Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session V47: Superconductivity: Mesoscopic, Nanometer Scale Phenomena andRuthenatesLive
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Sponsoring Units: DCMP Chair: Lei Wang, Yale University |
Thursday, March 18, 2021 3:00PM - 3:12PM Live |
V47.00001: Suppression of the susceptibility in superconducting Sr2RuO4 observed by polarized neutron scattering Alexander Petsch, Mengze Zhu, Mechthild Enderle, Zhiqiang Mao, Yoshiteru Maeno, Igor Mazin, Stephen Hayden The superconducting state of Sr2RuO4 was considered to inhere chiral-triplet pairing analogue to the superfluid 3He-A phase [1]. This has recently been challenged by observations of a reduced 17O-NMR Knight shift in the superconducting state [2]. Here we present a new measurement of the spin susceptibility by polarized neutron scattering. The results show consistent with NMR [2] a suppression below the superconducting transition and reject the previously accepted picture. Differences to a previous polarized neutron scattering study at higher magnetic field [3] are understood by a complex field dependence and lesser statistics. Quantitatively, these results are consistent with different gap states than NMR [2] but support recent proposals such as nodal s’+id or d+ig [4]. |
Thursday, March 18, 2021 3:12PM - 3:24PM Live |
V47.00002: Effect of uniaxial strain on the superconducting state of Sr2RuO4 Eli Mueller, Yusuke Iguchi, Christopher Watson, Clifford W Hicks, Yoshiteru Maeno, Kathryn Ann Moler The symmetry of the superconducting order parameter offers information on the mechanism of Cooper pair formation in unconventional superconductors. Until recently, Sr2RuO4 was a leading candidate for spin-triplet superconductivity. Recent evidence on the spin part of the order parameter suggests spin-singlet pairing with an even parity superconducting gap. Additional measurements on Sr2RuO4 suggests a two-component order parameter. Such a state may exhibit two transition temperatures under non-zero strain, which may be observable by magnetic susceptibility measurements. In this talk, we report on a scanning SQUID susceptometry measurement in which we map the diamagnetic response of Sr2RuO4 as a function of temperature and uniaxial strain with micron-scale spatial resolution. We also present the dependence of the superconducting transition temperature (Tc) on uniaxial strain. We observe both quadratic and linear cusp components in Tc vs strain, where the strength between each component is sensitive to position on the sample. |
Thursday, March 18, 2021 3:24PM - 3:36PM Live |
V47.00003: Quasiparticle properties of thin-film Sr2RuO4 Yawen Fang, Hari Nair, Ludi Miao, Nathaniel J Schreiber, Darrell Schlom, Kyle Shen, Brad Ramshaw Recent developments in the epitaxial growth of Sr2RuO4 have enabled the reproducible production of high quality superconducting films. These epitaxially-grown films provide a unique opportunity to the study of the effect of biaxial strain on Sr2RuO4, complementing the uniaxial strain studies on single-crystal, which shows a high sensitivity of Tc to strain. Tc in Sr2RuO4, however, is also extremely sensitive to disorder, and disentangling the combined effects of disorder and strain on Tc has proven difficult. We measure the Shubnikov-de Haas effect in Sr2RuO4 thin film grown on LSAT substrates, which corresponds to a strain state of 0.045% A1g tensile strain. We are able to observe all three Fermi surfaces and extract their Fermi surface areas, cyclotron effective masses, and the quantum lifetimes of the quasiparticles. To understand the limiting factors of film quality, we model the magnetotransport and find that the quantum lifetime agrees well with the transport lifetime, indicating that large-angle point scattering is likely the limiting factor of the quasiparticle lifetime, rather than extended defects like substrate step edges or strain gradients. |
Thursday, March 18, 2021 3:36PM - 3:48PM Live |
V47.00004: Inhomogeneous time-reversal symmetry breaking in Sr2RuO4 Roland Willa, Matthias Hecker, Rafael Fernandes, Joerg Schmalian We show that the observed time-reversal symmetry breaking (TRSB) of the superconducting state in Sr2RuO4 can be understood as originating from inhomogeneous strain fields near edge dislocations of the crystal. Specifically, we argue that, without strain inhomogeneities, Sr2RuO4 is a single-component, time-reversal symmetric superconductor, likely with dx2-y2 symmetry. However, due to the strong strain inhomogeneities generated by dislocations, a slowly-decaying sub-leading pairing state contributes to the condensate in significant portions of the sample. As it phase winds around the dislocation, time-reversal symmetry is locally broken. Global phase locking and TRSB occur at a sharp Ising transition that is not accompanied by a change of the single-particle gap and yields a very small heat capacity anomaly. Our model thus explains the puzzling absence of a measurable heat capacity anomaly at the TRSB transition in strained samples, and the dilute nature of the time-reversal symmetry broken state probed by muon spin rotation experiments. |
Thursday, March 18, 2021 3:48PM - 4:00PM Live |
