Bulletin of the American Physical Society
APS March Meeting 2024
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session T01: Nematicity, Correlations and Pairing |
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Sponsoring Units: DMP Chair: Qing-Ping Ding, Ames National Laboratory Room: L100A |
Thursday, March 7, 2024 11:30AM - 11:42AM |
T01.00001: Elastocaloric evidence for symmetry breaking within the superconducting state in an optimally doped iron-based superconductor Sayak Ghosh, Matthias S Ikeda, Anzumaan R Chakraborty, Thanapat Worasaran, Florian Theuss, Luciano B Peralta, Pedro M Lozano, Jong Woo Kim, Philip J Ryan, Linda Ye, Steven A Kivelson, Brad J Ramshaw, Rafael M Fernandes, Ian R Fisher The AC elastocaloric effect (ECE) is a highly sensitive, thermodynamic probe of phase transitions under uniaxial strain, directly probing the strain derivative of the entropy proximate to a transition. We report ECE measurements across optimal doping in the archetypal iron-based superconductor, Ba(Fe1-xCox)2As2. The ECE signature at Tc for an overdoped sample is standard and quantitatively consistent with other thermodynamic probes. In contrast, for an optimally doped sample, ECE reveals a second thermodynamic transition close to Tc. No antiferromagnetic order is present at this doping level, and we further rule out re-entrant tetragonality as the origin of this transition using X-ray diffraction. Our observations strongly suggest a phase transition into a multicomponent superconducting state, thereby implying the presence of a sub-dominant pairing instability near optimal doping which exhibits a pronounced dependence on external strain. Our results thus motivate a re-examination of the pairing state and its relation to nematicity in this well-studied iron-based superconductor, while also demonstrating the power of ECE in uncovering strain-tuned phase diagrams of quantum materials. |
Thursday, March 7, 2024 11:42AM - 11:54AM |
T01.00002: Nematic-Fluctuation-Driven Superconductivity and Quantum Criticality in Fe-Based Superconductors Youichi Yamakawa, Hiroshi Kontani In various iron-based superconductors, superconducting transition temperature Tc is enlarged in the vicinity of the nematic quantum point. At the same time, exotic quantum critical behaviors appear. These observations indicate the dominant roles of the orbital and bond-order fluctuations in the electronic states. Theoretically, nematic fluctuations are induced by the "paramagnon interference mechanism", which is represented by the Aslamazov-Larkin vertex corrections (AL-VCs) [1]. The nematic susceptibility due to the AL-VCs is obtained by the density-wave (DW) equations method [1], while the "pairing interaction due to nematic fluctuations Inem" is not given by this method. |
Thursday, March 7, 2024 11:54AM - 12:06PM |
T01.00003: Observation of strain wave in the nematic phase of the iron pnictide Ba(Fe1-xCux)2As2 using dark-field X-ray microscopy Kaan A Yay, Elliot Kisiel, Matthew J Krogstad, Doga Gursoy, Stephan O Hruszkewycz, Zahir Islam, Ian R Fisher To gain a better understanding of the nematic phase in iron pnictides, we study underdoped Ba(Fe1-xCux)2As2 (Cu-Ba122) using dark-field X-ray microscopy (DFXM). DFXM is a novel technique which enables one to image the real-space distribution of a selected diffraction peak emanating from a domain within the bulk of a sample. Cu-Ba122 undergoes a tetragonal-to-orthorhombic structural phase transition at low temperature due to electronic nematicity, at which point orthorhombic twin domains form along the ab-plane. By imaging a single domain, we observed (1) micron-scale periodic spatial modulations of diffraction intensity and strain within a domain, and (2) an increase in the amplitude and period of the spatial modulations as temperature is lowered. |
Thursday, March 7, 2024 12:06PM - 12:18PM |
T01.00004: Multiband strong-coupling superconductors with spontaneously broken time-reversal symmetry Niels Henrik Aase, Kristian Mæland, Asle Sudbø States that spontaneously break time-reversal symmetry in superconducting multiband systems have been intensely researched following the experimental discovery of Fe-based superconductors (FeSCs). So far, these states have been mainly studied by means of microscopic weak-coupling BCS theory or more phenomenological effective field theories such as multi-component Ginzburg-Landau theories. However, since some FeSCs are in the strong-coupling regime, we consider if and how the spontaneous breaking of time-reversal symmetry occurs in strong-coupling theories. To elucidate these questions, we employ Eliashberg theory to search for time-reversal symmetry-breaking states in multiband systems. Deriving the free energy of multiband systems, we use it to pin down the elusive nature of such states. From our results, we discuss the relevant microscopic mechanisms at play in breaking time-reversal symmetry, with special emphasis on the FeSCs. |
Thursday, March 7, 2024 12:18PM - 12:30PM |
