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The microscopic mechanism for the disappearance of superconductivity in overdoped cuprates is still under heated debate. Here we use scanning tunneling spectroscopy to investigate the evolution of quasiparticle interference phenomenon in Bi2Sr2CuO6+δ over a wide range of hole densities. We find that when the system enters the overdoped regime, a peculiar quasiparticle interference wavevector with arc-like pattern starts to emerge even at zero bias, and its intensity grows with increasing doping level. Its energy dispersion is incompatible with the octet model for d-wave superconductivity, but is highly consistent with the scattering interference of gapless normal carriers. The gapless quasiparticles are mainly located near the antinodes and are independent of temperature, consistent with the disorder scattering mechanism. We propose that a branch of normal fluid emerges from the pair-breaking scattering between flat antinodal bands in the quantum ground state, which is the primary cause for the reduction of superfluid density and suppression of superconductivity in overdoped cuprates.

As doping increases in cuprate superconductors, the superconducting transition temperature increases to a maximum at the so-called optimal doping, and then decreases in the overdoped regime. In the past few decades, research has primarily focused on the underdoped and optimally doped regions of the phase diagram. Here, phenomena such as the pseudogap and strange metal non-superconducting states make it difficult to determine the superconducting pairing mechanism. More recently, experiments have shown unconventional behaviour in strongly overdoped cuprates, in both the normal and superconducting states. However, a real-space investigation of the unconventional superconductivity in the absence of the pseudogap is lacking, and the superconductor-to-metal phase transition in the overdoped regime remains controversial. Here we use scanning tunnelling microscopy to investigate the atomic-scale electronic structure of overdoped Bi2Sr2Can − 1CunO2n + 4 + δ cuprates. We show that, at low energies, the spectroscopic maps are well described by dispersive d-wave quasiparticle interference patterns. However, as the bias increases to the superconducting coherence peak energy, a periodic and non-dispersive pattern emerges. The position of the coherence peaks exhibits particle–hole asymmetry that modulates with the same period. We propose that this behaviour is due to quasiparticle interference caused by pair-breaking scattering between flat antinodal Bogoliubov bands.

In this paper, the photocatalytic degradation of methyl orange solution by MnO2/TiO2 nanotube arrays (NTAs) with different structure was studied. Initially, bamboo-like TiO2 NTAs with folded tube walls were synthesized using the anodic oxidation method. Subsequently, MnO2 nanowires/TiO2 NTAs and MnO2 nanoparticles/TiO2 NTAs were prepared via high-temperature and low-temperature hydrothermal methods, respectively. Photocurrent-time transient tests revealed that MnO2 nanoparticles/TiO2 NTAs produced by the low-temperature hydrothermal method exhibited a relatively good photocurrent response. All the deposited MnO2/TiO2 bamboo-like nanotube nanocomposites were tested for photocatalytic decomposition under different pH and light conditions. The results showed that MnO2 could adsorb and degrade methyl orange in the absence of light and acidity, and the degradation degree was proportional to the concentrations of Mn. MnO2 was stimulated to produce photogenic electrons, which migrated to the surface of the TiO2 and extended the life of photogenic charge carriers. [ABSTRACT FROM AUTHOR]

Size distribution of aerosols and carbon fractions can help identify sources and explore formation mechanisms, and lung deposition surface area (LDSA) is an important indicator for health risk assessment of aerosol particles deposited in the alveolar region of the human respiratory tract. From December 2017 to November 2018, the size distribution and LDSA of indoor and outdoor aerosols in Nanchang was investigated by using the electrical low-pressure impactor (ELPI+), and the results showed that the major airborne particles in the regional mixing receptor sites, roadside, printing room, and students' dormitories during the sampling period were the Nucleation and Accumulation modes, the Aitken and Nucleation modes, the Nucleation mode, the Accumulation mode. The size distributions of organic carbon (OC) in outdoor and indoor air particles were similar, with a single peak, and the peak appeared in the 7 th particle size class (0.256~0.382 µm). The size distributions of elemental carbon (EC) in particles showed a single peak indoors, and multiple peaks outdoors. The size distribution of OC/EC ratios of different microenvironmental particles mostly showed a "L" shape, but there is no significant difference in the OC/EC ratio of particles with different particle sizes in the printing room, which is approximately in a "--" shape. The dominant carbon components of outdoor air particulate matter were OC2, OC3, OC4 and EC1, which mainly originated from coal combustion emissions and motor vehicle exhaust, while the dominant carbon components of indoor air particulate matter were OC1, OC2 and OC3, which mainly originated from cigarette combustion and outdoor air infiltration. The LDSA of different microenvironmental particles varied, and the daily mean values of LDSA were 49.0, 10.9, 29.9, and 31.0 µm²/m³ for the outdoor mixed-source receptor sites, the roadside, and the indoor printing room and the students' dormitory, respectively, and the LDSA of the particles was very high in the indoor environments with obvious contributing sources (e.g., printing work or cigarette combustion) for a short period of time, especially under the influence of the cigarette combustion, exceeding the maximum value of ambient air particulate LDSA. High percentage of LDSA was for particles smaller than 100 nm in roadside air, and high percentage of LDSA for particles in the 100~600 nm size range in indoor environments where there is a cigarette combustion source. [ABSTRACT FROM AUTHOR]

