Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session D61: Fe-Based Superconductors - Nematicity IIFocus
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Sponsoring Units: DMP DCMP DCOMP Chair: Peter Johnson, Brookhaven National Laboratory Room: Mile High Ballroom 4B |
Monday, March 2, 2020 2:30PM - 3:06PM |
D61.00001: Effect of pressure on the competing phases in FeSe and BaFe2As2: Insights from specific heat measurements and beyond Invited Speaker: Elena Gati Understanding the phase interplay in iron-based superconductors is considered to be crucial for unravelling the mechanism behind their superconductivity. In this talk, we focus on new insights into the phase interplay under pressure of two members, FeSe and BaFe2As2, from specific heat under pressures [1] up to ~ 2.5 GPa. |
Monday, March 2, 2020 3:06PM - 3:18PM |
D61.00002: Electronic phase diagram of FeSe1-xTex under high pressure Kiyotaka Mukasa, Kohei Matsuura, Yuichi Sugimura, Muku Otani, Mingwei Qiu, Mikihiko Saito, Yuta Mizukami, Kenichiro Hashimoto, Jun Gouchi, Yoshiya Uwatoko, Takasada Shibauchi FeSe has the simplest crystal structure among the iron-based superconductors and is known to have a nonmagnetic nematic order. When selenium is substituted by the isovalent element, sulfur, the nematic phase is suppressed and a nematic quantum critical point without magnetism appears. On the other hand, under pressure, a dome-shaped magnetic phase is induced and the superconducting transition temperature rises from 9 K to 37 K. |
Monday, March 2, 2020 3:18PM - 3:30PM |
D61.00003: Multiple Magnetic Phases Hiding in Plain (and Out-of-Plane) Sight in Coexistence with Superconductivity in LaFeAs1-xPxO 1111 System Ryan Stadel, Dmitry Khalyavin, Pascal Manuel, Rafael Fernandes, Morten Holm Christensen, Keith Taddei, Clarina Reloj Dela Cruz, Ashfia Huq, Saul Lapidus, Daniel Phelan, Duck Young Chung, Matthew Krogstad, Raymond Osborn, Stephan Rosenkranz, Omar Chmaissem Following the discrovery of the microscopic co-existence of antifermagnetic spin density waves and superconductivity in Ba1-xKxFe2As2 and the low temperature structural re-entrance to the magnetic C4 tetragonal phase in Ba1-xNaxFe2As2, an effort was made to seek similar phases in the related LaFeAs1-xPxO 1111 system. Previous work had reported two superconducting domes as well as two distinct magnetic regions. While the low doping magnetic phase had been well characterized by neutron diffraction, the higher doped magnetic region had been deduced from short range 31P-NMR measurements. We present a detailed phase diagram with nuclear and magnetic structural characterization based on a combination of x-ray and neutron diffraction, as well as magnetic temperature dependence thoroughly mapped by muon spin resonance. This work demonstrates three distinct magnetic phases evolving from in-plane orthorhombic to in-plane tetragonal to out-of-plane tetragonal permeating the entire phase diagram from the parent LaFeAsO to superconducting LaFeAs0.2P0.8O. |
Monday, March 2, 2020 3:30PM - 3:42PM |
D61.00004: Wang-Landau simulations of the coupled magnetic and nematic transitions in disordered iron-based superconductors Anzumaan Chakraborty, William J Meese, Rafael Fernandes, Thomas Vojta In many iron-based superconductors, nematicity and magnetism are found to be closely related and occurring at comparable temperatures. While many works have discussed the character of these coupled transitions in clean systems, the impact of disorder, like random strain, has not been elucidated. Here we perform Monte Carlo simulations of an appealing model that captures these two transitions, namely, the 2D anisotropic Ising-O(3) model. For sufficiently large anisotropy in the exchange coupling, there is a direct first-order transition from the paramagnetic tetragonal phase to the low-temperature phase that displays both spin and nematic (Ising) orders. This transition splits into two separate transitions as the anisotropy decreases, giving rise to a nematic intermediate phase. We study both clean and disordered systems and compare conventional algorithms, such as Metropolis and Wolff, to an implementation using the Wang-Landau algorithm. The latter avoids the supercritical slowing down associated with the first-order transitions, providing an efficient way to probe the complicated free energy landscapes near the multi-critical point. Phase diagrams are obtained and compared to experimental results. |
Monday, March 2, 2020 3:42PM - 3:54PM |
