Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B10: Fe-based Superconductors IIFocus
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Sponsoring Units: DMP DCOMP Chair: Vitalii Vlasko-Vlasov, Argonne National Laboratory Room: BCEC 151B |
Monday, March 4, 2019 11:15AM - 11:51AM |
B10.00001: Elastoresistive and elastocaloric anomalies in iron pnictides Invited Speaker: Matthias Ikeda Electronic nematicity is a prominent feature in Fe-based superconductors, but is also present in at least some cuprates, and heavy fermion superconductors. Being a possible common thread for unconventional superconductivity, the role of nematic fluctuations for superconductivity needs to be assessed. This calls for new techniques that allow for tuning nematicity continuously towards quantum criticality. In the first part of this talk I will discuss how to disentangle the response of nematicity to strain components of different symmetry, and will show that both symmetric (A1g) and antisymmetric (B1g) strain are suitable means to tune the critical temperature of the nematic phase transition in Fe based superconductors. In the second part of the talk, I will outline recent experimental advances exploring the thermoelastic properties of these materials. In particular, the finite response of nematicity to strain causes anomalies in the elastocaloric effect as well as in the elastoresistivity which can be measured via an AC technique. These anomalies are proportional to the corresponding heat capacity anomalies and are understood to be a direct consequence of the strain dependence of the nematic and the antiferromagnetic transition temperatures. A similar mechanism should more generally be expected for any phase transition tunable by strain. |
Monday, March 4, 2019 11:51AM - 12:03PM |
B10.00002: Suppression of TC in an underdoped iron-based superconductor through uniaxial strain Paul Malinowski, Shua Sanchez, Joshua Mutch, Qianni Jiang, Jong-Woo Kim, Philip Ryan, Jiun-Haw Chu The iron-based superconductors generically have been shown to host the electronic nematic phase which competes with superconductivity. Previous work has also shown that anisotropic strain is particularly well suited as a tunable, symmetry breaking field that can couple to the nematic order parameter. In this work, we present electrical transport, magnetic susceptibility, and single crystal x-ray diffraction measurements demonstrating that the superconducting transition in an underdoped iron-based superconductor is efficiently tuned towards zero temperature through the application of large, uniaxial strain that enhances the orthorhobmic distortion. This demonstrates that application of mechanical strain is a novel external parameter that is able to tune a superconductor to metal transition in a three-dimensional system. |
Monday, March 4, 2019 12:03PM - 12:15PM |
B10.00003: Elastoresistivity measurements in a 65 T pulsed magnet on Fe-based superconductors Joshua Straquadine, Johanna Palmstrom, Philip Walmsley, Alexander T Hristov, Franziska Weickert, Fedor F. Balakirev, Marcelo Jaime, Ross McDonald, Ian R Fisher One of the most striking signatures of the nematic transition in the underdoped iron-based superconductors is a diverging elastoresistivity, which is the linear response of the resistivity anisotropy to the corresponding symmetry-breaking strain. Elastoresistivity, however, cannot be measured in the superconducting state; tracking the nematic fluctuations down to the putative quantum critical point near optimal doping necessitates the use of extreme magnetic fields to suppress superconductivity. We report the first elastoresistivity experiments in pulsed magnetic fields up to 65 T on near-optimally-doped Ba(Fe1-xCox)2As2 at temperatures down to 1.3 K, and discuss the technical advances required to make such a measurement possible within the few millisecond window when the field is above Hc2. These new techniques expand the applicability of elastoresistivity measurement for disentangling the role of nematic fluctuations in strongly correlated systems. |
Monday, March 4, 2019 12:15PM - 12:27PM |
