Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K04: Tenth Anniversary of Iron-based High-temperature Superconductivity: Progresses and OpportunitiesInvited
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Sponsoring Units: DCMP DMP Chair: Zhi-Xun Shen, Stanford University Room: LACC 151 |
Wednesday, March 7, 2018 8:00AM - 8:36AM |
K04.00001: Materials discovery for iron-based superconductivity Invited Speaker: Hideo Hosono
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Wednesday, March 7, 2018 8:36AM - 9:12AM |
K04.00002: Electron Correlations and Iron-based Superconductivity Invited Speaker: Qimiao Si The past decade has witnessed enormous efforts in uncovering the microscopic physics of the iron-based superconductors. From the very beginning, the importance of the bad-metal characteristics and the associated electron correlations has been emphasized [1]. This talk will survey the recent progresses on this broad subject [2]. I will summarize the frustrated magnetism, quantum criticality [3], a wide variety of electronic orders which typically are nematic [3,4], and the orbital-selective Mott physics [2]. These normal-state features point to short-range magnetic correlations as driving the multi-orbital superconductivity. I will discuss the notion of orbital-selective pairing [5], which has been supported by experiments including the recent STM results; and, more generally, how the multi-orbital nature allows for unusual forms of superconducting pairing such as the “s-tau3” pairing state [6], which exhibits properties that seem to be mutually incompatible but have actually been observed. I will close by touching upon some outstanding questions, prospects for further progresses, as well as the implications these studies have for the overall field of unconventional superconductivity. |
Wednesday, March 7, 2018 9:12AM - 9:48AM |
K04.00003: Electronic nematicity in iron-based superconductors Invited Speaker: Anna Boehmer Nematicity – the breaking of rotational symmetry via an electronic mechanism – has been a central theme in the study of iron-based superconductors. This symmetry breaking manifests as a tetragonal-to-orthorhombic structural transition, which is observed in many iron-based compounds. Nematicity is clearly coupled to the stripe-type antiferromagnetism common to most of these systems. Nevertheless, the nature of this relationship has been a long-standing debate. In prototypical materials like BaFe2As2, the structural/nematic transition occurs very close to the magnetic one. A scenario in which nematicity is a “precurser phase” of the stripe-type magnetism is therefore plausible. A prominent exception, which puts this scenario into question, is FeSe. FeSe is well-known for its orthorhombic phase in the absence of magnetic order at ambient pressure, and may be considered an extreme case of nematicity. The application of hydrostatic pressure induces magnetic order in FeSe. In the low-pressure range, the structural/nematic transition temperature decreases whereas the magnetic transition temperature increases with increasing pressure. This opposing behavior raises the question of the origin of nematic order in FeSe. First, I will discuss how nematicity in BaFe2As2-based compounds is related to magnetism and magnetic fluctuations. Secondly, I will discuss the case of FeSe, in particular the relation between nematicity and magnetism under physical and chemical pressure. |
Wednesday, March 7, 2018 9:48AM - 10:24AM |
K04.00004: Fe-based superconductors from an ab initio prespective Invited Speaker: Roser Valenti First principles methods combined with many-body techniques have played an important role in unveiling the microscopic origin of the electronic properties of Fe-based superconductors. |
Wednesday, March 7, 2018 10:24AM - 11:00AM |
K04.00005: Understanding the cooperative optimization of FeSe/SrTiO3 thin films Invited Speaker: Shuolong Yang One unit-cell-thick FeSe on SrTiO3 substrates displays a superconducting gap opening temperature near 70 K, which exceeds the counterpart in bulk FeSe by one order of magnitude. Revealing the superconducting mechanism of FeSe/SrTiO3 can provide a road map toward high temperature superconductivity. In this talk I will discuss a series of in situ experiments aimed at highlighting the critical ingredients for superconductivity in FeSe/SrTiO3. Using time- and angle-resolved photoemission spectroscopy, we launch the coherent Se A1g mode. The mode frequency is abruptly softened from 5.25 to 5.00 terahertz in the one-unit-cell limit [1]. We quantify the electron-phonon coupling strength by combining two time-domain experiments into a "coherent lock-in" measurement in the terahertz regime. X-ray diffraction tracks the atomic displacement; photoemission monitors the corresponding electron energy shift [2]. Comparison with theory suggests a substantial enhancement of electron-phonon coupling in FeSe owing to strong correlations. In addition, we compare these spectroscopic results to new in situ 4-point resistivity measurements on FeSe thin films, where a complete characterization of the superconducting transition temperature as a function of thickness and surface doping is performed [3]. |
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