Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session B49: Superconductors: Complex Compounds, Borides, Organics, and Others |
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Sponsoring Units: DCMP Chair: Rongying Jin, Louisiana State University Room: Mile High Ballroom 1B |
Monday, March 2, 2020 11:15AM - 11:27AM |
B49.00001: Plasmon-Polaron Superconductivity in Strontium Titanate Alexander Edelman, Peter B Littlewood Strontium titanate (STO) is a bulk insulator that becomes a semiconducting superconductor at remarkably low carrier densities - below 1017 cm-3 - with a characteristic superconducting dome as a function of doping which peaks at Tc~300mK, all in very close proximity to a ferroelectric quantum critical point. We investigate a scenario of superconductivity mediated by coupling to a strongly anti-adiabatic longitudinal optic phonon by extending a simple Engelsberg-Schrieffer theory of electron-phonon coupling to include the effects of electronic Coulomb interactions. For the carrier densities of interest, we find that the plasmon hybridizes strongly with LO mode with one of the resulting coupled modes inherting the low energy scales of the softening ferroelectric mode. Working within the cumulant expansion, we calculate the spectral signatures of this unusual regime of coupling compare to experiment photoemssion[1] and tunneling[2] experiments, as well as the superconducting phase diagram including self-energy effects beyond one loop. |
Monday, March 2, 2020 11:27AM - 11:39AM |
B49.00002: Possible strongly correlated superconductivity in a copper-based metal-organic framework Kota Ishihara, Takaaki Takenaka, Kenichiro Hashimoto, Yijie Miao, Kiyoshi Torizuka, Jun Gouchi, Yoshiya Uwatoko, Junto Tsurumi, Shun Watanabe, Jun Takeya, Takahiko Sasaki, Xing Huang, Wei Xu, Daoben Zhu, Na Su, Jinguang Cheng, Takasada Shibauchi Recently the copper(II) benzenehexathiolate coordination polymer [Cu3(C6S6)]n (Cu-BHT) attracts significant interests as the first superconductor in metal-organic frameworks (MOFs) with a superconducting transition temperature Tc ~ 250 mK. Since Cu-BHT has a perfect 2D Kagome structure formed by S = 1/2 spins of Cu2+, unconventional superconductivity related to quantum fluctuations is expected. Although we have already reported that our magnetic penetration depth measurements suggest unconventional superconductivity in Cu-BHT, fundamental superconducting and normal state properties, such as dimensionality, magnetism, and the Fermi energy, which are important to elucidate the superconducting mechanism, are still unrevealed. In this study, therefore, we measured the angle-resolved upper critical field, magnetoresistance, electron spin resonance (ESR), and optical conductivity. By comparing the ratio of Tc to the Fermi temperature with other unconventional superconductors, we revealed that Cu-BHT is possibly a member of strongly correlated electron systems. |
Monday, March 2, 2020 11:39AM - 11:51AM |
B49.00003: Exploring superconductivity using muon spin resonance in chiral noncentrosymmetric superconductors. Daniel Mayoh, Matthew Pearce, Kathrin Goetze, Adrian Hillier, Geetha Balakrishnan, Martin Lees Unconventional superconductivity remains one of the most interesting problems in condensed matter physics. For all superconductors, the topology of the electronic band structure, along with the underlying crystal structure, play vital roles in determining the superconducting properties of the material. Systems lacking a centre of inversion exhibit a nonuniform lattice potential, giving rise to a Rashba-type antisymmetric spin-orbit coupling which allows for an admixture of singlet and triplet pairs. This may give rise to exotic superconducting band structures and magnetoelectric effects such as upper critical fields that exceed the Pauli limit. The discovery of two noncentrosymmetric superconductors with chiral structures, TaRh2B2 and NbRh2B2 [1], has added a new twist to an already exciting area of superconductivity. Here we present our investigation into the superconducting order parameter using muon spin resonance techniques in TaRh2B2 and NbRh2B2 [2, 3]. |
Monday, March 2, 2020 11:51AM - 12:03PM |
