arXiv subjects

J. G. Duque

Publications and source records attributed to J. G. Duque.

3 recordsLinked to original sources

arXiv2025

Ba-substitution induced evolution of structural and magnetic properties of La2-xBaxCoIrO6 double perovskites

The Iridium-based oxides are the subject of great recent interest due to the non-conventional physics that may emerge from the strong spin-orbit coupling present in 5d ions. Here, we explore the coupling between Ir and Co in the La2-xBaxCoIrO6 perovskites (x = 0, 0.5, 0.75 and 1.0), where the structural, electronic, and magnetic properties of the series are investigated by means of x-ray powder diffraction and magnetometry. The system's crystal structure evolves from the monoclinic P2_1/n to the triclinic I-1 space group as the Ba concentration increases. Measurements of magnetization revealed ferrimagnetic behavior in x = 0, 0.5 and 0.75 compounds, possibly resulting from antiferromagnetic coupling between Co2+/3+ and Ir4+. In contrast, for x = 1.0 a clear collinear antiferromagnetic character is observed for the Co2+ ions, resulting from the quenching of the Ir5+ magnetic moment. The evolution of the magnetic properties of the series is discussed in terms of the structural and electronic changes, as well as the spin-orbit coupling in Ir.

cond-mat.mtrl-sci↗

arXiv2012

Fundamental Optical Processes in Armchair Carbon Nanotubes

We have used post-synthesis separation methods based on density gradient ultracentrifugation and DNA-based ion-exchange chromatography to produce aqueous suspensions strongly enriched in armchair nanotubes for spectroscopic studies. Through resonant Raman spectroscopy of the radial breathing mode phonons, we provide macroscopic and unambiguous evidence that density gradient ultracentrifugation can enrich armchair nanotubes. Furthermore, using conventional, optical absorption spectroscopy in the near-infrared and visible range, we show that interband absorption in armchair nanotubes is strongly excitonic. Lastly, by examining the G-band mode in Raman spectra, we determine that observation of the broad, lower frequency (G^{-}) feature is a result of resonance with non-armchair "metallic" nanotubes. These findings regarding the fundamental optical absorption and scattering processes in metallic carbon nanotubes lay the foundation for further spectroscopic studies to probe many-body physical phenomena in one dimension.

cond-mat.mes-hall↗

arXiv2011

Resonant Raman Spectroscopy of Armchair Carbon Nanotubes: Absence of "Metallic" Signature

The appearance of a broad peak at $\sim$1550 cm$^{-1}$ (G$^{-}$ peak) in carbon nanotube resonant Raman scattering spectra has been conventionally attributed to the presence of metallic nanotubes. Here, we present resonant Raman measurements on macroscopic nanotube ensembles enriched in armchair species prepared through density gradient ultracentrifugation. Our data clearly demonstrate that the broad G$^{-}$ mode is absent for armchair structures and appears only when the excitation laser is resonant with non-armchair "metals." Due to the large number ($\sim$10$^{10}$) of nanotubes across several armchair species probed, our work firmly establishes a general correlation between G-band lineshape and nanotube structure.

cond-mat.mes-hall↗