A unit cell represents the smallest repeating structure in solid-state physics and serves as the fundamental building block of a material. In iron-based superconductors, each unit cell contains two iron atoms, which form two sublattices in the two-dimensional iron layers. Under normal circumstances, these sublattices are expected to have identical physical properties due to space inversion symmetry. However, we discover that this sublattice structure can introduce a novel degree of freedom for probing unconventional pairing mechanisms in iron-based superconductors. We observe distinct dual tunneling spectra within the pairing gap energy corresponding to the two sublattices in the monolayer FeSe with atomically homogeneous (1×1) structures on SrTiO_{3}(001) substrates-a phenomenon we term sublattice dichotomy. This dichotomy can be quantitatively explained by a parity-breaking superconducting state, characterized by the coexistence of conventional pairing and interband odd-parity pairing. The interband singlet pairing arises due to the lack of inversion symmetry, which is naturally broken from the interface coupling between the FeSe and TiO_{2} layer.

The upconversion luminescence (UCL) materials have the substantial advantages for deeper penetration and detection in tissue imaging and therapy owing to the dominant UCL wave located within the tissue optical transmission window. However, this application is limited by low red UCL efficiency. In this work, we synthesized Bi2O3: Yb3+/Er3+ that exhibits intense red UCL under 980 nm excitation, which is about 5 times as that in conventional Y2O3 sample. The red and green UCL intensity ratio is up to 229.6. Moreover, the red UCL can penetrate 8 mm fresh chicken breast tissue. Not only Bi2O3 host exhibits excellent photocatalytic activity, Bi2O3: Yb3+/Er3+ material also shows enhanced catalytic performance, achieving 91% degradation of methyl orange in 2 h under visible light (VIS). When combined with TiO2 owned ultraviolet (UV) dominant activity, TiO2-modified Bi2O3: Yb3+/Er3+ retains 96% activity under VIS. Furthermore, the degradation efficiency of Bi2O3: Yb3+/Er3+ in the near-infrared (NIR) region can also reach 36% within 3 h, implying it is a promising candidate for UV–VIS–NIR broad-spectrum photocatalytic activity. Our study indicates that Bi2O3: Yb3+/Er3+ is an outstanding multifunctional material that integrate strong red emission with capabilities for deep-tissue imaging and broad-spectrum-responsive photocatalysis.

High-temperature superconductivity has been successively realized in cuprates, iron pnictides/chalcogenides, and nickelates, whereas the cobalt-based high-temperature superconductors remain to be explored. We report the discovery of superconductivity with an onset temperature of 27 K in tetragonal CoSe monolayers synthesized on redox-engineered SrTiO3(001) substrates. Using molecular beam epitaxy, we prepared atomically thin CoSe films on FeOx overlayers that expand the in-plane lattice and reduce the surface work function relative to TiOx-terminated surfaces. In-situ scanning tunneling spectroscopy reveals a symmetric superconducting gap of 14 meV with well-defined coherence peaks. Ex-situ transport measurements confirm a sharp resistance drop with zero resistance at 11 K and a Meissner diamagnetic signal at 10 K. In contrast, CoSe monolayers on TiOx-terminated surfaces show no superconducting transition down to 4 K. These results demonstrate that interface engineering via metal oxide functionalization enables tunable lattice strain and charge doping, establishing CoSe as a new platform for exploring cobalt-based high-temperature superconductivity.

This article presents a novel nitrogen-vacancy (NV) center magnetic sensing probe that utilizes quantum dot light-emitting diodes (QLEDs) as the excitation light source for the NV centers. The QLED employed in this magnetic sensing probe offers several advantages, including high brightness, controllable light emission area, and ease of fabrication. Key steps in the preparation of the magnetic sensing probe are outlined, and the performance metrics of the NV center magnetic sensing probe are evaluated. Notably, the peak brightness of the quantum dot light-emitting diode reaches 83200 cd/m(2), with an electroluminescence (EL) peak at 532 nm. The probe is capable of measuring magnetic fields in the range of +/- 142.9 mu T, exhibiting a photon shot noise of 12 nT & sdot; Hz(-1/2) and an optimal magnetic noise spectral density of 22.6 nT Hz(-1/2), all within a compact volume of only 315 mm(3). This enables the device to detect weak magnetic fields across various scenarios. The design of the magnetic sensing probe validates the excitation effectiveness of QLEDs on diamond NV centers, providing a new solution for the future development of planar and integrated magnetometer devices through micro-nanofabrication techniques.

