Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F30: Copper Oxide Superconductors: ARPES and Tunneling |
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Sponsoring Units: DCMP Chair: Daniel Dessau, University of Colorado Room: LACC 406B |
Tuesday, March 6, 2018 11:15AM - 11:27AM |
F30.00001: Universality of scanning tunneling microscopy on cuprate superconductors Peter Hirschfeld, Peayush Choubey, Andreas Kreisel, Tom Berlijn, BRIAN ANDERSEN We consider the problem of local tunneling into cuprate superconductors, combining model based calculations for the superconducting order parameter with wavefunction information obtained from first principles electronic structure. We use a recently developed Wannier function based method to calculate topographies, spectra, conductance maps and normalized conductance maps close to impurities. We find that it is the local planar Cu d_{x^2-y^2} Wannier function, qualitatively similar for many systems several Angstrom above the surface, that controls the form of the tunneling spectrum and the spatial patterns near perturbations. In particular, we discuss why STM results on BSCCO and NaCCOC are essentially identical. |
Tuesday, March 6, 2018 11:27AM - 11:39AM |
F30.00002: Bosonic Mode in the Tunneling Spectra of Single Cu-O Layer Cuprate Superconductors John Zasadzinski, Beverly Lowell, Noah Samuelson The above-gap, SIN tunneling spectral dip feature in the bilayer cuprate Bi2Sr2CaCu2O8+δ (Bi2212) is highly reproducible and unambiguously linked to the resonance spin excitation. The search for similar bosonic mode features in the tunneling spectra of single Cu-O layer cuprates is discussed. Disorder effects which show up as a depairing rate, Γ, in the fitting of the density of states (DOS) become increasingly important for lower Tc compounds. High Tc (94K) Hg1201 tunneling spectra exhibit a relatively small Γ and a well resolved bosonic mode feature similar to Bi2212. It is demonstrated that SIS break junctions or intrinsic c-axis junctions reveal a strongly enhanced dip feature allowing the observation of a bosonic mode in strongly disordered Bi2201 with Tc values ≤ 5K. The mode energy Ω remains inside the superconducting gap 2Δ as found in high Tc cuprates. The conclusion is that irrespective of Tc, composition and degree of disorder, the bosonic mode Ω retains its character as a spin exciton as expected from an all-electronic pairing interaction. |
Tuesday, March 6, 2018 11:39AM - 11:51AM |
F30.00003: Scanning Tunneling Microscopy Study on Infinite-layer SrCuO2 Films Yong Zhong, Sha Han, Yang Wang, Zhi-Ling Luo, Can-Li Song, XUCUN MA, Qikun Xue We report on the growth of infinite-layer SrCuO2 films on SrTiO3 (001) substrate by molecular beam epitaxy. In situ scanning tunneling microscopy reveals a 2 × 2 reconstruction induced by oxygen vacancies, in consistent with the first-principles calculations that the terminated layer is CuO1.5. Depending on the film thickness and growth temperature, a striped structure is further observed on the surface of SrCuO2 films. Our results may pave a new way to directly study the superconducting layer in cuprates at the atomic scale. |
Tuesday, March 6, 2018 11:51AM - 12:03PM |
F30.00004: Coherent organization of electronic correlations as a mechanism to enhance and stabilize high-TC cuprate superconductivity Daniel Dessau, Haoxiang Li, Xiaoqing Zhou, Stephen Parham, Theodore Reber, Helmuth Berger, Gerald Arnold Utilizing a new development in the analysis of angle-resolved photoemission data of Pb-doped Bi2Sr2CaCu2O8 crystals, we show that the strange metal normal-state correlations don’t simply disappear in the superconducting state, but are instead converted into a strongly renormalized coherent state, with stronger normal state correlations leading to stronger superconducting state renormalization. Further, we show that this conversion begins well above TC at the onset of superconducting fluctuations and that it greatly increases the number of states that can pair. Therefore, there is positive feedback––the superconductive pairing creates the conversion that in turn strengthens the pairing. While such positive feedback should enhance a conventional pairing mechanism, it could potentially also sustain a fully electronic pairing mechanism. |
Tuesday, March 6, 2018 12:03PM - 12:15PM |
F30.00005: Spectroscopic Properties of the d-wave BCS Superconductivity in Extremely Overdoped Bi2Sr2CaCu2O8+δ Yu He, Su-Di Chen, Makoto Hashimoto, Kejun Xu, Dongjoon Song, Yoshiyuki Yoshida, Hiroshi Eisaki, Donghui Lu, Zhi-Xun Shen The apex of the high Tc cuprates' superconducting dome is often clouded by multiple closely degenerate electronic orders, which is preceded by the even more enigmatic quasiparticle-less "strange metal". These unconventional phenomena quickly fade when the hole concentration exceeds the putative "pseudogap quantum critical point", but the pairing mechanism is still unidentified even in such heavily overdoped region. We report angle-resolved photoemission spectroscopy measurement of Bi-2212 in this "clean" limit with a respectful Tc of over 50K. By quantitatively re-establishing the weakly-coupled BCS regime in the foothill of the otherwise highly complex phase diagram, a few conventional possibilities are examined to shed light on the true pairing mechanism. |
