Huixia Luo

The search for unconventional superconductors is a hot topic in materials science and condensed matter physics, yet remains challenging. Here we report a series of medium-entropy carbides (MECs) within the Ta–Nb–Hf–Zr–C system with finely tuned valence electron concentration (VEC). Through VEC engineering, the type-II Dirac points are deliberately shifted from approximately 0.19 eV below the Fermi level in the base composition Ta0.25Nb0.25Hf0.25Zr0.25C to within 6.7–59.1 meV of the Fermi level in the optimal composition Ta0.1875Nb0.1875Hf0.3125Zr0.3125C. All five compositions form single-phase rock-salt structures and exhibit type-II bulk superconductivity with TcMid ranging from 2.2 to 4.9 K. Among these, the equimolar Ta0.25Nb0.25Hf0.25Zr0.25C composition exhibits the highest Tc of 4.9 K, with μ0Hc2GL = 1.16 T, μ0Hc1(0) = 65.9 Oe, and ΔC/γTc = 1.16, alongside excellent stability in acidic/alkaline environments and under pressures up to 52 GPa. Our findings establish VEC engineering as a potentially transferable strategy for bridging topological band physics with superconductivity in medium/high-entropy ceramics, positioning this MEC family as a candidate platform for investigating topological superconductivity in disordered systems.

Quantum Griffiths singularity (QGS) has been a crucial phenomenon arising from quenched disorder in the superconductor-metal/insulator transitions (SMT/SITs) of superconducting systems, but it is rarely observed in bulk superconductors due to the weak fluctuations. Exploring the realization of enhanced fluctuations in disordered bulk superconductors is important for understanding the universality of QGS with different dimensionality. In this study, we reveal anisotropic quantum phase transition (QPT) in the bulk 1 T -NbSeTe showing quasi-2D superconductivity by systematic electrical transport measurements under magnetic fields applied in different orientations. Under a perpendicular magnetic field, the isothermal magnetoresistance curves show a series of crossing points in the SMT. The effective scaling analysis of the magnetoresistance behavior reveals divergent critical exponent z v values when the zero-temperature critical point B c ∗ is approached, which identifies a 2D QGS characteristic in the bulk crystals. In contrast, single criticality with fixed z ν occurs in the 1 T -NbSeTe subject to parallel magnetic fields. The finding of enhanced fluctuation effects in our bulk superconductor provides an extended and promising platform for the research of QPT and QGS. Moreover, compared to fragile low-dimensional systems requiring intricate fabrication technologies, our work offers a stable and accessible platform for studying 2D superconductivity.

Since the first report of a high-entropy alloy (HEA) superconductor in 2014, HEAs have continued to captivate the interest of superconducting researchers. Owing to the significant degree of disorder inherent in these systems, they serve as exemplary models for examining the properties of materials that exist in states intermediate between crystalline and amorphous structures. Here we present the superconductivity properties and crystal structure of TaNbHfZrAl and TiHfNbTaAl HEAs, which both have the valence electron count (VEC) of 4.2 and body-centered cubic (BCC) structure. Through resistivity, magnetic, and specific heat measurements, we prove that both samples are the bulk type-II superconductors with a critical temperature T _c of 5.5 K for TaNbHfZrAl and T _c of 3.2 K for TiHfNbTaAl. The T _c of HEA superconductors is influenced by the VEC and the element composition. And the incorporation of Al in high disorder HEA superconductors causes a more crystallinelike T _c dependence. We also found that the ΔC _el /γ   T c mid (2.31) and 2Δ ₀ / K _B T _c (4.48) of the TaNbHfZrAl sample are close to the known strongly coupled systems, suggesting that it is a strongly coupled superconductor. The TaNbHfZrAl HEA system serves as a novel material platform for exploring strongly coupled phenomena.

