Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session J42: Majorana Fermions in Nanowires |
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Sponsoring Units: DCMP Chair: Dan Dessau, University of Colorado, Boulder Room: Mile High Ballroom 4A |
Tuesday, March 4, 2014 2:30PM - 2:42PM |
J42.00001: Topological Superconductivity and Majorana Fermions in RKKY Systems Jelena Klinovaja, Peter Stano, Ali Yazdani, Daniel Loss We consider quasi one-dimensional RKKY systems in proximity to an s-wave superconductor [1]. We show that a $2k_F$ -peak in the spin susceptibility of the superconductor in the one-dimensional limit supports helical order of localized magnetic moments via RKKY interaction, where $k_F$ is the Fermi wavevector. The magnetic helix is equivalent to a uniform magnetic field and very strong spin-orbit interaction (SOI) with an effective SOI length $1/2k_F$ [2,3] . We find the conditions to establish such a magnetic state in atomic chains and semiconducting nanowires with magnetic atoms or nuclear spins. Generically, these systems are in a topological phase with Majorana fermions. The inherent self-tuning of the helix to $2k_F$ eliminates the need to tune the chemical potential [3-6]. [1] J. Klinovaja, P. Stano, A. Yazdani, and D. Loss, Phys. Rev. Lett. 111, 186805 (2013). [2] B. Braunecker, G. I. Japaridze, J. Klinovaja, and D. Loss, Phys. Rev. B 82, 045127 (2010). [3] J. Klinovaja, P. Stano, and D. Loss, Phys. Rev. Lett. 109, 236801 (2012). [4] J. Klinovaja and D. Loss, Phys. Rev. B 86, 085408 (2012). [5] J. Klinovaja and D. Loss, Phys. Rev. X 3, 011008 (2013). [6] J. Klinovaja and D. Loss, Phys. Rev. B 88, 075404 (2013). [Preview Abstract] |
Tuesday, March 4, 2014 2:42PM - 2:54PM |
J42.00002: Self-Organized Topological State with Majorana Fermions Mohammad Vazifeh, Marcel Franz A topological superconductor phase with a pair of localized spatially separated Majorana fermions can be achieved in semiconductor wires with strong spin-orbit interactions, however, it requires subtle fine tuning of the chemical potential of the order of 1meV. This makes it difficult to access the desired topological phase in experiments. We find that, remarkably, this fine tuning is not required for a magnetic chain of adatoms placed on top of an s-wave superconductor. Using a simple model, we show that for a wide range of the chemical potential the magnetic moments self-organize into a spiral state with a wave-vector that corresponds to the perfect configuration to achieve the topological superconductor phase for electrons. The local coupling between magnetic moments and electronic spins effectively plays the role of the spin-orbit interaction required for the topological phase and the phase remains stable against spin fluctuations at experimentally accessible temperatures. [Preview Abstract] |
Tuesday, March 4, 2014 2:54PM - 3:06PM |
J42.00003: Majorana fermions in hybrid superconductor-semiconductor nanowire devices Kun Zuo, Vincent Mourik, David van Woerkom, Fokko de Vries, Sebastien Plissard, Erik Bakkers, Leo Kouwenhoven Recently the first experimental signatures of Majorana fermions were reported. Experiments are now focusing on more rigorous ways to identify Majorana's. Since Majorana's should come in pairs, further experimental evidence could be given by measuring the correlated emergence of two Majorana's at both ends of the topological superconductor. Additionally, recent developed theories show that interacting Majorana's lead to an oscillation between a splitted zero bias peak and a single zero bias peak in both gate and magnetic field space. We perform our experiments in three terminal normal-superconductor-normal InSb nanowire devices. This enables us to simultaneously probe both Majorana fermions by using tunneling spectroscopy from the two normal contacts into the superconducting contact. An improved gate design enhances gating of Majorana's makes it possible to observe the oscillatory peak splitting behavior. Our preliminary results are in line with the expected behavior of interacting Majorana bound states at the ends of a topological superconductor. [Preview Abstract] |
Tuesday, March 4, 2014 3:06PM - 3:18PM |
