Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session D49: Superconductivity in Ruthenates |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Shirin Mozaffari Room: Mile High Ballroom 1B |
Monday, March 2, 2020 2:30PM - 2:42PM |
D49.00001: Effect of strain on critical temperature and Pauli-limit critical field of Sr2RuO4 with separable pairing interaction Yue YU, Stuart Brown, Srinivas Raghu We study the critical temperature and Pauli-limit critical field of Sr2RuO4 as a function of uniaxial strain. A three-band tight-binding model is studied that includes effects of spin-orbit and Zeeman couplings and a separable pairing interaction. We compare with the experiment results obtained assuming pairing in various channels (d-wave, extended s-wave and p-wave). We will highlight the relationship of Tc with Hc2 for different pairing symmetries. |
Monday, March 2, 2020 2:42PM - 2:54PM |
D49.00002: Development of new phase in ruthenium oxides using molecular beam epitaxy method Masahito Sakoda, Mizuki Higashiizumi, Satoshi Tanda The ruthenium oxides are known to have the layered structure and the anisotropic superconductivity. Especially, Ca2RuO4 shows remarkable property change applied by electrical field or pressure. We focus on Ca2RuO4 and its related compounds to research new phase in order to develop noble physical properties. |
Monday, March 2, 2020 2:54PM - 3:06PM |
D49.00003: Superconducting Sr2RuO4 thin film growth by controlling the structural defects Jinkwon Kim, Junsik Mun, Carla Palomares-Garcia, Jeong Rae Kim, Lingfei Wang, Seo Hyoung Chang, Miyoung Kim, Suk Bum Chung, Changyoung Kim, Jason Robinson, Yoshiteru Maeno, Tae Won Noh The layered perovskite superconductor Sr2RuO4 (bulk Tc ~ 1.5 K) has been studied extensively with its possible topological superconductivity and chiral gap function (px ± ipy) [1]. The superconducting Sr2RuO4 thin film has advantages not only for physical advances but also fruitful device application such as quantum computation [2]. However, superconducting Sr2RuO4 film growth has been limited since the superconductivity of Sr2RuO4 is extremely vulnerable to structural defects, especially out-of-phase boundaries (OPBs) [3]. |
Monday, March 2, 2020 3:06PM - 3:18PM |
D49.00004: Mimicking superconductivity of Sr2RuO4 using SrRuO3-SrTiO3 superlattice Bongjae Kim, Sergii Khmelevskyi, Cesare Franchini, Igor Mazin, Kyoo Kim The putative chiral spin-triplet superconductivity in ruthenate is under intense controversy, where the various theoretical and experimental studies discuss the diverse alternative pairing symmetries. Currently, the investigation is solely focused on only one material, Sr2RuO4, and the field suffers from the lack of comparison target. Here, employing density functional theory-based analysis, we show that the heterostructure composed of SrRuO3 and SrTiO3 is inherent with all the key characteristics of Sr2RuO4, and eventually can host superconductivity. Furthermore, we show that the competing magnetic phases and associated frustration entangled with the superconducting state can be tuned by epitaxial strain engineering. This system offers an excellent platform for the study of |
Monday, March 2, 2020 3:18PM - 3:30PM |
D49.00005: Pairing symmetry of SrRuO3-SrTiO3 ruthenate superlattice Jae-Ho Han, Kyoo Kim, Bongjae Kim The unconventional superconductivity of Sr2RuO4 has been studied extensively due to the claim of unique p-wave pairing state, which is under recent scrutiny. One of the main difficulties of determining the pairing symmetry is the accurate estimation of relevant energy scales, which are competing. Small tuning of the microscopic parameters and the resulting evolution of pairing symmetry can offer more insight in the field, which is not easy from the experimental side due to the requirement of extremely clean sample and high-precision measurement. Here, based on the recent proposal of possible superconductivity in SrRuO3-SrTiO3 superlattice, we investigate the pairing symmetry of the system, which can be comparable target of Sr2RuO4. From a DFT calculation, we construct a tight-binding Hamiltonian and search for the pairing symmetry of the heterostructure by calculating the superconducting phase transition temperature. We also study the possibility of pairing transition by tuning the external parameters, which is attainable through epitaxial strain. |
Monday, March 2, 2020 3:30PM - 3:42PM |
