Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session F45: Realization of Kitaev ChainFocus

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Sponsoring Units: DMP GMAG Room: 392 
Tuesday, March 14, 2017 11:15AM  11:51AM 
F45.00001: Kitaev model with quantum dot chains I: Andreev transport Invited Speaker: Zhaoen Su, Hao Wu, Moïra Hocevar, Diana Car, Sebastien Plissard, Erik Bakkers, Sergey Frolov Chains of quantum dots in semiconductor nanowires can be used to emulate important onedimensional Hamiltonians such as the topological pwave superconductor. We build a coupled triple dot chain in an InSb nanowire where each dot is tuned to be strongly coupled to a superconducting NbTiN lead. We use an array of closely spaces bottom gates to tune the Andreev bound states in each dot and observe Andreev state hybridization. We measure transport through Andreev bound states on individual dots, dot pairs and through the triple dot. We explore the influence of Coulomb energy on the Andreev spectra of the chains. [Preview Abstract] 
Tuesday, March 14, 2017 11:51AM  12:03PM 
F45.00002: Kitaev model with quantum dot chains II: zero bias peaks Hao Wu, Zhaoen Su, Moïra Hocevar, Diana Car, Sebastien Plissard, Erik Bakkers, Sergey Frolov We have implemented a triple dot chain in an InSb nanowire, with each dot strongly coupled to a separate superconducting NbTiN lead thus defining a threeterminal device. We use magnetic fields which are parallel to the nanowire axis to study the field dependence of the Andreev bound state resonances in electrical transport measurements. We observe zero bias peaks that appear at finite fields, as well as split peaks. By passing currents between different pairs of electrodes, we identify which dots in the chains host the observed resonances. We explore the resonances in the context of Majorana bound states, as well as considering supercurrents and trivial Andreev bound states.~ [Preview Abstract] 
Tuesday, March 14, 2017 12:03PM  12:15PM 
F45.00003: Spectroscopy of Majorana nanowires with quantum dots Ramon Aguado, Elsa Prada, Pablo SanJose An interacting quantum dot coupled to a superconducting contact is an artificial analogue of a quantum impurity in a superconductor. The physics of such hybrid device is governed by the fermionic parity and spin of the two possible ground states, doublet or singlet (and their corresponding Shiba subgap excitations). Here we generalise this paradigmatic model to the case where the superconductor becomes topological. Such a quantum dottopological superconductor junction can be experimentally realised by e. g. creating quantum dots at the end of epitaxial hybrid semiconductorsuperconductor nanowires. We study the hybridisation between Shiba states in the dot and Majoranas in the nanowire and show that specific and measurable spectral features arise from the interplay of these states. Interestingly, these features are enough to fully characterise the spin structure of the Majorana wavefunction, the degree of Majorana nonlocality and the Majorana splitting. Apart from a full numerical analysis, all the relevant results are derived from a lowenergy effective model, and are given in closed analytical form. We conclude that quantum dots used to perform spectroscopy of a Majorana nanowire are a powerful probe into the quantum structure of Majorana bound states. [Preview Abstract] 
Tuesday, March 14, 2017 12:15PM  12:27PM 
F45.00004: Majorana Fermion and bound states in the continuum on a crossshaped quantum dot hybrid structure David Zambrano, Juan Pablo Ramos, Pedro Orellana We show how transmission, differential conductance and density of states (DOS) behave when two superconductor/semiconductors topological nanowires are placed next to the ends of a quantumdot (QD) chain, where the central QD is attached to normal conductors leads. Results in a single QD coupled to two Kitaev chains within the topological phase [1] and a Tshaped QD hybrid structure [2] suggest these kind of system are strong candidates for qubits. We show how bound states in the continuum (BICs) arise as zero energy modes on conductance and DOS for different sets of system parameters showing evidence of Majorana fermions, and we also study how they behave for different numbers (even/odd) of QD in the crossshaped structure.\\~\\~[1] L. S. Ricco, Y. Marques, F. A. Dessotti, R. S. Machado, M. de Souza, and A. C. Seridonio, Phys. Rev. B \textbf{93}, 165116 (2016).\\~[2] WeiJiang Gong, ShuFeng Zhang, ZhiChao Li, Guangyu Yi, and YiSong Zheng, Phys. Rev. B \textbf{89}, 245413 (2014). [Preview Abstract] 
Tuesday, March 14, 2017 12:27PM  12:39PM 
F45.00005: Spin signature of Majorana zero modes in a Shiba chain Jian Li, Ali Yazdani, B. Andrei Bernevig We propose as a robust and definite spin signature to distinguish Majorana zero modes from trivial Shiba states accidentally tuned to zero energy due to strong local potential. This signature is rooted in two sum rules that dictate the distribution of spin densities in a superconducting state with respect to a normal state, and can be straightforwardly detected with the spinpolarized scanning tunneling microscope technique which implicitly takes advantage of these sum rules. [Preview Abstract] 