Environmental context: Dust is a heterogeneous material deposited on the ground surface and is a source and sink for potentially toxic elements (PTEs) originating from the air and soil. Tracking the distribution and effects of PTEs in an abandoned mining area is critical as few studies have quantified the speciation and bioavailability of PTEs contained in dust and PM2.5. In this paper, we track the distribution of PTEs in an abandoned mining area, quantifying the mobility of PTEs using the speciation of PTEs in dust and PM2.5 and quantitatively assess the environmental and ecological risks of PTE in a mining area. Rationale: This study aimed to gain a better understanding of the distribution, speciation, mobility and ecological risks of potentially toxic elements (PTEs) in an abandoned mining area by measuring the PTEs in dust (indoor or atmospheric) and particulate matter <2.5 μm (PM2.5) simultaneously. Methodology: The particle size of dust, PTEs and the speciation of PTEs in dust and PM2.5 were determined. The risk assessment code (RAC) was used to analyse the mobility of PTEs, and the geo-accumulation index (I geo), pollution load index (PLI) and potential ecological risk index (RI) were used to assess the ecological risks of PTEs. Results: The results showed that the particle size of dust was mainly distributed in the range of 0–2.5 µm (61–81%). Cd, Mn, Cu and Zn in dust were mainly distributed in the acid extractable fraction, whereas other PTEs were distributed in the residual fraction. Most PTEs in PM2.5 were distributed in the acid extractable fraction, but V and As were distributed in the reducible fraction. The risk of Cd, Zn and Mn in dust and PM2.5 was very high (RAC > 50%). I geo values showed that the dust were practically uncontaminated by most of the PTEs, whereas the PM2.5 was moderately to highly contaminated by most of the PTEs. The PTE in dust and PM2.5 with the highest ecological risk was Cd (E i  >  320). The PLI showed a potential deterioration in environmental quality (1.30 < PLI < 3.17) and the further away from the mining centre, the less environmental degradation. Discussion: There is a potential for PTEs contamination and a high ecological risk in abandoned mining areas, which deserves serious attention. Environmental context. Dust is a heterogeneous material deposited on the ground surface and is a source and sink for potentially toxic elements (PTEs) originating from the air and soil. Tracking the distribution and effects of PTEs in an abandoned mining area is critical as few studies have quantified the speciation and bioavailability of PTEs contained in dust and PM2.5. In this paper, we track the distribution of PTEs in an abandoned mining area, quantifying the mobility of PTEs using the speciation of PTEs in dust and PM2.5 and quantitatively assess the environmental and ecological risks of PTE in a mining area. [ABSTRACT FROM AUTHOR]

2D organic–inorganic layered halide perovskites have received tremendous interest as promising materials in electronics owing to their outstanding physical properties. However, the quantum confinement effect leads to the suppression of ion migration in the out‐of‐plane direction, restricting their applications in resistive switching (RS) memories with vertical structure. Herein, the 2D layered perovskite incorporated with TiO2 nanoparticles, denoted as TiO2–PEA2PbBr4, is employed, as the functional layers to construct RS memory devices with Al/TiO2–PEA2PbBr4/ITO structure. As compared to pure 2D layered perovskite counterparts without switching behaviors, the Al/TiO2–PEA2PbBr4/ITO memories demonstrate stable bipolar RS behaviors, along with striking characteristics, including the relatively centralized set/reset voltages, a large on/off ratio (≈102), and a long retention time (104 s). In addition, the devices also present the multilevel storage capability by controlling the compliance current. Moreover, the RS behaviors are attributable to the formation/rupture of synergy bromine and oxygen vacancy conductive filaments, owing to their migration/distribution of oxygen/bromine ions under electric fields. The oxide nanoparticles incorporation route provides an effective strategy for improving RS performance in 2D layered perovskite‐based RS memories. [ABSTRACT FROM AUTHOR]