The photochemical CO2 reduction reaction represents a zero-carbon pathway for converting CO2 into value-added chemicals, yet its industrial implementation has been constrained by low selectivity and product diversity. Dirac nodal arc semimetals characterized by ultrahigh carrier mobility with over 25000 cm2 V-1 s-1 offer a promising platform to search for efficient catalysts for CO2 conversion. Herein, we demonstrate that strategic Pt incorporation into PdSn4 optimizes the electronic structure and carrier dynamics of this Dirac semimetal. Experimental and theoretical analyses reveal that the resulting Pd-Sn-Pt local electronic structure redistributes charge density around Pd and Pt atoms, which facilitates C-C coupling via *OC-COH and *OC-CHOH intermediates and enhances carrier mobility by 40% versus the pristine PdSn4 single crystal. The optimized Pd0.4Pt0.6Sn4 single crystal achieves C2H4 with formation rate of 0.000328 mol g-1 h-1, product selectivity of 73.1% and electron-based selectivity of 89%. This work establishes electronic-structure-tunable Dirac semimetals as a new paradigm for multi-carbon photochemical CO2 reduction, providing a design strategy for next-generation photocatalysts.

Searching for new superconductors, especially unconventional superconductors, has been studied extensively for decades but remains one of the major outstanding challenges in condensed matter physics. Medium/high-entropy alloys (MEAs-HEAs) are new fertile soils of unconventional superconductors and generate widespread interest and questions on the existence of superconductivity in highly disordered materials. Here, we report on the effect of Ni-doped on the crystal structure and superconductivity properties of strongly coupled TiHfNbTa MEA. XRD results indicate that the maximum solid solution of (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix is about 7.7%. Resistivity, magnetic susceptibility, and specific heat measurements demonstrated that (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix HEAs are all bulk type-II superconductors and follow the trend of the increase of Tc with the increase of Ni-doped contents. The specific heat jump (∆Cel/γ"T" _"c" ^" mid" ) of all (Ti_1/4Hf1/4Nb_1/4Ta_1/4)_1-xNi_x are much larger than the BCS value of 1.43, suggesting all these HEAs are strongly coupled superconductors. Additionally, large Kadawaki-Woods ratio (KWR) values suggest that there is a strong electron correlation effect in this system. The (Ti_1/4Hf1/4Nb_1/4Ta_1/4)_1-xNi_x HEA system is a new ideal material platform for the study of strong correlation behavior and strongly coupled superconductivity, which provides an insight into the physics of high-temperature superconductors or other unconventional superconductors.

The class of unconventional superconductors, particularly noncentrosymmetric superconductors, has been highly considered as potential materials for understanding the complex properties of quantum materials. Here, five previously unreported Re3.5Os3.5Ta0.5Hf0.5Nb3, Re3Os3Ta0.5Hf0.5Nb3, Re3.5Os3.5Mo0.5Hf0.5Nb3, Re3.5Os3.5Mo0.5W0.5Nb3, and Re3Os3Mo0.5Hf0.5Nb3 Re-Os-based high/medium-entropy alloys (MEAs-HEAs) with valence electron count ranging from 6.45 to 6.81 were synthesized and investigated using x-ray diffraction, transport, magnetization, and specific heat measurements. Our analyses confirm that all five compounds crystallize in a noncentrosymmetric α-Mn-type structure and exhibit type-II superconductivity with Tc values from 4.20 K to 5.11 K, respectively. Unexpectedly, despite being immersed in an acidic environment for one month, the structures and superconducting properties of HEAs remain stable. Our findings indicate that the Tc increases with an increasing valence electron count in MEAs-HEAs. Furthermore, these noncentrosymmetric α-Mn-type HEA superconductors have large Kadowaki-Woods ratios (KWR), implying the presence of strong electronic correlations.

Searching for new superconductors, especially unconventional superconductors, has been studied extensively for decades but remains one of the major outstanding challenges in condensed matter physics. Medium/high-entropy alloys (MEAs-HEAs) are new fertile soils of unconventional superconductors and generate widespread interest and questions on the existence of superconductivity in highly disordered materials. Here, we report on the effect of Ni-doped on the crystal structure and superconductivity properties of strongly coupled TiHfNbTa MEA. XRD results indicate that the maximum solid solution of (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix is about 7.7%. Resistivity, magnetic susceptibility, and specific heat measurements demonstrated that (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix HEAs are all bulk type-II superconductors and follow the trend of the increase of Tc with the increase of Ni-doped contents. The specific heat jump of all (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix are much larger than the BCS value of 1.43, suggesting all these HEAs are strongly coupled superconductors. Additionally, large Kadawaki-Woods ratio values suggest that there is a strong electron correlation effect in this system. The (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix HEA system is a new ideal material platform for the study of strong correlation behavior and strongly coupled superconductivity, which provides an insight into the physics of high-temperature superconductors or other unconventional superconductors.