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We studied the effects of point defects and Hg impurities in the electronic properties of bismuth iodide (Bi$_4$I$_4$). Our transport measurements after annealing at different temperatures show that the resistivity of Bi$_4$I$_4$ depends on its thermal history, suggesting that the formation of native defects and impurities can shape the temperature dependence of electrical resistivity. Our density functional theory calculations indicate that the bismuth and iodine antisites, and bismuth vacancies are the dominant native point defects. We find that bismuth antisites introduce resonant states in the band-edges, while iodine antisites and bismuth vacancies lead to a $n$-type and $p$-type doping of Bi$_4$I$_4$, respectively. The Hg impurities are likely to be found at Bi substitutional sites, giving rise to the $p$-type doping of Bi$_4$I$_4$. Overall, our findings indicate that the presence of native point defects and impurities can significantly modify the electronic properties, and, thus, impact the resistivity profile of Bi$_4$I$_4$ due to modifications in the amount and type of carriers, and the associated defect(impurity) scattering. Our results suggest possible routes for pursuing fine-tuning of the electronic properties of quasi-one-dimensional quantum materials.

The bismuth-halide Bi$_4$I$_4$ undergoes a structural transition around $T_P\sim 300$K, which separates a high-temperature $\beta$ phase ($T>T_P$) from a low-temperature $\alpha$ phase ($T

We report on a modified chemical vapor transport (CVT) methodology for the growth of pure and intercalated Zr, Ti, and Hf dichalcogenide single crystals, e.g. ZrTe2, Gd0.05ZrTe2, HfTe2, and Cu0.05TiTe2. While the most common method for CVT growth is carried out in quartz tubes subjected to a temperature gradient between the charge and the growth location, the growth using this isothermal-CVT (ICVT) method takes place isothermally in sealed quartz tubes placed horizontally in box furnaces, using iodine (I2) as the transport agent. The structure and composition of crystals were determined by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and induced coupling plasma (ICP). The crystals grown with this method can be large, and show excellent crystallinity and homogeneity. Their morphology is plate-like, and the larger dimensions can be as long as 15 mm., Comment: submitted to journal of crystal growth

We report for the first time the occurrence of superconductivity in the quaternary silicide carbide YRe2SiC with Tc = 5.9 K. The emergence of superconductivity was confirmed by means of magnetic susceptibility, electrical resistivity, and heat capacity measurements. The presence of a well developed heat capacity feature at Tc confirms that superconductivity is a bulk phenomenon, while a second feature in the heat capacity near 0.5 Tc combined with the unusual temperature dependence of the upper critical field Hc2(T) indicate the presence of a multiband superconducting state. Additionally, the linear dependence of the lower critical field Hc1 with temperature resemble the behavior found in compounds with unconventional pairing symmetry. Band structure calculations reveal YRe2SiC could harbor a non-trivial topological state and that the low-energy states occupy multiple disconnected sheets at the Fermi surface, with different degrees of hybridization, nesting, and screening effects, therefore making unconventional multiband superconductivity plausible., Comment: 17 pages, 5 figures

We carried out a comprehensive study of the electronic, magnetic, and thermodynamic properties of Ni-doped ZrTe$_2$. High quality Ni$_{0.04}$ZrTe$_{1.89}$ single crystals show a possible coexistence of charge density waves (CDW, T$_{CDW}\approx287$\,K) with superconductivity (T$_c\approx 4.1$\,K), which we report here for the first time. The temperature dependence of the lower (H$_{c_1}$) and upper (H$_{c_2}$) critical magnetic fields both deviate significantly from the behaviors expected in conventional single-gap s-wave superconductors. However, the behaviors of the normalized superfluid density $\rho_s(T)$ and H$_{c_2}(T)$ can be described well using a two-gap model for the Fermi surface, in a manner consistent with conventional multiband superconductivity. Electrical resistivity and specific heat measurements show clear anomalies centered near 287\,K consistent with a CDW phase transition. Additionally, electronic-structure calculations support the coexistence of electron-phonon multiband superconductivity and CDW order due to the compensated disconnected nature of the electron- and hole-pockets at the Fermi surface. Our electronic structure calculations also suggest that ZrTe$_2$ could reach a non-trivial topological type-II Dirac semimetallic state. These findings highlight that Ni-doped ZrTe2 can be uniquely important for probing the coexistence of superconducting and CDW ground states in an electronic system with non-trivial topology.

In the present work, we investigated the electronic and elastic properties in equilibrium and under strain of the type-II Dirac semimetal NiTe$_2$ using density functional theory (DFT). Our results demonstrate the tunability of Dirac nodes' energy and momentum with strain and that it is possible to bring them closer to the Fermi level, while other metallic bands are supressed. We also derive a minimal 4-band effective model for the Dirac cones which accounts for the aforementioned strain effects by means of lattice regularization, providing an inexpensive way for further theoretical investigations and easy comparison with experiments. On an equal footing, we propose the static control of the electronic structure by intercalating alkali species into the van der Waals gap, resulting in the same effects obtained by strain-engineering and removing the requirement of in situ strain. Finally, evaluating the wavefunction's symmetry evolution as the lattice is deformed, we discuss possible consequences, such as Liftshitz transitions and the coexistence of type-I and type-II Dirac cones, thus motivating future investigations., Comment: 14 pages, 13 figures