Bulletin of the American Physical Society
2017 Annual Meeting of the APS Mid-Atlantic Section
Volume 62, Number 19
Friday–Sunday, November 3–5, 2017; Newark, New Jersey
Session J2: CMP-QM: Superconductivity and Strongly Correlated Systems - I |
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Chair: Igor Zaliznyak, Brookhaven National Laboratory Room: 215, Campus Center, NJIT |
Saturday, November 4, 2017 4:15PM - 4:51PM |
J2.00001: Raman spectroscopy of the iron-based superconductors Invited Speaker: Weilu Zhang The multiband nature of iron-based superconductors (FeSCs) give rise to a rich temperature-doping phase diagram of competing orders. The parent materials are antiferromagnetic metals. At low doping concentrations, a tetragonal to orthorhombic structure phase transition which breaks the four-fold rotational symmetry is closely followed by the formation of a spin-density wave order which breaks the translational symmetry by doubling the unit cell. The electronic nematic phase forms when the discrete four-fold rotational symmetry is broken while the translational symmetry remains. Superconductivity often emerges in close proximity to the nematic phase. The system provides a platform to study coexistence or competition between the nematic order, the density-wave order and superconductivity. Here we provide a comprehensive polarization resolved electronic Raman spectroscopy study of the intertwined phases in two systems of FeSCs: $A$Fe$_2$As$_2$($A$=Ba,Ca,Eu) and FeSe$_{1-x}$S$_x$. Critical enhancement of the nematic charge fluctuations is observed in the non-symmetric Raman response above the structure phase transition temperature in $A$Fe$_2$As$_2$ and FeSe$_{1-x}$S$_x$. The charge fluctuations are interpreted in terms of inter-orbital charge quadrupole excitations. We compare the susceptibilities measured by Raman scattering, elastic shear modulus C$_{66}$, elastoresistance m$_{66}$, and nuclear quadrupole resonance (NQR), and demonstrate the universality of the susceptibilities measured by these probes. Anisotropic gap opening in the Raman response is observed in the spin-density wave phase of $A$Fe$_2$As$_2$. In the non-magnetic FeSe$_{1-x}$S$_x$, we discover a gap in the Raman response, which is similar to the observations in $A$Fe$_2$As$_2$. The data in FeSe$_{1-x}$S$_x$ suggests a stripe type charge quadrupole order in the orthorhombic phase, which could result in strongly anisotropic electronic properties and orbital dependent superconductivity, as observed in ARPES and STM experiments. Research at Rutgers was done in collaboration with G. Blumberg and S.-F. Wu. [Preview Abstract] |
Saturday, November 4, 2017 4:51PM - 5:27PM |
J2.00002: Temperature dependence of dynamical magnetism in the iron chalcogenide superconductors: neutron scattering evidence for orbital selective Mottness. Invited Speaker: Igor Zaliznyak Inelastic neutron scattering studies of the temperature-dependent magnetism in FeTe [1], the antiferromagentic parent material of superconducting family, presented perhaps the first experimental indication of the orbital-selective electron localization in the iron chalcogenides. The follow-up neutron diffraction study [2] have established that development of the electronic coherence at low temperature leads to a ferro-orbital order where electrons delocalize in ferromagnetic zig-zag chains. These observations explain the "bicollinear" antiferromagnetism, the transition to metallic state observed in bulk resistivity, as well as the loss of magnetic susceptibility, which is consistent with the overall loss of local magnetic moment [1]. Further support for the physics of orbital-selective, temperature- and doping-dependent hybridization in “11” iron chalcogenide superconductors was obtained by studying dynamical local magnetic correlations in sulphur-doped FeTe1-xSx [3], which is located at the boundary of the superconducting state in their phase diagram. The observed liquid-like magnetic response is described by the coexistence of two distinct disordered magnetic phases with different local structures, whose relative abundance depends on temperature. The remarkable competition of these electronic spin-liquid polymorphs suggests new understanding of electronic nematicity and