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The three-dimensional Dirac semimetal $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$ has attracted intensive attention recently for its exotic properties. Understanding the hot carrier excitation and its subsequent relaxation is a prerequisite for $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$-based optoelectronics functional in the infrared (IR) and terahertz (THz) frequency range. In this work, the photoexcited hot carrier dynamics of a bulk single crystal $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$ in the mid-IR has been explored by using the time-resolved pump-probe reflectance ($\mathrm{\ensuremath{\Delta}}R/R$) measurement at room temperature under a strong optical pumping. By combining the experimental $\mathrm{\ensuremath{\Delta}}R/R$ results and theoretical modeling, we analyzed the transient hot carrier redistribution upon a strong photoexcitation and the subsequent interband transitions. We show that the $\mathrm{\ensuremath{\Delta}}R/R$ response of $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$ has a complex behavior, due to the interplay of transitions between Dirac bands and transitions involving both the Dirac and non-Dirac bands. Throughout the mid-IR region measured, we find that $\mathrm{\ensuremath{\Delta}}R/R$ is contributed primarily by changes in the refractive index, rather than by changes in the extinction coefficient. Our findings can help understanding the transient hot electron excitation and relaxation in $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$ under an intense optical pumping, and provide a valuable reference for the $\mathrm{C}{\mathrm{d}}_{3}\mathrm{A}{\mathrm{s}}_{2}$-based ultrafast optoelectronics application.

We report the discovery of superconductivity in high-quality single crystals of transition-metal pnictides WP grown by chemical vapor transport method. Bulk superconductivity is observed at ${T}_{\text{c}}\ensuremath{\sim}0.8\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ at ambient pressure by electrical resistivity, ac magnetic susceptibility, and specific-heat measurements. The effects of magnetic field on the superconducting transitions are studied, leading to a large anisotropy parameter around 2 with the in-plane and out-of-plane upper critical fields of ${\ensuremath{\mu}}_{0}{H}_{\text{c}2,\ensuremath{\parallel}}=17.2\phantom{\rule{0.28em}{0ex}}\mathrm{mT}$ and ${\ensuremath{\mu}}_{0}{H}_{\text{c}2,\ensuremath{\perp}}=8.5\phantom{\rule{0.28em}{0ex}}\mathrm{mT}$, respectively. The low value of electron-phonon coupling estimated from the normal-state resistivity and specific-heat measurements suggest that WP is a weak-coupling BCS superconductor. Our finding demonstrates that WP is the first superconductor among $5d$--transition metal pnictides with MnP-type structure at ambient pressure, which will help in the search for new superconductors in transition-metal pnictides.

Unconventional superconductivity frequently emerges as the transition temperature of a magnetic phase, typically antiferromagnetic (AFM), is suppressed continuously toward zero temperature. Here, we report contrary behavior in pressurized $\mathrm{CeRhG}{\mathrm{e}}_{3}$, a noncentrosymmetric heavy-fermion compound. We find that its pressure-tuned AFM transition temperature (${T}_{N}$) appears to avoid a continuous decrease to zero temperature by terminating abruptly above a dome of pressure-induced superconductivity. Near 21.5 GPa, evidence for ${T}_{N}$ suddenly vanishes, the electrical resistance becomes linear in temperature, and the superconducting transition reaches a maximum. Analysis of high-pressure resistance and x-ray-absorption spectroscopy measurements suggest that the anomalous connection between antiferromagnetic and superconducting phases in pressurized $\mathrm{CeRhG}{\mathrm{e}}_{3}$ is associated with proximity to a critical valence instability.

