Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P60: Topological Superconductivity in Iron-based SuperconductorsFocus
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Sponsoring Units: DMP Chair: Madhab Neupane Room: Mile High Ballroom 4A |
Wednesday, March 4, 2020 2:30PM - 3:06PM |
P60.00001: Recent progress of Majorana zero mode in iron-based superconductors Invited Speaker: Hong Ding In this talk I will report our recent progress of Majorana zero mode in iron-based superconductors. Following our original findings of superconducting topological surface state [1] and Majorana zero mode (MZM) [2] of Fe(Te, Se), we have recently observed a half-integer level shift of vortex bound states [3] and quantized Majorana conductance [4] in this material, which are hallmarks of MZMs. In addition, we have also found that most of iron-based superconductors [5], including monolayer Fe(Te, Se)/STO [6], have similar topological electronic structures. One of them, CaKFe4As4, an Fe-As bilayer superconductor (Tc ~ 35K), is found to possess MZM and other bound states that can be well reproduced by a simple theoretical model [7]. Our observations offer a new, robust platform for realizing and manipulating MZMs, which may be used for quantum computing at a relatively high temperature. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P60.00002: Superconducting and topological properties of CoX (X = As, Sb and Bi) Jiaqing Gao, Shunhong Zhang, Wenjun Ding, Ping Cui, Zhenyu Zhang Recent studies have revealed high transition temperature (Tc) topological superconductivity in FeSe-based superconductors in either monolayer or bulk form. Here we use first-principles approaches to demonstrate that the systems of CoX (X = As, Sb, and Bi) are not only isovalent to FeSe, but also adopt the same layered structure, thereby may serve as new promising platforms to realize high-Tc superconductivity. Our detailed band structure analyses further show that these systems are topologically nontrivial, and can be exploited for materialization of topological superconductivity. Moreover, all these layered CoX structures can be stabilized on SrTiO3(001), which not only could enhance Tc, but also preserve the topological nature. These findings characterize CoX as appealing new systems to achieve high-Tc superconductivity and topological properties. |
Wednesday, March 4, 2020 3:18PM - 3:30PM |
P60.00003: Effect of Zeeman coupling on the Majorana vortex modes in iron-based topological superconductors Pouyan Ghaemi, Areg Ghazaryan, Pedro Lopes, Pavan Hosur, Matthew Gilbert In the superconducting regime of FeTe(1−x)Sex, two types of vortices which are distinct by the presence or absence of zero energy states in their core are observed. To understand their origin, we examine the interplay of Zeeman coupling and superconducting pairings in three-dimensional metals with band inversion. Zeeman fields are found to suppress the intra-orbital spin-singlet pairing, known to localize the states at the ends of the vortices on the surface. On the other hand, an orbital-triplet pairing is shown to be stable against Zeeman interactions, leads to delocalized zero-energy Majorana modes. In contrast, the finite-energy vortex modes remain localized at the vortex ends for both types of pairings. Phenomenologically, this manifests as an observed disappearance of zero-bias peaks within the cores of topological vortices upon increase of the applied magnetic field. The presence of magnetic impurities in FeTe(1−x)Sex, which are attracted to the vortices, would lead to such Zeeman-induced delocalization of Majorana modes in a fraction of vortices that capture a large enough number of magnetic impurities. Our results provide an explanation to the dichotomy between topological and non-topological vortices recently observed in FeTe(1−x)Sex |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P60.00004: Exploring Higher-Order Topological Physics in FeTe0.55Se0.45 Mason Gray, Meaghan Doyle, Jazzmin R Victorin, Narendra Kumar, Ruidan Zhong, Takashi Taniguchi, Kenji Watanabe, Genda Gu, Kenneth Burch Higher order topological superconductors (HOTSC) are a new class of topological materials in which the “bulk-boundary correspondence” is generalized to higher dimensions. FeTe0.55Se0.45 is an ideal candidate to search for and manipulate such higher-order topological modes due to its intrinsic non-trivial topology and anisotropic superconductivity. In this work, we expand upon recent experimental studies which provide evidence for higher-order modes in FeTe0.55Se0.45. Furthermore, we explore predicitons for HOTSC in this recently emerging platform by studying the response of FeTe0.55Se0.45 to various angles of applied magnetic field. |
Wednesday, March 4, 2020 3:42PM - 3:54PM |
P60.00005: Topological Crystalline Superconductivity in Dirac Semimetal Phase of Iron-based Superconductors Takuto Kawakami, Masatoshi Sato Recently, topological states of iron-based superconductors have attracted much attention. In Fe(Se, Te) and LiFeAs, triple band inversions occur between a pz orbital and three d orbitals [1,2]. ARPES experiments showed that one of the inversions near the Fermi level forms topological insulating gap [1]. Furthermore, another inversion at higher energy causes a band touch with linear dispersion [2]. Therefore, these systems with carrier doping can be Dirac semimetal. |
Wednesday, March 4, 2020 3:54PM - 4:06PM |
P60.00006: Observation of conductance plateau of Majorana zero modes in Fe(Te,Se) Lingyuan Kong, Shiyu Zhu, Lu Cao, Hui Chen, Michal Papaj, Shixuan Du, Yuqing Xing, Wenyao Liu, Dongfei Wang, Chengmin Shen, Fazhi Yang, John Schneeloch, Ruidan Zhong, Genda Gu, Liang Fu, Yuyang Zhang, Hong Ding, Hongjun Gao
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Wednesday, March 4, 2020 4:06PM - 4:18PM |
