arXiv subjects

Benoit Baptiste

Publications and source records attributed to Benoit Baptiste.

5 recordsLinked to original sources

arXiv2024

Temperature-invariant heat conductivity from compensating crystalline and glassy transport: from the Steinbach meteorite to furnace bricks

The thermal conductivities of crystals and glasses vary strongly and with opposite trends upon heating, decreasing in crystals and increasing in glasses. Here, we show--both with first-principles predictions based on the Wigner transport equation and with thermoreflectance experiments--that the dominant transport mechanisms of crystals (particle-like propagation) and glasses (wave-like tunnelling) can coexist and compensate in materials with crystalline bond order and nearly glassy bond geometry. We demonstrate that ideal compensation emerges in a sample of silica in the form of tridymite, carved from a meteorite found in Steinbach (Germany) in 1724, and yields a "propagation-tunneling-invariant" (PTI) conductivity that is independent from temperature and intermediate between the opposite trends of $\alpha$-quartz crystal and silica glass. We show how such PTI conductivity occurs in the quantum regime below the Debye temperature, and can largely persist at high temperatures in a geometrically amorphous tridymite phase found in refractory bricks fired for years in furnaces for steel smelting. Last, we discuss implications to heat transfer in solids exposed to extreme temperature variations, ranging from planetary cooling to heating protocols to reduce the carbon footprint of industrial furnaces.

cond-mat.mtrl-sci↗

arXiv2023

Two-dimensional fluctuations and competing phases in the stripe-like antiferromagnet BaCoS$_2$

By means of a combined x-ray diffraction, magnetic susceptibility and specific heat study, we investigate the interplay between orthorhombic distortion and stripe-like antiferromagnetic (AFM) order in the Mott insulator BaCoS$_{2}$ at $T_N=290$ K. The data give evidence of a purely electronic AFM transition with no participation of the lattice. The observation of large thermal fluctuations in the vicinity of $T_N$ and a Schottky anomaly unveils competing ground states within a minute $\sim$1 meV energy range that differ in the orbital and spin configurations of the Co ions. This interpretation suggests that the stripe-like order results from a spontaneous symmetry breaking of the geometrically frustrated pristine tetragonal phase, which offers an ideal playground to study the driving force of multi-orbital Mott transitions without the participation of the lattice.

cond-mat.str-el↗

arXiv2022

When carbon impurities trigger the synthesis of alpha boron at high pressure and high temperature

The role of carbon in the formation of alpha boron at high pressure and high temperature (HPHT) has been investigated by combining HPHT experiments and density functional theory (DFT) calculations. Starting from beta rhombohedral or amorphous boron and amorphous carbon at 5 GPa, the alpha boron phase has been repeatedly observed between 1473 K and 2273 K, at temperatures that are much higher than those reported in the phase diagram of boron. The DFT investigation of the effect of carbon insertion into the alpha rhombohedral boron atomic structure on the formation enthalpy, volume and optical properties shows that only the (B11C) substituted icosahedron defect accounts for the slight volume contraction observed in {\alpha} boron. It is also compatible with the observed red colour of {\alpha} boron crystals, and consistently has a very low formation energy. Our calculations also provide a calibration tool to evaluate the carbon concentration in the samples. Finally, the synthesis temperature is found to be an easy means to tune the carbon concentration on demand.

cond-mat.mtrl-sci↗

arXiv2020

Structural phase transition and bandgap control through mechanical deformation in layered semiconductors 1T-ZrX2 (X = S, Se)

Applying elastic deformation can tune a material physical properties locally and reversibly. Spatially modulated lattice deformation can create a bandgap gradient, favouring photo-generated charge separation and collection in optoelectronic devices. These advantages are hindered by the maximum elastic strain that a material can withstand before breaking. Nanomaterials derived by exfoliating transition metal dichalcogenides TMDs are an ideal playground for elastic deformation, as they can sustain large elastic strains, up to a few percent. However, exfoliable TMDs with highly strain-tunable properties have proven challenging for researchers to identify. We investigated 1T-ZrS2 and 1T-ZrSe2, exfoliable semiconductors with large bandgaps. Under compressive deformation, both TMDs dramatically change their physical properties. 1T-ZrSe2 undergoes a reversible transformation into an exotic three-dimensional lattice, with a semiconductor-to-metal transition. In ZrS2, the irreversible transformation between two different layered structures is accompanied by a sudden 14 % bandgap reduction. These results establish that Zr-based TMDs are an optimal strain-tunable platform for spatially textured bandgaps, with a strong potential for novel optoelectronic devices and light harvesting.

cond-mat.mtrl-sci↗

arXiv2015

Anomalous metallic state in quasi-two-dimensional BaNiS$_{2}$

We report on a systematic study of the thermodynamic, electronic and charge transport properties of high-quality single crystals of BaNiS$_2$, the metallic end-member of the quasi-twodimensional BaCo$_{1-x}$Ni$_x$S$_2$ system characterized by a metal-insulator transition at $x_{cr}=0.22$. Our analysis of magnetoresistivity and specific heat data consistently suggests a picture of compensated semimetal with two hole- and one electron-bands, where electron-phonon scattering dominates charge transport and the minority holes exhibit, below $\sim$100 K, a very large mobility, $\mu_h\sim$ 15000 cm$^2$V$^{-1}$s$^{-1}$, which is explained by a Dirac-like band. Evidence of unconventional metallic properties is given by an intriguing crossover of the resistivity from a Bloch-Gr\"uneisen regime to a linear$-T$ regime occurring at 2 K and by a strong linear term in the paramagnetic susceptibility above 100 K. We discuss the possibility that these anomalies reflect a departure from conventional Fermi-liquid properties in presence of short-range AF fluctuations and of a large Hund coupling.

cond-mat.str-el↗