We report results of isothermal magnetotransport and susceptibility measurements at elevated magnetic fields B down to very low temperatures T on high-quality single crystals of the frustrated Kondo-lattice system CePdAl. They reveal a B*(T) line within the paramagnetic part of the phase diagram. This line denotes a thermally broadened 'small'-to-'large' Fermi surface crossover which substantially narrows upon cooling. At B_0* = B*(T=0) = (4.6 +/- 0.1) T, this B*(T) line merges with two other crossover lines, viz. Tp(B) below and T_FL(B) above B_0*. Tp characterizes a frustration-dominated spin-liquid state, while T_FL is the Fermi-liquid temperature associated with the lattice Kondo effect. Non-Fermi-liquid phenomena which are commonly observed near a 'Kondo destruction' quantum critical point cannot be resolved in CePdAl. Our observations reveal a rare case where Kondo coupling, frustration and quantum criticality are closely intertwined., Comment: 13 pages, 10 figures

We report the discovery of superconductivity in pressurized CeRhGe3, until now the only remaining non-superconducting member of the isostructural family of non-centrosymmetric heavy-fermion compounds CeTX3 (T = Co, Rh, Ir and X = Si, Ge). Superconductivity appears in CeRhGe3 at a pressure of 19.6 GPa and the transition temperature Tc reaches a maximum value of 1.3 K at 21.5 GPa. This finding provides an opportunity to establish systematic correlations between superconductivity and materials properties within this family. Though ambient-pressure unit-cell volumes and critical pressures for superconductivity vary substantially across the series, all family members reach a maximum Tcmax at a common critical cell volume Vcrit, and Tcmax at Vcrit increases with increasing spin-orbit coupling strength of the d-electrons. These correlations show that substantial Kondo hybridization and spin-orbit coupling favor superconductivity in this family, the latter reflecting the role of broken centro-symmetry.

We report a comprehensive investigation of the electrical, thermal, and thermoelectric transport properties of bulk single-crystalline black phosphorus in wide temperature (2--300 K) and field (0--9 T) ranges. Electrical transport below $T\ensuremath{\approx}$ 250 K is found to be dominated by extrinsic hole-type charge carriers with large mobility exceeding ${10}^{4}$ ${\mathrm{cm}}^{2}$/V s at low temperatures. While thermal transport measurements reveal an enhanced in-plane thermal conductivity maximum $\ensuremath{\kappa}$ = 180 W/m K at $T\ensuremath{\approx}$ 25 K, it appears still to be largely constrained by extrinsic phonon scattering processes, e.g., the electron-phonon process, in addition to intrinsic umklapp scattering. The thermoelectric power and Nernst effect seem to be strongly influenced by ambipolar transport of charge carriers with opposite signs in at least the high-temperature region above 200 K, which diminishes the thermoelectric power factor of this material. Our results provide a timely update to the transport properties of bulk black phosphorus for future fundamental and applied research.

From the electrical resistivity and ac susceptibility measurements down to $T$ = 40 mK, a rich temperature-field phase diagram has been constructed for the geometrically frustrated heavy-fermion compound CePdAl. In the limit of zero temperature, the field-induced suppression of the antiferromagnetism in this compound results in a sequence of phase transitions/corssovers, rather than a single critical point, in a critical region of field 3$-$5 T. In the lowest temperature region, a power-law description of the temperature-dependent resistivity yields $A$$\cdot$$T^n$ with $n$$>$2 for all applied fields. However, a quadratic-in-temperature resistivity term can be extracted when assuming an additional electron scattering channel from magnon-like excitations, with $A$ diverging upon approaching the critical regime. Our observations suggest CePdAl to be a new playground for exotic physics arising from the competition between Kondo screening and geometrical frustration., 5 pages, 5 figures

We report on magnetotransport properties of the Kondo semiconducting compound ${\mathrm{CeRu}}_{2}{\mathrm{Al}}_{10}$, focusing on its exotic phase below ${T}_{0}=27$ K. An excess thermal conductivity $\ensuremath{\kappa}$ emerges below ${T}_{0}$ and is gradually suppressed by magnetic field, strikingly resembling those observed in the hidden-order phase of ${\mathrm{URu}}_{2}{\mathrm{Si}}_{2}$. Our analysis indicates that low-energy magnetic excitation is the most likely origin, as was also proposed for ${\mathrm{URu}}_{2}{\mathrm{Si}}_{2}$ recently based on inelastic x-ray scattering measurements of phonon dynamics, despite the largely reduced magnetic moments. Likewise, other transport properties such as resistivity, thermopower, and Nernst effect exhibit distinct features characterizing the very different charge dynamics above and below ${T}_{0}$, sharing similarities to ${\mathrm{URu}}_{2}{\mathrm{Si}}_{2}$, too. Given the exotic nature of the ordered phase in both compounds, whether a unified interpretation to all these observations exists appears to be extremely interesting.

