Bulletin of the American Physical Society
83rd Annual Meeting of the APS Southeastern Section
Volume 61, Number 19
Thursday–Saturday, November 10–12, 2016; Charlottesville, Virginia
Session C3: New Developments in Superconductivity |
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Chair: Utpal Chatterjee, University of Virginia Room: Monroe Room |
Thursday, November 10, 2016 1:30PM - 2:00PM |
C3.00001: Spatial inhomogeneities in the Fe chalcogenide superconductors Invited Speaker: Despina Louca Much remains unknown of the microscopic origin of superconductivity when it materializes in atomically disordered systems as in amorphous alloys or in crystals riddled with defects. A manifestation of this conundrum is envisaged in the highly defective iron chalcogenide superconductors. How can superconductivity survive under such crude conditions that call for strong electron localization and scattering? With vacancies present both at the K and Fe sites in the K$_{\mathrm{x}}$Fe$_{\mathrm{2-y}}$Se$_{\mathrm{2}}$ superconductor, superconductivity is bordering a semi-metallic region below x \textasciitilde 0.7 and an insulating and antiferromagnetic region above x \textasciitilde 0.85. In this talk, I will discuss our recent results on the bulk local atomic structure and single crystal work that show striking differences between superconducting and non-superconducting compositions regarding the ordering of the Fe and K sublattices. In a related system, the intercalation of LiFeO$_{\mathrm{2}}$ in the tetragonal lattice of Fe$_{\mathrm{1-y}}$Se leads to a great enhancement of the superconducting transition temperature, T$_{\mathrm{C}}$ \textasciitilde 43 K and possibly to an antiferromagnetic transition at 8.5 K. While the LiFeO$_{\mathrm{2}}$ layer acts as a charge reservoir, its Fe$^{\mathrm{3+}}$ ion (3d$^{\mathrm{5}})$ is magnetic that may create a magnetic buffer layer. Most recently, we developed a new synthesis method to control the Fe concentration in the intercalating layer as well as the filling ratio of the Li$_{\mathrm{1-x}}$Fe$_{\mathrm{x}}$O$_{\mathrm{2}}$ : FeSe layers. Neutron scattering measurements were carried out on powder samples of (Li$_{\mathrm{1-x}}$Fe$_{\mathrm{x}}$O2)$_{\mathrm{y}}$FeSe. With the intercalation, no crystal structural transition from the P4/nmm symmetry occurs but the c-axis lattice constant expands substantially, evidence of the intercalation. Our results indicate that the amount of Fe in the LiFeO$_{\mathrm{2}}$ layer has a direct correlation to the transition temperature. [Preview Abstract] |
Thursday, November 10, 2016 2:00PM - 2:30PM |
C3.00002: Entanglement control of superconducting qubits Invited Speaker: Sophia Economou Entanglement is a key resource for novel quantum technologies, especially quantum computing. Each physical system has its own merits and challenges, which need to be considered when creating and manipulating entanglement. Superconducting qubits can be easily connected to cavities in the form of planar waveguides and to each other via the cavity modes. On the other hand, one of their most notorious challenges is their dense spectrum (`spectral crowding'), which makes fast quantum control challenging. In this talk, theoretical work addressing this challenge will be presented: we have developed a technique for fast entangling gates by Speeding up Waveforms by Inducing Phases to Harmful Transitions (SWIPHT gates), which we have used to design universal gates for quantum computing. Our results include high-fidelity two-qubit and three-qubit entangling gates that are fast and based on smooth, experimentally friendly pulse shapes. [Preview Abstract] |
Thursday, November 10, 2016 2:30PM - 3:00PM |
C3.00003: Vortex states in a non-Abelian magnetic field Invited Speaker: Predrag Nikolic A type-II superconductor survives in an external magnetic field by admitting an Abrikosov lattice of quantized vortices. This is an imprint of the Aharonov-Bohm effect created by the Abelian U(1) gauge field. The simplest non-Abelian analogue of such a gauge field, which belongs to the SU(2) symmetry group, can be found in topological insulators. This talk will present a lattice model calculation and a Landau-Ginzburg analysis of two-dimensional superconducting ground states that host a lattice of SU(2) vortices, arising from attractive interactions between electrons in an SU(2) “magnetic” field. The model directly captures a correlated topological insulator ultra-thin film, and approximates one channel for instabilities on the Kondo topological insulator surface. Due to its simplicity, the model might become amenable to cold atom simulations in the foreseeable future. The vitality of low-energy vortex states born out of SU(2) “magnetic” fields is promising for the creation of incompressible vortex liquids with non-Abelian fractional excitations. [Preview Abstract] |
Thursday, November 10, 2016 3:00PM - 3:30PM |
C3.00004: Magnetic States in Singlet-Triplet Superconducting Heterostructures Invited Speaker: Ilya Vekhter Surface and interface states in unconventionally ordered materials have become a focus of significant interest both because of their importance in fundamental physics, and because of their potential use in technological applications. Often the existence of these states is protected by symmetry or topology of the bulk, but their properties are not universal. I will discuss the surface and interface states appearing at the boundaries of triplet superconductors, such as Sr$_2$RuO$_4$, and show that, under rather general conditions, such states are spin-polarized. Moreover, their magnetization can be controlled by the phase difference in junctions with conventional superconductors. The behavior of the magnetization reflects the nature of underlying pairing interaction, and can be used to test symmetries of the order parameter in spin-triplet superconductors. [Preview Abstract] |
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