Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session E29: Majorana Fermions 
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Sponsoring Units: DCMP Chair: Sergey Frolovy, University of Pittsburgh Room: 328 
Tuesday, March 15, 2016 8:00AM  8:12AM 
E29.00001: Spinon Majorana fermion Rui Wang, HongYan Lu, Baigeng Wang, ChinSen Ting A new realization of Majorana fermions is proposed in the frustrated magnets via the topological proximity effect. Specifically, we consider the interface between a topological insulator and a frustrated magnetic material. Using the renormalization groupbased meanfield theory, and calculating the selfenergy correction due to the topological insulator, we find that the spin texture and the spinmomentum locking of the Dirac cone will be inherited by the spinons in the nearby frustrated magnets. This leads to a particular topological state of matter that supports the Majorana excitation. Unlike the conventional ones, these Majorana fermions are the composite states of spinons and antispinons, rather than electrons and holes. They can also participate in the transport of spinons, resulting in nontrivial spin current, while the charge current is completely frozen. [Preview Abstract] 
Tuesday, March 15, 2016 8:12AM  8:24AM 
E29.00002: Chiral Majorana Interference in Quantum Anomalous HallSuperconductor Junctions Biao Lian, Jing Wang, Shoucheng Zhang We study the interference of the edge chiral Majorana fermions in junctions of quantum anomalous Hall (QAH) insulators and superconductors (SCs). We show the two chiral Majorana fermions on a QAH edge in contact with an SC generically have a momentum difference $\Delta k$ that depends on the chemical potentials of both the QAH insulator and the SC. Due to the spacial interference induced by $\Delta k$, the longitudinal conductance of normal SC/QAH junctions exhibits an oscillation with respect to the edge lengths and the chemical potentials, which can be measured in transport experiments. Further, we show for QAH/chiral topological SC junctions where there is only one edge chiral Majorana fermion, the dynamical fluctuation of the SC phase yields a geometrical correction to the longitudinal conductance usually derived. [Preview Abstract] 
Tuesday, March 15, 2016 8:24AM  8:36AM 
E29.00003: Majorana Fermions at the End of Topological Insulator Nanoribbon Xiongjun Liu, Yuqin Chen Majorana zero modes can exist at the end of a 1D pwave SC. 1D semiconductor nanowire approximated a swave superconductor is a famous one of those proposals. In which, strong Zeeman field is required to have a large topological region, but unfortunately suppresses superconducting pairing and makes the system more sensitive to disorder. Here we propose a Nanoribbon system made of 2D topological insulator where finite size effect due to the narrow width between two edges plays an important role. A ferromagnetic insulator and an swave superconductor are attached at each edge, respectively. We introduce a low energy effective model to investigate the superconducting phase diagram. And, the disorder effect is studied analytically by using the selfconsistent Born approximation(SCBA). Furthermore, realistic numerically calculation is carried out with a tightbinding model. We demonstrate that, strong Zeeman field generates a large topological region, and at the same time enhances superconducting pairing and makes the system more immune to disorder. [Preview Abstract] 
Tuesday, March 15, 2016 8:36AM  8:48AM 
E29.00004: Molecular Andreev bound states and Majorana modes in a double dot system Edson Vernek, Joelson F. Silva Nanostructured systems such as quantum dots (QD) connected to superconductors has attracted a lot of attention in the recent years. One of the well known phenomena in such a system is the formation of a pair of bound called Andreev bound states (ABS)\footnote{T. Meng, S. Florens, and P. Simon, Phys. Rev. B {\bf 79}, 224521 (2009).}. Recently, it have been shown that when a QD is coupled to a topological superconductor wire, a Majorana bound state (MBS) leaks from the end of the wire into the dot\footnote{E. Vernek, P. H. Penteado, A. C. Seridonio, and J. C. Egues, Phys. Rev. B {\bf 89}, 165314 (2014).}. The character of these bound states is much reacher in structures like molecules and is far from being completely understood. In this work we study a system composed by a two interconnected QDs in which one of then is coupled to a normal superconductor and to a normal lead while the other is coupled to a topological superconductor and to a distinct normal metallic lead. We show that in the atomic limit (for small interdot coupling), one of the dot has a pair of ABS whereas the other has a single a MBS. More interestingly, in the molecular regime (large interdot coupling) we observe a localized Majorana mode coexisting with a delocalized molecular ABS. [Preview Abstract] 