V47.00005: Josephson effect experiments probing the pairing symmetry of Sr2RuO4 Nathan McKee, Karl Nelson, Zhiqiang Mao, Ying Liu Sr2RuO4 is an important unconventional superconductor predicted to be an odd-parity spin-triplet superconductor. Its order parameter (OP) symmetry has been the subject of intense scrutiny motivated by developments in the spin susceptibility measurements including NMR Knight shift and polarized neutron scattering that probe the spin part of the OP. While these new results do not exclude the odd parity, spin-triplet nature of the pairing state in this material, the phase-sensitive and spin counterflow half-quantum vortex measurements on Sr2RuO4 do exclude spin-singlet as the symmetry of the OP. Here we report measurements on Josephson effect devices of in-plane corner Josephson junctions prepared on both bulk crystals with two adjacent polished surfaces 90 degrees apart and thin crystals of a mesoscopic size obtained by mechanical exfoliation with two crystal edges of a known angle. Au0.5In0.5 or Al were used as the s-wave counter electrode for the junctions. The critical currents of these devices were measured as a function of the applied magnetic field. The results show the change in the phase of the OP under a rotation of 90 degrees or other angles. The implications of our results on the pairing symmetry in Sr2RuO4 will be discussed. |
Thursday, March 18, 2021 4:00PM - 4:12PM Live |
V47.00006: Topological transitions in curved superconductor nanostructures under a strong transport current R. O. Rezaev, E. I. Smirnova, O. G. Schmidt, V. M. Fomin We report on a topological transition between the vortex-chain and phase-slip regimes under a strong transport current in an open SC nanotube with a submicron-scale inhomogeneity of the normal-to-the-surface component of the applied magnetic field. When the magnetic field is orthogonal to the axis of the nanotube, which carries the transport current in the azimuthal direction, the induced voltage shows a pulse as a function of the magnetic field. This non-monotonous behavior is attributed to the occurrence of a phase-slip area at such magnetic fields, when the quasi-stationary pattern of vortices changes from single to double chains in each half-tube, followed by re-entrance of the superconducting state with a chain of moving vortices [1]. Fingerprints of vortex and phase-slip patterns experimentally identified in nanohelices are explained by a specific topology of screening superconducting currents [2]. |
Thursday, March 18, 2021 4:12PM - 4:24PM Live |
V47.00007: Negative Differential Conductance in Cooper Pair Box Based on InSb Nanowire Guang Yang, Jiayu Shi, Degui Qian, Jie Shen A hybrid semiconductor-superconductor device can be driven into non-trivial topological regime and Majorana zero modes appears at the ends. A typical topological qubit could be constructed with such a hybrid island. Here we fabricated Cooper pair box (CPB) based on InSb island with aluminum. Negative differential conductance (NDC) was observed in the CPB. To figure out the source of NDC, we performed the measurement of the NDC as a function of the junction barrier, chemical potential of the superconducting island and magnetic field. As the junction barrier increases, the NDC moves to a higher bias voltage. Additionally, the NDC is insensitive to the chemical potential of the superconducting island. When the magnetic field increases to the critical magnetic field of aluminum, the NDC gradually disappears, indicating it originates from the superconductivity of island. Futhermore, the NDC does not appear in the bijunction device, which means the island plays a key role. These interesting phenomena provide a new approach to study the physics inside a hybrid island, and potentially instruct the research on topological qubit based on the hybrid island. |
Thursday, March 18, 2021 4:24PM - 4:36PM Live |
V47.00008: Thermoelectric Current in a Graphene Cooper Pair Splitter Zhenbing Tan, Antti Laitinen, Nikita Kirsanov, Alexey Galda, Valerii Vinokour, Mohammad Tasnimul Haque, Alexander Savin, Dmitry Golubev, Gordey Lesovik, Pertti Juhani Hakonen Thermoelectric effect converting the temperature difference into the electric voltage and vice versa has a wealth of applications. Recent theoretical studies found that thermoelectricity may emerge as a result of the nonlocal Cooper pair splitting and elastic co-tunneling processes. We propose a coherent transport description of the nonlocal Seebeck effect and demonstrate its agreement with the experimental observations in a graphene-based Cooper pair splitting device. Our observation lays the ground for a new method of generating entangled electrons. |
Thursday, March 18, 2021 4:36PM - 4:48PM Live |
V47.00009: Superconducting gap symmetry in Sr2RuO4 from linearized Eliashberg equation and Two-Particle Self-Consistent approach. Karim Zantout, Roser Valenti In view of the ongoing discussion regarding the superconducting gap symmetry in Sr2RuO4 we present results for different low-energy Hubbard models. |
Thursday, March 18, 2021 4:48PM - 5:00PM Live |