T01.00005: Spin and orbital degrees of freedom in FeSe: ab-initio perspective (Part-I) Abyay Ghosh, Piotr Chudzinski, Myrta Gruening FeSe is the structurally simplest quasi-two-dimensional iron chalcogenide superconductor. In spite of the structural simplicity, its phase diagram presents exotic phases (superconductivity, spin density wave, nematicity) which are the object of intense study by the condensed matter community. At fundamental level, the description of the orbital and spin degrees of freedom and of their interaction is key to understand the properties of FeSe in its different phases. |
Thursday, March 7, 2024 12:30PM - 12:42PM |
T01.00006: Spin and orbital degrees of freedom in FeSe (Part-II): field-theory perspective Piotr Chudzinski, Myrta Gruening, Abyay Ghosh Motivated by our recent ab-initio results we propose an effective field-theory model for coupled spin and orbital degrees of freedom in FeSe. Both degrees of freedom are considered to be classical 2D quantities, thus the Kosterlitz-Thouless theory of collective modes applies. We first study how small momenta fluctuations renormalize DFT bands and then we move on to topological large momentum excitations, vortexes. The DFT study revealed that we need to develop a Renormalization Group (RG) method which, simultaneously with a relevance of usual instabilities, can capture formation of vortex crystal (VC) phase. We achieve it by incorporating vortex-vortex interactions. This allows us to derive a phase diagram including VC together with effects of the standard instabilities. The theoretical method that we developed will be useful not only for the specific case of FeSe but also for other systems where large vortex fugacity regime is reachable. However advantage of FeSe is that here the RG results can be experimentally tested: they enabled us to build a bridge between our former DFT results (that works best assuming a presence of magnetic phase) and experimental measurements (which had revealed the presence of magnetism only for a finite pressure). |
Thursday, March 7, 2024 12:42PM - 12:54PM |
T01.00007: ARPES view on electronic correlations in the iron-based superconductor RbFe2As2 – kinks, Hubbard bands, and electron localization Ming-Hua Chang, Steffen Backes, Donghui Lu, Nicolas Gauthier, Makoto Hashimoto, Brian Moritz, Guan-Yu Chen, Hai-Hu Wen, Sung-Kwan Mo, Zhixun Shen, Roser Valentí, Heike Pfau The electronic structure of iron-based superconductors is characterized by an interplay of Coulomb interaction and Hund’s rule coupling acting on a multiband system. It is currently debated which role electronic correlations play in the complex phase diagrams that contain superconducting, nematic, and magnetic phases as well as strange metal behavior. Correlation effects are particularly pronounced in the hole-doped AFe2As2 (A=K,Rb,Cs), which show large effective masses. We present a comprehensive ARPES study on RbFe2As2 and compare the results to DMFT. Our data reveal the existence of Hubbard bands. Their intensity increases with increasing temperature at the expense of quasiparticle spectral weight. The quasiparticle peak of the Fe 3dxy orbital is absent above 90K. We demonstrate that the electrons localize into the Hubbard bands across this coherent-incoherent transition. In addition, we identify two kinks in the dispersion of the dxz/yz orbital. The low energy kink strongly renormalizes the quasiparticle dispersion well beyond a weak-coupling description. We will discuss possible origins. The high-energy kink initiates a waterfall structure that separates the quasiparticle peak from the Hubbard bands. The kink is induced by electronic interactions. Our study reveals key signatures of electronic correlations in the spectral function of RbFe2As2 and provides a link between iron-based superconductors and other correlated systems such as cuprates, nickelates, and heavy fermions. |
Thursday, March 7, 2024 12:54PM - 1:06PM |
T01.00008: Unique interplay between magnetic irreversibility and vortex behaviour in the ferromagnetic Fe-based superconductor EuFe2(As1-xPx)2 Joseph A Wilcox, Tong Ren, Tsuyoshi Tamegai, Sven Friedemann, Milorad V Milošević, Simon J Bending The EuFe2(As1-xPx)2 system features a complex phase diagram characterised by various magnetically-ordered phases. Intriguingly, within the range of approximately 0.15 < x < 0.3, a region of superconductivity emerges, reaching a maximum transition temperature of Tc ≈ 25 K at x ≈ 0.21. Notably, this superconducting dome overlaps with a ferromagnetic phase that onsets at TFM ∼ 19 K. |
Thursday, March 7, 2024 1:06PM - 1:18PM |
T01.00009: Synthesis and physical properties of the Li1-xTMxFeAs, TM=Cu, Mn MING LIU, Morozov I V Polycrystalline Li1-xTMxFeAs with a degree of substitution x = 0, 0.05, 0.1, 0.3. 0.5 for TM = Cu and x = 0, 0.05, 0.1, 0.3. 0.5, 0.7, 1 for TM = Mn were prepared by two-stage solid state synthetic approach. According to the SEM, specimens consisted of partially sintered lamellar microcrystals having dimensions of 5-20 μm. The EDX analysis of individual microcrystals showed that for all samples the atomic iron content was equal to the content of arsenic, and the content of TM deviated from the nominal content by not more than 2.5%. |
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