Bulletin of the American Physical Society
2024 APS March Meeting
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session S01: FeSe: S Substitution and Spectroscopic ProbesFocus
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Sponsoring Units: DMP Chair: Joshua Ballard, Zyvex Labs Room: L100A |
Thursday, March 7, 2024 8:00AM - 8:36AM |
S01.00001: Unconventional Signatures of a Quantum Griffiths Phase in the Vicinity of a Quenched Nematic Quantum Critical Point Invited Speaker: Pascal Reiss Upon suppression of a continuous electronic phase transition towards 0K, for example through hydrostatic pressure as an external tuning parameter, a quantum critical point (QCP) occurs in many different material classes. These points constitute a fascinating research area as the diverging quantum fluctuations and electronic correlations could be linked to many unconventional and exciting quantum phases, including the emergence of high-Tc superconductivity. Nevertheless, even more exotic phase may be expected if the symmetry of the electronic order parameter allows for a bilinear coupling to the structural degrees of freedom. The electronic nematic order, ubiquitous in the iron-based superconductors, is one such candidate, where long-range interactions can be mediated through the lattices shear modes. |
Thursday, March 7, 2024 8:36AM - 8:48AM |
S01.00002: Tuning nematic electronic phases, electronic correlations and shifting the dxy hole band via isoelectronic substitution in FeSe1-xSx and FeSe1-xTex Amalia I Coldea Electronic nematic phase of iron-chalcogenides superconductors can be finely tuned via isoelectronic substitution and their electronic behaviour can be explored in detail via angle-dependent photoemission spectroscopy and quantum oscillations [1,2]. In this talk, I will compare angle-resolved photoemission studies probing the nematic electronic phase of FeSe1-xSx versus FeSe1-xTex [3,4,5]. I will discuss the evolution of the electronic bands, the quasiparticle effective masses as well as the sensitivity of the dxy hole band to the chalcogen height. We find that the dxy hole band shifts significantly with increasing the chalcogen height and it could be involved in promoting an additional pairing channel and enhance the density of states to stabilize the second superconducting dome in FeSe1−xTex systems [5]. This is in contrast to FeSe1-xSx series, where the dxy band does not shift and there is no enhancement in superconductivity outside the nematic phase, despite both series displaying large nematic susceptibility at the nematic end point. |
Thursday, March 7, 2024 8:48AM - 9:00AM |
S01.00003: Non-mean-field-like gap formation in the ultra-nodal pairing state of tetragonal FeSe1-xSx Shigeru Kasahara, Kazuto Akiba, Yuya Kitanishi, Kaoru Tanaka, Hideaki Fujii, Tatsuo C Kobayashi, Takumi Kihara The isovalently substituted FeSe1-xSx superconductors have attracted significant interest due to various exotic properties associated with the intertwining of nematicity, magnetism, and unconventional superconductivity [1]. Of particular interest is the abrupt change in the superconducting gap function that occurs at the nematic critical point at xc ~ 0.17 [2-6], above which the formation of an ultra-nodal pairing state with a putative Bogolubov Fermi surface has been proposed [5-10]. Although the emergence of the Bogoluvov Fermi surface appears to reasonably explain the huge residual density of states observed in the tetragonal FeSe1-xSx, the nature of the exotic pairing state remains largely elusive, including the links between the ultra-nodal state and the colossal fluctuation-like behavior reported in the previous experiments [11]. Here, using the high-quality single crystals of FeSe1-xSx and the precise measurements of thermodynamic and charge transport properties, we discuss the gap formation of the ultra-nodal pairing state, which deviates from the mean-field-like behavior. In addition, we report the evolution of the superconducting gap in FeSe1-xSx under high pressures, where striking enhancement of Tc is found in the non-magnetic tetragonal regime [12]. The results provide fresh insights into our understanding of the ultra-nodal pairing state. |
Thursday, March 7, 2024 9:00AM - 9:12AM |
S01.00004: Unconventional Superconductivity near a Nematic Instability in a Multi-Orbital system Kazi Ranjibul Islam, Andrey V Chubukov We analyze superconductivity in a multi-orbital fermionic system near the onset of a nematic order, using doped FeSe as an example. We |
Thursday, March 7, 2024 9:12AM - 9:24AM |
S01.00005: Two-fold rotational symmetric Bogoliubov Fermi surface in tetragonal Fe(Se,S Yifu Cao, Chandan Setty, Laura Fanfarillo, Andreas Kreisel, Peter J Hirschfeld The intriguing iron based superconductor FeSe exhibits rich phenomena at low temperatures upon chemical pressure, including time reversal symmetry breaking, nematic criticality and topological phases. For sufficiently large S-substitution, the system recovers C4 symmetry in its normal state, and at the same time acquires a nonzero density of states at zero energy at zero temperature in its superconducting state, consistent with the existence of a so-called Bogoliubov Fermi surface (BFS). Recent angle-resolved photoemission (ARPES) experiments has found more direct evidence for BFSs in such materials, but despite the tetragonal normal state, the BFSs seems to be curiously only two-fold symmetric. In this work we search for a microscopic model that can support the coexistence of singlet pairing with other orders, including interband nonunitary triplet pairing with magnetization, and discuss several candidates that indeed stabilize ground states with BFSs. We show that with proper choice of the coupling strength of the various orders in our model, spontaneous breaking of C4 rotational symmetry is realized at low temperatures. This feature resembles the findings of recent ARPES experiments. |