B10.00004: Changing nature of superconductivity in tetragonal FeS under pressure Makoto Shimizu, Nayuta Takemori, Daniel Guterding, Harald Jeschke Tetragonal FeS is an iron chalcogenide superconductor with similarities to FeSe but without nematic phase and with weaker electronic correlations. In contrast to pure FeSe, however, FeS shows two superconducting domes under pressure. We use electronic structure and spin fluctuation theory calculations for tetragonal FeS in order to study the nature of the superconducting order parameter [1]. In the random phase approximation, we find a gap function with d-wave symmetry at ambient pressure which is in agreement with several reports of a nodal superconducting order parameter in FeS. We find that, as a function of pressure, the superconducting pairing strength decreases until a Lifshitz transition takes place at 4.6 GPa. As a hole pocket with a large density of states appears at the Lifshitz transition, the gap symmetry is altered to sign-changing s-wave. At the same time the pairing strength is severely enhanced and increases up to a new maximum at 5.5 GPa. Therefore, our calculations explain the occurrence of two superconducting domes in FeS without any structural phase transition. |
Monday, March 4, 2019 12:27PM - 12:39PM |
B10.00005: Specific heat measurements of the high-temperature magnetic superconductor RbEuFe4As4 Kristin Willa, Roland Willa, Jinke Bao, Alexei E Koshelev, Duck Young Chung, Mercouri Kanatzidis, Wai-Kwong Kwok, Ulrich Welp We report specific heat measurements on the newly discovered magnetic superconductor RbEuFe4As4. We investigated the superconducting transition at Tc = 38K and extracted the phase boundary for in and out of plane magnetic fields and obtained an anisotropy ratio of 1.8. At small fields near the magnetic transition temperature Tm ~ 14.9K, we resolved a cusp-like behavior in the temperature dependence of the specific heat curve that shifts to lower temperatures for fields along the c-axis and a broad shoulder that shifts to higher temperatures for in-plane fields. We can reproduce our measured calorimetry data quantitatively by Monte-Carlo simulations of an anisotropic easy-plane 2D Heisenberg model that suggests that the cusp in specific heat is due to a BKT transition and the high temperature hump at higher fields marks a crossover from a paramagnetically disordered to an ordered state. |
Monday, March 4, 2019 12:39PM - 12:51PM |
B10.00006: Superconducting phase diagram of magnetically ordered superconductor RbEuFe4As4 in pulsed fields up to 65 T Matthew Smylie, Kristin Willa, Jinke Bao, Roland Willa, Alexei E Koshelev, Wai-Kwong Kwok, Duck Young Chung, Mercouri Kanatzidis, John Singleton, Fedor Balakirev, Prashanta Niraula, EIMAN Bokari, Asghar Kayani, Ulrich Welp The superconducting phase diagram of single-crystal RbEuFe4As4 (Tc ~ 36.5 K), which has long-range Eu magnetic order at Tm ~ 15 K, has been measured in pulsed magnetic fields up to 65 T using a proximity diode oscillator technique. Upon decreasing temperature, the anisotropy Hc2ab/Hc2c decreases from 1.8 near Tc towards unity indicating significant Pauli paramagnetic limiting effects for both H // (110) and H // (001). This is born out in theoretical fits for a Fermi surface in the form of warped cylinders, yielding a high in-plane Maki parameter of ~2.4, suggesting that a low temperature FFLO state may exist above 65 T. Irradiation with 5 MeV protons to a dose of 5x1016 p/cm2 suppresses Tc by ~ 3K, a substantial increase in vortex pinning and a reversal in anisotropy at temperatures below 15K. |
Monday, March 4, 2019 12:51PM - 1:03PM |
B10.00007: c-axis pressure effects on isovalent doped BaFe2(As1-xPx)2 superconductor Ding Hu, Pengcheng Dai, Zhiping Yin Superconductivity in BaFe2(As1−xPx)2 iron pnictides emerges when its nematic phase and stripe AF order at TN (Ts = TN) are gradually suppressed with increasing x, reaching optimal superconductivity around x = 0.30 with Tc ≈ 30 K. We show that a moderate uniaxial pressure along the c-axis in BaFe2(As0.70P0.30)2 spontaneously induces a 3D collinear antiferromagnetic order with TN = Ts > 30 K, while only slightly suppresses Tc. Furthermore, c-axis pressure pushes the underdoped BaFe2(As0.72P0.28)2 to optimal superconductivity with Tc = 30K without AF order firstly, then AF order emergencies at higher pressure region. We find that a c-axis pressure compresses the c-axis lattice while expanding the in-plane lattice and increasing the nearest-neighbor Fe–Fe distance, it barely changes the average iron-pnictogen height in BaFe2(As0.70P0.30)2. Therefore, the pressure-induced antiferromagnetic order must arise from a strong in-plane magnetoelastic coupling, suggesting the universal phase diagram under c-axis pressure in BaFe2(As1−xPx)2. |
Monday, March 4, 2019 1:03PM - 1:15PM |