Tuesday, March 14, 2017 12:39PM  12:51PM 
F45.00006: Orbital Picture of YuShibaRusinov Multiplets Benjamin W. Heinrich, Michael Ruby, Katharina J. Franke, Yang Peng, Felix von Oppen Magnetic impurities on an $s$wave superconductor induce YuShibaRusinov (YSR) bound states within the excitation gap of the superconductor. Here, we investigate single manganese (Mn) atoms adsorbed on different surface orientations of superconducting lead (Pb) and the nature of their YSR states. Depending on the adsorption site and surface, we detect a distinct number and characteristic patterns of YSR states around the Mn atoms. We show that the YSR states inherit their properties from the Mn $d$ levels, which are split by the surrounding crystal field [1]. The periodicity of the longrange YSR oscillations allows us to identify a dominant coupling of the $d$ states to the outer Fermi sheet of the twoband superconductor Pb. The longrange and directional nature of the states are promising for the design of coupled adatom structures, which could bear topological phases. \\ \mbox{[1]} M. Ruby {\it et al.}, Phys. Rev. Lett. {\bf 117}, 186801 (2016). [Preview Abstract] 
Tuesday, March 14, 2017 12:51PM  1:03PM 
F45.00007: Topological YuShibaRusinov chain in monolayer transitionmetal dichalcogenide superconductors Junhua Zhang, Vivek Aji Monolayers of transitionmetal dichalcogenides (TMDs) are twodimensional materials whose low energy sector consists of two inequivalent valleys. The valence bands have a large spin splitting due to lack of inversion symmetry and strong spinorbit coupling. Furthermore the spin is polarized up in one valley and down in the other (in directions perpendicular to the twodimensional crystal). We focus on lightly holedoped systems where the Fermi surface consists of two disconnected circles with opposite spins. For both proximity induced and intrinsic local attractive interaction induced superconductivity, a fully gapped intervalley pairing state is favored in this system, which is an equal superposition of the singlet and the m=0 triplet for the lack of centrosymmetry. We show that a ferromagnetically ordered magneticadatom chain placed on a monolayer TMD superconductor provides a platform to realize onedimensional topological superconducting state characterized by the presence of Majorana zero modes at its ends. We obtain the topological phase diagram and show that the topological superconducting phase is affected not only by the adatom spacing and the direction of the magnetic moment, but also by the orientation of the chain relative to the crystal. [Preview Abstract] 
Tuesday, March 14, 2017 1:03PM  1:15PM 
F45.00008: Approximating the SachdevYeKitaev model with Majorana wires Aaron Chew, Andrew Essin, Jason Alicea The SachdevYeKitaev (SYK) model describes a large collection of Majorana fermions coupled via random, `alltoall' fourfermion interactions. This model enjoys broad interdisciplinary interest because it provides a solvable realization of holography in 0+1 dimensions, exhibits unusual spectral and thermodynamic properties, and shares deep connections to chaos and black holes. We propose a solidstate implementation of the SYK Hamiltonian that employs quantum dots coupled to arrays of topological superconductors hosting Majorana endstates. Alltoall fourMajorana couplings are mediated by interactions in the dot, while the randomness originates from disorder in the hoppings between the Majorana modes and dot levels. Using perturbation theory and explicit numerics, we study the properties of the dotwire array system under various experimental conditions. Interestingly, our setup not only allows exploration of SYK physics, but also provides a controlled testbed for interaction effects on the topological classification of fermionic phases. [Preview Abstract] 
Tuesday, March 14, 2017 1:15PM  1:27PM 
F45.00009: Tunable topological superconductivity from a lattice of finitesize magnets Kim P\"oyh\"onen, Teemu Ojanen In this work we examine a system consisting of a square lattice of finitesize magnets on a twodimensional electron gas coupled to an $s$wave superconductor. We find that the system supports a rich spectrum of topological phases, including several with large Chern numbers. The advantages of the studied system are twofold: first, it is feasible to construct with preexisting experimental setups; second, the system parameters can be tuned after it has already been constructed, which enables finetuning the system into the desired topological phase. [Preview Abstract] 
Tuesday, March 14, 2017 1:27PM  1:39PM 
