Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session D28: Fe-Based Superconductors: Topological Superconductivity and Competing Phases |
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Sponsoring Units: DMP Chair: He Zhao, Brookhaven National Laboratory Room: Room 220 |
Monday, March 6, 2023 3:00PM - 3:12PM |
D28.00001: Strain-tuned vortex Majorana modes in Iron-based superconductor Wenyao Liu Iron-based superconductors (FeSC) with topological bands have become one of the most promising platforms for studying Majorana quasiparticles, owing to their intrinsically large topological gap between the Majorana zero mode (MZMs) and other bound states. However, a practical implementation of braiding remains elusive due to the inhomogeneity of current compounds, and the lack of control over MZMs. In this talk, we present our work of controlling topological band structure and vortex MZMs for topological FeSC LiFeAs by in-situ strain method. By performing ARPES and STM on LiFeAs under strain, we realized the controlling of the topological-Dirac-band in LiFeAs, thus we are capable to induce the topological phase transition and find that the MZMs are corrodingly tuned inside vortices. Our work for the controllable Majorana modes by strain not only directly reveals the significant relationship between the vortex zero modes and superconducting topological surface state, but also should enlighten the applicable design of FeSCs device for the future MZM-braiding experiment. |
Monday, March 6, 2023 3:12PM - 3:24PM Author not Attending |
D28.00002: The optical conductivity of (K,Rb,Cs)Fe2As2 Ricardo Lobo We measured the temperature dependence of the optical conductivity of XFe2As2 iron pnictides, where X = K, Rb, and Cs. A two-Drude analysis of the data quantitatively describes the data of all compositions. From this analysis, we extracted the scattering rate and effective mass for each Drude contribution. Both our parameters and the overall optical conductivity are compared to first principles DMFT calculations. We discuss the tempeature behavior of the scattering rate as a funciton of X. The comparison of the full optical conductivity to DMFT caculations allows us to infer the evolution of the electronic correlations strength with ionic replacement. |
Monday, March 6, 2023 3:24PM - 3:36PM |
D28.00003: Rationalizing doping and electronic correlations in LaFe2As2 Luca de' Medici, Tommaso Gorni, Diego Florez-Ablan We compute the electronic properties of the normal state of uncollapsed LaFe2As2, taking into account local dynamical correlations by means of slave-spin mean-field+density-functional theory. Assuming the same local interaction strength used to model the whole electron- and hole-doped BaFe2As2 family, our calculations reproduce the experimental Sommerfeld specific heat coefficient, which is twice the value predicted by uncorrelated band theory. We find that LaFe2As2 has a reduced bare bandwidth and this solves the apparent paradox of its sizeable correlations despite its nominal valence d6.5, which would imply extreme overdoping and uncorrelated behaviour in BaFe2As2. Our results yield a consistent picture of the whole 122 family and point at the importance of the correlation strength, rather than sheer doping, in the interpretation of the phase diagram of iron-based superconductors. |
Monday, March 6, 2023 3:36PM - 3:48PM |
D28.00004: Observation of superconducting vortices carrying a temperature-dependent fraction of the flux quantum Yusuke Iguchi, Ruby A Shi, Kunihiro Kihou, Chul-Ho Lee, Mats Barkman, Andrea Benfenati, Vadim Grinenko, Egor Babaev, Kathryn A Moler This work investigates isolated vortices in the hole-overdoped Ba1-xKxFe2As2 (x=0.77) by using scanning superconducting quantum interference device (SQUID) magnetometry. At low field, we observed vortices that were well separated from their neighbors. In many locations, we observed vortices that carried only part of a flux quantum, with a magnitude that varied continuously with temperature. We interpret these features as vortices with non-quantized magnetic flux, sometimes called fractional or partial vortices whose magnitude is determined by the temperature-dependent parameters of a multiband superconductor. We further characterize the mobility and manipulability of the fractional vortices. |
Monday, March 6, 2023 3:48PM - 4:00PM |
D28.00005: Soft-phonon and charge-density-wave formation in nematic BaNi2As2 Tom L Lacmann, Sofia M Souliou, Rolf Heid, Christoph Meingast, mehdi frachet, Luigi Paolasini, Amir A Haghighirad, Michael Merz, Alexei Bosak, Matthieu Le Tacon Signatures of nematic fluctuations have now been observed in various families of superconductors and have triggered intense investigations on the role of nematicity in the pairing mechanism. The superconductor BaNi2As2 (Tc = 0.6 K), a candidate system for charge-driven electronic nematicity, is a nonmagnetic, isostructural analogy of BaFe2As2. Instead of a spin density wave an incommensurate charge density wave (I-CDW) that orders in vicinity to a tetragonal to orthorhombic phase transition is observed [1-3]. We use diffuse and inelastic x-ray scattering to study the formation of the I-CDW in BaNi2As2. We present the evolution of the diffuse scattering at the I-CDW wave vector which is already present at room temperature and the continuous softening of the unstable phonon branch [4]. For the same phonon branch at the Γ-point recentlly a unsual large splitting emerging from a coupling with nematic fluctuations is reported [5]. The phonon instability and its reciprocal space position is well captured by our ab initio calculations. These however indicate that neither Fermi surface nesting, nor enhanced momentum-dependent electron-phonon coupling can account for the I-CDW formation, demonstrating its unconventional nature. |
Monday, March 6, 2023 4:00PM - 4:12PM |
