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 B28: Fe-Based Superconductors: Te-doped and S-doped FeSe |
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Sponsoring Units: DMP Chair: Gang Qiu, University of California, Los Angeles Room: Room 220 |
Monday, March 6, 2023 11:30AM - 11:42AM |
B28.00001: Superconducting gap structure and impurity effect in tetragonal FeSe1-xSx Kota Ishihara, Masayuki Kobayashi, Masaki Roppongi, Kohei Matsuura, Yuta Mizukami, Marcin Konczykowski, Kenichiro Hashimoto, Takasada Shibauchi FeSe-based materials have attracted much interest because of several unconventional superconducting features, such as the FFLO state, the BCS-BEC crossover, and the topological superconductivity. Furthermore, recent muon measurements revealed the time reversal symmetry breaking in orthorhombic and tetragonal phases of FeSe1-xSx. This result inspired theoretical studies on the ultranodal superconducting state with Bogoliubov Fermi surfaces, which is consistent with the large residual quasiparticle density of states experimentally observed in the tetragonal FeSe1-xSx. However, the nature of the superconducting gap structure in FeSe1-xSx is still elusive. Thus, we performed magnetic penetration depth measurements and electron irradiation to study the superconducting state in tetragonal FeSe1-xSx. We found a successive decrease in superconducting transition temperature and changes of the low-energy quasiparticle excitations with increasing the irradiation doses. From the experimental results, we will discuss the possibility of the ultranodal state in tetragonal FeSe1-xSx. |
Monday, March 6, 2023 11:42AM - 11:54AM |
B28.00002: Superconducting Stiffness and Coherence Length of FeSe0.5Te0.5 Measured in Zero-Applied Field Amit Keren, Motz Peri, Avior Almoalem, Amit Kanigel Superconducting stiffness ρs and coherence length ξ are usually determined by measuring the penetration depth λ of a magnetic field and the upper critical field Hc2 of a superconductor (SC), respectively. However, in magnetic SC, e.g. some of the iron-based, this could lead to erroneous results since the internal field could be very different from the applied one. To overcome this problem in Fe1+ySexTe1-x with x~0.5 and y~0 (FST), we measure both quantities with the Stiffnessometer technique. In this technique, one applies a rotor-free vector potential A to a superconducting ring and measures the current density j via the ring's magnetic moment m. ρs and ξ are determined from London’s equation j=- ρsA and its range of validity. This method is particularly accurate at temperatures close to the critical temperature Tc. We find weaker ρs and longer ξ than existing literature reports, and critical exponents which agree better with expectations based on the Ginzburg–Landau theory. |
Monday, March 6, 2023 11:54AM - 12:06PM |
B28.00003: Spatially dispersing impurity-driven states in the iron-based superconductor FeTe0.55Se0.45 Jinwon Lee, Sanghun Lee, Koen M Bastiaans, Damianos Chatzopoulos, Genda Gu, Doohee Cho, Milan P Allan An impurity in superconductors can break the Cooper pairs into quasiparticles, having quasiparticle states within the superconducting gap. The in-gap states are of importance because their characteristics manifest the superconducting ground state. For example, the impurity-induced in-gap states can be used to reveal the superconducting gap symmetry [1], and when they especially appear at the zero energy, they can indicate a topological superconductivity as Majorana bound states [2,3]. From this perspective, the iron-based superconductor FeTe0.55Se0.45 has been investigated by scanning tunneling microscopy with particular interest in spatially varying Yu-Shiba-Rusinov type impurity states [4] and zero-energy Majorana bound states at magnetic impurities [5] or in vortex cores [6]. In this talk, I will present Josephson scanning tunneling microscopy experiments with high energy resolution, showing another type of the spatially dispersing impurity states in FeTe0.55Se0.45, which can be connected to the surface topological nature of this material. |
Monday, March 6, 2023 12:06PM - 12:18PM |
B28.00004: Concurrent Ferromagnetism and Superconductivity in Fe(Te,Se) van der Waals Josephson Junctions Gang Qiu, Hung-Yu Yang, Christopher Eckberg, Chi-Yen Chen, Lunhui Hu, Yanfeng Lyu, Peng Deng, Huairuo Zhang, Albert Davydov, Ruixing Zhang, Kang-Lung Wang Iron-based 2D layered material FeTexSe1-x (FTS) has been identified as a high-Tc intrinsic topological superconductor (TSC) with s-wave bulk superconductivity proximitizing Dirac surface states. So far, the evidence of TSC and trace of Majorana bound states in FTS have only been reported using local scanning spectroscopy methods or ARPES experiments. Here we report the first device transport measurements with a convincing smoking gun of topological superconductivity in Fe(Te0.59Se0.41) van der Waals Josephson junctions (vJJ). We discovered an unconventional ferromagnetic ordering coexisting with superconductivity by observing magnetic hysteresis loops of junction resistance. Such hysteresis behavior only exists below superconducting temperature Tc, suggesting that the ferromagnetic ordering is strongly correlated with superconductivity. Fraunhofer patterns in vJJ exhibit features of mixing 0-π junctions confirming the non-trivial pairing mechanism in this system. The spontaneous time-reversal-symmetry breaking is also manifested through the field-free stochastic superconducting diode effect, which provides insights into the ferromagnetic domain behavior through thermal cycling above Tc. |