Tuesday, March 15, 2016 8:48AM  9:00AM 
E29.00005: Coupled wire model of symmetric Majorana surfaces of topological superconductors I: 4fermion gapping interactions Sharmistha Sahoo, Zhao Zhang, Jeffrey Teo Time reversal symmetric topological superconductors in three spatial dimensions carry gapless surface Majorana fermions. They are robust against any time reversal symmetric singlebody perturbation weaker than the bulk energy gap. We mimic the massless surface Majorana's by coupled wire models in two spatial dimensions. We introduce explicit manybody interwire interactions that preserve time reversal symmetry and give energy gaps to all low energy degrees of freedom. The gapping 4fermion interactions are constructed by interwire KacMoody current backscattering and rely on the fractionalization or conformal embedding of the Majorana wires. [Preview Abstract] 
Tuesday, March 15, 2016 9:00AM  9:12AM 
E29.00006: Coupled wire model of symmetric Majorana surfaces of topological superconductors II: 32fold periodic topological orders Zhao Zhang, Sharmistha Sahoo, Jeffrey Teo We mimic the massless surface Majorana's of topological superconductors by coupled wire models in two spatial dimensions, and introduce manybody gapping interactions that preserve time reversal symmetry. Coupling with a $\mathbb{Z}_2$ gauge theory, the symmetric gapped surface generically carries a nontrivial $G_N$ topological order, where $N$ is the number of Majorana species and $G_N$ is some $SO(r)_1$ or $SO(3)_3$like topological state. These form a 32fold periodic class $G_N\cong G_{N+32}$, and a $\mathbb{Z}_{32}$ {\em relative} tensor product structure $G_{N_1}\otimes_bG_{N_2}\cong G_{N_1+N_2}$ by anyon condensation. We present the anyon structures of these topological states, and understand the topological orders through bulkboundary correspondence and the Wilson structures on a torus geometry. [Preview Abstract] 
Tuesday, March 15, 2016 9:12AM  9:24AM 
E29.00007: Topological Massive Dirac Edge Modes and LongRange Superconducting Hamiltonians Oscar Viyuela, Davide Vodola, Guido Pupillo, Miguel Angel MartinDelgado We discover novel topological effects in the onedimensional Kitaev chain modified by longrange Hamiltonian deformations in the hopping and pairing terms. This class of models display symmetryprotected topological order measured by the Berry phase of the ground state and the winding number of the Hamiltonians. For exponentiallydecaying hopping amplitudes, the topological sector can be significantly augmented as the penetration length increases, something experimentally achievable. For powerlaw decaying superconducting pairings, the massless Majorana modes at the edges get paired together into a massive nonlocal Dirac fermion localised at both edges of the chain: a new topological quasiparticle that we call topological massive Dirac fermion. This topological phase has fractional topological numbers as a consequence of the longrange couplings. Possible applications to current experimental setups and topological quantum computation are also discussed. [Preview Abstract] 
Tuesday, March 15, 2016 9:24AM  9:36AM 
E29.00008: Local and nonlocal conductance of onedimensional topological superconductor with Majorana bound states Zhiqiang Bao, Fan Zhang A onedimensional topological superconductor has a full pairing gap in the bulk and Majorana bound states on the boundary. It is well known that the existence of Majorana bound states enables a quantized resonant local Andreev reflection. Here we find that nonlocal topological signatures can also be induced by the Majorana bound states in a simple setup, even though the bulk is fully gapped. The nonlocal conductance, which can even be quantized, depends crucially on the symmetries, the topological index, and the mesoscopic properties of the bulk. Coulomb interactions can further drive the hybrid system into a novel phase, which can be understood by a set of renormalizationgroup flow equations. [Preview Abstract] 
Tuesday, March 15, 2016 9:36AM  9:48AM 
