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- Menkveld, Albert J., et al.
(författare)
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Nonstandard Errors
- 2024
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Ingår i: JOURNAL OF FINANCE. - : Wiley-Blackwell. - 0022-1082 .- 1540-6261. ; 79:3, s. 2339-2390
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Tidskriftsartikel (refereegranskat)abstract
- In statistics, samples are drawn from a population in a data-generating process (DGP). Standard errors measure the uncertainty in estimates of population parameters. In science, evidence is generated to test hypotheses in an evidence-generating process (EGP). We claim that EGP variation across researchers adds uncertainty-nonstandard errors (NSEs). We study NSEs by letting 164 teams test the same hypotheses on the same data. NSEs turn out to be sizable, but smaller for more reproducible or higher rated research. Adding peer-review stages reduces NSEs. We further find that this type of uncertainty is underestimated by participants.
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- Martinelli, L., et al.
(författare)
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Collective Nature of Orbital Excitations in Layered Cuprates in the Absence of Apical Oxygens
- 2024
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 132:6
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the 3d orbital excitations in CaCuO2 (CCO), Nd2CuO4 (NCO), and La2CuO4 (LCO) using high-resolution resonant inelastic x-ray scattering. In LCO they behave as well-localized excitations, similarly to several other cuprates. On the contrary, in CCO and NCO the dxy orbital clearly disperses, pointing to a collective character of this excitation (orbiton) in compounds without apical oxygen. We ascribe the origin of the dispersion as stemming from a substantial next-nearest-neighbor (NNN) orbital superexchange. Such an exchange leads to the liberation of the orbiton from its coupling to magnons, which is associated with the orbiton hopping between nearest neighbor copper sites. Finally, we show that the exceptionally large NNN orbital superexchange can be traced back to the absence of apical oxygens suppressing the charge transfer energy.
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3. |
- Merzoni, Giacomo, et al.
(författare)
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Charge response function probed by resonant inelastic x-ray scattering: Signature of electronic gaps of YBa2Cu3O7-δ
- 2024
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 109:18
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Tidskriftsartikel (refereegranskat)abstract
- In strongly correlated systems, the complete determination of the dynamical susceptibility χ(q,ω) is of special relevance because of the entwinement of the spin and charge components. Although resonant inelastic x-ray scattering (RIXS) spectra are directly related to both the charge [χc′′(q,ω)] and the spin [χs′′(q,ω)] contributions, only the latter has been extensively studied with RIXS so far. Here we show how to extract from RIXS spectra of high-Tc superconducting cuprates relevant properties of χc′′, such as the presence of the superconducting gap and of the pseudogap. In particular, we exploit the temperature dependence of the Cu L3 edge RIXS spectra of underdoped YBa2Cu3O7-δ at specific wave vectors q. The signature of the two gaps is given by the departure of the low-energy excitation continuum from the Bosonic thermal evolution. This approach can be immediately used to investigate systematically the nature of the pseudogap in cuprates, thereby taking advantage of the RIXS technique that does not suffer the limitations of surface-sensitive electron spectroscopies. Its extension to other interesting materials is foreseen.
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