D61.00005: Coexistence of long-range magnetic ordering and superconductivity in FeSe/EuTiO3 heterostructure Chong Liu, Hyungki Shin, Ryan Roemer, Ke Zou Spin degree of freedom has played a key role in unconventional superconductivities. FeSe monolayer superconductors, with the highest transition temperature in Fe-based superconductors, remain not magnetically ordered, while spin density waves and nematicity have been observed in bulk FeSe. We grow heterostructures of FeSe on (001) antiferromagnetic EuTiO3 (ETO) using molecular beam epitaxy. Transport measurements showed clear anomalous Hall effect in both ETO and FeSe/ETO samples. Simultaneously, superconducting transition was also observed in FeSe films on ETO. Our work provides a new platform for the interplay of spins and superconductivity, which may promote integration of superconductors in new spintronics. |
Monday, March 2, 2020 3:54PM - 4:06PM |
D61.00006: Quasi-elastic scattering from short-range magnetic order in FeTe1-xSex compounds Guangyong Xu, Zhijun Xu, Genda Gu, John Tranquada, Robert J Birgeneau We report neutron scattering measurements on single crystals of FeTe1-xSex. Superconductivity (SC) and antiferromagnetic (AFM) order in these compounds can be tuned together by varying Se compositions and/or excess Fe. We show that in systems where long-range magnetic order develops, superconductivity is completely suppressed. The long-range magnetic order is static with long life-time. On the other hand, when the magnetic order is short-range and the system exhibits behaviors of a mixed phase or phase separation between AFM and SC, the energy profile of the magnetic order appears to be quasi-elastic with energy widths around 0.2 meV. We discuss the evolution of the quasi-elastic magnetic scattering with temperature and doping, and their implications on the understanding of the spin-glass/SC mixed phase in FeTe1-xSex systems. |
Monday, March 2, 2020 4:06PM - 4:18PM |
D61.00007: Elastoresistance of CaK(Fe,Ni)4As4 Anna Boehmer, William Meier, Mingyu Xu, Gil Drachuck, Paul Wiecki, Sergey L. Bud'ko, Christoph Meingast, Fei Chen, Morten Holm Christensen, Rafael Fernandes, Paul C Canfield Elastoresistance describes the resistance change induced by an elastic deformation. In the well-known compound BaFe2As2 with clear nematicity, a diverging elastoresistance has been taken as a measure of the nematic susceptibility [1]. In contrast to BaFe2As2, the related CaK(Fe,Ni)4As4 orders antiferromagnetically as a so-called spin-vortex crystal (SVC) [2], which does not entail any nematicity. Here, we have determined the elastoresistance of CaK(Fe1-xNix)4As4 (x=0-0.05), spanning the phase diagram from a superconducting sample with Tc=35 K and no magnetic order, to a sample with magnetic order at a high TN=51 K having Tc=10 K. The nematic susceptibility for SVC order is analyzed theoretically via a Ginzburg-Landau expansion and compared with the elastoresistance data. Implications on the place of CaK(Fe,Ni)4As4 in the wider material class and the factors contributing to elastoresistance are discussed. |
Monday, March 2, 2020 4:18PM - 4:30PM |
D61.00008: Prediction of Antiferromagnetism in Chromium Analog (BaCr2P2) of Iron Pnictide Confirmed by Synthesis Radi Jishi, Jose Rodriguez, Timothy Haugan, Michael Susner We have performed density-functional theory (DFT) calculations for BaCr2P2. It is a chromium analog to the parent compound BaFe2As2 for a series of iron-pnictide superconductors. By combining evolutionary methods with DFT, we predict that BaCr2P2 has the same crystal structure as its iron-pnictide analog[1]. DFT also predicts Neel antiferromagnetic order over the chromium sites. A simple hopping model over a square lattice of chromium atoms that includes only the principal 3dxz and 3dyz orbitals suggests that such checkerboard antiferromagnetic order is due to residual nesting of the Fermi surfaces that is obscured by a Lifshitz transition[1]. The DFT prediction has been confirmed experimentally after the synthesis of polycrystalline samples of BaCr2P2. X-ray diffraction recovers the predicted crystal structure to high accuracy, while magnetic susceptibility and specific-heat measurements are consistent with an antiferromagnetically ordered state at temperatures below TN ~ 60 K [1]. |
Monday, March 2, 2020 4:30PM - 4:42PM |
