Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Q69: Fe-based Superconductors: Topology, Fe-ChalcogenidesFocus Recordings Available
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Sponsoring Units: DMP DCMP DCOMP Chair: John Mangeri, Luxemburg Institute of Science and Technology Room: Hyatt Regency Hotel -Jackson Park A |
Wednesday, March 16, 2022 3:00PM - 3:36PM |
Q69.00001: Iron-based superconducting vortex: a nature-gifting platform for Majoranas Invited Speaker: Lingyuan Kong Iron-based superconducting vortex is emerging as a promising platform for Majorana quasiparticle. After four-year intensive studies, substantial achievements have been made on several compounds, including Fe(Te,Se), (Li,Fe)OHFeSe, CaKFe4As4and LiFeAs. For example, the discovery of integer series of quantized bound states manifests nontrivial topology of vortex zero mode, promises a hope to the field of Majorana research. In this talk, I will depict the main profile of this emerging Majorana platform, on the aspects of materials, bound states, experimental configurations, and etc. Its advantages on physics study and the major controversies owing to the practical diversity will be discussed in short. The systematic investigations accomplished on this platform is promoting the entrance to a second-phase research for manipulating Majorana zero modes in iron-based superconducting vortices. |
Wednesday, March 16, 2022 3:36PM - 3:48PM |
Q69.00002: Topological electronic structure near linear defects in iron-based superconductors Mainak Pal, Andreas Kreisel, Peter J Hirschfeld Recent experiments [1, 2] have suggested that topological superconducting states (TSS) in Fe-based superconductors may support Majorana zero modes near linear defects. Some studies [3] suggest that the defect constitutes an effective ferromagnetic chain, which is known to support Majorana end chain excitations when coupled to a superconductor in the presence of spin orbit coupling, whereas others suggest antiferromagnetic correlations may accomplish a similar goal. Ways to obtain TSS from singlet unconventional superconductors have also been proposed [4] via inversion symmetry breaking. Here we study realistic models of iron-based superconductors with linear defects within a spin-generalized and spin-rotationally invariant BdG framework, and discuss the defect-induced novel magnetic states and superconducting gap structures. |
Wednesday, March 16, 2022 3:48PM - 4:00PM |
Q69.00003: Majorana bound states in vortex lattices on iron-based superconductors Vedangi B Pathak, Stephan Plugge, Marcel Franz Majorana quasi-particles may arise as zero-energy bound states in vortices on the surface of a topological insulator that is proximity coupled to a conventional superconductor. Such a system finds its natural realization in the iron-based superconductor FeTe(0.55)Se(0.45). In this talk, I will present our recent work on vortex lattices that form in such materials, specifically discussing the emergence of Majorana vortex modes in the presence of magnetic field strength and vortex lattice disorder. I will introduce the technique of singular gauge transformation that we use for modelling vortex lattices under periodic boundary conditions that are normally forbidden. This approach allows us to go to larger vortex lattices that are otherwise inaccessible and is successful in replicating several experimental observations of Majorana vortex bound states in the FeTe(0.55)Se(0.45) platform. Our results can be related to a disordered Majorana lattice model that can be useful for further investigations on the role of interactions, and towards topological quantum computation. |
Wednesday, March 16, 2022 4:00PM - 4:12PM |
Q69.00004: Zero energy Shiba states in FeTe1-xSex Pouyan Ghaemi, Areg Ghazaryan, Ammar Kirmani, Rafael M Fernandes Motivated by recent experimental results on the topological iron-based superconductor FeSeTe, we examine the zero energy Shiba states in this compound. We show that, inside the superconducting phase, the orbital structure of the low-energy states near the Fermi energy leads to formation of zero-energy Shiba states close to the magnetic impurities. We compare the properties of such zero energy Shiba states with the available experimental results on this system. In particular, we show that the energy of Shiba states are highly sensitive to the location of the magnetic impurity in the unit cell. Moreover, the anomalous coupling of Shiba states near two nearby magnetic impurities is also discussed. |