B49.00004: Magnetism and superconductivity in alkali metal doped 2,2′-bipyridine from near room temperature synthesis Di Peng, Renshu Wang, Xiao-Jia Chen Organic superconductors have long been the major players in the development of modern physical chemistry. So far, many cases of introducing charge into π-electron networks in organic superconductors with Meissner effect have been found. However, most of them lack pivotal zero resistance measurements because of the high synthesized temperature leading to the decomposition of organic materials and forming non-homogeneous phases. To avoid this tendency, a design principle for low temperature synthetic reaction process is indispensable. |
Monday, March 2, 2020 12:03PM - 12:15PM |
B49.00005: Superconductivity in an organobismuth molecule Renshu Wang, Liucheng Chen, Xiao-Jia Chen, Hui Yang, Mingan Fu, Jia Cheng, Xiaolin Wu, yun gao, Zhongbing Huang Recently, novel quantum phenomena such as topological insulators and superconductors were suggested in organobismuth compounds. However, evidence for superconductivity from the zero-resistivity state in any organometallic compound has not been achieved yet, though much effort has been made. Here, we report the experimental realization of superconductivity in a critical temperature of 3.6 K in potassium-doped tri-o-tolylbismuthine, with evidence of both the Meissner effect and the zero-resistivity state through dc and ac magnetic susceptibility and resistivity measurements. The superconducting phase and its composition are determined by combined studies of X-ray diffraction and theoretical calculations as well as Raman spectroscopy measurements. These findings enrich the applications of organometallic compounds in superconductivity and add a new electron-acceptor family of organic superconductors. |
Monday, March 2, 2020 12:15PM - 12:27PM |
B49.00006: Li2xBC3: a two dimensional MgB2-like superconductor Yundi Quan, Warren Pickett Though most superconductors can be grouped into distinct structure classes, MgB2 remains in a class of its own almost two decades after its discovery. Previous efforts to design superconductors in the same structure class as MgB2 have been unsuccessful due to various complications. Recently, experimentalists are able to stabilize Li2xBC3 [1], a layered compound with Li sandwiched between alternating C-C and B-C honeycomb sheets similar to MgB2. By carrying out linear response calculations, we find that at half occupation (i. e. x= 0.5), Li2xBC3 is a phonon mediated superconductor with a Tc of around 45 K. Further increasing Li occupation (x) weakens electron-phonon coupling, thus lowering Tc. At occupation levels below 0.5, crystal structure of Li2xBC3 becomes dynamically unstable due to increased electron-phonon coupling. Electronic structure, Fermi surfaces and electron-phonon couplings etc of Li2xBC3 will be presented to help understand the origin of strong electron-phonon coupling. |
Monday, March 2, 2020 12:27PM - 12:39PM |
B49.00007: Inhomogeneity of superconductivity in a disordered charge density wave material Pd-intercalated ErTe3 measured using scanning SQUID microscopy Yusuke Iguchi, Joshua A Straquadine, John Robert Kirtley, Anisha Singh, Ian Fisher, Kathryn Ann Moler The rare-earth tri-tellurides RTe3 (R=La-Pr, Sm, Gd-Tm) are quasi-2D metals that show unidirectional incommensurate charge density wave (CDW) states. Pd intercalation introduces significant disorder to the crystal lattice, suppressing the CDW formation and leading to a superconducting ground state. The material presents an opportunity to explore in detail the interplay between superconductivity (SC) and CDW formation in the presence of disorder. Here we study the spatial variance of the superfluid response as a function of Pd concentration in PdxErTe3 (0<x<0.06) by using a scanning SQUID microscope with sub-micron spatial resolution. We quantify the inhomogeneity of the emergent superconductivity as the CDW is progressively disordered by the Pd intercalation. Our results clarify how the superconducting state emerges from the disordered CDW. |
Monday, March 2, 2020 12:39PM - 12:51PM |