D49.00006: Constraints on the superconducting order parameter in Sr2RuO4 from oxygen-17 nuclear magnetic resonance Andrej Pustogow, Yongkang Luo, Aaron Chronister, Yue-Shun Su, Dmitry Sokolov, Fabian Jerzembeck, Andrew P. Mackenzie, Clifford W. Hicks, Naoki Kikugawa, Srinivas Raghu, Eric Bauer, Stuart Brown The superconducting state of the quasi two-dimensional and strongly correlated perovskite Sr2RuO4 is considered to be a solid-state analogue to the superfluid 3He-A phase, with an odd-parity order parameter that breaks time-reversal symmetry. Recent experiments using in-plane uniaxial stress revealed a dramatic rise and peak of the transition temperature [1], related to a DOS enhancement [2]. Here we use 17O NMR spectroscopy to probe the nature of superconductivity in Sr2RuO4 and its evolution under uniaxial strain. A reduction of the Knight shift is observed below Tc for all strain values, consistent with a drop in spin polarization in the superconducting state [3]. In unstrained samples, our results rule out a chiral p-wave order parameter. We discuss the issue of sample heating on a sub-millisecond time scale after the NMR pulse, which is particularly relevant to superconductors with a small transition temperature (Tc ≈ 1 K). |
Monday, March 2, 2020 3:42PM - 3:54PM |
D49.00007: Reduced spin suscpetibility in superconducting Sr2RuO4 measured by polarized neutron diffraction Alexander Petsch, Mengze Zhu, Yoshiteru Maeno, Zhiqiang Mao, Mechthild Enderle, Stephen Hayden Superconducting Sr2RuO4 has previously been considered as an analogue of superfluid 3He-A [1]. But the picture of odd-order parameter superconductivity with chiral triplet-pairing got recently challenged by the observation of a drop in the 17O-NMR Knight shift below the superconducting transition [2]. Herein, we present new data on the magnetic susceptibility in Sr2RuO4 collected by polarized neutron scattering. Consistent with the observations in NMR, a reduction below the superconducting transition is observed. In relation to previous work [3] we propose a complicated field dependence alongside large residual susceptibilities at zero temperature, arising from orbital and spin-orbit contributions. Our results support singlet-pairing with a complicated gap-symmetry or triplet-pairing with an in-plane d-vector, where time-reversal symmetry is still broken [4]. |
Monday, March 2, 2020 3:54PM - 4:06PM |
D49.00008: Understanding reduced NMR signals in Sr2RuO4 Austin Lindquist, Hae-Young Kee The superconducting order parameter of Sr2RuO4 has been a topic of recent interest, as new NMR experiments are in contradiction with the previously proposed px±ipy triplet superconducting state [1]. The multi-orbital nature of the Fermi surface, in combination with the Hund’s and spin-orbit coupling, allows various types of superconducting order parameters. We propose inter-orbital spin triplet pairing based on the Hund’s and spin-orbit coupling [2], and study the NMR signals with and without uniaxial strain. These results are compared with recent NMR experiments, and future experiments which can test the validity of the proposed pairing symmetry are also discussed. |
Monday, March 2, 2020 4:06PM - 4:18PM |
D49.00009: Muon spin relaxation studies of time-reversal symmetry breaking superconductivity in Sr2RuO4 along with the application of uniaxial stress and disorder Shreenanda Ghosh, Vadim Grinenko, Felix Brückner, Rajib Sarkar, Jean-Christophe Orain, Artem Nikitin, Debarchan Das, Zurab Guguchia, Joonbum Park, Mark E Barber, Naoki Kikugawa, Jake Bobowski, Dmitry Sokolov, Takuto Miyoshi, Yoshiteru Maeno, Andrew Mackenzie, Hubertus Luetkens, Clifford W Hicks, Hans-Henning Klauss After extensive research, idea regarding the symmetry of the superconducting order parameter of Sr2RuO4 is still lacking a consensus. Recently, NMR experiments have ruled out the well-discussed px ± ipy state [1]. Nevertheless, complex two-component order parameters are conventionally indicated by time-reversal-symmetry breaking (TRSB) superconductivity. In order to lift the degeneracy between such components application of uniaxial stress is a plausible method [2]. One key prediction for Sr2RuO4, a splitting of the superconducting and TRSB transitions under uniaxial stress has not been observed so far. We report a large stress-induced splitting between the onset temperatures of superconductivity and TRSB transitions observed by muon spin relaxation (µSR) measurements under uniaxial stress. To perform these technically challenging experiments, a customized uniaxial pressure cell was developed which will be presented. We also discuss the effect of disorder on the superconducting and TRSB states by µSR, concerning the chirality of the order parameter. |
Monday, March 2, 2020 4:18PM - 4:30PM |
D49.00010: Spin-orbital coupling and spin-triplet pairing symmetry in Sr2RuO4 Xin Wang, Zhiqiang Wang, Catherine Kallin Spin-orbital coupling (SOC) plays a crucial role in determining the spin structure of an odd parity pseudospin-triplet Cooper pairing state. We discuss how SOC lifts the degeneracy among different p-wave pseudospin-triplet pairing states in a widely used microscopic model for Sr2RuO4 combining a Ginzburg-Landau free energy expansion, a symmetry analysis of the model, and numerical weak-coupling renormalization group, as well as random phase approximation, calculations. These analyses are also used to critically re-examine previous numerical results on the stability of chiral p-wave pairing. The symmetry analysis can serve as a guide for future studies, especially numerical calculations, on the pairing instability in Sr2RuO4 and can be useful for studying other multi-band spin-triplet superconductors where SOC plays an important role. |
