Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B27: Semiconductors and the Hall Effect I. |
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Sponsoring Units: FIAP Chair: Jun Zhu, Penn State University Room: 290 |
Monday, March 13, 2017 11:15AM - 11:27AM |
B27.00001: Spin Mixing in GaAs Quantum Wells William Mayer, Areg Ghazaryan, Pouyan Ghaemi, Sergey Vitkalov, Alexey Bykov Transport properties of highly mobile 2D electrons are studied in symmetric GaAs quantum wells placed in titled magnetic fields. Quantum positive magnetoresistance (QPMR) is observed in magnetic fields perpendicular to the 2D layer. Application of in-plane magnetic field produces a dramatic decrease of the QPMR. This decrease correlates strongly with the reduction of the amplitude of Shubnikov de Haas resistance oscillations due to modification of the electron spectrum via enhanced Zeeman splitting. Surprisingly no quantization of the spectrum is detected when the Zeeman energy exceeds the half of the cyclotron energy suggesting an abrupt transformation of the electron spin-orbital dynamics. Observed angular evolution of QPMR implies strong mixing between spin subbands. Theoretical estimations indicate that in the presence of spin-orbital interaction the elastic impurity scattering provides significant contribution to the spin mixing in GaAs quantum wells at high filling factors. [Preview Abstract] |
Monday, March 13, 2017 11:27AM - 11:39AM |
B27.00002: Gate-controlled tunneling of quantum Hall edge states in bilayer graphene Jun Zhu, Jing Li, Hua Wen Controlled tunneling of integer and fractional quantum Hall edge states provides a powerful tool to probe the physics of 1D systems and exotic particle statistics. Experiments in GaAs 2DEGs employ either a quantum point contact or a line junction tunnel barrier. It is generally difficult to independently control the filling factors $\nu_{L}$ and $\nu_{R}$ on the two sides of the barrier. Here we show that in bilayer graphene both $\nu_{L}$ and $\nu_{R}$ as well as their Landau level structures can be independently controlled using a dual-split-gate structure. In addition, the height of the line-junction tunnel barrier implemented in our experiments is tunable via a 5$^{th}$ gate. By measuring the tunneling resistance across the junction $R_T$ we examine the equilibration of the edge states in a variety of $\nu_{L}$/$\nu_{R}$ scenarios and under different barrier heights. Edge states from both sides are fully mixed in the case of a low barrier. As the barrier height increases, we observe plateaus in $R_T$ that correspond to sequential complete backscattering of edge states. Gate-controlled manipulation of edge states offers a new angle to the exploration of quantum Hall magnetism and fractional quantum Hall effect in bilayer graphene. [Preview Abstract] |
Monday, March 13, 2017 11:39AM - 11:51AM |
B27.00003: Controlling quantum Hall edge state interaction in a graphene pn junction via device geometry modification Son T. Le, Joseph Hagmann, Guangjun Cheng, Angela Hight Walker, Nikolai Klimov, David Newell, Curt Richter, Ji ung Lee, Jun Yan The electrostatic profile of a pn junction may determine the way quantized Landau level (LL) edge states interact with each other [1,2]. Edge states at an electrostatically smooth junction are spatially further apart than those at a relatively abrupt junction, which decreases the probability of edge states mixing. We present a way to control LL edge state interaction through device geometry modification. A pnJ device with an electrostatic junction profile comparable to the one presented in [2] was experimentally fabricated and measured; however, it has a new geometry that alters the LL edge state interaction. In this device, we observe the lowest and second lowest LL edge states mix with each other in the quantum Hall regime. This ability to tune LL mixing opens up a new degree of freedom to fine tune quantum Hall resistance values for scalable resistance standard application. [1] J. R. Williams, L. DiCarlo, and C. M. Marcus, Science 317, 638 (2007) [2] Nikolai N. Klimov, Son T. Le, et al., Phys. Rev. B: Rapid Comm. (2015) [Preview Abstract] |
Monday, March 13, 2017 11:51AM - 12:03PM |
B27.00004: Geometrically disordered network models, quenched quantum gravity, and critical behavior at quantum Hall plateau transitions Ilya Gruzberg, Andreas Kl\"umper, Win Nuding, Ara Serdakyan Recent results for the critical exponent of the localization length at the integer quantum Hall transition (IQHT) differ considerably between experimental ($\nu_\text{exp} \approx 2.38$) and numerical ($\nu_\text{CC} \approx 2.6$) values obtained in simulations of the Chalker-Coddington (CC) network model. The difference is at least partially due to effects of the electron-electron interaction present in experiments. Here we propose a mechanism that changes the value of $\nu$ even within the single-particle picture. We revisit the arguments leading to the CC model and consider more general networks with structural disorder. Numerical simulations of the new model lead to the value $\nu \approx 2.37$. We argue that in a continuum limit the structurally disordered model maps to free Dirac fermions coupled to various random potentials (similar to the CC model) but also to quenched two-dimensional quantum gravity. This explains the possible reason for the considerable difference between critical exponents for the CC model and the structurally disordered model. We extend our results to network models in other symmetry classes. [Preview Abstract] |