B49.00008: In-plane anisotropy of the c-axis magnetoresistance for BiCh2-based superconductor Kazuhisa Hoshi, Yoshikazu Mizuguchi, Yosuke Goto, Tatsuma D. Matsuda, Motoi Kimata BiCh2-based (Ch = S, Se) superconductor was discovered in 2012, the crystal structure is similar to that of high temperature superconductor, such as cuprate superconductor and iron-based superconductor. The pairing mechanisms of the superconductivity has not been completely understood. However, theoretical calculation, ARPES, and isotope effect suggest that unconventional superconductivity is essential for BiCh2-based superconductor. |
Monday, March 2, 2020 12:51PM - 1:03PM |
B49.00009: Superconductivity at 262 K in Yttrium Superhydride at High Pressures Elliot M Snider, Nathan M Dasenbrock-Gammon, Raymond McBride, Ranga Dias Superconductivity has been one of the most profound quantum phases in condensed matter physics. Efforts to identify and develop room temperature superconducting materials are an intensive area of research, motivated by both fundamental science and the prospects for applications. We report the synthesis and superconductivity in Yttrium superhydride with highest Tc of 262K at 183 GPa. The Tc is the highest ever recorded at this pressure. The superconductivity in Yttrium superhydride arises from clathrate based hydrogenic lattices. The electrical resistance measurements and magnetic field dependence transport measurement shows the clear indication of the observed superconductivity. Based on the Raman spectra, we suggest that YH6, is responsible observed superconductivity, which is in good agreement with recent theoretical studies. The hydrogen-rich materials are in the vicinity of achieving room temperature superconductivity. |
Monday, March 2, 2020 1:03PM - 1:15PM |
B49.00010: Anisotropic energy gap in single crystals of isotropic superconductor SrPt3P Kyuil Cho, Serafim Teknowijoyo, Elizabeth Krenkel, Makariy A Tanatar, Ruslan Prozorov, Nikolai D Zhigadlo Antiperovskie pnictide SrPt3P shows the highest superconducting transition temperature, Tc, among the 5d element - based compounds, possibly with somewhat strong coupling, 2△0 /Tc ∼5. While the material itself is quite isotropic, its energy gap structure and pairing state remain uncertain due to the lack of single crystals. Here we report directional measurements of electrical resistivity and London penetration depth in single crystals SrPt3P. Surprisingly, our results show highly anisotropic nature of the superconducting energy gap. |
Monday, March 2, 2020 1:15PM - 1:27PM |
B49.00011: New muon spin rotation/relaxation measurements of the non-centrosymmetric superconductor LaNiC2 Shyam Sundar, Sarah Dunsiger, Shayan Gheidi, Krishant S Akella, Andre M Côté, Yoshiki J Sato, Takatsugu Koizumi, Rikio Settai, Yusuke Hirose, Ismardo Bonalde, Fuminori Honda, Jeff Sonier Non-centrosymmetric superconductors (NCSs) lack inversion center in their crystal structure, and consequently one of the typical symmetries for the formation of Cooper pairs. The absence of inversion symmetry strongly influences the Cooper pairing states possible in these materials. Here we report a muon spin rotation/relaxation (μSR) study of LaNiC2 single crystals, a non-magnetic, NCS with weak electronic correlations and a superconducting transition temperature, Tc ~ 2.7 K. Previous zero-field μSR measurements on a pressed pellet of LaNiC2 powder revealed the onset of spontaneous magnetic fields at Tc. This finding signifies time-reversal symmetry breaking (TRSB) in superconducting phase, which is compatible with a non-unitary triplet-pairing state. However, other kinds of experiments have provided evidence for conventional BCS s-wave pairing, point nodes in the gap function and even two-gap superconductivity. Our new μSR investigation of LaNiC2 provides a fresh perspective on the nature of the superconducting pairing state, by yielding the temperature and magnetic field dependencies of the magnetic penetration depth and vortex core size in the mixed state and through a new test of TRSB. |
Monday, March 2, 2020 1:27PM - 1:39PM |
