We report thermodynamic and transport properties of LaCuxSb2 (0.92 x 1.12), synthesized by controlling the initial loading composition and investigated by magnetization, electrical resistivity, and specific heat measurements. The physical properties of this system are highly dependent on Cu-site occupancy x, where residual resistivity ratio (RRR), magnetoresistance (MR), superconducting transition temperature (Tc), and electronic specific heat coefficient (gamma ) indicate a systematic variation as a function of x. The Shubnikov-de Haas quantum oscillations are observed in magnetoresistance measurements for samples close to the Cu stoichiometry x <^> 1, while the de Haas-van Alphen oscillations are detected in a wide range of x (0.92 x 1.12). For H H c, the oscillation frequency indicates a clear x-dependence, implying a systematic change of Fermi surface. DFT calculations for the sample closest to ideal Cu stoichiometry reveal electronic structures with a common feature of the square-net-based semimetals, which is in good agreement with the experimental observations. The magnetic response of LaCuxSb2 to magnetic fields is anisotropic owing to the Fermi surface anisotropy. Our results show how the physical properties are influenced by the Cu-site occupancy x, linked to the electronic bands arising from the Sb square net.

CeCd$_3$P$_3$ and CeCd$_3$As$_3$ compounds adopt the hexagonal ScAl$_3$C$_3$-type structure, where magnetic Ce ions on a triangular lattice order antiferromagnetically below $T_\text{N} \sim$0.42~K. Their crystalline electric field (CEF) level scheme has been determined by fitting magnetic susceptibility curves, magnetization isotherms, and Schottky anomalies in specific heat. The calculated results, incorporating the CEF excitation, Zeeman splitting, and molecular field, are in good agreement with the experimental data. The CEF model, with Ce$^{3+}$ ions in a trigonal symmetry, explains the strong easy-plane magnetic anisotropy that has been observed in this family of materials. A detailed examination of the CEF parameters suggests that the fourth order CEF parameter $B_{4}^{3}$ is responsible for the strong CEF induced magnetocrystalline anisotropy, with a large $ab$-plane moment and a small $c$-axis moment. The reliability of our CEF analysis is assessed by comparing the current study with earlier reports of CeCd$_{3}$As$_{3}$. For both CeCd$_{3}X_{3}$ ($X$ = P and As) compounds, less than 40 \% of $R\ln(2)$ magnetic entropy is recovered by $T_\text{N}$ and full $R\ln(2)$ entropy is achieved at the Weiss temperature $\theta_{p}$. Although the observed magnetic entropy is reminiscent of delocalized 4$f$-electron magnetism with significant Kondo screening, the electrical resistivity of these compounds follows a typical metallic behavior. Measurements of thermoelectric power further validate the absence of Kondo contribution in CeCd$_{3}X_{3}$.

Single crystals of RCd0.67As2 (R = La and Ce) have been synthesized by a high-temperature ternary melt and their physical properties have been explored by means of magnetization, specific heat, electrical resistivity, Hall coefficient, and thermoelectric power measurements. RCd0.67As2 compounds indicate a (structural) phase transition at high temperatures, accompanied by a remarkable increase of the electrical resistivity with an extremely low carrier concentration. CeCd0.67As2 exhibits a large magnetic anisotropy and an antiferromagnetic (AFM) order below TN = 4 K. Magnetic susceptibility curves, together with magnetization isotherms and specific heat, are analyzed by the point charge model of the crystalline electric field (CEF). In the paramagnetic state, the observed magnetic properties can be well explained by the CEF effects, implying that the 4 f moments remain localized. Electrical resistivity measurements, together with Hall resistivity and thermoelectric power, also suggest highly localized 4 f electrons, where Kondo contributions are negligible. The low-temperature physical properties manifest strong magnetic field dependencies. For H perpendicular to c, T-N shifts to lower temperature as magnetic field increases and eventually disappears at Hc similar to 60 kOe. Inside the AFM state, three metamagnetic transitions are clearly evidenced from the magnetization isotherms. The RKKY interaction may be responsible for the AFM ordering in CeCd0.67As2; however, it would have to be mediated by extremely low charge carriers. Although the AFM ordering temperature in CeCd0.67As2 can be continuously suppressed to zero, no AFM quantum phase transition is expected due to the lack of conduction electron clouds to screen the 4f moments.

Superconductivity emerges in $1T$-TiSe$_2$ when its charge density wave (CDW) order is suppressed by Cu intercalation or pressure. Since the CDW state is thought to be an excitonic insulator, an interesting question is whether the superconductivity is also mediated by the excitonic fluctuations. We investigated this question as to the nature of doping induced superconductivity in Cu$_x$TiSe$_2$ by asking if it is consistent with the phonon-mediated pairing. We employed the {\it ab initio} density functional theory and density functional perturbation theory to compute the electron-phonon coupling Eliashberg function from which to calculate the superconducting (SC) critical temperature $T_c$. The calculated $T_c $ as a function of the doping concentration $x$ exhibits a dome shape with the maximum $T_c$ of $2-6$ K at $x \approx 0.05$ for the Coulomb pseudopotential $0 \leq \mu^* \leq 0.1$. The maximal $T_c$ was found to be pinned to the quantum critical point at which the CDW is completely suppressed and the corresponding phonon mode becomes soft. Underlying physics is that the reduced phonon frequency enhances the electron-phonon coupling constant $\lambda$ which overcompensates the frequency decrease to produce a net increase of $T_c$. The doping induced superconductivity in Cu$_x$TiSe$_2$ seems to be consistent with the phonon-mediated pairing. Comparative discussion was made with the pressure induced superconductivity in TiSe$_2$.