Monday, March 13, 2017 12:03PM - 12:15PM |
B27.00005: Anti-levitation of Landau levels in vanishing magnetic fields W. Pan, K.W. Baldwin, K.W. West, L.N. Pfeiffer, D.C. Tsui Soon after the discovery of the quantum Hall effects in two-dimensional electron systems, the question on the fate of the extended states in a Landau level in vanishing magnetic (B) field arose. Many theoretical models have since been proposed, and experimental results remain inconclusive. In this talk, we report experimental observation of anti-levitation behavior of Landau levels in vanishing B fields (down to as low as B \textasciitilde 58 mT) in a high quality heterojunction insulated-gated field-effect transistor (HIGFET). We observed that, in the Landau fan diagram of electron density versus magnetic field, the positions of the magneto-resistance minima at Landau level fillings $\nu =$4, 5, 6 move below the ``traditional'' Landau level line to lower electron densities. This clearly differs from what was observed in the earlier experiments where in the same Landau fan plot the density moved up. Our result strongly supports the anti-levitation behavior predicted recently. Moreover, the even and odd Landau level filling states show quantitatively different behaviors in anti-levitation, suggesting that the exchange interactions, which are important at odd fillings, may play a role. [Preview Abstract] |
Monday, March 13, 2017 12:15PM - 12:27PM |
B27.00006: Strain-induced Landau Levels in arbitrary dimensions with an exact spectrum Stephan Rachel, Ilja Goethel, Daniel P. Arovas, Matthias Vojta Certain non-uniform strain applied to graphene flakes has been shown to induce pseudo-Landau levels in the single-particle spectrum, which can be rationalized in terms of a pseudo-magnetic field for electrons near the Dirac points. However, this Landau level structure is in general approximate and restricted to low energies. Here we introduce a family of strained bipartite tight-binding models in arbitrary spatial dimension $d$ and analytically prove that their entire spectrum consists of perfectly degenerate pseudo-Landau levels. This construction generalizes the case of triaxial strain on graphene's honeycomb lattice to arbitrary $d$; in $d=3$ our model corresponds to tetraxial strain on the diamond lattice. We discuss general aspects of pseudo-Landau levels in arbitrary $d$. [Preview Abstract] |
Monday, March 13, 2017 12:27PM - 12:39PM |
B27.00007: Melting of a bubble solid in the presence of disorder probed by microwave spectroscopy Lloyd Engel, Anthony Hatke, Byoung Moon, Geoff Gardner, John Watson, Michael Manfra Two dimensional electron systems can form several different types of solid phases. These solid phases are pinned by disorder and can exhibit a resonance in their microwave or rf spectrum due to oscillation within the residual disorder potential. Here we examine the effect of intentional disorder doping in the quantum well on the melting temperature of Wigner solids formed both of quasiparticles of the integer quantum Hall effect (IQHE) [1] and bubble and stripe phases [2] in high Landau levels through changes in the microwave resonance intensity. We observe that the presence of disorder increases both the resonance peak frequency and the melting temperature of the Wigner solids formed from quasiparticles of the IQHE but has limited effect on the bubble and stripe resonances. [1] Chen et al., Phys. Rev. Lett. 93, 206805 (2004). [2] Lewis et al., Phys. Rev. Lett. 93, 176808 (2004). [Preview Abstract] |
Monday, March 13, 2017 12:39PM - 12:51PM |
B27.00008: Study of possible electron heating induced by microwave excitation in the GaAs/AlGaAs 2D electron system. Tharanga Nanayakkara, Rasanga Samaraweera, Zhuo Wang, Binuka Gunawardana, Christian Reichl, Werner Wegscheider, Ramesh Mani Under the steady state of microwave excitation, there is a possibility of microwave induced electron heating in the two-dimensional electron system (2DES), due to absorption of energy from the radiation field. Electron-phonon scattering in the 2DES can then dissipate this excess energy onto the host lattice. According to previous studies, the electron temperature, longitudinal magnetoresistance, and energy absorption rate, show a non-monotonic variation with $\omega_{c}$/$\omega $, where $\omega _{c}$ is the cyclotron frequency, and $\omega $ is the radiation frequency [1]. It is also known that the Shubnikov de Haas (SdH) oscillation amplitude is sensitive to the electron-temperature [2]. In our experiment, we attempt to determine the effect of intense microwave photoexcitation on the resistance in a two-dimensional GaAs/AlGaAs electron system and try to correlate the observed resistance changes with the electron temperature extracted from the SdH oscillations. [1] X. L. Lei and S. Y. Liu, Phys. Rev. B 72, 075345 (2005). [2] A. N. Ramanayaka, R. G. Mani, and W. Wegscheider, Phys. Rev. B 83, 165303 (2011). [Preview Abstract] |