F45.00010: Impurity bound states in $d$wave superconductors with subdominant order parameters Mahdi Mashkoori, Kristofer Bj\"{o}rnson, Annica BlackSchaffer Single magnetic impurity induces intragap bound states in conventional $s$wave superconductors (SCs) but, in $d$wave SCs only virtual bound states can be induced. However, in small cuprate islands a fully gapped spectrum has recently been discovered [1,2]. In this work, we investigate the real bound states due to potential and magnetic impurities in the two candidate fully gapped states for this system: the topologically trivial $d+is$wave state and the topologically nontrivial $d+id'$wave (chiral $d$wave state). Using the analytic Tmatrix formalism and selfconsistent numerical tightbinding lattice calculations, we show that potential and magnetic impurities create entirely different intragap bound states in $d+is$wave and chiral $d$wave SCs. Therefore, our results suggest that the bound states mainly depend on the subdominant order parameter. Considering that recent experiments have demonstrated an access to adjustable coupling $J$ [3], impurities thus offer an intriguing way to clearly distinguish between the chiral $d$wave and topologically trivial $d+is$wave state. [1] Gustafsson, David, et al., Nat. Nanotechnol. 8, 25 (2013). [2] BlackSchaffer, Annica M., et al., Phys. Rev. Lett. 110, 197001 (2013). [3] Hatter, Nino, et al. Nat., Comm. 6, 8988 (2015). [Preview Abstract] 
Tuesday, March 14, 2017 1:39PM  1:51PM 
F45.00011: Topological transition and topological number in an interacting numberconserving BoseFermi mixture in onedimensional lattices Kuei Sun, Y.H. Chan, ChingKai Chiu We study topological properties of a BoseFermi mixture in onedimensional lattices, in which a boson is regarded as a composite particle of two spinless fermions. Under a meanfield approximation, our model exhibits the same form as Kitaev's chain model of superconducting spinless fermions and can hence have symmetryprotected topological ground states hosting Majorana fermions. Beyond the meanfield level, interactions naturally lead to manybody eigenstates of the system, and the total number conservation constrains the fermionnumber parity such that the even/odd groundstate degeneracy no longer exists. Topological characterization of such a manybody ground state thus needs further investigation. Based on multiple signatures, we hereby report a finding of topological states and topological transitions in this model. We also identify a topological number that is protected by inversion symmetry. Our work might have applications on characterizing topological states in various manybody systems. [Preview Abstract] 
Tuesday, March 14, 2017 1:51PM  2:03PM 
F45.00012: Topological superfluidity with repulsive fermionic atoms in optical superlattice Leonid Isaev, Johannes Schachenmayer, Gerardo Ortiz, Ana Maria Rey We present a novel route to fermionic superfluidity in repulsive systems, that employs local kineticenergy fluctuations as a ``pairing glue'' between the fermions. In a system with two bands, one itinerant and one localized, we show how quantum fluctuations in the latter mediate an attractive interaction between the itinerant fermions. In the spinpolarized case, this mechanism gives rise to a topological $p$wave superfluid state in 1D, and a chiral $p_x + {\rm i} p_y$ superfluid in 2D. We derive an effective lowenergy model and demonstrate stability of these states against chargedensity wave formation and phase separation. We also propose to observe this phenomenon with alkalineearth atoms, e.g. ${\rm Yb}$ or ${\rm Sr}$, in an optical superlattice, and discuss several probes for characterizing the topological superfluid state, including momentumresolved RF spectroscopy and an analog of the Edelstein magnetoelectric effect. [Preview Abstract] 
Tuesday, March 14, 2017 2:03PM  2:15PM 
F45.00013: FanoFeshbach resonances in multigap superconductors near electronic topological transitions. Antonio Bianconi The unconventional superconductivity where the chemical potential is tuned near electronic topological transitions, Lifshitz transitions, in multiband systems was first proposed for striped textures in cuprate perovskites. This scenario is emerges in a large variety of superconducting heterostructures made of nanowires and atomic chains. Near a Lifshitz transition a strongly interacting electron fluid shows a complex phase separation characterized by lattice, spin and charge inhomogeneity from atomic to mesoscale range. Here we discuss experimental and theoretical features of this scenario in iron based superconductors and pressurized sulfur hydride. In sulfur hydride by increasing pressure above 120 GPa the chemical potential is tuned to the electronic topological Lifshitz transition for the appearing of a new Fermi surface pocket at Gamma. We discuss the physics of a FanoFeshbach resonance triggering unconventional multigap superconductivity in this scenario. This is characterized by pressure dependent isotope effect.and antiresonance giving a suppression of the critical temperature if the pairing in the appearing Fermi surface is in the BEC regime while the maximum critical temperature appears where the pairing in the appearing Fermi surface is in the BCSBEC regime. [Preview Abstract] 
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