J42.00004: Measuring fermion parity correlations in 1D topological superconducting wires F.J. Burnell, Alexander Shnirman, Yuval Oreg Zero energy Majorana fermion states (Majoranas) can arise at the ends of a semiconducting wire in proximity with a superconductor. A first generation of experiments has detected a zero bias conductance peak in these systems that strongly suggests these Majoranas do exist; however, a definitive demonstration of the long-ranged entanglement that is crucial for potential applications in quantum computing has yet to be carried out. We will discuss a possible measurement scheme to detect this long-ranged entanglement in a wire system with two coupled pairs of Majoranas, by varying the coupling between one pair and measuring the effect this has on the state of the second pair. [Preview Abstract] |
Tuesday, March 4, 2014 3:18PM - 3:30PM |
J42.00005: Nonequilibrium transport between helical Luttinger liquids leads or helical Majorana modes Sung Po Chao, Salman Silotri, Chung Hou Chung We study a steady state non-equilibrium transport between (i) two interacting helical edge states of a two dimensional topological insulator, described by helical Luttinger liquids, through a quantum dot [1] or tunneling junction [2]. (ii) one Luttinger liquids lead and a helical Majorana modes lead connected by tunneling junction(s). We find the metal-to-insulator quantum phase transition for attractive or repulsive interactions in the leads when the magnitude of the interaction strength characterized by a charge sector Luttinger parameter goes beyond a critical value.\\[4pt] [1] S. P. Chao, S. A. Silotri, C. H. Chung, Phys. Rev. B 88, 085109 (2013)\\[0pt] [2] Y. W. Lee, Y. L. Lee, C. H. Chung, Phys. Rev. B 86, 235121 (2012) [Preview Abstract] |
Tuesday, March 4, 2014 3:30PM - 3:42PM |
J42.00006: Conductance plateau due to Majorana bound state in a quantum dot coupled to a topological quantum wire Edson Vernek, Poliana Penteado, Antonio Seridonio, Jos\'e C. Egues The search for Majorana bound state (MBS) is topological superconductor nanowires is currently a topic of great interest. Despite the various theoretical proposals and the experimental results, the question of whether the possible signatures of MBS can be distinguished from those arising from other phenomena such as the Kondo effect is still under debate. A recent proposal for detecting MBS using a quantum dot coupled to normal two leads and to a topological quantum wire has proven to be very appropriate structure to investigate this problem. In this system, the presence of MBS in the wire is marked as a $e^2/2h$ conductance through the dot. In this work we find, that the $e^2/2h$ conductance peak is not per se an distinct signature of a MBS in the wire. We show instead that it results from a leaking of the Majorana state into the dot [1]. Moreover, by gating the dot level ($\varepsilon_d$) far away below and above the Fermi level of the leads ($\varepsilon_F$), the conductance remains at $e^2/2h$. The surviving of the conductance plateau for $\varepsilon_d>\varepsilon_F$ contrasts with Kondo effect plateau known to emerge only for $\varepsilon_d<\varepsilon_F$.\\[4pt] [1] E. Vernek, P. H. Penteado, A. C. Seridonio and J. C. Egues, arXiv:1308.0092 (2013). [Preview Abstract] |
Tuesday, March 4, 2014 3:42PM - 3:54PM |
J42.00007: Capacitive Signal of Majorana States in a Finite 1D wire Gilad Ben-Shach, Arbel Haim, Ian Appelbaum, Amir Yacoby, Bertrand Halperin, Yuval Oreg We propose a new measurement technique for the observation of Majorana fermion end states in finite-length semiconductor-superconductor hybrid nanowire systems. We demonstrate how a charge measurement, say by an external single-electron transistor, as a function of external magnetic field and chemical potential, could reveal the presence -- or lack -- of localised Majorana end states. Whereas existing experimental proposals require direct contact to the wire for tunneling measurements, our proposal avoids this issue and provides an orthogonal measurement to confirm recent experimental developments. Furthermore, we shed light on a new parameter regime for nanowire-superconductor hybrid systems. [Preview Abstract] |
Tuesday, March 4, 2014 3:54PM - 4:06PM |