D61.00009: Novel Fe-based superconductor LaFe2As2 in comparison with traditional pnictides Igor Mazin, Harald Jeschke, Makoto Shimizu, Nayuta Takemori The recently discovered Fe-based superconductor (FeBS) LaFe2As2 seems to break away from an established pattern that doping FeBS beyond 0.2 e/Fe destroys superconductivity. LaFe2As2 has an apparent doping of 0.5 e, yet superconducts at 12.1 K. Its Fermi surface bears no visual resemblance with the canonical FeBS Fermiology. It also exhibits two phases, none magnetic and only one superconducting. We show that the difference between them has nonetheless magnetic origin, the one featuring disordered moments, and the other locally nonmagnetic. We find that La there assumes an unusual valence of +2.6 to +2.7, so that the effective doping is reduced to 0.30-0.35 e. A closer look reveals the same key elements: hole Fermi surfaces near the Γ-Z and electron ones near the X-P lines, with the corresponding peak in susceptibility, and a strong tendency to stripe magnetism. The physics of LaFe2As2 is thus more similar to the FeBS paradigm than hitherto appreciated. |
Monday, March 2, 2020 4:42PM - 4:54PM |
D61.00010: Biaxial Strain Tuning of Strong Electronic Correlations in CsFe2As2 Paul Wiecki, Amir-Abbas Haghighirad, Thomas Wolf, Anna Boehmer CsFe2As2 is an iron-based superconductor with Tc ~ 2.3 K and a large Sommerfeld coefficient of 180 mJ / mol K, indicating strong electronic correlations at low temperature [1]. In addition, CsFe2As2 shows a coherence-incoherence crossover, reminiscent of heavy fermion systems [2,3]. In this contribution, using transport and x-ray diffraction measurements, we demonstrate that in-plane biaxial tension strain, applied by gluing the sample to a rigid substrate with a large mismatch in thermal expansivity, can modify the low-temperature electronic correlations as well as the coherence-incoherence crossover temperature in this material. |
Monday, March 2, 2020 4:54PM - 5:06PM |
D61.00011: Emergent electronic properties of FeTe by strain tuning Soumendra Panja, Craig V Topping, Chi Ming Yim, Christopher Trainer, Dorina Croitori, Vladimi Tsurkan, Alois Loidl, Peter Wahl, Andreas Rost FeTe is an ‘11’ non-superconducting parent compound with properties significantly different from those of other iron-based high-temperature superconductors. Most discernible is the double stripe antiferromagnetic order with the (π,0) propagation vector contrary to the more typical (π, π) order. That these properties can be significantly tuned by tensile strain has for example been shown by thin film experiments in which superconductivity was stabilised at 13K. |
Monday, March 2, 2020 5:06PM - 5:18PM |
D61.00012: Unconventional charge density wave order in the pnictide superconductors Ba(Ni1-xCox)2As2 and Ba1-xSrxNi2As2 Sangjun Lee, Xiaolan Sun, Xuefei Guo, John Collini, Chris Eckberg, Johnpierre Paglione, Peter Abbamonte BaNi2As2 is a structural homologue of the pnictide high temperature superconductor parent compound, BaFe2As2, in which the Fe atoms are replaced by Ni. Superconductivity is highly suppressed in this system, reaching a maximum Tc = 2.3 K upon Co doping, compared to 24 K in its iron-based cousin, and the origin of this Tc suppression is not known. Using x-ray scattering, we present the discovery of CDW order in BaNi2As2 and its evolution upon Co and Sr doping. The chemical doping suppresses the CDW, paralleling the behavior of antiferromagnetism in iron-based superconductors. Our study demonstrates that pnictide superconductors can exhibit CDW order which may be closely related to the Tc suppression in this system. We also present the response of CDW in Ba1-xSrxNi2As2 under external strain and discuss how it relates to the strong nematic susceptibility recently discovered in these compounds via elastoresistivity measurements. |
Monday, March 2, 2020 5:18PM - 5:30PM |
D61.00013: Emergence of Fulde-Ferrell-Larkin-Ovchinnikov phase in FeSe in the BCS-BEC crossover Shigeru Kasahara, Yuki Sato, Salvatore Licciardello, Matija Čulo, Stevan Arsenijevic, Thom Ottenbros, Takahito Tominaga, Jakob Böker, Ilya Eremin, Joachim Wosnitza, Takasada Shibauchi, Nigel Hussey, Yuji Matsuda The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, predicted more than a half-century ago, is a highly exotic state of fermionic condensate, in which oscillations of the order parameter emerge in real space. Yet, quest of the FFLO phase has been a challenge for a broad range of scientists, including solid-state, ultracold atomic and high-energy physics. Here, via thermal transport measurements in intense magnetic fields up to 33 T, we present compelling evidence for a distinct high-field superconducting phase in an iron-chalcogenide superconductor FeSe for the field H || ab-plane. A discontinuous downward jump in the quasiparticle thermal transport indicates the presence of a first-order transition line within the superconducting phase. We attribute the high-field phase to the FFLO phase, where planar nodes are formed. We discuss the importance of the extremely small Fermi energies, strong spin-orbit coupling and multiband nature for the FFLO phase in FeSe. |
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