High-density mirror twin boundaries (MTBs) embedded in two-dimensional (2D) transition metal dichalcogenides (TMDCs) have emerged as fascinating platforms for exploring charge density wave and Tomonaga-Luttinger liquid-related issues. However, the reversible manipulation of high-density MTBs in 2D TMDCs remains challenging. Herein, we report the first fabrication of high-density MTB loops in ultrathin 1T-NiTe2 on the SrTiO3(001) substrate, by postannealing as-grown 1T-NiTe2 under Te-deficient conditions. This formation process is found to be mediated by the generation, accumulation, and assembly of Te vacancies into triangular vacancy loops in ultrathin 1T-NiTe2, according to on-site scanning tunneling microscopy/spectroscopy (STM/STS) characterizations combined with density functional theory (DFT) calculations. Unique charge density modification is also observed to be correlated with the length of the one-dimensional MTBs. Overall, this work should inspire further investigations of the formation mechanism and exotic physical properties of one-dimensional electron systems in ultrathin TMDCs.

Surface with well-defined components and structures possesses unique electronic, magnetic, optical and chemical properties. As a result, surface chemistry research plays a crucial role in various fields such as catalysis, energy, materials, quantum, and microelectronics. Surface science mainly investigates the correspondence between surface property and functionality. Scanning probe microscopy (SPM) techniques are important tools to characterize surface properties because of the capability of atomic-scale imaging, spectroscopy and manipulation at the single-atom level. In this review, we summarize recent advances in surface electronic, magnetic and optical properties characterized mainly by SPM-based methods. We focus on elucidating the π-magnetism in graphene-based nanostructures, construction of spin qubits on surfaces, topology properties of surface organic structures, STM-based light emission, tip-enhanced Raman spectroscopy and integration of machine learning in SPM studies.

Interface-enhanced superconductivity in single-unit-cell FeSe on SrTiO_{3} has been extensively pursued recently. The interfacial electron-phonon coupling (EPC) is widely proposed to enhance pairing, yet to be directly verified. Herein, using ultrafast pump-probe spectroscopy, we discover a coherent 4.2 THz optical phonon mode that emerges only upon photoexcitation in FeTe/FeSe/SrTiO_{3} or FeTe/SrTiO_{3} heterostructures, but is absent in bare Nb-doped SrTiO_{3} under identical subgap pumping. Atomic-scale electron energy loss spectroscopy in scanning transmission electron microscopy identifies this mode as out-of-plane oxygen vibrations localized at double TiO_{x} terminated interface. Crucially, the phonon amplitude in FeTe/FeSe/SrTiO_{3} is more than twice as large as that in FeTe/SrTiO_{3}, which can be attributed to higher electron doping that strengthens dipole moments penetrating the FeSe layer, thereby resulting in an enhanced interfacial EPC. Temperature-dependent dynamics further highlight the unique electronic nature of monolayer FeSe in sustaining this robust coupling. These findings provide direct evidence for dipole-mediated interfacial EPC as a critical mechanism of interfacial superconductivity in FeSe/SrTiO_{3}.

Single-crystal Au(111), renowned for its chemically inert surface, long-range "herringbone" reconstruction, and high electrical conductivity, has long served as an exemplary template in diverse fields, e.g., crystal epitaxy, electronics, and electrocatalysis. However, commercial Au(111) products are high-priced and limited to centimeter sizes, largely restricting their broad applications. Herein, a low-cost, high-reproducible method is developed to produce 4 in. Au(111) single crystals from commercial Au foils, via an abnormal grain growth process. This methodology involves the initial preparation of a (100)-textured Au polycrystalline foil, followed by the evolution and continuous expansion of an Au(111) abnormal grain through one-site stress loading and stress-relief annealing in an Ar/H2 atmosphere. Theoretical simulations indicate that stress/strain and high-temperature treatments in the H2 atmosphere induce an intermediate disordered state, facilitating the evolution from polycrystalline Au(100) foil to single-crystal Au(111) foil. Furthermore, the resulting Au(111) foils have been utilized as model substrates for the oriented growth of two-dimensional transition metal dichalcogenides and their heterostructures with graphene. This work hereby puts forward an effective approach for large-scale, cost-effective production of metal single crystals, potentially revolutionizing their applications across various fields, from materials sciences to electronics and catalysis.

