used to selectively address the electrons of one specific valley, a feature relevant for the emerging field of valleytronics. We speculate that electrons in proximity to a Skyrmion lattice could exhibit the same phenomenology, and that the resulting spin-polarized plasmons at the boundary of Skyrmion lattices could be exploited for spintronics applications. Our solution highlights new features missing in previous (similar) results obtained with uncontrolled approximations, namely a logarithmic divergence of the plasmon velocity, and the absence of gapped edge modes inside the bulk-plasmon gap. [Preview Abstract] |
Thursday, March 16, 2017 4:42PM - 4:54PM |
V33.00012: Universality of quadratic to linear magnetoresistance crossover in disordered conductors Silvia Lara, Navneeth Ramakrishnan, Ying Tong Lai, Shaffique Adam Many experiments measuring Magnetoresistance (MR) showed unsaturating linear behavior at high magnetic fields and quadratic behavior at low fields. In the literature, two very different theoretical models have been used to explain this classical MR as a consequence of sample disorder. The phenomenological Random Resistor Network (RRN) model constructs a grid of four-terminal resistors each with a varying random resistance. The Effective Medium Theory (EMT) model imagines a smoothly varying disorder potential that causes a continuous variation of the local conductivity. In this theoretical work, we demonstrate numerically that both the RRN and EMT models belong to the same universality class, and that a single parameter (the ratio of the fluctuations in the carrier density to the average carrier density) completely determines both the magnitude of the MR and the B-field scale for the crossover from quadratic to linear MR. By considering several experimental data sets in the literature, ranging from thin films of InSb to graphene to Weyl semimetals like Na3Bi, we show that this disorder-induced mechanism for MR is in good agreement with the experiments, and that this comparison of MR with theory reveals information about the spatial carrier density inhomogeneity. [Preview Abstract] |
Thursday, March 16, 2017 4:54PM - 5:06PM |
V33.00013: Emergence of Topological Interface States at Chern Insulator Junctions: Complete Mode-Mixing and Gate-Tunable Beam Splitting Nojoon Myoung, Hee Chul Park Chern insulator junctions have introduced by using p-n junctions in graphene quantum Hall systems, which are characterized by different Chern numbers. It is theoretically demonstrated that topological states emerge at the interface of the Chern insulator junctions. The existence of the topological interface states are interpreted by the bulk-boundary correspondence of topological matters, indicating their number of states are the same as the Chern number difference between two Chern insulators. Interestingly, it is revealed that there is the intriguing splitting nature of the topological interface states via four-terminal conductance calculations. As a consequence of the mode-mixing of the topological states at junctions, the quantum Hall conductance is split into two opposite directions at the system boundary, satisfying the flux conservation. Such splitting nature is sensitively dependent on the size of system, resulting from the width-dependent electronic states for armchair edge terminations. Further, it is also investigated that how the topological interface states are robust against realistic p-n junctions, i.e., smoothly varying potentials instead of the abrupt step potential. As expected, the topological states still exist at smooth junctions [Preview Abstract] |
Thursday, March 16, 2017 5:06PM - 5:18PM |
V33.00014: Floquet High Chern Insulators in Periodically Driven Chirally Stacked Multilayer Graphene Cheng-Cheng Liu, Si Li, Yugui Yao Chirally stacked N-layer graphene is a semimetal with p$^{\mathrm{N}}$ band-touching at two nonequivalent corners in its Brillioun zone. We predict that a off-resonant circularly polarized light (CPL) drives chirally stacked N-layer graphene into a Floquet Chern Insulators (FCIs), a.k.a. quantum anomalous Hall insulators, with tunable high Chern number C$_{\mathrm{F}}=+$/-N and large gaps. A topological phase transition between such a FCI and a valley Hall (VH) insulator with high valley Chern number C$_{\mathrm{v}}=+$/-N induced by a voltage gate can be engineered by the parameters of the CPL and voltage gate. We propose a topological domain wall between the FCI and VH phases, along which perfectly valley-polarized N-channel edge states propagate unidirectionally without backscattering. [Preview Abstract] |
Thursday, March 16, 2017 5:18PM - 5:30PM |
V33.00015: Role of disorder in superconducting Chern insulator Yingyi Huang, Jay Sau Motivated by a recent experiment in which a half-integer quantized conductance plateau ($0.5e^2/h$) has been observed on a superconducting quantum anomalous Hall insulator film, we carry out a simulation of a two-dimensional disordered Chern insulator coupled with superconductor. In particular we calculate the magnetic field dependence of the longitudinal and Hall conductance in the Hall bar geometry of a disordered Chern insulator both with a superconductor and without. Our specific focus is on the behavior of this conductance near the transition between topological phase ($\nu$=0) and trivial phase ($\nu$=1), where we expect to reproduce the conductance plateau. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700