Monday, March 2, 2020 4:30PM - 4:42PM |
D49.00011: Strontium Ruthenate's Superconducting Symmetries from First-Principles Calculations Olivier Gingras, Michel Cote, Reza Nourafkan, Andre-Marie Tremblay The normal state of Sr2RuO4 is well understood but its superconducting state is still a subject of major debates [1]. From a first-principles correlated multiorbital calculation, we construct the spin and charge fluctuation pairing interactions. These interactions depend on the proximity to an instability and on the size of the screened Hund's coupling. We present the leading gap function symmetries obtained by solving the frequency-dependent linearized Eliashberg equation for the case where spin-orbit coupling is neglected [2]. Close to magnetic instabilities, we find spin-singlet d-wave pairing. Away, where charge fluctuations increase, we observe the emergence of two even-parity spin-triplet states: an odd in frequency s wave and two degenerate momentum-independent states that pair electrons on different orbitals and are odd in orbital indices. These exotic states are compared with experiments. Moreover, we discuss and present the effects of spin-orbit coupling and uniaxial strain on the system. |
Monday, March 2, 2020 4:42PM - 4:54PM |
D49.00012: Effects of spin-orbit coupling on the superconducting pairing in Sr2RuO4 Wen Huang, Yi Zhou, Hong Yao In a superconductor with finite spin-orbit coupling (SOC), neither the orbital nor the spin angular momentum of a Cooper pair is good quantum number, but their sum is. We focus on two aspects of the SOC-influenced superconductivity in Sr2RuO4. In the first[1,2], we argue that the most frequently discussed p-wave state in the Eu representation, which has Cooper pair angular momentum |Lz,Sz〉= |±1,0〉, must coexist with another pairing with |Lz,Sz〉=|0,±1〉. The two correspond respectively to the gap functions (kx,ky)\hat{z} and kz(\hat{x},\hat{y}) in the d-vector notation. If the latter dominates, the Eu superconducting channel would favor a nematic rather than a chiral state. Moreover, in-plane uniaxial strains, which primarily perturb the orbital angular momentum Lz of the Cooper pairs, split the components in the |±1,0〉pairing linearly and those in the |0,±1〉 pairing quadratically. In the second[3], we show how SOC may inherently entangle spin-triplet and spin-singlet pairings in multi-orbital models of Sr2RuO4. Possible relevance to the recent experiments, such as the uniaxial strain and NMR Knight shift measurements, will be discussed. Refs: [1] Huang and Yao, PRL 121, 157002 (2018); [2] Huang, Zhou, and Yao, arXiv:1901.07041; [3] Huang, Zhou, and Yao, PRB 100, 134506 (2019). |
Monday, March 2, 2020 4:54PM - 5:06PM |
D49.00013: Emergence of high-temperature superconductivity in a Ca2RuO4 nanocrystals Hiroyoshi Nobukane, Kosei Yanagihara, Yuji Kunisada, Yunito Ogasawara, Kakeru Isono, Kazushige Nomura, Keita Tanahashi, Takahiro Nomura, Tomohiro Akiyama, Satoshi Tanda The search for high-temperature (high-Tc) superconductors is a fascinating topic in condensed matter physics. It is widely believed that high-Tc superconductivity in cuprates emerges from doped Mott insulators. Recently, 4d and 5d transition metal oxides with a layer perovskite structure have attracted much attention because the possibility of the emergence of high-Tc superconductivity has been recognized in several studies. |
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D49.00014: Possible 'symmetry-imposed' near-nodal superconducting pairing in Sr2RuO4 Yu Li, Wen Huang One key feature of the multi-orbital superconducting Sr2RuO4 is the presence of nodal or near-nodal quasiparticle excitations revealed in a wide variety of experiments. Typically, a nodal gap structure in a two-dimensional model would be inconsistent with the chiral or helical p-wave interpretations. However, we demonstrate that true gap nodes may emerge along certain high-symmetry directions on the quasi-one-dimensional Fermi surfaces, if the multi-orbital chiral or helical p-wave pairings acquire peculiar forms wherein the dxz and dyz orbitals develop ky- and kx-like pairings, respectively. Spin-orbit coupling η induces a near-nodal gap of order (η2/W2)Δ0, where Δ0 is the gap amplitude and W roughly the bandwidth. Provided the aforementioned pairing is predominant, the near-nodal gap structure is robust upon the inclusion of other multi-orbital pairings that share the same symmetries. In light of the recent experimental progresses, our proposal suggests that two-dimensional p-wave pairings may still be viable candidate ground states for Sr2RuO4. A near-nodal helical p-wave order, for example, would also be consistent with the substantial drop in the NMR Knight shift under an in-plane magnetic field. |
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