A distinctly temperature-dependent Nernst coefficient, ν, which is strongly enhanced over that of LaCu(2)Si(2), is observed between T=2 and 300 K for CeCu(2)Si(2) and Ce(0.8)La(0.2)Cu(2)Si(2). The enhanced ν(T) is determined by the asymmetry of the on-site Kondo (conduction electron -4f electron) scattering rate. Taking into account the measured Hall mobility, μ(H), the highly unusual thermopower, S, of these systems can be semiquantitatively described by S(T)=-ν(T)/μ(H)(T), which explicitly demonstrates that the thermopower originates from the local Kondo scattering process over a wide temperature range from far above to well below the coherence temperature (≈20 K for CeCu(2)Si(2)). Our results suggest that the Nernst effect can act as a proper probe of local charge-carrier scattering. This promises to impact on exploring the unconventional enhancement of the thermopower in correlated materials suited for potential applications.

Substitution of Cu for Ni in the Kondo lattice system CeNi$_2$Al$_3$ results in a simultaneous optimization of the three interdependent thermoelectric parameters: thermoelectric power, electrical and thermal conductivities, where the electronic change in conduction band induced by the extra electron of Cu is shown to be crucial. The obtained thermoelectric figure of merit $zT$ amounts to 0.125 at around 100 K, comparable to the best values known for Kondo compounds. The realization of ideal thermoelectric optimization in Ce(Ni$_{1-x}$Cu$_x$)$_2$Al$_3$ indicates that proper electronic tuning of Kondo compounds is a promising approach to efficient thermoelectric materials for cryogenic application.

Huge negative values of both the thermopower, $S=\ensuremath{-}10\text{ }\text{mV}/\text{K}$ at 10 K, and the Nernst coefficient, $\ensuremath{\nu}=\ensuremath{-}550\text{ }\ensuremath{\mu}\text{V}/\text{K}\text{ }\text{T}$ at 7.5 K, are observed for ${\text{FeSb}}_{2}$, a narrow-gap semiconductor showing strong indications of correlation effects. A semiquantitative interpretation based on electron diffusion is presented, which suggests that the dominant term in $S(T)$, although electronic in origin, is enhanced by a factor larger than 10. This is ascribed to the presence of electron-electron correlations in ${\text{FeSb}}_{2}$ and excludes phonon drag as the dominating mechanism for the large thermopower. The correlation-enhanced thermoelectricity is of great interest for theoretical exploration as well as potential application in cooling devices at cryogenic temperatures.

The filled skutterudite compound $\mathrm{Sm}{\mathrm{Ru}}_{4}{\mathrm{P}}_{12}$ undergoes a complex evolution from a paramagnetic metal (phase I) to a probable multipolar ordering insulator (phase II) at ${T}_{\mathrm{MI}}\ensuremath{\sim}16.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, then to a magnetically ordered phase (phase III) at ${T}_{\mathrm{N}}\ensuremath{\sim}14\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Elastic properties under hydrostatic pressures were investigated to study the nature of the ordering phases. We found that distinct elastic softening above ${T}_{\mathrm{MI}}$ is induced by pressure, giving evidence of quadrupole degeneracy of the ground state in the crystalline electric field. It also suggests that quadrupole moment may be one of the order parameters below ${T}_{\mathrm{MI}}$. Strangely, the largest degree of softening is found in the transverse elastic constant ${C}_{T}$ at around $0.5--0.6\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, presumably having relevance to the competing and very different Gr\"uneisen parameters $\ensuremath{\Omega}$ of ${T}_{\mathrm{MI}}$ and ${T}_{\mathrm{N}}$. The interplay between the two phase transitions is also verified by the rapid increase of ${T}_{\mathrm{MI}}$ under pressure with a considerably large $\ensuremath{\Omega}$ of 9. These results can be understood on the basis of the proposed octupole scenario for $\mathrm{Sm}{\mathrm{Ru}}_{4}{\mathrm{P}}_{12}$.