V47.00010: Evidence for even parity unconventional superconductivity in Sr2RuO4 Andrej Pustogow, Yongkang Luo, Aaron Chronister, Yue-Shun Su, Dmitry Sokolov, Fabian Jerzembeck, Andrew Mackenzie, Clifford W Hicks, Naoki Kikugawa, Srinivas Raghu, Eric D Bauer, Stuart Brown The physical picture of unconventional superconductivity (SC) in Sr2RuO4, which was considered a solid-state analogue to the superfluid 3He-A phase for more than two decades [1,2], has been recently overturned [3]. Here we use 17O NMR spectroscopy to probe the nature of the SC state in Sr2RuO4 and its evolution with magnetic field. The drop of Knight shift K is measured in the limit T → 0 across the field-tuned transition down to B/Bc2 < 0.2. While K includes contributions of both field-induced quasiparticles (QP) and a possible spin polarization of the condensate (of order unity for a p-wave state), the specific heat C/T includes only the QP term. By comparing the field dependence of K and C/T, we establish an upper bound for the condensate magnetic response of < 10% of the normal-state susceptibility, which is sufficient to exclude odd-parity candidates [4]. |
Thursday, March 18, 2021 5:00PM - 5:12PM Live |
V47.00011: Evolution of Shadowed Triplet Superconductor to Spin-Density Wave in Sr2RuO4 and Sr3Ru2O7 Austin Lindquist, Jonathan Clepkens, Hae-Young Kee The superconducting order parameter of Sr2RuO4 has again become a topic of great interest after recent NMR experiments have contradicted the once popular px±ipy spin-triplet superconducting state. We have previously explored a microscopic route to inter-orbital spin-triplet superconducting pairing with spin-orbit coupling to explain recent experimental data in Sr2RuO4 [1-3]. Here, we extend this microscopic theory to Sr3Ru2O7, the bilayer version of Sr2RuO4 to explain why Sr3Ru2O7 does not exhibit superconductivity, but spin-density wave order under a magnetic field. |
Thursday, March 18, 2021 5:12PM - 5:24PM Live |
V47.00012: Direct-writing of complex 3D nano-superconductors Rosa Córdoba, Dominique Mailly, Alfonso Ibarra, R. O. Rezaev, E. Smirnova, O. G. Schmidt, V. M. Fomin, Uli Zeitler, Isabel Guillamon, Hermann Suderow, JOSE MARIA DE TERESA NOGUERAS Innovative schemes have taken advantage of the third dimension (3D) for the development of advanced electronic components. Thus, 3D nano-superconductors could be implemented in the next generation of energy efficient electronic devices. Here, we introduce a template-free nano-lithography method to fabricate in a single-step 3D nano-superconductors with arbitrary geometry. They become superconducting at 7 K and show large critical magnetic field and critical current density. Particularly, we have prepared 3D superconducting WC hollow nanowires by decomposing tungsten hexacarbonyl molecules with a highly-focused He+ ion beam, with outer diameters down to 32 nm and inner ones down to 6 nm [1, 2]. In addition, we have grown nanohelices with on-demand geometries, with dimensions down to 100 nm in diameter, and aspect ratio up to 65. Given its helical 3D geometry, fingerprints of vortex and phase-slip patterns are experimentally identified and supported by numerical simulations based on the time-dependent Ginzburg-Landau equation [3]. |
Thursday, March 18, 2021 5:24PM - 5:36PM On Demand |
V47.00013: Identifying possible pairing states in Sr2RuO4 by tunneling spectroscopy Shu Suzuki, Masatoshi Sato, Yukio Tanaka We examine the tunneling spectroscopy of three-dimensional normal-metal/Sr2RuO4 junctions as an experimental means to identify pairing symmetry in Sr2RuO4. In particular, we consider three different possible pairing states in Sr2RuO4: spin-singlet chiral d-wave, spin-triplet helical p-wave, and spin-nematic f-wave ones, all of which are consistent with recent nuclear-magnetic-resonance experiments [A. Pustogow et al., Nature (London) 574, 72 (2019)]. The Blonder-Tinkham-Klapwijk theory is employed to calculate the tunneling conductance. It is pointed out that the chiral d-wave pairing state is inconsistent with previous tunneling conductance experiments along the c axis. We also find that the remaining candidates, the spin-triplet helical p-wave pairing state and the spin-nematic f-wave ones, can be distinguished from each other by the in-plane tunneling spectroscopy along the a and b axes. |
Thursday, March 18, 2021 5:36PM - 5:48PM On Demand |
V47.00014: Superconducting gap-symmetry from Bogoliubov quasiparticle interference analysis on Strontium Ruthenate Shinibali Bhattacharyya, Marvin Mueller, Astrid Rømer, Miguel Antonio D Sulangi, Andreas Kreisel, Ilya Eremin, Brian M Andersen, Peter Hirschfeld We study the effects of disorder in the superconducting state of Strontium Ruthenate (SRO). Using the T-matrix approach in conjunction with Bogoluibov-de-Gennes formalism, we evaluate the real-space continuum electronic density of states to compare with Scanning tunneling microscopy (STM) conductance map, and its Fourier transform to compare with Bogoliubov quasiparticle interference (BQPI) images, providing information about the momentum-resolved superconducting gap structure. In this context, we use different gap order parameters, as obtained within weak coupling spin-fluctuation theory in the work by Romer et al (PRL, 123.247001, 2019). We aim to address recent experimental data (PNAS 117(10): 5222-5227, 2020) that claim d_(x^2-y^2) symmetry of the order parameter to be the most consistent with the BQPI analysis for SRO gap-structure. |
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