Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C43: New Experimental Developments in the CupratesInvited
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Sponsoring Units: DCMP Chair: Martin Greven, University of Minnesota Room: BCEC 210B |
Monday, March 4, 2019 2:30PM - 3:06PM |
C43.00001: Locating the missing superconducting electrons in overdoped cuprates Invited Speaker: Peter Armitage Overdoped high-temperature cuprate superconductors have been widely believed to be described by the physics of d-wave BCS-like superconductivity. However, recent measurements indicate that as the doping is increased, the superfluid density decreases smoothly to zero rather than increasing as expected by BCS theory in the absence of disorder. Here, we combine time-domain THz spectroscopy with kHz range mutual inductance measurements on the same overdoped La2-xSrxCuO4 films to determine both the superfluid and the uncondensed carrier density as a function of doping. A significant fraction of the carriers remains uncondensed in a wide Drude-like peak even as T→0, which, when taken with the linear-in-temperature superfluid density, is inconsistent with existing theories for the role of disorder in suppressing the superfluid density in a d-wave superconductor. Our almost eight orders of magnitude in measurement frequency range gives us a unique look at the low frequency spectral weight distribution, which may suggest the presence of quantum phase fluctuations as the critical doping is approached. |
Monday, March 4, 2019 3:06PM - 3:42PM |
C43.00002: Density fluctuations in strange metals Invited Speaker: Peter Abbamonte Metals exhibit plasmon excitations, which are collective modes one can think of as sound waves in the electron density (as opposed to the atomic density). The so-called "strange metals" are bizarre phases of matter that fail to exhibit well-defined quasiparticles but somehow are still good conductors, leading one to wonder what degree of freedom is actually carrying the charge. A sensible question to ask is, Do strange metals exhibit plasmons? In this talk I will describe momentum-resolved EELS (M-EELS) measurements of several strange metals, notably Bi2Sr2CaCu2O8+x which is also a high-temperature superconductor. I will show that plasmon excitations are barely defined in these materials, which instead exhibit an incoherent continuum of charge fluctuations with no particular length or time scale. These fluctuations obey a simple, power law form, suggesting some kind of scale-invariant phase is present, though the data are not consistent with a (textbook) quantum critical point. I will discuss efforts by theorists to explain this phenomenon using holographic |
Monday, March 4, 2019 3:42PM - 4:18PM |
C43.00003: Universal superconducting precursor in perovskite-based oxides Invited Speaker: Damjan Pelc A pivotal challenge posed by unconventional superconductors is to unravel how superconductivity emerges upon cooling from the generally complex normal state. Some of the most prominent unconventional superconductors are oxides: strontium titanate, strontium ruthenate, and the cuprates exhibit greatly different superconducting transition temperatures Tc, and although their respective superconducting pairing mechanisms remain unknown, they are thought to differ as well. We use nonlinear magnetic response – a probe that is uniquely sensitive to the superconducting precursor – to uncover remarkable universal behavior in these three distinct classes of oxide superconductors [1]. We find an unusual exponential temperature dependence of the diamagnetic response above the transition temperature Tc, with a characteristic temperature scale that strongly varies with Tc. We correlate this scale with the sensitivity of Tc to local stress, indicating that the universal behavior is caused by intrinsic, self-organized structural inhomogeneity inherent to the oxides’ perovskite-based structure. Furthermore, the precursor can be strongly influenced by structural disorder, intentionally induced by uniaxial plastic deformation. The results show that structural inhomogeneity is prevalent in perovskite-related superconductors, with far-reaching implications for the interpretation of their electronic properties in general. |
Monday, March 4, 2019 4:18PM - 4:54PM |
C43.00004: NMR study of the effect of hydrostatic pressure on charge-density waves and superconductivity in YBa2Cu3Oy Invited Speaker: Marc-Henri Julien High-Tc superconductivity in the cuprates arises in close proximity to a charge-density wave (CDW) phase. A challenge in the field is to understand how both phenomena compete and whether, behind pure competition, there is a more involved relationship between them. To tackle this question, experiments have used temperature, magnetic field, hole-doping or uniaxial strain as tuning parameters. The effect of hydrostatic pressure, on the other hand, is controversial. Here, using nuclear magnetic resonance (NMR) in YBa2Cu3Oy, we find that the short-range CDW in the normal state as well as the long-range CDW in high fields are weakened only slightly at a pressure of 1.9 GPa. Quantitative analysis of the data supports the hypothesis that virtually all of the increase in Tc upon increasing pressure arises from a gradual decrease of CDW strength up to ~15 GPa. We propose explanations for some of the conflicting conclusions drawn from different experiments and suggest that they may actually shed light on the CDW. |
Monday, March 4, 2019 4:54PM - 5:30PM |
C43.00005: Uniaxial Pressure Control of Competing Orders in a High Temperature Superconductor Invited Speaker: Matthieu Le Tacon External control of electronic phases in correlated-electron materials is a long-standing challenge of condensed-matter research. Layered cuprates exhibit antiferromagnetic, charge density-wave (CDW), and high-temperature superconducting ground states which can be tuned by doping and external magnetic fields. However, disorder generated by lattice defects and randomly pinned magnetic vortices greatly complicates the interpretation of these experiments. |
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