Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S45: Transport Signature of Majorana NanowiresFocus
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Sponsoring Units: DMP Room: 392 |
Thursday, March 16, 2017 11:15AM - 11:27AM |
S45.00001: Zero-bias peaks in InSb nanowire hybrid devices: magnetic field anisotropy, peak splittings and phase diagrams Peng Yu, Jun Chen, Moïra Hocevar, Diana Car, Sébastien Plissard, Erik Bakkers, Sergey Frolov Majorana bound states (MBS) are predicted to emerge in a 1D nanowire system with spin-orbit interaction, induced superconductivity and external magnetic field. We made devices using InSb nanowires based on that prescription with different electrode geometries. Zero-bias peaks (ZBPs) are observed at finite field and in some devices persist to over 2 Tesla. At high fields, some devices show split ZBPs, which is in agreement with the theory of two overlapping MBS in a finite-length topological superconductor. Field and gate scans at different field angles confirm those Zero-bias peaks only appear within a small angle around the nanowire axis. Ongoing measurements in three-terminal devices are used to extract additional information about the origin of the ZBP and its splitting. [Preview Abstract] |
Thursday, March 16, 2017 11:27AM - 12:03PM |
S45.00002: tbd Invited Speaker: Tudor Stanescu tbd [Preview Abstract] |
Thursday, March 16, 2017 12:03PM - 12:15PM |
S45.00003: 2e-periodic switching current in nanowire-based single-Cooper-pair transistors John Watson, Jasper van Veen, Alex Proutski, Attila Geresdi, Peter Krogstrup, Jesper Nygard, Charles Marcus, Leo Kouwenhoven We report on measurements of the switching current of mesoscopic superconducting islands in hybrid InAs/Al core/shell nanowires. We find a switching current which is 2e periodic in the island gate charge in several devices for a wide range of temperatures and tunnel barrier conductances. Such 2e periodicity is evidence of a low quasiparticle poisoning rate and represents an important starting point for implementing theoretical proposals to investigate Majorana fusion channels in hybrid semiconductor-superconductor nanowires. In addition, our measurements demonstrate that the devices can be tuned between Coulomb-dominated and Josephson-dominated regimes. Taken together, our results indicate these systems are promising candidates for fusion experiments, and we discuss the path forward. [Preview Abstract] |
Thursday, March 16, 2017 12:15PM - 12:27PM |
S45.00004: Conductance of a superconducting Coulomb blockade nanowire at finite temperature Ching-Kai Chiu By applying a magnetic field, a superconducting proximity nanowire in the presence of spin-orbital coupling can pass through topological phase transition and possesses Majorana bound states on the ends. One of the promising platforms to detect the Majorana modes is a Coulomb blockade island by measuring its two-terminal conductance. Here, we study the transportation of a single electron across the superconducting Coulomb blockade nanowire at finite temperature to obtain the generic conductance equation. By considering all possible scenarios that Majorana modes appear in the nanowire, we compute the nanowire conductance as the magnetic field and the gate voltage of the nanowire vary. The oscillation behavior of the conductance peak is temperature independent and the oscillation amplitude of the conductance peak spacings increases as the magnetic field increases. [Preview Abstract] |
Thursday, March 16, 2017 12:27PM - 12:39PM |
S45.00005: Quantum charge fluctuations of a proximitized nanowire Roman Lutchyn, Karsten Flensberg, Leonid Glazman Motivated by recent experiment by Albrecht et al., Nature (2016), we consider charging of a nanowire which is proximitized by a superconductor and connected to a normal-state lead by a single-channel junction. The charge $Q$ of the nanowire is controlled by gate voltage $e N_g/C$. A finite conductance of the contact allows for quantum charge fluctuations, making the function $Q(N_g)$ continuous. It depends on the relation between the superconducting gap $\Delta$ and the effective charging energy $E^*_C$. The latter is determined by the junction conductance, in addition to the geometrical capacitance of the nanowire. We investigate $Q(N_g)$ at zero magnetic field $B$, and at fields exceeding the critical value $B_c$ corresponding to the topological phase transition. Unlike the case of $\Delta = 0$, the function $Q(N_g)$ is analytic even in the limit of negligible level spacing in the nanowire. At $B=0$ and $\Delta>E^*_C$, the maxima of $dQ/d N_g$ are smeared by $2e$-fluctuations described by a single-channel ``charge Kondo'' physics, while the $B=0$, $\Delta |