Tuesday, March 6, 2018 12:15PM - 12:27PM |
F30.00006: ARPES research of Bi2Sr2CaCu2O8+x by in-situ doping Yigui Zhong, Jianyu Guan, Zheng-Yu Weng, Ziqiang Wang, Genda Gu, Yujie Sun, Hong Ding Cuprate high temperature superconductors have been studied 40 years now, but there still are many questions unresolved. A systematic study on cuprates is necessary to figure out these questions. Recently,we succeed in tuning the doping level of Bi2Sr2CaCu2O8+x (Bi2212) in-situ by ozone annealing and vacuum annealing. Compared to the previously angle-resolved photoemission spectroscopy (ARPES) works which carried on different doped samples, our results are more reliable because the we detect the same surface. We tune the doping in a large range, from 0.05 to 0.25, almost including the whole superconducting region. Using in-situ high resolution ARPES, we get the doping evolution of gap, kink and Quasiparticle information. Our work give a overall look of cuprate superconductivity and is helpful to establish the electronic phase diagram in Bi2212 that can be extended to other cuprate superconductors. |
Tuesday, March 6, 2018 12:27PM - 12:39PM |
F30.00007: Interplay of the Gap and Kink in Bi2212 with Time-Resolved ARPES Tristan Miller, Wentao Zhang, Hiroshi Eisaki, Alessandra Lanzara In conventional superconductors, electron-boson coupling plays a key role in the mechanism for superconductivity. Strong electron-boson coupling is present in cuprate superconductors as well, but its relation to superconductivity is unknown. Angle-resolved photoemission spectroscopy (ARPES) sees superconductivity as a gap, and sees electron-boson coupling as a dispersion kink. Here we identify a feature that arises from the interplay of the gap and kink, and isolate the feature using time-resolved ARPES. We discuss how this feature could be used to establish whether there is a relationship between electron-boson coupling and superconductivity. |
Tuesday, March 6, 2018 12:39PM - 12:51PM |
F30.00008: Photoemission in the strange metal region of Bi2212 Su-Di Chen, Makoto Hashimoto, Yu He, Dongjoon Song, Kejun Xu, Junfeng He, Donghui Lu, Hiroshi Eisaki, Zhi-Xun Shen In the study of cuprate high temperature superconductors, it remains a major task to understand the strange metal region above the pseudogap temperature. Angle-resolved photoemission spectroscopy (ARPES), a powerful surface-sensitive probe of electronic structure, becomes challenging in this region due to the worsened vacuum condition at high temperature. Using improved experimental setup, we perform high-precision ARPES measurements on Bi2212 deep in the strange metal region while free from sample aging. We will present the doping and temperature evolutions of spectral coherence in this region, and discuss the implication of our results on the generic phase diagram of high temperature superconductors. |
Tuesday, March 6, 2018 12:51PM - 1:03PM |
F30.00009: Doping and Momentum-Dependent Scattering Rate in Bi2201 Superconductor Measured By Laser-ARPES Ying Ding, Lin Zhao, yingying peng, Li Yu, Cheng Hu, Xuan Sun, Jing Liu, Ping Ai, Guodong Liu, Chuangtian Chen, Zuyan Xu, Xingjiang Zhou We will present our high-resolution laser-based angle-resolved photoemission (ARPES) measurements on electron scattering rate in Bi2Sr2CuO6 (Bi2201) superconductors over a wide doping range. With substitution of lead (Pb) and high oxygen pressure annealing, overdoped and heavily overdoped Pb-doped Bi2201 single crystals have been prepared. Underdoped and optimally doped Bi2201 samples have been obtained by lanthanum(La) substitution and flowing oxygen annealing. Laser-based ARPES measurements with super-high energy and momentum resolutions have been carried out to study the electron scattering rate as a function of momentum and temperature for Bi2201 over a wide range of doping levels. The implication of these results on understanding the anomalous normal state properties of the high temperature cuprate superconductors will be discussed. |
Tuesday, March 6, 2018 1:03PM - 1:15PM |
F30.00010: Observation of Nodal Superconducting Gaps in Bi2Sr2CaCu2O8+x Topped With Copper-Oxide Films Jianyu Guan, Xun Shi, yigui zhong, Pierre Richard, hangjiang liu, Ziqiang Wang, Genda Gu, Yujie Sun, Hong Ding We have grown CuO thin films on Bi2Sr2CaCu2O8+x substrates by ozone-assisted molecular beam epitaxy and investigated the electronic structure by in-situ angle-resolved photoemission spectroscopy. We observe similar low-energy band structure compared as in Bi2Sr2CaCu2O8+x, while the wide energy spectrum is consistent with an insulating state,even with different amount of CuO. The superconducting gap structure fits well to the dX2-Y2 gap form. Our results suggest that the d-wave is robust in this system and that the reported U-like gap by STM is possibly a minority and “local” state, to which ARPES is not very sensitive. |
Tuesday, March 6, 2018 1:15PM - 1:27PM |