Ultrafast temperature field detection and identification is crucial for applications ranging from environmental sensing and biomedical monitoring to thermal management in advanced energy systems. Conventional temperature sensors—comprising discrete sensing arrays, data storage units, and external processors—suffer from high latency due to slow sensor response, repeated analog-to-digital conversions, and extensive data transmission inherent to von Neumann architectures. Here, we report a diamond array-based quantum sensor that integrates temperature sensing and real-time processing within a unified in-sensor computing (ISC) architecture. Exploiting the strong linear correlation between temperature and the zero-field splitting of nitrogen-vacancy (NV) color center centers in diamond, we realize a fixed-frequency temperature sensor with ultrafast response and tunable responsivity, enabled by multi-parameter microwave modulate. Matrix-vector multiplication of temperature intensity and responsivity, combined with Kirchhoff’s current summation, enables direct execution of neural-network-style computations on sensed data. The proposed system achieves a single-shot detection and identification latency of just 196.8 μs, as experimentally validated. This work demonstrates a scalable ISC-enabled quantum sensing paradigm, offering a promising route toward high-speed, low-power intelligent temperature field detection.

The nature of the anomalous metal state has been a major puzzle in condensed matter physics for more than three decades. Here, we report systematic investigation and modulation of the anomalous metal states in high-temperature interface superconductor FeSe films on SrTiO3 substrate. Remarkably, under zero magnetic field, the anomalous metal state persists up to 20 K in pristine FeSe films, an exceptionally high temperature standing out from previous observations. In stark contrast, for the FeSe films with nano-hole arrays, the characteristic temperature of the anomalous metal state is considerably reduced. We demonstrate that the observed anomalous metal states originate from the quantum tunneling of vortices adjusted by the Ohmic dissipation. Our work offers a perspective for understanding the origin and modulation of the anomalous metal states in two-dimensional bosonic systems.

The interface-enhanced superconductivity in monolayer iron selenide (FeSe) films on SrTiO3 has been actively pursued in the past decade. Although a synergistic effect between interfacial charge transfer and interfacial electron-phonon coupling (EPC) is proposed to be responsible for the mechanism, the microscopic nature of the interfacial EPC in the enhancement of superconductivity remains highly controversial. Herein we experimentally reveal that a coherent optical phonon mode at 4.2 THz from the SrTiO3 substrate couples to FeSe electrons and modulates the quasiparticle relaxations using ultrafast pump-probe spectroscopy. This mode originates from the antiferrodistortive (AFD) transition in SrTiO3 and is significantly stronger in the presence of monolayer FeSe than that in purely FeTe-capped Nb-doped SrTiO3. Pump fluence and temperature-dependent spectroscopy measurements suggest that SrTiO3 substrate facilitates the stabilization of FeSe structure and possibly prevents the occurrence of nematic phase transition, supporting that SrTiO3 substrate modifies the electronic structure of monolayer FeSe through a strong interfacial EPC strength as large as 0.77. Our results provide unprecedented direct evidence that the strong coupling of SrTiO3 coherent phonon to FeSe electrons is indeed responsible for the high-temperature superconductivity in monolayer FeSe and SrTiO3 heterostructure.