Wednesday, March 16, 2022 4:12PM - 4:48PM |
Q69.00005: Topological Superconductivity in an Extended s-wave Superconductor and Its Implication to Iron-based Superconductors Invited Speaker: Shengshan Qin In the presence of both space and time reversal symmetries, an s-wave A1g superconducting state is usually topologically trivial. Here we demonstrate that an exception can take place in a type of nonsymmorphic lattice structures. We specify the demonstration in a system with a centrosymmetric space group P4/nmm, the symmetry that governs iron-based superconductors, by showing the existence of a second-order topological state protected by a mirror symmetry. The topological superconductivity is featured by 2Z degenerate Dirac cones on the (1,0) edge, and Z pairs of Majorana modes at the intersection between the (1,1) and (1,-1) edges. The topological invariance and Fermi surface criterion for the topological state are provided. Moreover, we point out that the previously proposed s-wave state in iron-based superconductors, which features a sign-changed superconducting order parameter between two electron pockets, is such a topological state. Thus, these results not only open a new route to pursue topological superconductivity, but also establish a measurable quantity to settle one long-lasting debate on the pairing nature of iron-based superconductors. |
Wednesday, March 16, 2022 4:48PM - 5:00PM |
Q69.00006: Elucidating the Interplay between Ferromagnetism and Superconductivity in Fe-Chalcogenide Superconductor FeTe1−xSex Camron Farhang, Nader Zaki, Peter D Johnson, Congjun Wu, Jing Xia The high-Tc family of superconductors, FeTe1−xSex, have recently been shown to display topological superconductivity, and evidence has been found for the presence of Majorana fermions, which carry the potential for the advancement of quantum-computing technology. The presence of time-reversal symmetry breaking (TRSB) is an important factor in understanding the pairing mechanisms in strongly correlated superconductors, and so it is of great interest to study the magnetic properties of FeTe1−xSex. Recent high-resolution laser-based photoemission measurements have shown the opening of a second gap at the Dirac point, suggesting the onset of TRSB which is suspected to be associated with the formation of magnetism in the surface layer. In addition, NV optical detection of magnetic resonance (ODMR) measurements have observed the coexistence of superconductivity and ferromagnetism in FeTe1−xSex. Here we perform high resolution magneto-optic Kerr effect (MOKE) and angle-resolved-photoemission (ARPES) measurements on superconducting and non-superconducting FeTe1−xSex crystals, and use these results to elucidate the relation between the onset of ferromagnetism and superconductivity in FeTe1−xSex . |
Wednesday, March 16, 2022 5:00PM - 5:12PM |
Q69.00007: Quantum imaging of an Fe-Chalcogenide topological superconductor Nathan J McLaughlin, Hailong Wang, Mengqi Huang, Eric J Lee-Wong, Lunhui Hu, Hanyi Lu, Gerald Q Yan, Genda Gu, Congjun Wu, Yizhuang You, Chunhui R Du The family of Fe-chalcogenide superconductors FeTexSe1-x possess intrinsic topological band structure, high-temperature superconductivity, and unconventional pairing symmetry, promising to develop novel, quantum-based computing strategies with improved information processing speeds and energy efficiency. To date, the magnetic properties of FeTexSe1-x have remained largely unexplored, which prevents a comprehensive understanding of their underlying material properties. Exploiting nitrogen-vacancy (NV) centers in diamond, we have performed nanoscale quantum sensing and imaging of magnetic flux generated by exfoliated FeTe0.7Se0.3 flakes, demonstrating the strong correlation between superconductivity and emergence of ferromagnetism in FeTe0.7Se0.3. The coexistence of superconductivity and ferromagnetism in an established topological superconductor provides new opportunities for exploring exotic spin and charge transport behaviors in quantum materials. |
Wednesday, March 16, 2022 5:12PM - 5:24PM |
