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Correa, V. F., P. Pedrazzini, D. G. Franco, A. J. Rosa, B. Rubrecht, N. Haberkorn. "Low-temperature thermal expansion of the topological material candidates β-PtBi2 and β-PdBi2." Physica B – Condensed Matter 641 (2022): 414102.
Abstract: We report on the low-temperature ($T <$ 120 K) thermal expansion of the bismuth-based topological semimetal $\beta$-PtBi$2$ and topological superconductor $\beta$-PdBi$2$ candidates.
The linear thermal-expansion coefficient of tetragonal $\beta$-PdBi$2$ shows a pronounced anisotropy between the $a$- and $c$-axis while the volume thermal-expansion coefficient $\alphaV$($\beta$-PdBi$2$) is considerable larger than $\alphaV$($\beta$-PtBi$_2$).
The coefficient $\alphaV$($\beta$-PtBi$2$) nearly matches the experimental specific heat, from which a Debye temperature $\thetaD =$ 199 K is obtained. On the other hand, $\alphaV$($\beta$-PdBi$2$) reasonably fits the Debye model with $\thetaD =$ 138 K, extracted from the low-temperature specific heat.
An almost constant Gr\"uneisen parameter $\Gamma \approx$ 2 is obtained for both compounds.
No magnetostriction is observed in any of both compounds up to $\mu_0 H =$ 16 T.
We compare our results with other Bi-based topological materials.
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Haberkorn, N., and V. F. Correa. "Effect of low-temperature thermal annealing on the vortex dynamics of metastable β-Bi2Pd single crystals." Physica C: Superconductivity and its Applications 598 (2022): 1354051.
Abstract: We study the vortex dynamics on β-Bi2Pd single crystals with a superconducting critical temperature of 5.1 K. The upper critical fields and magnetic penetration depth are determined from magnetization measurements. At low temperatures, the self-field critical current density (Jc) is ≈ 20 kA/cm2. The vortex pinning energy, extracted from an Anderson-Kim approximation, is between 340 K and 140 K for fields between 100 G and 600 G. Differential scanning calorimetric measurements show that the crystals start to transform into the alpha-phase at temperatures as low as 60 °C. Short annealing at 100 °C modifies the pinning landscape increasing Jc mainly at temperatures below 3 K. The angular dependence of Jc from electrical transport experiments shows a broad peak when the magnetic field is parallel to the crystallographic c-axis, indicating the presence of correlated disorder.
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Correa, V. F., I. Curci, J. G. Sereni, N. Caroca Canales, and C. Geibel. "Magnetic-field-tuned valence susceptibility in CeCo1−xFexSi revealed by magnetostriction." In Journal of Physics: Conference Series, 012042. Vol. 2164., 2022.
Abstract: We report magnetoelastic studies in the CeCo1−xFexSi alloys. Iron doping has a profound effect on the low temperature linear magnetostriction. At T = 2 K, the strength of the magnetostriction peaks at x = 0.23 where it reaches a value as large as $\[\frac{{\Delta L}}{L} = 3 \times {10^{ – 3}}\]$ in an applied magnetic field B = 16 T. This Fe concentration corresponds to the critical one xc above which long-range antiferromagnetic order is no longer observed. The progressive increment of the hibridization between the Ce 4f orbital and the conduction band, as the magnetic order vanishes, gives rise to a sizeable valence susceptibility that can be finely tuned by the magnetic field explaining the large magnetostrictive effect around xc. At higher x, the magnetostriction decreases, in agreement with a weaker valence susceptibility resulting from a stronger hibridization.
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Correa, V. F., and F. J. Castro. "First-Order Phase Transformation at Constant Volume: A Continuous Transition?" Entropy 24 (2022): 31.
Abstract: We describe a first-order phase transition of a simple system in a process where the
volume is kept constant. We show that, unlike what happens when the pressure is constant, (i) the
transformation extends over a finite temperature (and pressure) range, (ii) each and every extensive
potential (internal energy U, enthalpy H, Helmholtz energy F, and Gibbs energy G), and the entropy
S is continuous across the transition, and (iii) the constant-volume heat capacity does not diverge
during the transition and only exhibits discrete jumps. These non-intuitive results highlight the
importance of controlling the correct variables in order to distinguish between continuous and
discontinuous transitions. We apply our results to describe the transition between ice VI and liquid
water using thermodynamic information available in the literature and also to show that a firstorder
phase transition driven in isochoric condition can be used as the operating principle of a
mechanical actuator.
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Puig, J., N. R. Cejas Bolecek, J. Aragón Sánchez, M. I. Dolz, M. Konczykowski, and Y. Fasano. "Bridge in micron-sized Bi2Sr2CaCu2O8 sample act as converging lens for vortices." Physica C: Superconductivity and its Applications 590 (2021): 1353948.
Abstract: We report on direct imaging of vortex matter nucleated in micron-sized BiSrCaCuO superconducting samples that incidentally present a bridge structure. We find that when nucleating vortices in a field-cooling condition the deck of the bridge acts as a converging lens for vortices. By means of Bitter decoration images allowing us to quantify the enhancement of vortex-vortex interaction energy per unit length in the deck of the bridge, we are able to estimate that the deck is thinner than m. We show that the structural properties of vortex matter nucleated in micron-sized thin samples are not significantly affected by sample-thickness variations of the order of half a micron, an important information for type-II superconductors-based mesoscopic technological devices.
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