AbstractOne-unit-cell FeSe films on SrTiO3 substrates are of great interest owing to significantly enlarged pairing gaps characterized by two coherence peaks at ±10 meV and ±20 meV. In-situ transport measurement is desired to reveal novel properties. Here, we performed in-situ microscale electrical transport and combined scanning tunneling microscopy measurements on continuous one-unit-cell FeSe films with twin boundaries. We observed two spatially coexisting superconducting phases in domains and on boundaries, characterized by distinct superconducting gaps ($${\Delta }_{1}$$ Δ 1 ~15 meV vs. $${\Delta }_{2}$$ Δ 2 ~10 meV) and pairing temperatures (Tp1~52.0 K vs. Tp2~37.3 K), and correspondingly two-step nonlinear $$V \sim {I}^{\alpha }$$ V ~ I α behavior but a concurrent Berezinskii–Kosterlitz–Thouless (BKT)-like transition occurring at $${T}_{{{{{{\rm{BKT}}}}}}}$$ T BKT ~28.7 K. Moreover, the onset transition temperature $${T}_{{{{{{\rm{c}}}}}}}^{{{{{{\rm{onset}}}}}}}$$ T c onset ~54 K and zero-resistivity temperature $${T}_{{{{{{\rm{c}}}}}}}^{{{{{{\rm{zero}}}}}}}$$ T c zero ~31 K are consistent with Tp1 and $${T}_{{{{{{\rm{BKT}}}}}}}$$ T BKT , respectively. Our results indicate the broadened superconducting transition in FeSe/SrTiO3 is related to intrinsic electronic inhomogeneity due to distinct two-gap features and phase fluctuations of two-dimensional superconductivity.

The intrinsic magnetic order, large topological-magnetic gap and rich topological phases make MnBi2Te4 a wonderful platform to study exotic topological quantum states such as axion insulator and Chern insulator. To realize and manipulate these topological phases in a MnBi2Te4 thin film, precise manipulation of the electric field across the film is essential, which requires a dual-gate structure. In this work, we achieve dual-gate tuning of MnBi2Te4 thin films grown with molecular beam epitaxy on SrTiO3(111) substrates by applying the substrate and an AlOx layer as the gate dielectrics of bottom and top gates, respectively. Under magnetic field of 9T and temperature of 20 mK, the Hall and longitudinal resistivities of the films show inversed gate-voltage dependence, for both top- and bottom-gates, signifying the existence of the dissipationless edge state contributed by Chern insulator phase in the ferromagnetic configuration. The maximum of the Hall resistivity only reaches 0.8 h/e2, even with dual-gate tuning, probably due to the high density of bulk carriers introduced by secondary phases. In the antiferromagnetic state under zero magnetic field, the films show normal insulator behavior. The dual-gated MnBi2Te4 thin films lay the foundation for developing devices based on electrically tunable topological quantum states.

Surface chemistry focuses on the investigation of the adsorption, migration, assembly, activation, reaction, and desorption of atoms and molecules at surfaces. Surface chemistry plays the pivotal roles in both fundamental science and applied technology. This review will summarize the recent progresses on surface assembly, synthesis and catalysis investigated mainly by scanning tunneling microscopy and atomic force microscopy. Surface assemblies of water and small biomolecules, construction of Sierpiński triangles and surface chirality are summarized. On-surface synthesis of conjugated carbo- and heterocycles and other kinds of carbon nanostructures are surveyed. Surface model catalysis, including single-atom catalysis and electrochemical catalysis, are discussed at the single-atom level.

Exploring emerging two-dimensional (2D) van der Waals (vdW) semiconducting materials and precisely tuning their electronic properties at the atomic level have long been recognized as crucial issues for developing their high-end electronic and optoelectronic applications. As a III-VI semiconductor, ultrathin layered hexagonal GaTe (h-GaTe) remains unexplored in terms of its intrinsic electronic properties and band engineering strategies. Herein, we report the successful synthesis of ultrathin h-GaTe layers on a selected graphene/SiC(0001) substrate, via molecular beam epitaxy (MBE). The widely tunable quasiparticle band gaps (similar to 2.60-1.55 eV), as well as the vdW quantum well states (QWSs) that can be strictly counted by the layer numbers, are well characterized by onsite scanning tunneling microscopy/spectroscopy (STM/STS), and their origins are clearly addressed by density functional theory (DFT) calculations. More intriguingly, distinctive 8|8E and 4|4P (Ga) mirror twin boundaries (MTBs) are identified in the ultrathin h-GaTe flakes, which can induce decreased band gaps and prominent p-doping effects. This work should deepen our understanding on the electronic tunability of 2D III-VI semiconductors by thickness control and line defect engineering, which may hold promise for fabricating atomic-scale vertical and lateral homojunctions toward ultrascaled electronics and optoelectronics.