Monday, March 6, 2023 12:18PM - 12:30PM |
B28.00005: Probing time-reversal symmetry breaking in FeSe1-xTex superconductors by muon spin relaxation Masaki Roppongi, Koki Ogawa, Yipeng Cai, Guoqiang Zhao, Mohamed Oudah, Supeng Liu, Marta-Villa De Toro Sanchez, Cyrus Young, Jinsong Zhang, Igor Markovic, Takao Watanabe, Takenori Fujii, Kohei Matsuura, Kota Ishihara, Kenichiro Hashimoto, Douglas A Bonn, Kenji M Kojima, Yasutomo J Uemura, Takasada Shibauchi The FeSe-based superconductor is an attractive quantum material that exhibits inherently exotic quantum phenomena such as nontrivial topology, superconductivity, nematicity, and magnetism. In particular, FeSe1-xTex superconductors have nontrivial band topology, which provides a promising platform for hosting Majorana particles. In addition, recent reports on FeSe1-xTex have found a nematic quantum critical point (QCP) near x = 0.5. In a sister system FeSe1-xSx, which also has a nematic QCP at x ~ 0.17, the time-reversal symmetry breaking (TRSB) in the superconducting state has been reported by the muon spin relaxation (μSR) measurements and a possible ultranodal state for the tetragonal phase at x > 0.17 has been discussed. Therefore, it is important to study how the TRSB superconducting state evolves in the FeSe1-xTex system. |
Monday, March 6, 2023 12:30PM - 12:42PM |
B28.00006: FeTe/FeSe Superlattices: Epitaxial Growth and Transport Properties THI HOA VU Tetragonal FeSe is a well-known superconductor with a transition temperature TC of 8 K in bulk form and shows a huge enhancement in TC up to 65 K by reducing thickness to the monolayer level. Whereas β-phase FeTe, a parent compound of FeSe, does not exhibit superconductivity at either ambient or high hydrostatic pressure. According to current findings, non-superconducting FeTe might become superconducting via alloying with FeSe, annealing in oxygen, and/or heterostructuring with topological insulators. However, till now, the maximum TC values of FeTe films have been so far from room temperature. In this work, the concept of interface superconductivity and superconducting proximity of FeSe on FeTe layers are included to design FeTe/FeSe superlattice system. [(FeTe)m/(FeSe)n]N superlattices with varying thicknesses down to sub-unit cell of each constituent layer were successfully grown on As-terminated GaAs (111) substrates with 300-nm-thick CdTe buffer layers via molecular beam epitaxy. The observation of streaky reflection high energy electron diffraction patterns indicates the layer-by-layer epitaxial growth mode. X-ray diffraction patterns show clear satellite peaks demonstrating the periodic stacking structures of FeSe and FeTe. Interestingly, the superlattice films exhibit the onset superconducting transition temperatures around 15 K. Our results offer a possible way to tune the superconducting properties of Fe(Se,Te) thin films. |
Monday, March 6, 2023 12:42PM - 12:54PM |
B28.00007: Broken symmetry states in FeSe1-xSx measured with STM/S MORGAN A WALKER, Journey K Byland, Timothy J Boyle, Adrian Gozar, Zitong Zhao, Marvin A Muller, Jakob Boeker, Ryan Day, Matteo Michiardi, Sergey Zhadanovich, Sergey Gorovikov, Tor Pedersen, Andrea Damascelli, Ilya Eremin, Valentin Taufour, Eduardo H Da Silva Neto, Kirsty Scott, Steffen Boetzel We used scanning tunneling microscopy and spectroscopy to investigate the local symmetries of the electronic states in FeSe1-xSx. In tetragonal samples with x=0.23 , where nematic order is absent, our spectroscopic mapping experiments reveal a myriad of quasiparticle interference wave vectors in the -60 to 25 meV region, all of which are accurately captured by our and ARPES-calibrated theoretical simulations. The experiments also demonstrate the existence of a periodic pattern for states near the Fermi level that breaks both translational and rotational symmetry. These patterns are non-dispersive and are not seen in the theoretical calculations. Phenomenologically, this broken-symmetry state reminds us of the charge order in the cuprates, suggesting that strong electron correlations might be involved in its formation. |
Monday, March 6, 2023 12:54PM - 1:06PM |
B28.00008: Vertex dominated superconductivity in intercalated FeSe Mark van Schilfgaarde, Swagata Acharya, Mikhail Katsnelson Bulk FeSe becomes superconducting below 9K but the critical temperature (Tc) is enhanced almost universally by a factor of ~4-5 when it is intercalated with alkali elements. How intercalation modifies the structure is known from in-situ X-ray and neutron scattering techniques, but there no consensus why Tc changes so dramatically. Here we show that there is one-to-one correspondence between the enhancement in magnetic instabilities and superconducting pairing vertex. Intercalation modifies electronic screening both in the plane and also between layers. We disentangle quantitatively how superconducting pairing vertex gains from each such changes in electronic screening. Intercalated FeSe provides an archetypal example of superconductivity where information derived from the single-particle electronic structure is not sufficient to account for the origins of superconductivity, even when they are computed including correlation effects. Finally, we show that, whether intercalated or not, Tc is not sensitive to the exact position of the dxy level at the Gamma point, as dxy character is always present in the electron pockets and can mediate similar Tc enhancements. |
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