P60.00007: FeTe1-xSex: Magnetism, electronic coherence, superconductivity, and surface state Yangmu Li, Nader Zaki, David Michael Fobes, Zhijun Xu, Genda Gu, Rongwei Hu, Cedomir Petrovic, Andrei T Savici, Vasile O Garlea, Peter Johnson, John Tranquada, Igor Zaliznyak Local inhomogeneity has a great impact on the electronic band structure and magnetic properties of correlated quantum materials. We apply neutron spectroscopy, together with spatially-resolved chemical and electrical analysis, to a topological superconductor candidate, FeTe1-xSex. Combining with photoemission spectroscopy, we obtain detailed physical and chemical information, which points to an underlying connection among magnetism, electronic coherence, superconductivity, and the topological surface state. |
Wednesday, March 4, 2020 4:18PM - 4:30PM |
P60.00008: High-Tc Superconductor Fe(Se,Te) Monolayer: an Intrinsic, Scalable and Electrically-tunable Majorana Platform Xianxin Wu, Xin Liu, Ronny Thomale, Chaoxing Liu A monolayer of the high-Tc superconductor FeTe1-xSex has been predicted to realize a topologically non-trivial state with helical edge modes at its boundary, providing a novel intrinsic system to search for topological superconductivity and Majorana zero modes. Evidence in favor of a topological phase transition and helical edge modes has been given in recent experiments. We propose to create Majorana zero modes by applying an in-plane magnetic field to the FeTe1-xSex monolayer and by tuning the local chemical potential via electric gating. We demonstrate that, for appropriate parameter regimes, Majorana zero modes can exist at several different locations, including the corner between two perpendicular edges, the domain wall of chemical potentials at one edge, and certain type of tri-junction in the 2D bulk. The scalability and electrical tunability of our proposal render FeTe1-xSex monolayer a promising Majorana platform which is in reach of contemporary experimental capability. |
Wednesday, March 4, 2020 4:30PM - 4:42PM |
P60.00009: Zero-Energy Modes on Superconducting Bismuth Islands Deposited on Fe(Te,Se) Hai-Hu Wen Topological superconductivity is one of the frontier research directions in condensed matter physics. One of the unique elementary excitations in topological superconducting state is the Majorana fermion (mode) which is its own antiparticle and obeys the non-Abelian statistics, and thus useful for constructing the fault-tolerant quantum computation. The evidence for Majorana fermions (mode) in condensed matter state is now quickly accumulated. Here we report the easily achievable zero-energy mode on the tunneling spectra on Bi islands deposited on the Fe(Te,Se) superconducting single crystals. We interpret this result as the consequence of proximity effect induced topological superconductivity on the Bi islands with strong spin-orbit coupling effect. The zero-energy mode is argued to be the signature of the Majorana modes in this size confined system. |
Wednesday, March 4, 2020 4:42PM - 4:54PM |
P60.00010: Yu-Shiba-Russinov states around an excess iron in FeSe0.4Te0.6 Tadashi Machida, Yue Sun, Sunseng Pyon, Shun Takeda, Yuhki Kohsaka, Tetsuo Hanaguri, Takao Sasagawa, Tsuyoshi Tamegai Zero-energy bound states have been detected at interstitial excess irons in the iron-based superconductor Fe(Se,Te) by using a scanning tunneling microscope (STM) [1], and its relationship to the Majorana quasiparticles (QP) has been discussed [2]. However, higher energy resolution of the order of ~10 μeV is necessary to make clear the origin of the bound states at the excess irons. |
Wednesday, March 4, 2020 4:54PM - 5:06PM |
P60.00011: Field-free platform for Majorana modes in superconductors Songtian Sonia Zhang, Jiaxin Yin, Guangyang Dai, Kun Jiang, Tay-Rong Chang, Lingxiao Zhao, Hsin Lin, Guoqing Chang, Genfu Chen, Raman Sankar, Changqing Jin, Ziqiang Wang, Zahid Hasan Superconducting materials exhibiting topological properties are emerging as an exciting platform to realize fundamentally new excitations from topological quantum states of matter. Finding a systematic and controllable path to generate nonabelian Majorana zero energy excitations has been the central task in this research direction. Here, we explore the possibility of a field-free platform by depositing magnetic impurities on the surface of candidate topological superconductors. We use scanning tunnelling microscopy to probe localised states induced at the Fe atoms on the atomic scale at sub Kelvin temperatures and find that each Fe adatom generates a striking zero-energy bound state inside the superconducting gap. Our findings point to magnetic adatoms evaporated on bulk superconductors with topological surface states as a new platform for exploring Majorana zero modes under field-free conditions. |
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P60.00012: Topological superconducting and Majorana zero mode in a new Fe-As bilayer superconductor Wenyao Liu By combining the topological band structure and superconductivity, Fe-based superconductor Fe(Te,Se) is found to host a Majorana Zero Mode (MZM) inside its vortex core. However, the strong intrinsic inhomogeneity induced by the difference between Te and Se atom constraints further researching and practical application of MZM in this material. Recently, we found a Fe-As bilayer superconductor (Tc~35 K), CaKFe4As4, which could host the topological nontrivial surface state and homogeneous bulk meanwhile. Here I will introduce our observation in CaKFe4As4. Our ARPES and STM results mention that MZM and other bound states are derived from the topological surface state, which can be well reproduced by a simple theoretical model for topological superconducting, thus CaKFe4As4 is promising to be a new and more practical Majorana platform. |
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