J42.00008: New topological types of Majorana modes at ends of one-dimensional topological superconductors Yuxin Zhao, Zidan Wang As being known, topological insulators/superconductors are completely classified into various topological types with respect to their anti-unitary symmetries and dimensions, and for a certian dimension different topological types correspond to different boundary gapless modes, which is quantitatively described as a general index theorem. Based on this and Kitaev's model in class D, we construct models for all the other types of D1 topological superconductors and analyze their topologically protected Majorana zero-modes at ends. We highlight that: 1)The two kinds of $\mathbf{Z}_2$ topological numbers imply distinct forms of Majorana zero-modes. 2) The two-fold degenerate ground state of the DIII model with Majorana fermions can be effectively regarded as a spin when the model is coupled to a weak external magnetic field. 3)The BDI model with $\mathbf{Z}$-type unit topological number can be assigned topological charges $\pm1$ to its Majorana zero-modes at two ends in agreement with the general index theorem. 4)The CII model with $\mathbf{Z}$-type topological number $2$ may be regarded as two copies of the BDI model with certain spin-pairing patterns, and consistently the topological charge of its Majorana zero-modes is defined in the same sense of that of the BDI model. [Preview Abstract] |
Tuesday, March 4, 2014 4:06PM - 4:18PM |
J42.00009: Realistic models for Majorana wires Alexey Soluyanov, Roman Lutchyn, Chetan Nayak, Bela Bauer, Matthias Troyer We construct realistic effective models to theoretically facilitate the experimental search for Majorana modes in quantum wires. Starting with an accurate first-principles calculation, we provide a detailed discussion of finite size and multiband effects, and of the spin-orbit splitting. We also present a thorough consideration of proximity induced superconductivity, extensively supporting it with numerical evidence. The comparison of our results to previously used models and actual experiments is done. [Preview Abstract] |
Tuesday, March 4, 2014 4:18PM - 4:30PM |
J42.00010: Majorana zero modes through domain wall wires in inhomogeneous gated silicene Xiaoting Zhou, Cheng-Yi Huang, Wei-Feng Tsai We report a new way to realize Majorana zero-modes in one-dimensional (1D) domain wall wires generated in inhomogeneous gated silicene sheet. By applying inhomogeneous perpendicular electric field to the gapped silicene sheet, 1D domain walls, which can host either propagating spinful fermions or spin-polarized fermions (in the presence of a Zeeman field), can be created at the desired positions with great flexibility. Since the appreciable spin-orbit couplings (SOC) due to the buckled structure of silicene are present, such domain wall propagating channels can be a good alternative of 1D semiconducting quantum wires with strong SOC, usually taken as an essential starting point to generate the end-point Majorana zero modes. By the proximity with a conventional s-wave superconductor and a modest magnetic field applied on the domain wall, our approach provides a clean way in sharp contrast to using the semiconducting wires, where the complexity of the sub-band issue could be significant, to realize the 1D Kitaev's chain with Majorana zero modes at the ends. [Preview Abstract] |
Tuesday, March 4, 2014 4:30PM - 4:42PM |
J42.00011: Possibility of disorder-induced sub-gap states near Majorana modes in topological insulator edges Hoi-Yin Hui, Jay Sau We study the effects of multiple channel and disorder in the topological insulator(TI)-superconductor(SC)-ferromagnetic insulator(FI) hybrid structure, which has been proposed to realize Majorana modes. According to Anderson's theorem, proximity-induced SC in a TI is robust to all non-magnetic impurities. This however cannot be applied to the SC/FI interface where the end Majorana is located, since the time-reversal symmetry is locally broken. In this paper we study the spectrum near a SC/FI interface on a disordered TI edge. While we find that only the Majorana mode is induced single-channel case, inter-channel scatterings in a multichannel TI can induce extra localized states. We shalll comment on its effects in the detection and manipulations of the Majorana. [Preview Abstract] |
Tuesday, March 4, 2014 4:42PM - 4:54PM |