Monday, March 13, 2017 12:51PM - 1:03PM |
B27.00009: Quantum selection rules for electron backscattering in wide quantum wells placed in tilted magnetic fields Sergey Vitkalov, William Mayer, Alexey Bykov The effect of dc electric field on transport of highly mobile two-dimensional electrons is studied in wide GaAs single quantum wells placed in titled magnetic fields. The study shows resistance oscillates in perpendicular magnetic field due to electric-field induced Landau-Zener transitions between quantum levels that correspond to geometric resonances between cyclotron orbits and periodic modulation of electron density of states. Magnetic field tilt inverts these resistance oscillations. Surprisingly the strongest inverted oscillations are observed at a tilt corresponding to nearly absent modulation of the electron density of states in the regime of magnetic breakdown of semiclassical electron orbits. The effect reveals new quantum selection rules for elastic electron scattering in multi-subband electron systems leading to significant modification of the electron backscattering [1]. [1] William Mayer, Sergey Vitkalov and A. A. Bykov, Phys. Rev. B 93, 245436 (2016) [Preview Abstract] |
Monday, March 13, 2017 1:03PM - 1:15PM |
B27.00010: Charge density wave with meronlike spin texture induced by a lateral superlattice in a two-dimensional electron gas Rene Cote, Xavier Bazier-Matte The combined effect of a lateral square superlattice potential and the Coulomb interaction on the ground state of a two-dimensional electron gas in a perpendicular magnetic field is studied for different rational values of $\Gamma$, the inverse of the number of flux quanta per unit cell of the external potential, at filling factor $\nu =1$ in Landau level $N=0.$ When Landau level mixing and disorder effects are neglected, increasing the strength $W_{0}$ of the potential induces a transition, at a critical strength $W_{0}^{\left( c\right) },$ from a uniform and fully spin polarized state to a two-dimensional charge density wave (CDW) with a meronlike spin texture at each maximum and minimum of the CDW. The collective excitations of this \textquotedblleft vortex-CDW\textquotedblright\ are similar to those of the Skyrme crystal that is expected to be the ground state \textit{near} filling factor $\nu =1$. In particular, a broken U(1) symmetry in the vortex-CDW results in an extra gapless phase mode that could provide a fast channel for the relaxation of nuclear spins. The average spin polarization $S_{z}$ changes in a continuous or discontinuous manner as $W_{0}$ is increased depending on whether $\Gamma \in \left[ 1/2,1\right] $ or $\Gamma\in \left[ 0,1/2\right]$. [Preview Abstract] |
Monday, March 13, 2017 1:15PM - 1:27PM |
B27.00011: Fractional Solitons in Excitonic Josephson Junctions Jung-Jung Su, Ya-Fen Hsu The Josephson effect is especially appealing because it reveals macroscopically the quantum order and phase. Here we study this effect in an excitonic Josephson junction: a conjunct of two exciton condensates with a relative phase $\phi_0$ applied. Such a junction is proposed to take place in the quantum Hall bilayer (QHB) that makes it subtler than in superconductor because of the counterflow of excitonic supercurrent and the interlayer tunneling in QHB. We treat the system theoretically by first mapping it into a pseudospin ferromagnet then describing it by the Landau-Lifshitz-Gilbert equation. In the presence of interlayer tunneling, the excitonic Josephson junction can possess a family of fractional sine-Gordon solitons that resemble the static fractional Josephson vortices in the extended superconducting Josephson junctions. Interestingly, each fractional soliton carries a topological charge $Q$ which is not necessarily a half/full integer but can vary continuously. The resultant current-phase relation (CPR) shows that solitons with $Q=\phi_0/2\pi$ are the lowest energy states for small $\phi_0$. When $\phi_0> \pi$, solitons with $Q=\phi_0/2\pi-1$ take place -- the polarity of CPR is then switched. [Preview Abstract] |
Monday, March 13, 2017 1:27PM - 1:39PM |
