Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session J54: Fe-Based Superconductors: NematicityFocus Live
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Sponsoring Units: DMP Chair: Heike Pfau, Lawrence Berkeley National Laboratory |
Tuesday, March 16, 2021 3:00PM - 3:12PM Live |
J54.00001: Nanoscale decoupling of electronic nematicity and structural anisotropy in FeSe thin films Zheng Ren, Hong Li, He Zhao, Shrinkhala Sharma, Ziqiang Wang, Ilija Zeljkovic In a material prone to a nematic instability, anisotropic strain provides a preferred symmetry-breaking direction for the electronic nematic state to follow. Here we discover that electronic nematicity can be locally decoupled from the underlying structural anisotropy in strain-engineered thin films of iron-selenide (FeSe). We use heteroepitaxial molecular beam epitaxy to grow FeSe with a nanoscale network of modulations that give rise to spatially varying strain. By analyzing small atomic displacements in scanning tunneling microscopy (STM) topographs, we map the local direction and magnitude of anisotropic strain. Concomitantly, by using spectroscopic imaging STM, we visualize how electronic nematic domains arrange themselves in response to a spatially inhomogeneous strain landscape. Overall, while the domains form so that the energy of nemato-elastic coupling is minimized, there are distinct regions where electronic nematic ordering fails to “flip” direction, even though the underlying structural anisotropy has been locally reversed. We conclude by discussing the implications of this finding. |
Tuesday, March 16, 2021 3:12PM - 3:24PM Live |
J54.00002: NMR Studies of Anisotropy in FeSe Igor Vinograd, Zhipan Wang, Sarah Edwards, Tanat Kissikov, Journey Byland, Valentin Taufour, Nicholas Curro FeSe is one of the most intriguing correlated electron superconductors because superconductivity emerges from a nematic phase without any long-range antiferromagnetic order. Nevertheless, antiferromagnetic fluctuations are present that may play a role in the superconducting pairing. We report 77Se NMR spectra and relaxation rates for a high quality single crystal as a function of field orientation and temperature. |
Tuesday, March 16, 2021 3:24PM - 3:36PM Live |
J54.00003: Anomalous transport and magnetotransport of the nematic superconductors FeSe1-xSx Amalia Coldea, Matt Bristow, Oliver Humphries, Pascal Reiss, Zachary Zajicek, Amir-Abbas Haghighirad, Alix McCollam A nematic electronic state that breaks the rotational symmetry of the lattice can potentially promote unique conditions for anomalous scattering relevant for superconductivity. Here, we present magnetotransport behaviour of the superconducting FeSe1−xSx across a nematic phase transition probed in magnetic fields up to 38T. Inside the nematic phase, the transverse magnetoresistance is very large and anomalous and the Hall coefficient changes sign both as a function of temperature and substitution, beyond the expectation for a two-band model system. A region of linear resistivity is detected inside the nematic phase, where spin fluctuations are present. Near the nematic end point, the resistivity displays a T3/2 dependence [1,2,3] and the divergent critical fluctuations are suppressed by a finite nematoelastic coupling [2]. We discuss the role played by the high mobility bands and the scattering processes with spin fluctuations, phonos and impurities on the overall magnetotransport behaviour of FeSe1−xSx [3]. [1] M. Bristow et al., PRR 2,013309 (2020); [2] P. Reiss et al., Nat. Phys. 16,89 (2020); [3] A.I. Coldea, arXiv:2009.05523. |
Tuesday, March 16, 2021 3:36PM - 3:48PM Live |
J54.00004: Impact of nematicity on the relationship between antiferromagnetic fluctuations and superconductivity in FeSe0.91S0.09 under pressure Khusboo Rana, Li Xiang, Paul Wiecki, RAQUEL DE ALMEIDA RIBEIRO, Guilherme Gorgen Lesseux, Anna E. Böhmer, Sergey L. Bud'ko, Paul C Canfield, Yuji Furukawa
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Tuesday, March 16, 2021 3:48PM - 4:00PM Live |
J54.00005: Suppression of long range magnetic order accompanying structural transition in TbFeAs1-xPxO Ryan Stadel, Dmitry Khalyavin, Pascal Manuel, Qiang Zhang, Matthew Krogstad, Daniel Phelan, Raymond Osborn, Stephan Rosenkranz, Omar Chmaissem We report the results of neutron scattering on powder samples of TbFeAs1-xPxO. Many pnictide superconductors share a ubiquitous set of traits in their parent compounds. The un-doped parent compounds exhibit a structural transition from tetragonal to orthohombic between ~100-200K related to an antiferromagnetic spin density wave ordering that is either concurrent with the structural transition or at a slightly lower temperature. We find no evidence through neutron diffraction of this magnetic order at typical length scales in the Tb-1111 system. The sensitivity of our measurements allows us to rule out ordered magnetic moments above 0.08 µB. Furthermore, suppression of the structural transition by isovalent doping of phosphorous onto the arsenic site has shown no evidence of inducing the common superconductivity seen with similar doping in related materials down to 1.8K. |