The pairing mechanism behind the monolayer FeSe is one essential question for iron-based superconductors. In this work, we show the sublattice degree of freedoms of monolayer FeSe plays a special role in its pairing properties, namely the sublattice dichotomy. The high-quality monolayer FeSe samples with atomic flat 1×1 topography on the SrTiO_3(001) substrates are grown by molecular beam epitaxy. By comparing the tunneling spectra at α and β Fe sublattices, we find the coherence peak of α-Fe at the inner gap +V_i is higher than β-Fe while the coherence peak of β-Fe at -V_i is higher than α-Fe with a similar amount. We also observed a reversed effect at the outer gap ± V_o. We propose the η-pairing mechanism between k and -k+Q is the key mechanism for this unconventional sublattice dichotomy effect.

The discovery of high-mobility two-dimensional electron gas and low carrier density superconductivity in multiple SrTiO3-based heterostructures has stimulated intense interest in the surface properties of SrTiO3. The recent discovery of high-Tc superconductivity in the monolayer FeSe/SrTiO3 led to the upsurge and underscored the atomic precision probe of the surface structure. By performing atomically resolved cryogenic scanning tunneling microscopy/spectroscopy characterization on dual-TiO2-δ-terminated SrTiO3(001) surfaces with (√13 × √13), c(4 × 2), mixed (2 × 1), and (2 × 2) reconstructions, we disclosed universally broken rotational symmetry and contrasting bias- and temperature-dependent electronic states for apical and equatorial oxygen sites. With the sequentially evolved surface reconstructions and simultaneously increasing equatorial oxygen vacancies, the surface anisotropy reduces and the work function lowers. Intriguingly, unidirectional stripe orders appear on the c(4 × 2) surface, whereas local (4 × 4) order emerges and eventually forms long-range unidirectional c(4 × 4) charge order on the (2 × 2) surface. This work reveals robust unidirectional charge orders induced by oxygen vacancies due to strong and delicate electronic-lattice interaction under broken rotational symmetry, providing insights into understanding the complex behaviors in perovskite oxide-based heterostructures.

The interfacial FeSe/TiO2-δ coupling induces high-temperature superconductivity in monolayer FeSe films. Using cryogenic atomically resolved scanning tunneling microscopy/spectroscopy, we obtained atomic-site dependent surface density of states, work function, and the pairing gap in the monolayer FeSe on the SrTiO3(001)-(√13 × √13)-R33.7° surface. Our results disclosed the out-of-plane Se-Fe-Se triple layer gradient variation, switched DOS for Fe sites on and off TiO5□, and inequivalent Fe sublattices, which gives global spatial modulation of pairing gap contaminants with the (√13 × √13) pattern. Moreover, the coherent lattice coupling induces strong inversion asymmetry and in-plane anisotropy in the monolayer FeSe, which is demonstrated to correlate with the particle-hole asymmetry in coherence peaks. These results disclose delicate atomic-scale correlations between pairing and lattice-electronic coupling in the Bardeen-Cooper-Schrieffer to Bose-Einstein condensation crossover regime, providing insights into understanding the pairing mechanism of multiorbital superconductivity.

Determining the pairing symmetry of single-layer FeSe on SrTiO 3 is the key to understanding the enhanced pairing mechanism. It also guides the search for superconductors with high transition temperatures. Despite considerable efforts, it remains controversial whether the symmetry is the sign-preserving s - or the sign-changing s ± -wave. Here, we investigate the pairing symmetry of single-layer FeSe from a topological point of view. Using low-temperature scanning tunneling microscopy/spectroscopy, we systematically characterize the superconducting states at edges and corners of single-layer FeSe. The tunneling spectra collected at edges and corners show a full energy gap and a substantial dip, respectively, suggesting the absence of topologically non-trivial edge and corner modes. According to our theoretical calculations, these spectroscopic features can be considered as strong evidence for the sign-preserving s -wave pairing in single-layer FeSe.