Thursday, March 16, 2017 12:39PM - 12:51PM |
S45.00006: Transport signatures of topology protected quantum criticality in Majorana islands Michal Papaj, Zheng Zhu, Liang Fu Using numerical renormalization group we study a topological superconductor island coupled to three metallic leads in the vicinity of the charge degeneracy point. We show that the system flows to a non-Fermi liquid fixed point at low temperatures with fractional quantized DC conductance of $2/3\, e^2/h$. Our proposal is experimentally feasible due to a much larger crossover temperature than in the previously studied cases and the robustness of the setup against the channel coupling anisotropy and charge degeneracy detuning. Including Majorana hybridization drives the system into a Fermi liquid phase at very low temperatures. The two proposed experimental signatures of multi-terminal electron teleportation include nonmonotonic temperature dependence of DC conductance and emergence of a plateau at $2/3\, e^2/h$ in tunnel coupling dependence of DC conductance. [Preview Abstract] |
Thursday, March 16, 2017 12:51PM - 1:03PM |
S45.00007: Topological Two-Channel Kondo Effect in Majorana Transistor Zhi-qiang Bao, Fan Zhang A one-dimensional time-reversal-invariant topological superconductor hosts a Majorana Kramers pair at each end, where time-reversal symmetry acts as a supersymmetry that flips local fermion parity. We examine the transport anomaly of such a superconductor, floating and tunnel-coupled to normal leads at its two ends. We demonstrate the realization of a topologically-protected, channel-symmetric, two-channel Kondo effect without fine-tuning. Whereas the nonlocal teleportation vanishes, a lead present at one end telecontrols the universal transport through the other end. (arXiv:1607.04303 (2016)) [Preview Abstract] |
Thursday, March 16, 2017 1:03PM - 1:15PM |
S45.00008: Coulomb Blockade in 1D Fractional Topological Superconductors Younghyun Kim, David J. Clarke, Roman M. Lutchyn We study transport through a one dimensional fractional topological superconductor with localized parafermionic zero modes. We consider a mesoscopic floating superconductor placed on a narrow trench between two fractional quantum Hall states with filling fraction $\nu=2/3$ and calculate dependence of the conductance on charging energy, gate voltage and other physical parameters. We find that generically the system flows to strong tunneling fixed point at which effective charging energy is renormalized to zero. As a result, there is a perfect transmission through the device even in the presence of a large bare charging energy. This result is very different from a non-superconducting case where the system exhibits Coulomb blockade in the low temperature limit. [Preview Abstract] |
Thursday, March 16, 2017 1:15PM - 1:27PM |
S45.00009: Modeling superconductor-semiconductor heterostructures in the presence of gate-induced electric fields Andrey E. Antipov, Enrico Rossi, Bela Bauer, Roman M. Lutchyn We study the effect of gate-induced electric fields on the properties of semiconductor-superconductor heterostructures. Using a model that describes the semiconductor and the superconductor on the same footing we are able to describe the changes of the heterostrtuctures' states induced by external electric fields and quantify the effect that these changes have on the effective parameters of the heterostructures. The effective g-factor of the heterostructure is a key parameter for the realization and observation of Majorana modes in these systems. We show that the changes of the heterostructure's wawefunctions induced by external electric fields can significantly modify the effective g-factor of superconductor-semiconductor heterostructures. [Preview Abstract] |