B27.00012: Strong electronic interaction and multiple quantum Hall ferromagnetic phases in trilayer graphene Biswajit Datta, Santanu Dey, Abhisek Samanta, Abhinandan Borah, Hitesh Agarwal, Kenji Watanabe, Takashi Taniguchi, Rajdeep Sensarma, Mandar Deshmukh There is an increasing interest in the electronic properties of few layer graphene as it offers a platform to study electronic interactions because the dispersion of bands can be tuned with number and stacking of layers in combination with electric field. Here, we report evidence of strong electronic interactions and quantum Hall ferromagnetism (QHF) seen in a dual gated ABA trilayer graphene sample. Due to high mobility (500,000 cm$^{\mathrm{2}}$V$^{\mathrm{-1}}$s$^{\mathrm{-1}})$ in our device compared to previous studies, we find all symmetry broken states including $\nu =$0 filling factor at relatively low magnetic field (6T). Activation measurements show that Landau Level (LL) gaps are enhanced by interactions. Moreover, we observe hysteresis as a function of filling factor and spikes in the longitudinal resistance which, together, signal the formation of QHF states at low magnetic field. [Preview Abstract] |
Monday, March 13, 2017 1:39PM - 1:51PM |
B27.00013: Photovoltage detection of edge magnetoplasmon oscillations and giant magnetoplasmon resonances in a two-dimensional hole system Jian Mi, Jianli Wang, Loren N. Pfeiffer, Ken W. West, Kirk W. Baldwin, Chi Zhang In our high mobility p-type AlGaAs/GaAs two-dimensional hole samples, we originally observe the $B-$periodic oscillation induced by microwave (MW) in photovoltage (PV) measurements. In the frequency range of our measurements ($5-40$ GHz), the period is inversely proportional to the microwave frequency ($f$). The distinct oscillations come from the edge magnetoplasmon (EMP) in the high quality heavy hole system. Simultaneously, we observe the giant plasmon resonance signals in our measurements on the shallow two-dimensional hole system (2DHS). [Preview Abstract] |
Monday, March 13, 2017 1:51PM - 2:03PM |
B27.00014: Electrostatically defined isolated domain wall in integer quantum Hall regime as precursor for reconfigurable Majorana network Alexander Kazakov, George Simion, Valery Kolkovsky, Zbigniew Adamus, Grzegorz Karczewski, Tomasz Wojtowicz, Yuli Lyanda-Geller, Leonid Rokhinson Development of a two-dimensional systems with reconfigurable one-dimensional topological superconductor channels became primary direction in experimental branch of Majorana physics. Such system would allow to probe non-Abelian properties of Majorana quasiparticles and realize the ultimate goal of Majorana research - topological qubit for topologically protected quantum computations. In order to create and exchange Majorana quasiparticles desired system may be spin-full, but fermion doubling should be lifted. These requirements may be fulfilled in domain walls (DW) which are formed during quantum Hall ferromagnet (QHF) transition when two Landau levels with opposite spin polarization become degenerate. We developed a system based on CdMnTe quantum well with engineered placement of Mn ions where exchange interaction and, consequently, QHF transition can be controlled by electrostatic gating [1]. Using electrostatic control of exchange we create conductive channels of DWs which, unlike conventional edge channels, are not chiral and should contain both spin polarizations. We will present results on the formation of isolated DWs of various widths and discuss their transport properties. [1] A. Kazakov, {\it et al.}, Phys. Rev. B {\bf 94}, 075309 (2016). [Preview Abstract] |
Monday, March 13, 2017 2:03PM - 2:15PM |
B27.00015: Bosonic integer quantum Hall effect as topological pumping Masaya Nakagawa, Shunsuke Furukawa Topological pumping, originally proposed by Thouless, is a remarkable manifestation of topological nature of quantum states in transport phenomena. The Thouless pumping is induced by an adiabatic cycle of Hamiltonian of non-interacting fermions, and the total current during one cycle is given by the Chern number in parameter space which shares the same origin as the integer quantum Hall effect. Thus, a natural question is whether the connection between the topological pumping and the quantum Hall effect is also held in interacting systems. In this talk, we construct a novel interaction-induced topological pump corresponding to the bosonic integer quantum Hall (BIQH) state, which is a typical example of two-dimensional symmetry-protected topological phases of interacting bosons. The construction is based on a quasi-one-dimensional limit of quantum Hall states on a thin torus, and the resulting one-dimensional limit of the BIQH state is identified as the Haldane phase composed of two-component bosons which form effective spin-1 degrees of freedom. We also interpret the topological pumping by using the Berry phase of the topological Haldane phase under twisted boundary conditions. [Preview Abstract] |
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