arXiv subjects

Edmondo Gilioli

Publications and source records attributed to Edmondo Gilioli.

6 recordsLinked to original sources

arXiv2026

Superconductivity in strongly overdoped cuprates: beyond the single-band model

In order to explain the observation of an extended superconducting region in several overdoped cuprates, which contrasts the dome scenario, by means of neutron and synchrotron x-ray powder diffraction we study the crystal structure of YBa$_2$Cu$_3$O$_{y}$, where strong oxygen overdoping up to $y = 7.4$ is achieved under high-pressure. A bond valence sum analysis indicates that 1/5 of the extra holes created by the excess oxygen are transferred to the CuO$_2$ planes, thus increasing the hole density up to $p=0.27$ hole/Cu, where superconductivity is expected to vanish according to the dome scenario. Instead, our data confirm a previous observation [Okai, Ono and Mitsuhashi, Physica C: Superconductivity {\bf 366}, 164 (2002)] that the superconducting critical temperature, $T_c$, remains constant with $y$. Our data analysis accounts for this discrepancy in terms of the much shorter bond between the apical oxygen and the planar Cu ion, which suggests that the extra holes occupy the $a_1$-symmetry states formed by $d_{3z^2-r^2}$ orbitals, instead of the usual $b_1$-symmetry Zhang-Rice singlet states formed by $d_{x^2-y^2}$ orbitals. Suitable spectroscopic measurements on single crystals may support such a two-band scenario, which would require a totally different theoretical approach to explain superconductivity in cuprates.

cond-mat.supr-con↗

arXiv2023

High pressure bulk synthesis of InN by solid state reaction of binary oxide in a multi-anvil apparatus

We present a new method to synthesize bulk indium nitride by means of a simple solid-state chemical reaction carried out under hydrostatic high pressure/high temperature conditions in a multi-anvil apparatus, not involving gases or solvents during the process. The reaction occurs between the binary oxide $In_2O_3$ and the highly reactive $Li_3N$ as nitrogen source, in powder form. The formation of the hexagonal phase of InN, occurring at 350 °C and P $\geq$ 3 GPa, was successfully confirmed by powder X-ray diffraction, with the presence of $Li_2O$ as unique byproduct. A simple washing process in weak acidic solution followed by centrifugation, allowed to obtain pure InN polycrystalline powders as precipitate. With an analogous procedure it was possible to obtain pure bulk GaN, from $Ga_2O_3$ and $Li_3N$ at T $\geq$ 600°C and P $\geq$ 2.5 GPa. These results point out, particularly for InN, a clean, and innovative way to produce significant quantities of one of the most promising nitrides in the field of electronics and energy technologies.

cond-mat.mtrl-sci↗

arXiv2022

Correlation of strontium anharmonicity with charge-lattice dynamics of the apical oxygens and their coupling to cuprate superconductivity

Cu K edge X-ray absorption spectra of overdoped superconducting $YSr_2Cu_{2.75}Mo_{0.25}O_{7.54}$ and $Sr_2CuO_{3.3}$ show a remarkably strong correlation of their superconductivity with the local dynamics of their Cu-Sr and Cu-apical-O pairs. This finding that the entire alkaline earth cation-apical O "dielectric" layer has an active role in the unusual electronic properties of cuprates has not been previously considered and has far reaching implications. We develop this idea of a possible role for the apical oxygen charge dynamics via a soft mode of the Sr by applying Kuramoto's synchronization technique to exact diagonalization calculations of two neighboring Cu-apical O pairs bridged by Sr and a planar O atom. These calculations show a first order phase transition to a synchronized state of the Internal Quantum Tunneling Polarons (IQTPs) in which a fraction of the hole originally confined to the apical O atoms of the cluster is transferred onto the planar O. This combination of experimental results and theory demonstrates that the Sr-O dielectric layer of cuprates most likely plays an important role in high temperature superconductivity via its collective charge dynamics that extends into the $CuO_2$ conducting planes.

cond-mat.supr-con↗

arXiv2021

Direct observation of Jahn-Teller critical dynamics at a charge-order Verwey transition

By means of diffuse and inelastic x-ray scattering (DS,IXS), we probe directly the charge-ordering (CO) dynamics in the Verwey system (NaMn$_3$)Mn$_4$O$_{12}$, where a peculiar quadruple perovskite structure with no oxygen disorder stabilizes a nearly full Mn$^{3+}$/Mn$^{4+}$ static charge order at $T_{\rm CO}$=175 K concomitant to a commensurate structural modulation with propagation vector ${\bf q}_{\rm CO}=(\frac{1}{2},\frac{1}{2},0)$. At $T_{\rm CO}$, the IXS spectra unveil a softening of a 35.3 meV phonon at ${\bf q}_{\rm CO}$. Lattice dynamical calculations enable us to attribute this soft phonon to a A$_g$ mode whose polarization matches the Jahn-Teller-like distortion pattern of the structural modulation. This result demonstrates that the Jahn-Teller instability is the driving force of the CO Verwey transition in (NaMn$_3$)Mn$_4$O$_{12}$, thus elucidating a long-standing controversy regarding the mechanism of this transition observed in other mixed-valence systems like magnetite.

cond-mat.str-el↗

arXiv2020

Unconventional magnetic ferroelectricity in the quadruple perovskite NaMn$_7$O$_{12}$

By means of magnetic, specific heat and pyroelectric measurements, we report on magnetic ferroelectricity in the quadruple perovskite \namno, characterized by a canted antiferromagnetic (AFM) CE structure. Surprisingly, ferroelectricity is concomitant to a dramatic broadening of the magnetic hysteresis loop, well below the AFM ordering temperature. This unconventional behavior shows that the formation of ferroelectric domains is induced by the symmetric exchange interaction in the local scale, e.g. at magnetic domain boundaries or defects. The value of electric polarization, $P = 0.027 μ$C cm$^{-2}$, measured in polycrystalline samples is comparatively large as compared to other magnetic multiferroics, suggesting that the above scenario is promising indeed for the rational design of practical multiferroic materials.

cond-mat.mtrl-sci↗

arXiv2013

Thermally activated magnetization reversal in bulk BiFe0.5Mn0.5O3

We report on the synthesis and characterization of BiFe0.5Mn0.5O3, a potential type-I multiferroic compound displaying temperature induced magnetization reversal. Bulk samples were obtained by means of solid state reaction carried out under the application of hydrostatic pressure at 6 GPa and 1100°C. The crystal structure is an highly distorted perovskite with no cation order on the B site, where, besides a complex scheme of tilt and rotations of the TM-O6 octahedra, large off-centering of the bismuth ions is detected. Below T1 = 420 K the compound undergoes a first weak ferromagnetic transition related to the ordering of iron rich clusters. At lower temperatures (just below RT) two distinct thermally activated mechanisms are superimposed, inducing at first an enhancement of the magnetization at T2 = 288 K, then a spontaneous reversal process centered at T3 = 250 K, finally giving rise to a negative response. The application of fields higher than 1500 Oe suppresses the process, yielding a ferromagnetic like behaviour. The complementary use of SQuID magnetometry and Mössbauer spectroscopy allowed the interpretation of the overall magnetic behaviour in terms of an uncompensated weak competitive coupling between non-equivalent clusters of interactions characterized by different critical temperatures and resultant magnetizations. PACS numbers: 75.85.+t, 75.60.Jk, 76.80.+y, 75.30.Et, 75.30.Kz

cond-mat.mtrl-sci↗