Thursday, March 16, 2017 1:27PM - 1:39PM |
S45.00010: Majorana fermions in few-layer NbSe$_{\mathrm{2}}$/nanowires heterostructures Benjamin T. ZHOU, Yingming XIE, Kam Tuen LAW Recently, the novel Ising superconductivity has been discovered in NbSe$_{\mathrm{2}}$ atomic layers with strongly enhanced in-plane upper critical fields. This arises from the strong Ising spin-orbit coupling (SOC) in NbSe$_{\mathrm{2}}$ which protects electron spins from being aligned by in-plane fields. In this work, we show that the Ising SOC generates spin-triplet Cooper pairs in superconducting few-layer NbSe$_{\mathrm{2}}$. By placing paramagnetic nanowires in proximity to superconducting NbSe$_{\mathrm{2}}$, spin-triplet pairings can be induced in the nanowires, and the system becomes a topological superconductor supporting Majorana fermions (MFs) upon application of in-plane magnetic fields. Advantages of our proposal in the experimental realization of MFs and their braiding scheme in 1D wire networks are discussed. [Preview Abstract] |
Thursday, March 16, 2017 1:39PM - 1:51PM |
S45.00011: The properties of Majorana fermions and normal metal rings coupled systems Lei Fang, David Schmeltzer The systems of coupled Majorana fermions and normal metal rings are studied. The rings are threaded by magnetic fluxes. We find that by adjusting the chemical potentials or the magnetic fluxes, exact zero modes can appear when resonance happens. The zero mode is consisted of the counterclockwise propagating electron mode paired with the clockwise propagating hole mode, or vice verse. The transport properties of these zero modes are then studied by attaching the rings to external leads. [Preview Abstract] |
Thursday, March 16, 2017 1:51PM - 2:03PM |
S45.00012: Non-Abelian fermion parity interferometry of Majorana bound states in a Fermi sea Daniel Dahan, Mostafa Tanhayi Ahari, Gerardo Ortiz, Babak Seradjeh, Eytan Grosfeld We study the quantum dynamics of Majorana and regular fermion bound states coupled to a one-dimensional lead. The dynamics following the quench in the coupling to the lead exhibits a series of dynamical revivals as the bound state propagates in the lead and reflects from the boundaries. We show that the nature of revivals for a single Majorana bound state depends uniquely on the presence of a resonant level in the lead. When two spatially separated Majorana modes are coupled to the lead, the revivals depend only on the phase difference between their host superconductors. Remarkably, the quench in this case effectively performs a fermion-parity interferometry between Majorana bound states, revealing their unique non-Abelian braiding. Using both analytical and numerical techniques, we find the pattern of fermion parity transfers following the quench, study its evolution in the presence of disorder and interactions, and thus, ascertain the fate of Majorana in a rough Fermi sea. [Preview Abstract] |
Thursday, March 16, 2017 2:03PM - 2:15PM |
S45.00013: Zero-energy pinning from interactions in Majorana nanowires Elsa Prada, Fernando Dom\'inguez, Jorge Cayao, Pablo San-Jose, Ram\'on Aguado, Alfredo Levy Yeyati Majorana zero modes at the boundaries of topological superconductors are charge-neutral, an equal superposition of electrons and holes. This ideal situation is, however, hard to achieve in physical implementations, such as proximitised semiconducting nanowires of realistic length. In such systems Majorana overlaps are unavoidable and lead to their hybridisation into \emph{charged} Bogoliubov quasiparticles of finite energy which, unlike true zero modes, are affected by electronic interactions. We here demonstrate that these interactions, particularly with bound charges in the dielectric surroundings, drastically change the non-interacting paradigm. Remarkably, interactions may completely suppress Majorana hybridisation around parity crossings, where the total charge in the nanowire changes. This effect, dubbed zero-energy pinning, stabilises Majoranas back to zero energy and charge, and leads to electronically incompressible regions with suppressed Majorana susceptibility to external noise, despite their overlap. [Preview Abstract] |
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