E29.00009: Phase diagrams and transport signatures of Luttinger liquid  Majorana Kramers pair junction. Erikas Gaidamauskas, Dong E. Liu, Younghyun Kim, Jens Paaske, Karsten Flensberg, Roman M. Lutchyn Majorana Kramers pairs appearing at the ends of a time reversal invariant topological superconductor lead to a quantized conductance of {\$}4e\textasciicircum 2/h{\$} due to perfect Andreev reflection. We study the stability of Andreev reflection fixed point with respect to electronelectron interactions present in the nanowire and calculate the phase diagram for the system. We find that the low energy properties are determined by local or crossed Andreev reflection fixed points. We analyze transport properties of the junction at these fixed points. [Preview Abstract] 

E29.00010: ABSTRACT WITHDRAWN 
Tuesday, March 15, 2016 10:00AM  10:12AM 
E29.00011: Topological Phases of Inhomogeneous Superconductivity Silas Hoffman, Jelena Klinovaja, Daniel Loss We theoretically consider the effect of a spatially periodic modulation of the superconducting order parameter on the formation of Majorana fermions induced by a onedimensional system with magnetic impurities brought into close proximity to an $s$wave superconductor. When the magnetic exchange energy is larger than the interimpurity electron hopping we model the effective system as a chain of coupled Shiba states. While in the opposite regime, the effective system is accurately described by a quantum wire model. Upon including a spatially modulated superconducting pairing, we find, for sufficiently large magnetic exchange energy, the system is able to support a single pair of Majorana fermions with one Majorana fermion on the left end of the system and one on the right end. When the modulation of superconductivity is large compared to the magnetic exchange energy, the Shiba chain returns to a trivially gapped regime while the quantum wire enters a new topological phase capable of supporting two pairs of Majorana fermions. [Preview Abstract] 

E29.00012: ABSTRACT WITHDRAWN 
Tuesday, March 15, 2016 10:24AM  10:36AM 
E29.00013: Kramers pair of Majoranas in contact with a Luttinger Liquid Dmitry Pikulin, Yashar Komijani, Ian Affleck I will discuss the signatures of the Kramers pair of Majorana coupled to a quantum wire. I will start from the noninteracting case, showing perfect Andreev process at zero energy  either intrachannel, or interchannel. I will show that turning on the interactions will make one of the Andreev process stable, and another unstable. I will discuss the stability diagram of the fixed points as a function of interactions strength and show that strong enough interactions lead to a nontrivial fixed point. [Preview Abstract] 
Tuesday, March 15, 2016 10:36AM  10:48AM 
E29.00014: Superconductor disorder and strong proximity coupling effects in Majorana nanowires William Cole, Jay Sau Topological superconductivity induced by proximity to a conventional superconductor is only robust against moderate disorder in the parent superconductor, and only when the energy scale of the interface coupling is much smaller than the parent gap. I present detailed calculations of proximityinduced superconductivity in onedimensional, spinorbit coupled, semiconductor nanowires when the parent superconductor disorder and interface coupling exceed this limit. This parameter regime is characterized by unique spectroscopic signatures on both sides of the external field tuned topological phase transition. [Preview Abstract] 
Tuesday, March 15, 2016 10:48AM  11:00AM 
E29.00015: Disorderinduced topological transitions in multichannel Majorana wires Inanc Adagideli, Baris Pekerten, Aykut Teker, Michael Wimmer, Ozgur Bozat In this work, we investigate the effect of disorder on the topological properties of multichannel superconductor nanowires. While the standard expectation is that the spectral gap is closed and opened at transitions changing the topological property of the ground state, we show that the closing and opening of a \textit{transport} gap can also cause topological transitions, even in the presence of (localized) states at both sides of the transition. Such transport gaps, induced by disorder, can thus change the topological index, driving a topologically trivial wire into a nontrivial state. We focus on nanowires exhibiting \textit{p}wave superconductivity as well as Rashba semiconductor nanowires in proximity to a conventional superconductor, and obtain analytical formulas for topological transitions in these wires, valid for generic realizations of disorder, generalizing earlier results. Full tightbinding simulations show excellent agreement with our analytical results without any fitting parameters. [Preview Abstract] 
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