Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session S49: Electronic Structure of Superconductors (photoemission, etc.) |
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Sponsoring Units: DCMP Chair: Anton Vorontsov, Montana State University, Bozeman Room: Mile High Ballroom 1B |
Thursday, March 5, 2020 11:15AM - 11:27AM |
S49.00001: ARPES Study on the Electronic Structure of Ferromagnet Rb0.93Co1.87Se2 Jianwei Huang, Han Wu, Zhicai Wang, Hongsheng Pang, Sung-Kwan Mo, Alexander F Kemper, Robert J Birgeneau, MENG WANG, Ming Yi As an isostructural analogue of AFe2Se2 (A=K,Rb,Cs) iron-based superconductors, ACo2Se2 (A=K,Rb,Cs) exhibits distinct magnetic ground states without manifestation of superconductivity. Specifically, in Rb0.93Co1.87Se2, a ferromagnetic transition occurs at 83K. Here we use angle-resolved photoemission spectroscopy to study the electronic structure of Rb0.93Co1.87Se2 across the ferromagnetic transition. Clear spin-splitting of bands of different orbitals are observed across the transition. Detailed comparison with first-principle calculations both in the normal state and the magnetic state will be presented. The contribution of different orbitals to the ordered moment as well as the nature of the ferromagnetism in Rb0.93Co1.87Se2 will be discussed. |
Thursday, March 5, 2020 11:27AM - 11:39AM |
S49.00002: ARPES studies of model cuprate high-temperature superconductor Sudheer Anand Sreedhar, Zachary Anderson, Yang Tang, Martin Greven, Robert J Birgeneau, Ming Yi, Inna Vishik HgBa2CuO4+d (Hg1201) is a model single-layer cuprate which has uniquely elucidated the cuprate phase diagram via transport, scattering, and optics studies, but it has received relatively little ARPES study owing to the difficulty in cleaving and achieving good photoemission cross-section. We will discuss recent progress in identifying three energy scales of interactions near the node and evaluating their evolution with doping, temperature, and momentum. We will also discuss recent progress in identifying experimental conditions which optimize antinodal spectra. |
Thursday, March 5, 2020 11:39AM - 11:51AM |
S49.00003: Further evidence of concurrent mass enhancement and superconductivity in a topological state Nader Zaki, Genda Gu, Peter Johnson Previously1,2, we reported on the concurrent onset of mass enhancement at the Dirac point below the superconducting transition in FeSexTe1-x. In this talk, we will review these results and provide more evidence of this phenomenon using low energy laser-based ARPES measurements. Given the increased interest in this system, due in part to the co-existence of superconductivity and non-trivial topology, our results show that this system is even more complicated than perhaps previously presumed and may require re-interpretation of recent experimental reports. |
Thursday, March 5, 2020 11:51AM - 12:03PM |
S49.00004: Evolution of Electronic Spectral Weight in the Hubbard ladder Masanori Kohno Although the number of electronic bands is usually considered invariant in a conventional band picture, the electronic states can generally emerge, grow, and disappear as the electron density changes in strongly correlated systems. Here, the evolution of the electronic states as a function of the electron density is illustrated in the Hubbard ladder in the strong Coulomb repulsion and strong intra-rung hopping regime using the non-Abelian dynamical density-matrix renormalization group method and perturbation theory. An emergent mode in the low-electron density regime grows with the electron density and plays a significant role in the dimer Mott physics at quarter filling, whereas an originally non-interacting band at zero electron density loses the spectral weight and disappears in the Mott transition at half filling, which leads to the spin excitation of the Mott insulator. The emergence and disappearance of electronic states, which have almost been overlooked in conventional band theory and Fermi liquid theory, are particularly important in understanding of the physics around the Mott transition. |
Thursday, March 5, 2020 12:03PM - 12:15PM |
S49.00005: Non-local correlation effect in iron-based superconductors Karim Zantout, Steffen Backes, Roser Valenti While experimental studies of many iron-based superconductors observe momentum-dependent effects like the so-called blue/red shift that describes oppposite energetic shifts of electron- and hole-parabolas with respect to bandstructure calculations, DMFT by construction is not able to capture such features. We therefore present a momentum-dependent and dynamical many-body method, the Two-Particle Self-Consistent (TPSC) approach, and apply it to an ab-initio-derived multi-orbital Hubbard model. |