non–Fermi-liquid behavior in a chalcogenide material on the threshold of unconventional superconductivity. Finally, recent polarized neutron surveys of the temperature-dependent magnetic response of FeTe and the optimally doped FeTe0.55Se0.45 also indicate the unusual and temperature-dependent orbital composition of the observed dynamical magnetism. [1] I. A. Zaliznyak, Z. Xu, J. M. Tranquada, G. Gu, A. M. Tsvelik, M. B. Stone, ``Unconventional temperature enhanced magnetism in iron telluride'', Phys. Rev. Lett. 107, 216403 (2011). [2] D. Fobes, I. A. Zaliznyak, Z. Xu, R. Zhong, G. Gu, J. M. Tranquada, L. Harriger, D. Singh, V. O. Garlea, M. Lumsden, B. Winn, ``Ferro-orbital ordering transition in iron telluride Fe$_{1+y}$Te'', Phys. Rev. Lett. 112, 187202 (2014). [3] I. Zaliznyak, A. T. Savici, M. Lumsden, A. Tsvelik, R. Hu, C. Petrovic.``Spin-liquid polymorphism in a correlated electron system on the threshold of superconductivity'', Proc Natl Acad Sci USA, www.pnas.org/cgi/doi/10.1073/pnas.1503559112 (2015) [Preview Abstract] |
Saturday, November 4, 2017 5:27PM - 5:39PM |
J2.00003: Superinductors for Quantum Circuits Michael Gershenson Many Josephson circuits intended for quantum computing would benefit from realization of a “superinductor”: a decoherence-free element whose microwave impedance greatly exceeds the resistance quantum $R_Q=h/(2e)^2$. An ability to change the inductance of this element at a short time scale ($<1\mu s$) would be also an important advantage that could help to realize fault-tolerant operations with superconducting qubits. I will discuss two approaches to the development of superinductors based on Josephson junctions with small Josephson energies and strongly disordered superconductors and the related experimental challenges. M.T. Bell, I.A. Sadovskyy, L.B. Ioffe, A.Yu. Kitaev, and M.E. Gershenson, Quantum Superinductor with Tunable Non-Linearity, Phys. Rev. Lett. 109, 137003 (2012). M. T. Bell, W. Zhang, L. B. Ioffe, and M. E. Gershenson. Spectroscopic Evidence of the Aharonov-Casher Effect in a Cooper Pair Box. Phys. Rev. Lett. 116, 107002 (2016). [Preview Abstract] |
Saturday, November 4, 2017 5:39PM - 6:15PM |
J2.00004: Optical effects in multiband conductors and superconductors Invited Speaker: Christopher Homes Multiband materials display a wide variety of interesting transport phenomena, often with striking optical effects. Two examples are the colossal magnetoresistance in the semimetal WTe$_2$, and the emergence of superconductivity in the iron-based material FeTe$_{0.55}$Se$_{0.45}$ with a critical temperature ($T_c$) of $\simeq 14$ K. The complex optical properties are determined from a Kramers-Kronig analysis of the reflectance, which is measured in the transition metal-chalcogenide ({\em a-b}) planes over a wide energy range. % A poor metal at room temperature, WTe$_2$ undergoes a Lifschitz transition to become a perfectly-compensated semimetal at low temperature, leading to the formation of a striking plasma edge in the far-infrared reflectance. By considering Drude components for the electron and hole pockets, and by examining both the real and imaginary parts of the optical conductivity, it can be demonstrated that one of the scattering rates collapses at low temperature.\footnote{C. C. Homes, M. N. Ali, and R. J. Cava, Phys. Rev. B {\bf 92}, 161109(R) (2015).} Dirac and Weyl semimetals display very small scattering rates, and WTe$_2$ is thought to be a type-II Weyl semimetal. % FeTe$_{0.55}$Se$_{0.45}$ is also a poor metal at room temperature, with a flat and almost frequency-independent optical conductivity. Just above $T_c$, a narrow Drude response emerges, superimposed on a broad, temperature-independent Drude component. Below $T_c$, dramatic changes in the in-plane reflectance signal the formation of multiple superconducting energy gaps which may be determined from the real part of the optical conductivity to be $2\Delta_1 = 5.6$ and $2\Delta_2 = 11.2$ meV on the broad and narrow bands, respectively. Interestingly, this material is simultaneously in both the clean and dirty limit.\footnote{C. C. Homes, Y. M. Dai, J. S. Wen, Z. J. Xu, and G. D. Gu, Phys. Rev. B {\bf 91}, 144503 (2015).} [Preview Abstract] |
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