D28.00006: Quantum critical behavior of the charge-density-wave in Fe-doped BaNi2As2 Christoph Meingast, Liran Wang, Frederic Hardy, Anna E Böhmer, Michael Merz, Thomas Wolf, Peter Schweiss BaNi2As2 has recently received considerable attention due to unconventional charge density wave (CDW) transitions, a proposed nematic-liquid state, as well as nematicity and/or soft phonon strongly enhanced superconductivity [1-8]. Here we investigate Fe-doped BaNi2As2 using various thermodynamic and transport probes. In contrast to P- and Sr-substituted BaNi2As2 , the suppression of the CDWs occurs smoothly to zero temperature, terminating at a second-order quantum phase transition (QPT). We find anomalously large, and sign-changing, phonon Grüneisen parameters at this QPT, suggestive of a novel CDW/structural quantum phase transition. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D28.00007: High temperature resistivity of electron doped BaFe2As2 based superconductors Makariy A Tanatar M. A. Tanatar, E. H. Krenkel, S. L. Bud’ko, P.C. Canfield, R. Prozorov [1] M. A. Tanatar, N. Ni, A. Thaler, S. L. Bud’ko, P. C. Canfield, and R. Prozorov, Phys. Rev. B82, 134528 (2010). |
Monday, March 6, 2023 4:24PM - 4:36PM |
D28.00008: Smectic pair density wave order in EuRbFe4As4 He Zhao, Raymond E Blackwell, Shigeyuki Ishida, Akira Iyo, Hiroshi Eisaki, Abhay N Pasupathy, Kazuhiro Fujita Pair density wave (PDW) is an exotic state of matter featuring a spatially modulated gap induced by superconducting pairs with nonzero center-of-mass momentum in equilibrium, predicted initially by Fulde, Ferrel, Larkin and Ovchinnikov. Experimental evidence demonstrate that such state exists in high magnetic field and break the translational symmetry of the lattice. However, to our knowledge, the existence of PDW states in the absence of external magnetic field has not been reported. Utilizing scanning tunneling microscope/microscopy (STM/S), we study such zero-field PDW state in a magnetic iron-based superconductor — EuRbFe4As4 (ER1144), which has coexisting helical magnetism (Tm ~15K) and superconductivity (Tc ~ 37K). In this material, at low temperature, we observed a long range, unidirectional, modulated superconducting gap with an incommensurate period of ~8 unit cells. Both our STM/S results and other bulk measurements show the absence of charge or spin density waves, indicating that the PDW state in ER1144 is a primary, zero-field superconducting instability, in contrast to previous PDW measurements in cuprates, Kagome materials and charge density wave materials. Interestingly, we found that the PDW state is absent inside the vortex core upon applying external magnetic field. When the temperature rises above the Tm, the spatial modulations are completely suppressed but only a uniform superconducting gap survives. And both four-fold rotational symmetry and translational symmetry recover, indicating that the PDW is a smectic order. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D28.00009: Strain-Switchable Field-Induced Superconductivity Joshua J Sanchez, Paul Malinowski, Yue Shi, Gilberto Fabbris, Yongseong Choi, Jong-Woo Kim, Philip J Ryan, Igor I Mazin, Yina Huang, Jiun-Haw Chu The generation of new phases in quantum materials by external tuning parameters has become a central focus of condensed matter physics. Here, we demonstrate field-induced superconductivity at T = 10 K and B = 0.27 T which can be turned on and off by applying uniaxial stress. We use a sample of Eu(Fe0.85Co0.15)2As2 in which ferromagnetism and superconductivity coexist in a delicate balance. We combine tunable uniaxial stress and applied magnetic field to induce superconductivity above the zero-field transition temperature. We identify the Eu moment alignment as the mechanism of the field-induced superconductivity by using x-ray magnetic circular dichroism to monitor the field reorientation of Eu moments from out of plane to in-plane. Finally, we do a comprehensive x-ray diffraction characterization of the lattice response to stress and show how strain applied in the B1g symmetry channel can suppress nematic order which likely enhances superconductivity. This result presents this material as a platform for switchable field induced superconductivity. |
Monday, March 6, 2023 4:48PM - 5:00PM |
D28.00010: Phenomenological theory of magnetic 90° helical state in RbEuFe4As4 Alexei E Koshelev Helical state with 90° turn angle between magnetic moments in the neighboring Eu layers is formed in the superconducting iron arsenide RbEuFe4As4. Such spin state is not realized within the standard Heisenberg model with bilinear exchange interactions and requires the biquadratic interaction term. In addition, the helix orientation may be fixed by the in-plane four-fold anisotropy term. We explored a rich phase diagram for such a state in the magnetic field applied perpendicular to the helix direction. The magnetic field induces the metamagnetic transition to the double-periodic state with the moment angles (α, α, - α, - α) with respect to the field for the four subsequent spins at the transition field determined by the strength of biquadratic interaction. The transition is second order for small biquadratic coupling and becomes first order when this coupling exceeds the critical value. On the other hand, at high magnetic fields, the aligned state becomes unstable with respect to formation of an incommensurate fan state which transforms into the double-periodic state with decreasing magnetic field. In addition, when the magnetic field is applied along one of four the equilibrium moment directions, the deformed helix state experiences the first-order rotation transition at the field determined by the four-fold anisotropy. We will discuss possible experiments to detect these metamagnetic transitions. |
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