Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session S62: Nematic Order and Correlated Electrons in Iron Pnictides and ChalcogenidesInvited
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Sponsoring Units: DCMP Chair: Ming Yi Room: BCEC 258C |
Thursday, March 7, 2019 11:15AM - 11:51AM |
S62.00001: Local orthorhombic lattice distortions in the paramagnetic tetragonal phase of superconducting NaFe$_{1−x}$Ni$_x$As Invited Speaker: Pengcheng Dai Understanding the interplay between nematicity, magnetism and superconductivity is pivotal for elucidating the physics of iron-based superconductors. Here we use neutron scattering to probe magnetic and nematic orders throughout the phase diagram of NaFe$_{1−x}$Ni$_x$As, finding that while both static antiferromagnetic and nematic orders compete with superconductivity, the onset temperatures for these two orders remain well separated approaching the putative quantum critical points. We uncover local orthorhombic distortions that persist well above the tetragonal-to-orthorhombic structural transition temperature Ts in underdoped samples and extend well into the overdoped regime that exhibits neither magnetic nor structural phase transitions. These unexpected local orthorhombic distortions display Curie–Weiss temperature dependence and become suppressed below the superconducting transition temperature Tc, suggesting that they result from the large nematic susceptibility near optimal superconductivity. Our results account for observations of rotational symmetry breaking above Ts, and attest to the presence of significant nematic fluctuations near optimal superconductivity. |
Thursday, March 7, 2019 11:51AM - 12:27PM |
S62.00002: Orbital-selective correlations and superconductivity in the nematic FeSe Invited Speaker: Jian-Xin Zhu The interplay between electronic orders, orbital-selective electronic correlations and associated superconductivity, has played a central role in the physics of emergent phases and unconventional superconductivity. This interplay has been found to be particularly pronounced in recently discovered iron-based superconductors. Motivated by the recent low-temperature experiments on iron selenide (FeSe), we theoretically study the electronic correlation effects and emerging superconductivity in a multiorbital model for this compound. We propose that the combination of various bond nematic orders with the ferro-orbital order can give rise to a surprisingly large orbital selectivity among the Fe-3d t2g orbitals in the normal state. This enhanced orbital selectivity is also reflected in the superconducting pairing amplitudes, which gives rise to a large gap anisotropy on the Fermi surface. Our results naturally explain the seemingly unusual observation of strong orbital selectivity and related unconventional superconductivity in the nematic phase of FeSe, thereby providing new insight into the nature of both the nematic order and the iron-based superconductivity in general. |
Thursday, March 7, 2019 12:27PM - 1:03PM |
S62.00003: Orbital selective magnetism, nematicity, and fluctuations in FeSe Invited Speaker: Rudolf Hackl Iron pnictides and chalcogenides have rich phase diagrams displaying superconductivity, nematic and spin density wave order, fluctuations and short-range magnetism. Yet, the magnetism observed in FeSe, for instance, is not necessarily of the same type as that in the pnictides since the typical nesting conditions of the Fermi surfaces are much less robust in the chalcogenides and the question as to strong versus weak coupling magnetism arises. Raman scattering experiments afford a window into the type of ordering and allow one to distinguish between itinerant and localized magnetism. We show how the response from a weakly coupled itinerant system can be distinguished from that of a Heisenberg-type localized magnet. We present results of light scattering experiments as a function of polarization and temperature. In the pnictides the Raman spectra display all features of a spin density wave while the spectra of FeSe the are similar to those of systems with localized spins such as the cuprates. Our numerical simulations using exact diagonalization of a 4x4 cluster reproduce the experiments semi-quantitatively in the limit of a nearly frustrated spin-1 Heisenberg model (localized spins), in particular the low energy peak in B1g symmetry. The results indicate that the electrons in some of the orbitals are more localized in FeSe than in the pnictides and reopen the discussion on the type of nematic fluctuations observed recently. |
Thursday, March 7, 2019 1:03PM - 1:39PM |
S62.00004: ARPES probe of the electronic structure in the detwinned FeSe Invited Speaker: Donghui Lu The nature of the nematic order remains to be an important issue for a comprehensive understanding of phase competition in iron-based superconductors and has strong implications on the mechanism of high temperature superconductivity. However, the strong coupling between the nematic order and spin density wave order makes it very challenging to disentangle the contribution from the orbital and magnetic degree of freedom in iron pnictides. FeSe, due to the lack of long range magnetic order, is an ideal system for isolating the contribution of nematicity to the fundamental physics of the iron-based superconductors. Angle-resolved photoemission spectroscopy (ARPES) has played a critical role in unveiling the strong in-plane orbital anisotropy associated with the nematic order in iron pnictide compounds. On the other hand, conflicting results on the magnitude of nematic splitting in FeSe have been reported. |
Thursday, March 7, 2019 1:39PM - 2:15PM |
S62.00005: Intertwined and vestigial electronic phases in hole-doped Sr1-xNaxFe2As2 Invited Speaker: Christoph Meingast Hole-doped ReFe2As2 (Re = Ba, Sr, Ca) exhibit much richer phase diagrams than the corresponding electron-doped systems. In particular, the phase diagram of Na-doped BaFe2As2 exhibits a small pocket of a double-Q reentrant C4 magnetic phase [1], as well as another yet unidentified magnetic phase [2]. In strong analogy with the charge order observed in underdoped cuprates [3], these additional phases compete strongly with the emerging superconducting order [2,4]. |
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