Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Y3: Invited Session: New Directions in Fractional Quantum Hall Phenomena |
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Sponsoring Units: DCMP DCOMP Chair: Mansour Shayegan, Princeton University Room: Ballroom III |
Friday, March 22, 2013 8:00AM - 8:36AM |
Y3.00001: Local thermometry and compressibility measurements as new probes of strongly correlated states Invited Speaker: Amir Yacoby Electrons in two dimensions and strong magnetic fields can form an insulating two-dimensional system with conducting one-dimensional channels along the edge. Electron interactions in these systems can have fractionalized charge excitations and chiral edges with independent transport of charge and heat, even in opposite directions. Here, we use a quantum dot as a local thermometer to explore such heat transport along the edge at filling factor one and 2/3 in a GaAs 2DEG. Moreover, using a scanning quantum dot as a local charge sensor allows us to extract the charge of elementary excitations at filling factor 5/2 as well as to observe a delicate sequence of fractional quantum Hall states in suspended graphene. [Preview Abstract] |
Friday, March 22, 2013 8:36AM - 9:12AM |
Y3.00002: Quantum Hall Transitions and Quantum Number Fractionalization in Trapped Cold Atom Systems Invited Speaker: Kun Yang Recently there have been experimental attempts to realize quantum Hall physics in trapped cold atom systems, either through rotation or synthetic gauge fields. This can potentially open up a completely new direction in the study of quantum Hall effects. In this talk I will discuss possible quantum phase transitions between integer and fractional quantum Hall states, driven by attractive interactions between fermionic atoms. Such transitions have no counterparts in electronic quantum Hall liquids, but are related to fractionalization transitions studied in other strongly correlated systems. In one of these examples charge fractionalization is associated with the confinement-deconfinement transition of the (2$+$1D) Z2 gauge theory, which is in the Ising universality class. [Preview Abstract] |
Friday, March 22, 2013 9:12AM - 9:48AM |
Y3.00003: Fractional Quantum Hall in the Diluted Magnetic Semiconductor CdMnTe Invited Speaker: Dieter Weiss |
Friday, March 22, 2013 9:48AM - 10:24AM |
Y3.00004: Tunable interactions and the fractional quantum Hall effect Invited Speaker: Zlatko Papic We explore several realistic methods of tuning the interactions in two-dimensional electronic systems in high magnetic fields. We argue that these experimental probes can be useful in studying the interplay of topology, quantum geometry and symmetry breaking in the fractional quantum Hall effect (FQHE). In particular, we show that the mixing of subbands and Landau levels in GaAs wide quantum wells breaks the particle-hole symmetry between the Moore-Read Pfaffian state and its particle-hole conjugate, the anti-Pfaffian, in such a way that the latter is unambiguously favored and generically describes the ground state at 5/2 filling [1]. Furthermore, the tilting of the magnetic field, or more generally variation of the band mass tensor, probes the fluctuation of the intrinsic metric degree of freedom of the incompressible fluids, and ultimately induces the crossover to the broken-symmetry and nematic phases in higher Landau levels [2]. Some of these mechanisms also lead to an enhancement of the excitation gap of the non-Abelian states, as observed in recent experiments. Finally, we compare the tuning capabilities in conventional systems with that in multilayer graphene and related materials with Dirac-type carriers where tuning the band structure and dielectric environment provides a simple and direct method to engineer more robust FQHE states and to study quantum transitions between them [3]. \\[4pt] [1] Z. Papic, F. D. M. Haldane, and E. H. Rezayi, arXiv:1209.6606 (2012).\\[0pt] [2] Bo Yang, Z. Papic, E. H. Rezayi, R. N. Bhatt, F. D. M. Haldane, Phys. Rev. B 85, 165318 (2012).\\[0pt] [3] Z. Papic, R. Thomale, D. A. Abanin, Phys. Rev. Lett. 107, 176602 (2011); Z. Papic, D. A. Abanin, Y. Barlas, and R. N. Bhatt, Phys. Rev. B 84, 241306(R) (2011); D. A. Abanin, Z. Papic, Y. Barlas, and R. N. Bhatt, New J. Phys. 14, 025009 (2012). [Preview Abstract] |
Friday, March 22, 2013 10:24AM - 11:00AM |
Y3.00005: Fractional quantum Hall effect in AlAs quantum wells: Role of valley degree of freedom Invited Speaker: Tayfun Gokmen When interacting two-dimensional electrons are placed in a large perpendicular magnetic field, to minimize their energy, they capture an even number of flux quanta and create new particles called composite fermions (CFs). These complex electron-flux-bound states offer an elegant explanation for the fractional quantum Hall effect. Thanks to the flux attachment, the effective field vanishes at half-filled Landau levels ($\nu =$ 1/2 and 3/2) and CFs exhibit Fermi-liquid-like properties, similar to their zero-field electron counterparts. Here, we study a two-dimensional electron system in AlAs quantum wells where the electrons occupy two conduction band valleys with anisotropic Fermi contours and strain-tunable occupation. We address a fundamental question whether the anisotropy of the electron effective mass and Fermi surface is transferred to the CFs formed around filling factors $\nu =$ 1/2 and 3/2. Similar to their electron counter parts, CFs also exhibit anisotropic transport, suggesting an anisotropy of CF effective mass and Fermi surface. We also study quantum Hall ferromagnetism for fractional quantum Hall states formed at $\nu =$ 1/3 and 5/3 as a function of valley splitting. Within the framework of the CF theory, electronic fractional filling factors $\nu =$ 1/3 and 5/3 are equivalent to the integer filling factor $p=$ 1 of CFs. Reminiscent of the quantum Hall ferromagnetism observed at $\nu =$ 1, we report persistent fractional quantum Hall states at filling factors $\nu =$ 1/3 and 5/3 when the two valleys are degenerate. However, the comparison of the energy gaps measured at $\nu =$ 1/3 and 5/3 to the available theory developed for single-valley, two-spin systems reveals that the gaps and their rates of rise with strain are much smaller than predicted.\\[4pt] [1] ``Transference of Transport Anisotropy to Composite Fermions,'' T. Gokmen, M. Padmanabhan, and M. Shayegan, \textit{Nature Physics }\textbf{6}, 621-624 (2010).\\[4pt] [2] `Ferromagnetic Fractional Quantum Hall States in a Valley-Degenerate Two-Dimensional Electron System,'' M. Padmanabhan, T. Gokmen, and M. Shayegan, \textit{Phys. Rev. Lett.} \textbf{104}, 016805 (2010). [Preview Abstract] |
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