Thursday, March 7, 2024 9:24AM - 9:36AM |
S01.00006: Decoding Chemical Inhomogeneity in Iron Chalcogenides: Insight from Self-Organizing Map Analysis of STM/S Data Pedram Tavadze, Qiang Zou, Basu D Oli, Joseph A Benigno, Lian Li Chemical pressure from the isovalent substitution in the epitaxial film iron chalcogenide can effectively tune their properties. However, such substitution during epitaxial growth inherently leads to chemical inhomogeneity, making the determination of alloy composition and substitutional sites challenging. To address this issue, we have employed two-step machine learning solution using K-mean and SVD [1,2] to analyze scanning tunneling microscopy/spectroscopy (STM/S) data. In this study, we introduce a different approach using self-organizing map (SOM), a type of artificial neural network, to discern the Se/S ratio in superconducting single layer FeSe1-xSx alloys. Similar to previous methodologies, this unsupervised competitive learning method can determine the Se/S ratio effectively. However, this SOM-based approach offers an improved approach to interpret non-linear STM data, while eliminating the need to pre-specify the number of clusters. |
Thursday, March 7, 2024 9:36AM - 9:48AM |
S01.00007: Visualizing superconductivity mediated by nematic fluctuations in the Fe-based superconductor FeSe1-xSx: Part 1 Kirsty Scott, Pranab Kumar Nag, Vanuildo S. de Carvahlo, Journey K Byland, Xinze Yang, Morgan Walker, Aaron G Greenberg, Peter Klavins, Eduardo Miranda, Adrian Gozar, Valentin Taufour, Rafael M Fernandes, Eduardo H Da Silva Neto The FeSe1-xSx system presents an ideal platform for studies of intertwined nematicity and superconductivity, a topic of ongoing interest in Fe-based superconductors, due to the lack of magnetic ground state at ambient pressure. In the parent compound FeSe, the superconductivity, mediated by spin fluctuations, coexists with a nematic phase. S-substitution (x) in FeSe1-xSx suppresses the nematic phase at the quantum critical point (QCP), xc~0.17, where nematic fluctuations become largest. The pairing mechanism in the x>xc regime is undetermined, presenting an ideal test for theoretically-predicted superconductivity mediated by nematic fluctuations. |
Thursday, March 7, 2024 9:48AM - 10:00AM |
S01.00008: Visualizing superconductivity mediated by nematic fluctuations in the Fe-based superconductor FeSe1-xSx: Part 2 Pranab Kumar Nag, Kirsty Scott, Vanuildo S. de Carvalho, Journey K Byland, Xinze Yang, Morgan Walker, Aaron G Greenberg, Peter Klavins, Eduardo Miranda, Adrian Gozar, Valentin Taufour, Rafael M Fernandes, Eduardo H Da Silva Neto The FeSe1-xSx system presents an ideal platform for studies of intertwined nematicity and superconductivity (SC), a topic of ongoing interest in Fe-based superconductors, due to its lack of magnetic ground state at ambient pressure. In the parent compound FeSe, the SC, mediated by spin fluctuations, coexists with a nematic phase. S-substitution (x) in FeSe1-xSx suppresses the nematic phase at the quantum critical point (QCP), xc~0.17, where nematic fluctuations become largest. The pairing mechanism in the x>xc regime is undetermined, presenting an ideal test for theoretically-predicted SC mediated by nematic fluctuations. |
Thursday, March 7, 2024 10:00AM - 10:12AM |
S01.00009: Qualitative Analysis of Quasiparticle Interference Using Feynman Parametrization Xinze Yang, Alexander F Kemper, Adrian Gozar, Eduardo H Da Silva Neto Quasiparticle interference (QPI) is observed in Scanning Tunneling Spectroscopy (STS) where an impurity causes oscillating patterns of the local density of states (LDOS) [1].Green's function methods commonly used to simulate QPI [2-4] often show disagreement with experiments, especially when computing inter-band scattering. Motivated by our own STS data [5] on Fe-based superconductors we developed a new scheme to help experimentalists to qualitatively analyze the calculated QPI. It relies on Feynman parametrization (FP), a technique widely used in quantum field theory for loop evaluation. We show that the interband QPI problem can be represented by a collection of new 'intermediate bands' possessing relatively easier geometries. We discuss two example applications. First, the QPI between two quadratic bands, where IBA predicts DOS divergences at momentum values that are confirmed by straight numerical calculations. Second, Bogoliubov QPI of FeSexS1-x, where IBA provides a qualitative explanation for the particle-hole asymmetric Intensity in the calculation and experiments. |
Thursday, March 7, 2024 10:12AM - 10:24AM |
S01.00010: Study on nematic superconductivity in tetragonal Fe(Se, S) using magnetic torque measurements Reona Kondo, Kota Ishihara, Kohei Matsuura, Supeng Liu, Yuta Mizukami, Kenichiro Hashimoto, Takasada Shibauchi The iron-based superconductor FeSe undergoes a nematic transition at 90 K accompanied by a structural transition from orthorhombic to tetragonal structure. Also, this nematic transition temperature is suppressed as the amount of S-substitutions increases in FeSe1-xSx, and it becomes zero at x = 0.17 (nematic quantum critical point). Recently, in a SC phase outside this nematic phase (x > 0.17), a large residual quasiparticle density of states appears and anomalously suppressed superfluid density has been found in the zero-temperature limit [1-3]. These are the characteristics of theoretically suggested new gap structure for superconductivity with broken time-reversal symmetry, in which the gap closes in two-dimensional planes (Bogoliubov Fermi surfaces, BFSs) [4].
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