Q69.00008: Tomonaga−Luttinger Liquid in the Topological Edge Channel of Multilayer FeSe Lian Li, Huimin Zhang, Qiang Zou A two-dimensional topological insulator exhibits helical edge states topologically protected against single-particle backscattering. Such protection breaks down, however, when electron-electron interactions are significant or when edge reconstruction occurs, leading to a suppressed density of states (DOS) at the Fermi level that follows universal scaling with temperature and energy, characteristic of Tomonaga−Luttinger liquid (TLL). Here, we grow multilayer FeSe on SrTiO3(001) by molecular beam epitaxy and observe robust edge states at both the {100}Se and the {110}Se steps using scanning tunneling microscopy/spectroscopy. We determine the DOS follows a power law, resulting in the Luttinger parameter K of 0.26 and 0.43 for the {100}Se and {110}Se edges, respectively. The smaller K for the {100}Se edge also indicates strong correlations, attributed to ferromagnetic ordering likely present due to checkerboard antiferromagnetic fluctuations in FeSe. These results demonstrate TLL in FeSe helical edge channels, providing an exciting model system for novel topological excitations arising from superconductivity and interacting helical edge states. |
Wednesday, March 16, 2022 5:24PM - 5:36PM |
Q69.00009: Quasiparticle scattering in a superconductor near a nematic critical point: resonance mode and multiple attractive channels. Dimitri Pimenov, Andrey V Chubukov, Alex Kamenev We analyze the scattering rate for 2D fermions interacting via soft nematic fluctuations. The ground state is an s-wave superconductor, but other pairing channels are almost equally attractive. This strongly alters the scattering rate: At energies beyond the pairing gap Δ, it is renormalized by contributions from all pairing channels. At energies of order Δ, it is determined by the competition between scattering into a gapped continuum and dispersing nematic resonance. The outcome is a "peak-peak-dip-hump" spectrum, similar, but not identical, to the "peak-dip-hump" structure in the cuprates. |
Wednesday, March 16, 2022 5:36PM - 5:48PM |
Q69.00010: Multifractal analysis on disordered superconductors under magnetic fields Kyungyong Park Multifractality is one of the main characteristics of the Anderson transition [1]. It is also found in several disordered superconducting materials such as monolayer niobium dichalcogenides [2]. While these results are mainly focused on the multifractal behavior of the local density of states (LDOS) this analysis has not been shown for the superconducting gaps yet. Therefore, in this talk we attempt to reveal the multifractal behavior of not only the LDOS but also superconducting gaps based on numerical simulations in real space along with scanning tunneling microscopic (STM) measurement for Fe-based superconductors. Analyzing the distribution functions and the multifractal spectrum both for LDOS and superconducting gaps, we observed that Bogoliubons become Anderson-delocalized under magnetic fields. |
Wednesday, March 16, 2022 5:48PM - 6:00PM |
Q69.00011: Origin of possible nonunitary pairing in Fe(Se,S) driving Bogoliubov Fermi surface Yifu Cao, Chandan Setty, Laura Fanfarillo, Peter J Hirschfeld FeSe based materials have been extensively studied as hosts for exotic superconducting and topological phases. Of particular interest is the finding that Fe(Se, S) upon sulfur doping exhibits a nematic quantum critical point, which separates two distinct superconducting phases on its two sides at low temperature. One of the unusual aspects of the superconducting phases is the abrupt increase in the zero energy spectral weight across the nematic QCP. We have previously proposed a mean-field level model that gives rise to Bogoliubov Fermi surfaces and is consistent with the experimental finds near the QCP. The existence of Bogoliubov Fermi surfaces in our model relies on interband as well as non-unitary triplet pairing, but identifying a microscopic model giving rise to such a state has proven elusive. Here we discuss possible microscopic Hamiltonians that preserve time reversal symmetry but break it in the ground state of nonunitary triplet pairs. |
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