Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session D39: Invited Session: Quantum Anomalous Hall Effect in Magnetic Topological Insulators |
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Sponsoring Units: DCMP Chair: Nitin Samarth, Pennsylvania State University Room: Mile High Ballroom 2A-3A |
Monday, March 3, 2014 2:30PM - 3:06PM |
D39.00001: Theory of the quantum anomalous Hall effect in magnetic topological insulators Invited Speaker: Shoucheng Zhang We give a theoretical introduction to the QAH effect based on magnetic topological insulators in 2D and 3D. In 2D topological insulators, magnetic order breaks the symmetry between the counter-propagating helical edge states, and as a result, the quantum spin Hall effect (QSH) can evolve into the QAH effect. In 3D, magnetic order opens up a gap for the topological surface states, and chiral edge state can exist on the magnetic domain walls. We discuss realistic materials for magnetic topological insulators with QAH. We also discuss more recent theoretical work on the coexistence of the helical and chiral edge states, multi-channel chiral edge states, and the theory of the plateau transition in the QAH. [Preview Abstract] |
Monday, March 3, 2014 3:06PM - 3:42PM |
D39.00002: Experimental realization of quantized anomalous Hall effect Invited Speaker: Qi-Kun Xue Anomalous Hall effect was discovered by Edwin Hall in 1880. In this talk, we report the experimental observation of the quantized version of AHE, the quantum anomalous Hall effect (QAHE) in thin films of Cr-doped (Bi,Sb)$_{\mathrm{2}}$Te$_{\mathrm{3}}$ magnetic topological insulator. At zero magnetic field, the gate-tuned anomalous Hall resistance exhibits a quantized value of $h/e^{2}$ accompanied by a significant drop of the longitudinal resistance. The longitudinal resistance vanishes under a strong magnetic field whereas the Hall resistance remains at the quantized value. The realization of QAHE paves a way for developing low-power-consumption electronics. Implications on observing Majorana fermions and other exotic phenomena in magnetic topological insulators will also be discussed. The work was collaborated with Ke He, Yayu Wang, Xucun Ma, Xi Chen, Li Lv, Dai Xi, Zhong Fang and Shoucheng Zhang. [Preview Abstract] |
Monday, March 3, 2014 3:42PM - 4:18PM |
D39.00003: Quantum Anomalous Hall Effect in Hetero Magnetic Topological Insulator Structures Invited Speaker: Kang Wang The quantum anomalous Hall effect (QAHE), which has the quantized Hall conductance of $h/e^{2}$ in the absence of external field, was expected to happen in a magnetic 3-D topological insulators (TIs) system. In this talk, we report recent progress of QAHE-related physics in the TRS-breaking field. In the first part, we show the generation of robust magnetism by doping magnetic ions (Cr) into the host (Bi$_{\mathrm{x}}$Sb$_{\mathrm{1-x}})_{2}$Te$_{3}$ materials. With gate-controlled magneto-transport measurements, we demonstrate the presence of both the hole-mediated RKKY coupling and carrier-independent van Vleck magnetism. By adjusting the Cr doping concentration and Bi/Sb ratio, we establish an effective way to experimentally approach to the QAHE region. The second part of this talk discusses the manipulation of surface-related magnetism in the modulation-doped TI/Cr-doped TI heterostructures. We investigate the role of massive surface Dirac fermions in the bulk RKKY mediation process. Both our theoretical models and experimental results reveal that the topological surface-related magnetic order can be either enhanced or suppressed, depending on the magnetic interaction range between the surface states and Cr ions. Based on such TI heterostructures, we also demonstrate the magnetization switching via giant spin-orbit torque induced by the in-plane current. Finally, in order to make these effects observable at 300K, we describe the use of magnetic proximity effects to manipulate the surface magnetism of TI. These results not only demonstrate additional important steps to further explore fundamental properties of the TRS-breaking TI systems but also may help the realization of many functionalities of TI-based spintronics applications. [Preview Abstract] |
Monday, March 3, 2014 4:18PM - 4:54PM |
D39.00004: Chern Insulators from Heavy Atoms on Magnetic Substrates Invited Speaker: Kevin Garrity Chern insulators, or quantum anomalous Hall insulators, would display a variety interesting and potentially useful properties; however, existing methods for constructing Chern insulators have proven challenging, and have thus far been limited to low temperatures. We propose a new method for searching for Chern insulators by depositing atomic layers of elements with large spin-orbit coupling (e.g., Bi) on the surface of a magnetic insulator. We argue that such systems will typically have isolated surface bands with nonzero Chern numbers. If these bands overlap in energy, a metallic surface with large anomalous Hall conductivity will result; if not, a Chern-insulator state will typically occur. We use first principles calculations to verify this search strategy by considering heavy atoms on the surfaces of MnTe, MnSe, and EuS, as well as more recent results on several promising oxide and nitride surfaces. We find many Chern insulators in both cases, including examples with large band gaps. [Preview Abstract] |
Monday, March 3, 2014 4:54PM - 5:30PM |
D39.00005: Experimental Studies of Ferromagnetism in Topological Insulators Invited Speaker: Joseph Checkelsky Breaking of time reversal symmetry has proven to be an incisive method for experimentally drawing out the exotic nature of topological insulators. In particular, the introduction of magnetic dopants in to three dimensional topological insulators has led to the realization of theoretically predicted novel types of ferromagnetic order and a quantized version of the anomalous Hall effect. Here, I will present recent work on the synthesis and measurement of bulk and thin film topological insulators doped with 3$d$ transition metals. I will discuss the ferromagnetic order that arises in various systems and the associated electrical transport response of the surface modes. [Preview Abstract] |
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