B10.00008: Magnetotransport and structural properties of the Ni-doped FeTe0.65 Se0.35 crystals Marta Cieplak, Iryna Zaytseva, Irina Abaloszewa, Katarzyna Kosyl, Dariusz Gawryluk The structural disorder, frequently present in crystals of iron chalcogenides, sometimes leads to unexpected improvement of superconducting properties, as reported in the case of FeTe0.65Se0.35 crystals [1]. In an effort to find the origin of such behavior, here we study the structure, the Hall effect, and the angle-dependent magnetoresistance (AMR) of the Fe1−yNiyTe0.65Se0.35 crystals, with y in the range from 0 to 0.08, grown by Bridgman’s method with different cooling rates, slow (S) and fast (F). The S crystals with single, tetragonal phase show inferior superconducting properties to these shown by F crystals, in which an admixture of monoclinic phase is found. The Hall effect of crystals with y>0.03, in which superconductivity is suppressed, confirms the electron doping of both types of crystals, while the AMR is an order of magnitude larger in F crystals, with y-dependent anisotropy at low temperatures (T < 8K), which disappears on warming. The analysis of the AMR suggest that it may originate in the magnetism of monoclinic inclusions, most likely of the type Fe3(Se-Te)4. The relation of these findings to superconductivity will be discussed. |
Monday, March 4, 2019 1:15PM - 1:27PM |
B10.00009: Effect of disorder on strange metal transport in a high-temperature superconductor Nikola Maksimovic, Ian M Hayes, Vikram Nagarajan, John Singleton, Fedor Balakirev, James G. Analytis The "strange metal" parent phase of high-temperature superconductors displays a resistivity that scales linearly with temperature. Recent experiments reveal that the resistivity of these compounds also increases linearly with applied magnetic field, and is characterized by a striking scaling law between magnetic field and temperature. It has been suggested that this behavior is governed by physics beyond the standard quasiparticle picture of metals, but it is necessary to determine to what extent conventional transport theory is applicable; for example, elastic scattering from lattice imperfections typically has a well-defined effect on magnetotransport. In this study, we measure high-field transport of systematically disordered samples of a high-Tc iron-pnictide superconductor near an antiferromagnetic instability. Our data suggest that antiferromagnetic fluctuations dominate at low temperatures, producing robust transport scaling between temperature and magnetic field which is intimately tied to the onset of superconductivity. |
Monday, March 4, 2019 1:27PM - 1:39PM |
B10.00010: Precision Controlled Detwinning of Orthorhombic Twin Domains in Underdoped BaFe2As2 Shua Sanchez, Jiun-Haw Chu, Philip Ryan, Jong-Woo Kim Underdoped BaFe2As2 exhibits an orthorhombic structural phase transition driven by electronic nematic ordering. In the past, the relation between lattice distortion and electronic anisotropy above the phase transition has been studied comprehensively by the technique of elastoresistivity. In contrast, the relation between spontaneous orthorhombicity ((a-b)/(a+b)) and spontaneous resistivity anisotropy ((Ra - Rb )/ (Ra + Rb)) below the phase transition has never been measured to the same level of precision. Several previous detwinning experiments have used samples under a constant uni-axial stress, which results in additional lattice distortion especially close to phase transition. Here we present x-ray diffraction data on a crystal sample in which in-situ tunable uniaxial stress is used to precisely control the detwinning of domains. Lattice constant data showing both the relative domain populations and the elastic response to stress are matched with simultaneous resistivity measurements to yield a precise determination of the domain resistivity anisotropy. Elastoresistivity tensor coefficients are also computed in the fully detwinned single domain state, which cannot be inferred from macroscopic strain measurements alone. |
Monday, March 4, 2019 1:39PM - 1:51PM |
B10.00011: Post annealing effect on Ca(Fe1-xCox)2As2 and AeFe2As2 (Ae = Ca, Sr, Ba) single crystals Shuyuan Huyan, Liangzi Deng, Yanfeng Lyu, Zheng Wu, Hanming Yuan, Fei Tian, Yuanyuan Zhao, Kui Zhao, Jingying Sun, Melissa Gooch, James K Meen, Shuo Chen, Zhifeng Ren, Ching-Wu Chu Through post annealing & quenching process, we could induce superconductivity in the non-superconducting single crystals of Ca(Fe1-xCox)2As2 and AeFe2As2 (Ae = Ca, Sr, Ba) grown by self-flux solution method, with onset-Tc below 15 K, 16 K, 22 K and 24 K, respectively. A series of experiments were designed in order to look for the differences between as-grown samples and post annealed samples. By systematical characterization, including resistivity, Hall coefficient, magnetization, X-ray diffraction and wavelength dispersive spectroscopy results, the possible cause for the superconductivity in these samples is discussed. These experimental results help to shed light on the underlying mechanism for the repotted superconductivity in Fe-based 122 system. |
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