Tuesday, March 16, 2021 4:00PM - 4:12PM Live |
J54.00006: Nonlinear elasto-Hall effect in Co-doped BaFe2As2 Paul Malinowski, Qianni Jiang, Yue Shi, Zhaoyu Liu, Jiun-Haw Chu It is well established that a rotational symmetry breaking electronic nematic phase is ubiquitous in the phase diagrams of iron-based superconductors and that anisotropic strain is a uniquely powerful in-situ probe of electronic anisotropy in these systems. In this work we present a new transport coefficient, the elasto-Hall coefficient, which is the response of the Hall coefficient to externally applied strain. We show that in the Co-doped BaFe2As2 system, this effect is dominated by a nonlinear response in the B2g symmetry channel which is large and strongly temperature dependent. In the optimally doped composition near the nematic quantum critical point, this nonlinear coefficient diverges towards zero temperature. Combining this elasto-Hall measurement with elastoresistivity, we argue that our observations are consistent with enhanced interband scattering from spin fluctuations as a result of B2g strain. |
Tuesday, March 16, 2021 4:12PM - 4:24PM Live |
J54.00007: Nematic fluctuations in iron-based superconductors BaFe2(As1-xPx)2 Zhaoyu Liu, Qianni Jiang, Yue Shi, Zaiyao Fei, Paul Malinowski, Joshua Sanchez, Joshua Mutch, Philip James Ryan, Jong-Woo Kim, Xiaodong Xu, Jiun-Haw Chu Nematicity is a many-body quantum phase that breaks rotational symmetry while preserving translational symmetry. It has been discovered in the phase diagrams of both iron-based and cuprate high-temperature superconductors [1-3]. In the iron-based superconductors, the optimal doping of the superconducting phase coincides with the putative nematic quantum critical point, suggesting the possibility of superconducting pairing enhanced by nematic quantum fluctuations [2,4]. However, a comprehensive study of the nematic fluctuations is still absent in the BaFe2(As1-xPx)2, which exhibits the cleanest signature of quantum criticality among all the iron-based superconductors. In this talk, I will present a detailed study of the nematic fluctuations of BaFe2(As1-xPx)2 using the elastoresistivity measurement. I will also present the study of strain dependence of superconducting Tc, which shed light on the intricate relations between nematicity and superconductivity. |
Tuesday, March 16, 2021 4:24PM - 4:36PM Live |
J54.00008: Imaging Nematic Transitions in Iron-Pnictide Superconductors with a Quantum Gas Fan Yang, Stephen Taylor, Stephen D Edkins, Johanna Palmstrom, Ian R Fisher, Benjamin L Lev The SQCRAMscope is a recently realized Scanning Quantum CRyogenic Atom Microscope that utilizes an atomic Bose-Einstein condensate to measure magnetic fields emanating from solid-state samples. Here, we combine the SQCRAMscope with an in situ microscope that measures optical birefringence near the surface of a sample to study iron-pnictide superconductors, where the relationship between electronic and structural symmetry-breaking resulting in a nematic phase is under debate. We conduct simultaneous and spatially resolved measurements of both bulk and surface manifestations of nematicity via transport and structural deformation channels, respectively. By performing local measurements of emergent resistivity anisotropy in iron pnictides, we observe sharp, nearly concurrent transport and structural transitions. More broadly, these measurements demonstrate the SQCRAMscope's ability to reveal important insights into the physics of complex quantum materials. |
Tuesday, March 16, 2021 4:36PM - 4:48PM Live |
J54.00009: Hidden antiferro-nematic order in Fe-based superconductor BaFe2As2 and NaFeAs above TS Seiichiro Onari, Hiroshi Kontani In several Fe-based superconductors, slight C4 symmetry breaking occurs at T*, which is tens of Kelvin higher than the structural transition temperature TS. In this "hidden" nematic state at TS<T<T*, the orthorhombicity is tiny [φ=(a−b)/(a+b)<<0.1%], but clear evidences of bulk phase transition have been accumulated. To explain this long-standing mystery, we propose the emergence of antiferro-bond (AFB) order with the antiferro wavevector q=(0,π) at T=T*, by which the characteristic phenomena below T* are satisfactorily explained [1]. This AFB order originates from the inter-orbital nesting between the dxy-orbital hole-pocket and the electron-pocket, and this inter-orbital bond order naturally explains the pseudogap, band-folding, and tiny nematicity that is linear in T*−T. The hidden AFB order explains key experiments in both BaFe2As2 and NaFeAs, but it is not expected to occur in FeSe because of the absence of the dxy-orbital hole-pocket. [1] |
Tuesday, March 16, 2021 4:48PM - 5:00PM Live |