Thursday, March 5, 2020 12:15PM - 12:27PM |
S49.00006: Electronic structure and superconductivity in unconventional cuprates
Ba$_2$CuO$_{3+\delta}$ Kun Jiang, Congcong Le, Fu-Chun Zhang, Ziqiang Wang, Jiangping Hu We study the recently discovered $73$K high-$T_c$ superconductor Ba$_2$CuO$_{3+\delta}$ at $\delta\simeq0.2$ |
Thursday, March 5, 2020 12:27PM - 12:39PM |
S49.00007: Photoemission studies of BSCCO-2212 across the phase diagram with in-situ control of doping Ilya Drozdov, Genda Gu, Tonica Valla I will present angle-resolved photoemission studies of Bi2Sr2CaCu2O8+δ enabled by oxide MBE [1]. Single crystals were cleaved and annealed in ultra-high vacuum or in ozone (O3) to reduce or increase the doping level. Photoemission studies have been carried out on a wide range of dopings spanning the superconducting dome and covering the previously inaccessible, metallic, non-superconducting phase on the overdoped side (OD0K). This allowed us to study the evolution of the Fermi surface with doping [2], the reconstruction of the Fermi surface due to the superstructure modulation [3], and the renormalization of the electronic spectrum concomitant with the onset of superconductivity [4]. In this talk, I will focus on the sample preparation aspects and cover the first two results. |
Thursday, March 5, 2020 12:39PM - 12:51PM |
S49.00008: Disappearance of Superconductivity Due to Vanishing Coupling in the Overdoped Cuprate Superconductors Tonica Valla, Ilya Drozdov, Genda Gu In high-temperature cuprate superconductors, superconductivity is accompanied by a "plethora of orders" and phenomena that may compete, or cooperate with superconductivity, but which certainly complicate our understanding of origins of superconductivity. While prominent in the underdoped regime, these orders weaken or completely vanish with overdoping. Here, we approach the superconducting phase from the more conventional highly overdoped side. We present angle-resolved photoemission studies of Bi2Sr2CaCu2O8+δ single crystals cleaved and annealed in ozone to increase the doping all the way to the non-superconducting phase. We show that the mass renormalization in the antinodal region of the Fermi surface, associated with the structure in the quasiparticle self-energy, that possibly reflects the pairing interaction, monotonically weakens with increasing doping and completely disappears precisely where superconductivity disapears. This is the evidence that in the overdoped regime, superconductivity is determined by the coupling strength. A strong doping dependence and an abrupt disapearance above Tc eliminate the conventional phononic mechanism of the observed mass renormalization. |
Thursday, March 5, 2020 12:51PM - 1:03PM |
S49.00009: ARPES on Unusual Superconducting Properties of Single-Layer FeSe/SrTiO3 Films Yu Xu, qingyan wang, Hongtao Rong, Dingsong Wu, Yong Hu, Xinxuan Guo, Lin Zhao, Guodong Liu, Zuyan Xu, Xingjiang Zhou Single-layer FeSe films grown on SrTiO3 substrates have attracted much attention because of their record high superconducting critical temperature and distinct electronic structure. Here we report MBE growth of very high-quality single-layer FeSe/STO films, and systematic investigations of their electronic structure and superconducting properties by high-resolution angle-resolved photoemission spectroscopy measurements. Two ellipse-like electron pockets are clearly resolved at one Brillouin zone corner and obvious band splitting is observed. The anisotropic superconducting gap along the Fermi surface is measured with high precision. In particular, we observe very strong superconductivity-induced band back-bending that extends to rather high binding energy. The implications of these observation on superconductivity mechanism of the single-layer FeSe/SrTiO3 films will be discussed. |
Thursday, March 5, 2020 1:03PM - 1:15PM |
S49.00010: Angle-resolved photoemission spectroscopy of in-situ grown cuprate heterostructures by molecular beam epitaxy Zhuoyu Chen, Yuntian Li, Yong Zhong, Slavko Rebec, Tao Jia, Makoto Hashimoto, Donghui Lu, Robert G Moore, Zhixun Shen The molecular beam epitaxy (MBE) system in-situ connected to the beam-line angle-resolved photoemission spectroscopy (ARPES) in Stanford Synchrotron Radiation Lightsource (SSRL) enables rational design of complex material systems and direct electronic structure measurements. The in-situ connected scanning tunneling microscopy (STM) further enables electronic property mapping in the spatial dimensions. Particularly, cuprate films and heterostructures grown atomic-layer-by-layer are of great interest to be explored. In this talk, we will present the newest results about ARPES on cuprate heterostructures. |