J42.00012: Majorana Fermions on Zigzag Edge of Monolayer Transition Metal Dichalcogenides Ruilin Chu Majorana fermions, quantum particles with non-Abelian exchange statistics, are not only of fundamental importance, but also building blocks for fault-tolerant quantum computation. Although certain experimental breakthroughs for observing Majorana fermions have been made recently, their conclusive detection is still challenging due to the lack of proper material properties of the underlined experimental systems. Here we propose a new platform for Majorana fermions based on edge states of certain non-topological two-dimensional semiconductors with strong spin-orbit coupling, such as monolayer group-VI transition metal dichalcogenides (TMD). Using first-principles calculations and tight-binding modeling, we show that zigzag edges of monolayer TMD can host well isolated single edge band with strong spin-orbit coupling energy. Combining with proximity induced \textit{s}-wave superconductivity and in-plane magnetic fields, the zigzag edge supports robust topological Majorana bound states at the edge ends, although the two-dimensional bulk itself is non-topological. Our findings points to a controllable and integrable platform for searching and manipulating Majorana fermions. [Preview Abstract] |
Tuesday, March 4, 2014 4:54PM - 5:06PM |
J42.00013: Boosting Majorana zero modes Gil Refael, Torsten Karzig, Felix von Oppen When Majorana bound states are driven at high speeds, competing processes may destroy quantum coherence. To study this regime we exploit an effective Lorentz invariance of a generic Majorana supporting Hamiltonian to obtain an exact solution of the domain wall bound states for arbitrary velocities. An effective 'speed of light' emerges, which acts as an absolute speed limit for braiding Majorana states. We also use our exact solutions to study further restrictions on the domain wall motion due to the presence of static impurities in the system. Looking beyond the context of topological quantum computing, our insights and analysis can also be viewed as theoretical basis for creating extreme relativistic phenomena, such as the Unruh effect, in solid state systems. [Preview Abstract] |
Tuesday, March 4, 2014 5:06PM - 5:18PM |
J42.00014: Majorana mode in vortex core of Bi$_{2}$Te$_{3}$/NbSe$_{2}$ topological insulator-superconductor heterostructure Jinfeng Jia Majorana fermions have been intensively studied in recent years for their importance to both fundamental science and potential applications in topological quantum computing. Majorana fermions are predicted to exist in a vortex core of superconducting topological insulators. However, they are difficult to be distinguished experimentally from other quasiparticle states for the tiny energy difference between Majorana fermions and these states, which is beyond the energy resolution of most available techniques. Here, we overcome the problem by systematically investigating the spatial profile of the Majorana mode and the bound quasiparticle states within a vortex in Bi$_{2}$Te$_{3}$/NbSe$_{2}$. While the zero bias peak in local conductance splits right off the vortex center in conventional superconductors, it splits off at a finite distance $\sim$ 20nm away from the vortex center in Bi$_{2}$Te$_{3}$/NbSe$_{2}$, primarily due to the Majorana fermion zero mode. While the Majorana mode is destroyed by reducing the distance between vortices, the zero bias peak splits as a conventional superconductor again. This work provides strong evidence of Majorana fermions and also suggests a possible route to manipulating them. [Preview Abstract] |
Tuesday, March 4, 2014 5:18PM - 5:30PM |
J42.00015: Mapping the topological phase diagram of multiband semiconductors with supercurrents Elsa Prada, Pablo San-Jose, Ramon Aguado We show that Josephson junctions made of multiband semiconductors with strong spin-orbit coupling carry a critical supercurrent $I_c$ that contains information about the non-trivial topology of the system. In particular, we find that the emergence and annihilation of Majorana bound states in the junction is reflected in strong even-odd effects in $I_c$ under specific conditions. This effect allows for a mapping between $I_c$ and the topological phase diagram of the junction, thus providing a dc measurement of its topology. [Preview Abstract] |
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