J54.00010: Local structural study of Fe1.1Te using pair distribution function techniques Bhupendra Karki, Alaa Alfailakawi, Benjamin Frandsen, Joerg Neuefeind, Michelle Everett, Byron Freelon The link between electronic nematicity, magnetic and orbital order and their influence on high-Tc superconductivity is a highly controversial aspect in the physics of iron-based superconductors (FeSCs). It is believed that nematicity and superconductivity has a deep connection since optimal superconductivity occurs near nematic instabilities in FeSCs. Fe1+yTe are promising candidates to understand the mechanism of superconductivity in the family of Fe-based superconductors. Here, we used the neutron pair distribution function (PDF) techniques to study the local structure of Fe1.1Te above and below the structural transition temperature. We observed the first order transition from paramagnetic to commensurate antiferromagnetic ordering at 75 K corresponding to a tetragonal P4/nmm to monoclinic P21/m transition around 70 K. By tracking the monoclinicity parameter we observe the local scale distortions of the tetragonal and monoclinic structure in a typical range of 1-2 nm. These spatially limited distortions represent fluctuating nematic order which suggests the ubiquity of nematic fluctuations in iron-based superconductors. Our results agree well with the recent local structure study on FeSe and (Sr, Na)Fe2As2 which reveal the presence of short range orthorhombic distortions. |
Tuesday, March 16, 2021 5:00PM - 5:12PM Live |
J54.00011: Specific Heat and the Gap Structure of a Nematic Superconductor, application to FeSe Kazi Ranjibul Islam, Andrey Chubukov, Jakob Böker, Ilya Eremin We report the results of our in-depth analysis of spectroscopic and thermodynamic properties of a multi-orbital system, like FeSe, which first develops a nematic order upon lowering temperature, and then undergoes a transition into a superconducting state, which co-exists with the nematic order. We analyze the the angular dependence of the gap function and the behavior of the specific heat Cv (T) of such nematic superconductor. Specifically, we address three issues: |
Tuesday, March 16, 2021 5:12PM - 5:24PM Live |
J54.00012: Strain-tuned metamagnetic transition in EuFe2As2 Joshua J Sanchez, Gilberto F L Fabbris, Yongseong Choi, Yue Shi, Paul Malinowski, Jian Liu, Igor Mazin, Jong-Woo Kim, Philip James Ryan, Jiun-Haw Chu Of all the parent compounds of iron-based high-temperature superconductors, EuFe2As2 exhibits by far the largest magnetostructural coupling due to the strong interaction between localized Eu 4f moments and the Fe spin density wave order. However, the formation of structural/antiferromagnetic domains couples the Eu antiferromagnetic order to a series of complex field detwinning processes, which impedes a simple magnetometry measurement from extracting the critical fields of the metamagnetic transition. Here we make a measurement of these critical fields by combining x-ray magnetic circular dichroism with in-situ tunable uniaxial stress and applied magnetic field. The combination of two tuning knobs allows us to separate the stress-detwinning of structural domains from the field reorientation of Eu moments. Intriguingly, the spin flip and saturation field values reveal that in addition to the effective single ion anisotropy from a Eu-Fe biquadratic interaction, the Eu interplanar exchange is also strongly anisotropic. This anisotropic exchange term is likely a consequence of the strong anisotropy in the magnetically ordered Fe layer, revealing the non-trivial interplay between Eu-Fe magnetism in this system. |
Tuesday, March 16, 2021 5:24PM - 6:00PM Live |
J54.00013: A local structure perspective on iron pnictides and chalcogenides: Insights gained from pair distribution function analysis Invited Speaker: Benjamin Frandsen The field of iron-based superconductivity, now well into its second decade of existence, continues to challenge and stimulate condensed matter physicists. One perennial issue of debate is the origin and implications of the electronic nematic phase. This state is characterized by a spontaneous breaking of four-fold rotational symmetry, which manifests as unequal occupations of the dxz and dyz orbitals, a tetragonal-to-orthorhombic structural phase transition, and (in many cases) stripe-type magnetic order. In addition to the statically ordered nematic phase observed widely in various families of iron-based superconductors, strong nematic fluctuations have also been found in broad regions of parameter space outside the ordered nematic state. Pair distribution function (PDF) analysis of x-ray and neutron total scattering data is a proven method of studying local, short-range structural correlations that deviate from the average structure, such as the orthorhombic distortions associated with nematic fluctuations in iron-based superconductors. Here, I will present recent PDF investigations of several representative families of iron-based superconductors. The results reveal the presence of local orthorhombic distortions across large regions of temperature-composition space and provide a detailed look at the temperature dependence and characteristic length scale of these distortions. The deeper understanding of the local structure of iron-based superconductors enabled by these PDF experiments will help clarify some of the outstanding questions relating to these fascinating materials. |
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