Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session S69: Fe-based Superconductors: Nematicity in 122 SystemsFocus Recordings Available
|
Hide Abstracts |
Sponsoring Units: DMP DCMP DCOMP Chair: Andreas Kreisel, Univ Leipzig Room: Hyatt Regency Hotel -Jackson Park A |
Thursday, March 17, 2022 8:00AM - 8:36AM |
S69.00001: Probing nematicity and magnetism with combined tunable strain and x-ray scattering/fluorescence techniques Invited Speaker: Joshua J Sanchez In this talk I will review our recent progress at the Advanced Photon Source in combining in situ tunable uniaxial stress with simultaneous transport measurements and several synchrotron x-ray techniques to perform unique characterizations of several iron-based superconductors. In Co-doped BaFe2As2 we use x-ray diffraction (XRD) to carefully monitor the strain detwinning of the orthorhombic structural domains and make a precise determination of the spontaneous resistivity anisotropy across temperature within the nematic phase. In EuFe2As2 we use x-ray magnetic circular dichroism (XMCD) to make the first observation of a magnetic field-induced spin flip transition of antiferromagnetic Eu moments in a strain-detwinned sample. In Co-doped EuFe2As2 we use XMCD to monitor the magnetic field-induced reorientation of ferromagnetic Eu moments from out of plane to in-plane, which we correlate with a strain-tunable field-induced superconductivity. Finally, in FeSe we combine XRD and x-ray linear dichroism (XLD) to observe the nematic orbital polarization anisotropy within the nematic phase across a range of strain and detwinning values. This unique combination of tuning and probing techniques has so far given new insight into these interesting materials and presents a new approach to answering unresolved questions in iron-based superconductors and beyond. |
Thursday, March 17, 2022 8:36AM - 8:48AM |
S69.00002: Nematicity and charge density wave in BaNi2As2 Yucheng Guo, Mason Klemm, Ji Seop Oh, David J Singh, Yaofeng Xie, Robert G Moore, Sergey Gorovikov, Tor Pedersen, Matteo Michiardi, Jonathan D Denlinger, Makoto Hashimoto, Donghui Lu, Sung-Kwan Mo, Robert J Birgeneau, Pengcheng Dai, Ming Yi Unconventional superconductivity always emerges in proximity to emergent electronic orders. In the iron-based superconductors, a ubiquitous intertwined order persists that consists of a C4-symmetry breaking structural transition and collinear spin-density wave. BaNi2As2, like its well-known iron-based superconductor analogue, BaFe2As2, also hosts a C4-symmetry-breaking structural transition coupled to a unidirectional charge density wave (CDW), providing an exciting platform to study the interplay of nematicity and CDW. In this talk, I will present our systematic angle-resolved photoemission spectroscopy study of the BaNi2As2 system. In particular, we report clear spectroscopic signatures that correspond to the distinct structural and CDW transitions. In addition, I will also present a comparison of the electronic structure measurements in the presence and absence of an external uniaxial strain and discuss the implications of the existence of nematic fluctuations in this system. |
Thursday, March 17, 2022 8:48AM - 9:00AM |
S69.00003: Tuning the superconducting dome of Ba(Fe1-xCox)2As2 with symmetric and antisymmetric strain Paul T Malinowski, Qianni Jiang, Zhaoyu Liu, Jiun-Haw Chu We present comprehensive doping dependence in Ba(Fe1-xCox)2As2 of superconducting Tc versus strain for uniaxial stress along both [100] and [110] crystallographic axes. The response for stress along [100] is dominated by a linear response to the symmetric A1g strain, demonstrating a systematic doping dependence suggesting that A1g strain and composition act similarly as tuning parameters across the whole superconducting dome. Moreover, this linear response becomes very large in the heavily overdoped region of the phase diagram; for x = 0.124, 1% of strain modulates Tc by 30%. In contrast, the behavior for stress along [110] demonstrates a nonlinear response to the antisymmetric B2g strain in addition to the linear A1g contribution. This nonlinear contribution diverges towards optimal doping where superconductivity is insensitive to A1g strain but extremely sensitive to the anisotropic B2g strain enhancing nematic order. Additionally, we identify a qualitative difference between the two types of strain-tuned transitions; B2g strain significantly broadens the transition while A1g strain does not. |
Thursday, March 17, 2022 9:00AM - 9:12AM |