F30.00011: Superconductivity proximate to antiferromagnetism in copper oxide monolayer grown on Bi2Sr2CaCu2O8+δ Shuai Wang, Long Zhang, Fa Wang Nodeless superconducting (SC) gap was reported in a recent scanning tunneling spectroscopy experiment in the copper oxide monolayer grown on the Bi2Sr2CaCu2O8+δ (Bi2212) substrate [Y. Zhong et al, Sci. Bull. 61, 1239 (2016)], which is in stark contrast to the nodal d-wave pairing gap in the bulk cuprates. Motivated by this experiment, we first show with first-principles calculations that the tetragonal CuO (T-CuO) monolayer on the Bi2212 substrate is more stable than the commonly postulated CuO2 structure. The T-CuO monolayer is composed of two CuO2 layers sharing the same O atoms. The band structure is obtained by first-principles calculations, and its strong electron correlation is treated with the renormalized mean field theory. We argue that one CuO2 sublattice is hole-doped while the other sublattice remains half-filled and may have antiferromagnetic (AF) order. The doped Cu sublattice can show d-wave SC; however, its proximity to the AF Cu sublattice induces a spin-dependent hopping, which split the Fermi surface and may lead to a full SC gap. Therefore, the nodeless SC gap observed in the experiment could be accounted for by the d-wave SC proximity to an AF order, thus it is extrinsic rather than intrinsic to the CuO2 layers. |
Tuesday, March 6, 2018 1:27PM - 1:39PM |
F30.00012: Electronic Structure of Bi2-xPbxSr2CaCu2O8+δSuperconductors with Various Pb Concentrations Measured by Laser-Based ARPES Liu Jing, Jianwei Huang, Qiang Gao, Cheng Hu, Ying Ding, Xuan Sun, Ping Ai, Guodong Liu, Li Yu, Chuangtian Chen, Zuyan Xu, Chandra Varma, Han-Yong Choi, Xingjiang Zhou The Bi2Sr2CaCu2O8+δ(Bi2212) high temperature superconductors have been extensively studied by angle-resolved photoemission spectroscopy (ARPES). However, the Bi2212 system suffers from two main shortcomings:one is the difficulty in obtaining heavily over-doped samples; the other is the complications of the measured electronic structure caused by superstructure bands, particularly near the anti-nodal region. We will present our results on single crystal growth and ARPES measurement on Pb-doped Bi2212 with various Pb concentrations in order to address the above problems. High quality single crystals of Bi2-xPbxSr2CaCu2O8+δwith wide Pb range (x=0~0.8) have been successfully grown by the traveling solvent floating zone technique. Their electronic structure is measured by our new generation laser-based ARPES system based on the angle-resolved Time-of-Flight (ARToF) electron energy analyzer. The effect of Pb-doping on the electronic structure of Bi2212 will be presented. |
Tuesday, March 6, 2018 1:39PM - 1:51PM |
F30.00013: ARPES studies of the model cuprate HgBa2CuO4+δ (Hg1201) Benjamin Gregory, Ming Yi, Zachary Anderson, Vikram Nagarajan, Yuka Nakato, Yang Tang, Martin Greven, Inna Vishik HgBa2CuO4+δ (Hg1201) is considered to be a model cuprate and has been well characterized by transport and scattering experiments. It has recently been studied with angle-resolved photoemission spectroscopy (ARPES), and we build on these initial investigations with measurements in the underdoped regime. We discuss mode-coupling, surface effects on spectra, and temperature-dependent scattering rates, making connections to various bulk characterizations. |
Tuesday, March 6, 2018 1:51PM - 2:03PM |
F30.00014: Resonant soft x-ray scattering and angle-resolved photoemission spectroscopy studies on electron doped cuprates Hoyoung Jang, S. Asano, M. Fujita, Makoto Hashimoto, Donghui Lu, Clement Burns, Chi-Chang Kao, Jun-Sik Lee As charge density wave (CDW) order has been recently observed in the electron-doped cuprates, the CDW is thought to be a universal feature in high-Tc cuprates. Here we present comprehensive studies on CDW phenomena in an electron-doped cuprates, Nd1.86Ce0.14CuO4 (NCCO). Interestingly, we observed reflections with a wavevector (~1/4, 0) for a CDW order in both annealed (superconducting) and as-grown (non-superconducting) NCCO. We found that ordering behavior of this reflection is quite different than what is found in Y/La-based hold-doped cuprates. Moreover the angle-resolved photoemission spectroscopy (ARPES) results indicate that Fermiology cannot account for the wavevector. These findings are important to understand the nature of CDW correlations in both in hole- and electron-doped cuprate systems. More details will be discussed in this presentation. |
Tuesday, March 6, 2018 2:03PM - 2:15PM |
F30.00015: Phenomenological Theories of the Low-Temperature Pseudogap: Hall Number, Specific Heat, and Seebeck Coefficient Simon Verret, Olivier Simard, Maxime Charlebois, David Senechal, A.-M. Tremblay Many phenomenological models have successfully reproduced the jump from p to 1+p found for the Hall number at the critical doping p* for the pseudogap in YBCO [1], at low temperature and with superconductivity supressed. More experiments and theoretical calculations are needed to discriminate between those theories. |
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