Thursday, March 5, 2020 1:15PM - 1:27PM |
S49.00011: Improved Understanding of Gap Dynamics from Time- and Angle-Resolved Photoemission Spectroscopy of a Nonequilibrium Superconductor Tianrui Xu, Daniel Eilbott, Claudia Fatuzzo, Takahiro Morimoto, Joel Moore, Alessandra Lanzara Time- and angle- resolved photoemission spectroscopy (tr-ARPES) has shown to be a useful tool in studying non-equilibrium states of matter. However, the absence of time-translation invariance presents a challenge to understanding the underlying dynamics of the system from the measurements in a straightforward manner. In equilibrium, ARPES intensity is understood to be I(k, ω) ∝ f(ω) A(k, ω) with broadening, where f(ω) is the Fermi-Dirac distribution, and A(k, ω) is the electronic spectral function. Here we study how one should interpret I(k, ω, t), now as a function of time t. We focus our study on tr-ARPES measurements of a non-equilibrium superconducting system where the superconducting gap changes with time. With a focus on situations where the standard quasi-static analysis method fails, we present a possible better way to obtain superconducting gap dynamics. |
Thursday, March 5, 2020 1:27PM - 1:39PM |
S49.00012: Gap opening in monolayer FeSe/TiO2(100) at low doping Chenhui Yan, Brendan D. Faeth, Darrell Schlom, Shuolong Yang, Kyle M Shen Monolayer FeSe grown on SrTiO3(001) has been established to host a high-temperature superconducting state, with the gap-opening temperature between 60 and 70 K. On the other hand, it was shown that monolayer FeSe exhibits an insulating gap when the electron doping level is below 0.09 electron per iron atom. This insulating gap is temperature independent, in contrast to the gap-opening phenomenology in superconducting monolayer FeSe. Here we grow monolayer FeSe on rutile TiO2(100), and show that the gap opens below 40 K with an electron doping of 0.08 electron per iron atom. This doping level is lower than the previously reported doping threshold for superconductivity. We will discuss the origin of this gap. |
Thursday, March 5, 2020 1:39PM - 1:51PM |
S49.00013: Strong particle-hole asymmetry in a 200 Kelvin superconductor Soham Ghosh, Yundi Quan, Warren E Pickett The superconducting state of metals have long provided a classic example of particle-hole symmetry at low energy. We present fermionic self-energy results based on first-principles theory for the electron-phonon coupling in H3S which illustrates strong particle-hole asymmetry in the dynamics arising from the underlying sharp structure in the fermionic density of states. We evaluate the momentum-resolved and zone-averaged spectral densities and interacting thermal distribution function, all of which clearly illustrate strong particle-hole asymmetry. The results allow us to study the infrared conductivity and to note that the strength and position of extrema are affected by electron-phonon coupling. |
Thursday, March 5, 2020 1:51PM - 2:03PM |
S49.00014: Band structure motif and bosonic excitations in the fluctuating superconductivity of overdoped cuprates Yu He, Su-Di Chen, Makoto Hashimoto, Shan Wu, Xiang Chen, Yu Song, Hiroshi Eisaki, Zhixun Shen, Robert J Birgeneau Superconducting fluctuation is one of the central discussions in the physics of high-Tc superconductivity, especially when the system is optimally doped. Recent years have seen a renewed interest in this topic regarding overdoped cuprates, where the expectation is to seek a resolution closer to various BCS premises. However, a series of transport and optical experiments reveal substantial departure from the conventional wisdom. |
Thursday, March 5, 2020 2:03PM - 2:15PM |
S49.00015: Interface-enhanced superconductivity of single layer FeSe grown on non-TiO2 based oxides Yuan-He Song, Xia Lou, Xiaoyang Chen, Ran Tao, Tianlun Yu, Rui Peng, Haichao Xu, Hao Ru, Yi-Hua Wang, Zheng Chen, Yan-Wu Xie, qinghua zhang, lin gu, Xuetao Zhu, Jiandong Guo, Donglai Feng The single layer FeSe film on SrTiO3 indicates that interfaces can play a significant role in high-temperature superconductivity. Here we report a new FeSe-based interface, single layer FeSe grown on non-TiO2 based oxides by molecular beam epitaxy (MBE) method, was successfully obtained. The structure of the interface was determined by high resolution transmission electron microscopy (HRTEM). The angle-resolved photoemission spectroscopy (ARPES) shows that it is superconducting with a large gap, while the ex-situ mutual inductance measurements indicate it has a high onset temperature for diamagnetism. This heterostructure can provide a new platform for understanding the interface-enhanced superconductivity. |
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