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Although nodal spin-triplet topological superconductivity appears probable in uranium ditelluride (UTe₂), its superconductive order parameter Δ_kremains unestablished. In theory, a distinctive identifier would be the existence of a superconductive topological surface band, which could facilitate zero-energy Andreev tunneling to an s-wave superconductor and also distinguish a chiral from a nonchiral Δ_kthrough enhanced s-wave proximity. In this study, we used s-wave superconductive scan tips and detected intense zero-energy Andreev conductance at the UTe₂(0-11) termination surface. Imaging revealed subgap quasiparticle scattering interference signatures witha-axis orientation. The observed zero-energy Andreev peak splitting with enhanced s-wave proximity signifies that Δ_kof UTe₂is a nonchiral state:B_1u,B_2u, orB_3u. However, if the quasiparticle scattering along theaaxis is internodal, then a nonchiralB_3ustate is the most consistent for UTe₂. 

Here, we report CdS quantum dot (QD) gels, a three‐dimensional network of interconnected CdS QDs, as a new type of direct hydrogen atom transfer (d‐HAT) photocatalyst for C‐H activation. We discovered that the photoexcited CdS QD gel could generate various neutral radicals, including α‐amido, heterocyclic, acyl, and benzylic radicals, from their corresponding stable molecular substrates, including amides, thio/ethers, aldehydes, and benzylic compounds. Its C‐H activation ability imparts a broad substrate and reaction scope. The mechanistic study reveals that this reactivity is intrinsic to CdS materials, and the neutral radical generation did not proceed via the conventional sequential electron transfer and proton transfer pathway. Instead, the C‐H bonds are activated by the photoexcited CdS QD gel via a d‐HAT mechanism. This d‐HAT mechanism is supported by the linear correlation between the logarithm of the C‐H bond activation rate constant and the C‐H bond dissociation energy (BDE) with a Brønsted slope α = 0.5. Our findings expand the currently limited direct hydrogen atom transfer photocatalysis toolbox and provide new possibilities for photocatalytic C‐H activation. 

Abstract Although no known material exhibits intrinsic topological superconductivity, where a spin-triplet electron pairing potential has odd parity, UTe₂is now the leading candidate. Generally, the parity of a superconducting order parameter can be established using Bogoliubov quasiparticle interference imaging. However, odd-parity superconductors should support a topological quasiparticle surface band at energies within the maximum superconducting energy gap. Quasiparticle interference should then be dominated by the electronic structure of the quasiparticle surface band and only reveal the characteristics of the bulk order parameter indirectly. Here we demonstrate that at the (0–11) cleave surface of UTe₂, a band of Bogoliubov quasiparticles appears only in the superconducting state. Performing high-resolution quasiparticle interference measurements then allows us to explore the dispersion of states in this superconductive surface band, showing that they exist only within the range of Fermi momenta projected onto the (0–11) surface. Finally, we develop a theoretical framework to predict the quasiparticle interference signatures of this surface band at the (0–11) surface. Its predictions are consistent with the experimental results if the bulk superconducting order parameter exhibits time-reversal conserving, odd-parity,a-axis nodal,B_3usymmetry. 

As a neighbor of carbon in the periodic table, boron exhibits versatile structural and electronic configurations, with its allotropes predicted to possess intriguing structures and properties. Since the experimental realization of two-dimensional (2D) boron sheets (borophene) on Ag(111) substrates in 2015, the experimental study of the realization and characteristics of borophene has drawn increasing interest. In this review, we summarize the synthesis and properties of borophene, which are mainly based on experimental results. First, the synthesis of borophene on different substrates, as well as borophane and bilayer borophene, featuring unique phases and properties, are discussed. Next, the chemistry of borophene, such as oxidation, hydrogenation, and its integration into heterostructures with other materials, is summarized. We also mention a few works focused on the physical properties of borophene, specifically its electronic properties. Lastly, the brief outlook addresses challenges toward practical applications of borophene and possible solutions. 

Bilayer (BL) two-dimensional boron (i.e., borophene) emerges very recently and holds promise for fascinating physical properties and a variety of electronic applications. Despite this potential, the fundamental chemical properties of BL borophene which form the critical foundation of practical applications has been unexplored. Here, we present atomic-level chemical studies of BL borophene using ultrahigh vacuum tip-enhanced Raman spectroscopy (UHV-TERS). UHV-TERS identifies the vibrational fingerprint of BL borophene from mixed-dimensional borophene polymorphs with angstrom-scale chemical spatial resolution. The observed Raman mode is directly correlated with the vibrations of interlayer boron-boron bonds, validating the three-dimensional lattice geometry of BL borophene. By virtue of the single-bond sensitivity of UHV-TERS to oxygen adatoms, we demonstrate the enhanced chemical stability of BL borophene compared to its monolayer counterpart by exposure to controlled oxidizing atmospheres under UHV. In addition to revealing fundamental chemical insights into BL borophene, this work establishes UHV-TERS as a powerful tool to probe interlayer bonding and chemical properties of layered materials at the atomic scale.