B49.00012: Superconductivity in Cu-doped TiSe2: A first-principles calculation Obinna Uzoh, Tae-Ho Park, Han-Yong Choi We present the superconducting properties of Cu-doped TiSe2 materials based on first-principles calculations. Experimental study of Cu intercalated 1T-TiSe2 under various copper doping concentrations (x = 0.04 – 0.10) has been investigated extensively. Such study has shown that as doping concentrations increase charge density wave is steadily suppressed until about x = 0.04 where a dome-shaped superconductivity emerges with maximum Tc of 4.15 K at x = 0.08 [1]. In order to understand this observation theoretically, we perform first-principles calculations based on density functional theory and density functional perturbation theory incorporated with maximally localized Wannier functions. We calculate the electronic structures at various doping concentrations by modeling doping using virtual crystal approximation. Also, we estimate the superconducting Tc by calculating the electron-phonon coupling and the Eliashberg spectral function. Further, we analyze all possible phonon modes in CuxTiSe2 and ascertain dominant modes contributing to the superconductivity. |
Monday, March 2, 2020 1:39PM - 1:51PM |
B49.00013: Strain-stabilized superconductivity in RuO2 Jacob Ruf, Hanjong Paik, Nathaniel Schreiber, Hari Nair, Ludi Miao, Jason Kawasaki, Jocienne Nelson, Brendan Faeth, Yonghun Lee, Berit Goodge, Betul Pamuk, Craig Fennie, Lena Fitting Kourkoutis, Darrell Schlom, Kyle M Shen The rational control of superconductivity and the possibility of deterministically enhancing the superconducting transition temperature (Tc) by design, rather than by serendipity, has been an elusive and long sought-after goal in solid-state physics. Here, we report the first instance of transmuting a normal metal into a superconductor through the application of epitaxial strain. We demonstrate that synthesizing RuO2 thin films on TiO2(110) substrates stabilizes superconductivity under strain, having Tcs up to 2 K; by contrast, RuO2 thin films grown on TiO2(101) substrates are non-superconducting down to the lowest measured temperatures (Tc < 0.4 K), consistent with the behavior of bulk RuO2. Using a comprehensive combination of characterization techniques—including electrical transport, x-ray diffraction, scanning transmission electron microscopy, angle-resolved photoemission spectroscopy, and density functional theory—we reveal the primary electronic mechanism underlying this strain-stabilized superconductivity: the anisotropic strains redistribute the carriers amongst the manifold of 4d states near the Fermi level (EF), partially depopulating flat bands with d|| orbital character, and thereby increase the density of states at EF. |
Monday, March 2, 2020 1:51PM - 2:03PM |
B49.00014: Physical Properties of New Alkaline Earth Tantalum Sulfides Shermane Benjamin, Michael Smith, John J Neumeier Transition-metal sulfides serve as an interesting class of compounds for comparison to transition-metal oxides. They also often demonstrate properties such as metal-insulator transitions, superconductivity, and magnetism. In this work, single crystals of CaTa5S10, Sr3Ta5S10 and BaTa10S10 samples were synthesized via chemical vapor deposition. CaTa5S10, Sr3Ta5S10 and BaTa10S10 superconduct at Tc_onset = 3.25 K, 3.8 K and 2.8 K, respectively. The magnetic properties, specific heat, electrical resistivity, structural analysis, and compositional analysis will be discussed. |
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B49.00015: Coexistence of superconductivity and weak ferromagnetism in Rb-doped triphenylbismuthine and tri-p-tolylbismuthine Zhongbing Huang, Ren-Shu Wang, Jia Cheng, Ming-An Fu, Hui Yang, yun gao, Xiao-Jia Chen By using a two-step method - ultrasound treatment and low temperature annealing, we successfully synthesize Rb-doped triphenylbismuthine and tri-p-tolylbismuthine. The dc magnetic measurements show a coexistence of superconductivity at 4.0 K and weak ferromagnetism at 35 K in all synthesized samples, which is strongly supported by the resistivity measurements. The calculated electronic structure indicates that superconductivity is realized by transferring electron from rubidium to carbon atom, and the weak ferromagnetism is produced by nonparallel arrangement of magnetic moments on the phenyl rings. Our study provides a new platform for understanding the interplay between superconductivity and ferromagnetism. |
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