S69.00004: Elastocaloric measurements of BaFe2(As1-xPx)2 Elliott W Rosenberg, Zhaoyu Liu, Qianni Jiang, Jiun-Haw Chu The isovalently substituted iron-based superconductor family BaFe2(As1-xPx)2 provides a clean system to investigate the interplay between magnetic and nematic quantum criticality and high-Tc superconductivity. Notably, although the AFM and structural phase transitions occur simultaneously in a first order transition across the doping phase diagram, inducing B2g strain smears the structural transition into a crossover, while the AFM transition remains sharply identifiable. We present measurements of this system via the AC elastocaloric effect, a recently developed thermodynamic probe which is sensitive to strain derivatives of the entropy. This technique, which can sensitively track the antiferromagnetic phase transition as strain is applied, establishes that 1/TNo (dTN/dεB2g) increases by nearly 6-fold as optimal doping is approached. These measurements also show that the thermodynamic nematic susceptibility decreases as optimal doping is approached, in contrast to simultaneous elastoresistivity measurements in which 1/ρo(dρB2g/dεB2g) increases in magnitude. This suggests that the resistivity anisotropy/order parameter proportionality constant increases dramatically towards optimal Tc, which has been shown to be the case as well in the more disordered Co-doped Ba122 system. |
Thursday, March 17, 2022 9:12AM - 9:24AM |
S69.00005: Emerging giant symmetric strain response in strongly hole-doped iron-based superconductors Anna Böhmer, Paul Wiecki, mehdi frachet, Thomas Wolf, Amir A Haghighirad, Christoph Meingast, Frank Weber, Michael Merz, Rolf Heid The symmetry channel and strength of nematic fluctuations, as well as possible nematic order, in the strongly hole-doped iron-based superconductors remain obscure. We address these questions using transport measurements under elastic strain and elucidate the evolution of the elastoresistance induced by hole doping BaFe2As2 from optimal to the fully overdoped end-members AFe2As2 (A = K, Rb, Cs) [1,2]. Our technical development takes into consideration the extreme thermal expansion of some of these compounds [1]. By decomposing the strain response into the appropriate symmetry channels, we demonstrate the emergence of a giant in-plane symmetric contribution, associated with the growth of strong electronic correlations and their growing strain-sensitivity. We find weakened remnants of the nematic fluctuations that are present at optimal doping, but no change in the symmetry channel of nematic fluctuations with hole doping [2]. Furthermore, we find no indication of a nematic ordered state in the AFe2As2 (A = K, Rb, Cs) superconductors above Tc. |
Thursday, March 17, 2022 9:24AM - 9:36AM |
S69.00006: Field-induced suppression of the C2-reentrant phase in Ba1-xKxFe2As2 Kristin Willa, Roland Willa, Frederic Hardy, Liran Wang, Thomas Wolf, Peter Schweiss, Christoph Meingast Hole doped Fe-based 122 materials all reveal in a narrow doping concentration a low temperature transition from the usual orthorhombic C2-stripe magnetic phase into a magnetic double-Q phase, in which the C4 symmetry is restored. Ba1-xKxFe2As2 is special, because here superconductivity induces a transition from this double-Q phase back into the C2-stripe phase [1]. By applying a magnetic field, we investigate how the delicate balance between these competing phases changes. In particular, we present specific heat and thermal expansion measurements with applied magnetic fields of up to 10T along the [100] and [001] direction. While a suppression of the orthorhombic phase is observed for both field directions, the orthorhombic distortion itself behaves very anisotropic. It is largely suppressed for fields along [001] while being slightly enhanced for in-plane fields. In addition to the measurements we present a phenomenological model that qualitatively reproduces the observed thermodynamic measurements and the phase diagram. [1] Böhmer et al., Nature Communications, 6, 7911 (2015) |
Thursday, March 17, 2022 9:36AM - 9:48AM |
S69.00007: Nematic correlation length in hole-doped and isovalent-doped superconductors Shan Wu, Yu Song, Yu He, Ming Yi, Frano Alex, Xiang Chen, Hiroshi Uchiyama, Ahmet Alatas, Ayman H Said, Liran Wang, Thomas Wolf, Christoph Meingast, Nikola Maksimovic, James G Analytis, Alfred Q Baron, Daisuke Ishikawa, Robert J Birgeneau Abundant evidence indicates that nematic fluctuations are closely related to unconventional superconductivity (SC). For carrier-doped iron-based superconductors, the underdoped phase is widely inhabited by intertwined nematic and magnetic orders. In isovalent-doped samples, in which chemical disorder plays a less role, optimal SC appears near a putative nematic quantum critical point. The strength of the nematic fluctuations, characterized by the nematic susceptibility χ, reveals a marked enhancement upon cooling. However, the spatial dependence of the nematic fluctuations, namely the nematic correlation length ξ has only recently been measured by Fernandes and Reznick through the in-plane transverse acoustic phonon (IPTA). We studied the IPTA phonon via inelastic X-ray, and observed a softening of phonons in Sr1-xNaxFe2As2 samples. Building on earlier work, we extract both χ and ξ simultaneously by an exact mean field method of analysis without additional inputs. We find a large nematic susceptibility persisting in the AFM-T phase, and a short nematic correlation length ξ ~ 10 Å that is much smaller than that on the electron-doped side. Finally, we will present recent measurements on isovalent-doped BaFe2(As1-xPx)2 superconductors. These results indicate that short-range nematic fluctuations may be an important ingredient favorable for superconductivity. |
Thursday, March 17, 2022 9:48AM - 10:00AM |
S69.00008: Phonon softening and possible nematicity in BaNi2(As1-xPx)2 Christoph Meingast, Liran Wang, Anmol Shukla, Kristin Willa, Frederic Hardy, Tom Lacmann, Michael Merz, Amir Haghighirad, Thomas Wolf BaNi2As2 undergoes a series of charge-ordering phase transitions upon cooling, first from a tetragonal to an incommensurately charge-ordered orthorhombic phase and then to a commensurate triclinic phase [1]. The suppression of these phase transition by either P-substitution of As, or by Sr-substitution of Ba leads to an increase of Tc up to about 3.5 K, which has been attributed to either soft phonon behavior [2] or B1g nematic fluctuations [3]. Here we study P-substituted BaNi2As2 using high-resolution thermal expansion, Young's modulus, heat capacity and transport measurements, from which a detailed phase diagram is obtained. Both the phonon softening (via a Grueneisen analysis) and the question of nematicity (via Young's modulus data) will be addressed. |
Thursday, March 17, 2022 10:00AM - 10:12AM |
S69.00009: Quantum critical fluctuations in an Fe-based superconductor Leander Peis, Daniel Jost, Rudolf U Hackl We show that the characteristic scaling of a marginal Fermi liquid is present in inelastic light scattering data of an Fe-based superconductor tuned through a QCP by chemical doping. From the doping dependence of the imaginary time dynamics we were able to distinguish regions dominated by quantum critical behavior from those of classical critical responses. This dichotomy reveals a connection between the marginal Fermi liquid behavior and quantum criticality. In particular, the overlap between regions of high superconducting transition temperatures and quantum critical scaling suggests a contribution from quantum fluctuations to the formation of superconductivity. |
Thursday, March 17, 2022 10:12AM - 10:24AM |
S69.00010: Contrasting the signatures of nematic order in 122 iron pnictides and 11 iron chalcogenides: a group theoretical analysis Fan Yang, Morten Holm Christensen, Rafael M Fernandes, Turan Birol Iron-based unconventional superconductors (FeSC) continue to draw interest because of the exotic electronic phases they host. The nematic order, which lowers the 4-fold rotational symmetry of the crystal structure, is widely observed in the normal phase of different FeSC families. Experiments reveal strong in-plane electronic anisotropy upon the onset of nematicity, however, a complete symmetry analysis of how the band structures of different FeSC families are affected by different types of nematic order parameters is still missing. In this work, we use group theory to contrast signatures of nematic order on the band dispersions of FeSC with space group P4/nmm (such as FeSe) and space group I4/mmm (such as BaFe2As2). We also perform density functional theory calculations to extract coefficients that determine the nematic-induced splittings of the relevant band degeneracies. Our predictions shed light on the interpretation of observed electronic degeneracies in these systems. |
Thursday, March 17, 2022 10:24AM - 10:36AM |
S69.00011: Using Nuclear Quadrupolar Resonance, Combined with First Principles Calculations, to Investigate Spin Fluctuation Dynamics in Iron Pnictides Jaafar N Ansari, Igor Mazin, Karen L Sauer Magnetic and superconducting properties of Fe-based superconductors are linked to spin fluctuations. Long-range slow Mermin-Wagner fluctuations (MWF), due to continuous degeneracy of the Heisenberg Hamiltonian, are believed to play a key role in the “nematic” phase, but also in the paramagnetic one close to the transition, and in the reduction of the ordered moments compared to fluctuating local ones. It is crucial to understand how low in frequency MWF extend. A finite asymmetry of the electric field gradient was reported in Ba(Fe1-xCox)2As2 even in the tetragonal phase [1]. We explain this odd result in terms of the MWF tail being slower than anticipated, so even at the typical nuclear quadrupole resonance (NQR) frequency ν = 2-3 MHz there remains a residual stripe order. This tail can be characterized by an effective moment M emerging from averaging spin fluctuations faster than ν. We calculate M as a function of T and Co x in Ba122 by comparing the experimental NQR data with modified DFT calculations with tunable Stoner interaction, both in the antiferro- and paramagnetic phase. We also compare the extracted M with those from neutron studies (i.e., averaged over all spin fluctuations). |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700