Surface doping manipulation of the insulating ground states in Ta_(2)Pd_(3)Te_(5) and Ta_(2)Ni_(3)Te_(5)

Manipulating emergent quantum phenomena is a key issue for understanding the underlying physics and contributing to possible applications.Here we study the evolution of insulating ground states of Ta_(2)Pu_(3)Te_(5) and Ta_(2)Ni_(3)Te_(5) under in-situ surface potassium deposition via angle-resolved photoemission spectroscopy.Our results confirm the excitonic insulator character of Ta_(2)d_(3)Te_(5).Upon surface doping,the size of its global gap decreases obviously.After a deposition time of more than 7 min,the potassium atoms induce a metal-insulator phase transition and make the system recover to a normal state.In contrast,our results show that the isostructural compound Ta_(2)Ni_(3)Te_(5) is a conventional insulator.The size of its global gap decreases upon surface doping,but persists positive throughout the doping process.Our results not only confirm the excitonic origin of the band gap in Ta_(2)Pd_(3)Te_(5),but also offer an effective method for designing functional quantum devices in the future.

Visualizing the Local Twist Angle Variation within and between Domains of Twisted Bilayer Graphene

Moirésuperlattices in twisted two-dimensional materials have emerged as ideal platforms for engineering quantum phenomena,which are highly sensitive to twist angles,including both the global value and the spatial inhomogeneity.However,only a few methods provide spatial-resolved information for characterizing local twist angle distribution.

Intercalation of hafnium oxide between epitaxially-grown monolayer graphene and Ir(111)substrate

Intercalation of insulating materials between epitaxial graphene and the metal substrates is highly demanded to restore the intrinsic properties of graphene,and thus essential for the graphene-based devices.Here we demonstrate a successful solution for the intercalation of hafnium oxide into the interface between full-layer graphene and Ir(111)substrate.We first intercalate hafnium atoms beneath the epitaxial graphene.The intercalation of the hafnium atoms leads to the variation of the graphene moire superstructure periodicity,which is characterized by low-energy electron diffraction(LEED)and lowtemperature scanning tunneling microscopy(LT-STM).Subsequently,we introduce oxygen into the interface,resulting in oxidization of the intercalated hafnium.STM and Raman's characterizations reveal that the intercalated hafnium oxide layer could effectively decouple the graphene from the metallic substrate,while the graphene maintains its high quality.Our work suggests a high-k dielectric layer has been successfully intercalated between high-quality epitaxial graphene and metal substrate,providing a platform for applications of large-scale,high-quality graphene for electronic devices.

Electronic states of domain walls in commensurate charge density wave ground state and mosaic phase in 1T-TaS_(2)

Domain walls(DWs)in the charge-density-wave(CDW)Mott insulator 1T-TaS_(2)have unique localized states,which play an important role in exploring the electronic properties of the material.However,the electronic states in DWs in 1TTaS_(2)have not been clearly understood,mostly due to the complex structures,phases,and interlayer stacking orders in the DW areas.Here,we explored the electronic states of DWs in the large-area CDW phase and mosaic phase of 1T-TaS_(2)by scanning tunneling spectroscopy.Due to the different densities of DWs,the electronic states of DWs show distinct features in these phases.In the large area CDW phase,both the domain and the DWs(DW1,DW2,DW4)have zero conductance at the Fermi level;while in the mosaic phase,they can be metallic or insulating depending on their environments.In areas with a high density of DWs,some electronic states were observed both on the DWs and within the domains,indicating delocalized states over the whole region.Our work contributes to further understanding of the interplay between CDW and electron correlations in 1T-TaS_(2).

Magnetocaloric properties and Griffiths phase of ferrimagnetic cobaltite CaBaCo_(4)O_(7)

We present a study on the magnetocaloric properties of a CaBaCo_(4)O_(7) polycrystalline cobaltite along with research on the nature of magnetic phase transition.The magnetization as a function of temperature identifies the ferrimagnetic to paramagnetic transition at a Curie temperature of 60 K.Moreover,a Griffiths-like phase is confirmed in a temperature range above T_(C).The compound undergoes a crossover from the first to second-order ferrimagnetic transformation,as evidenced by the Arrott plots,scaling of the universal entropy curve,and field-dependent magnetic entropy change.The maximum of entropy change is 3 J/kg⋅K for ΔH=7 T at T_(C),and a broadening of the entropy peak with increasing magnetic field indicates a field-induced transition above T_(C).The analysis of the magnetic entropy change using the Landau theory reveals the second-order phase transition and indicates that the magnetocaloric properties of CaBaCo_(4)O_(7) are dominated by the magnetoelastic coupling and electron interaction.The corresponding values of refrigerant capacity and relative cooling power are estimated to be 33 J/kg and 42 J/kg,respectively.

Determination of Work Function for p-and n-Type 4H-SiC Single Crystals via Scanning Kelvin Probe Force Microscopy

Silicon carbide(SiC) is a promising platform for fabricating high-voltage, high-frequency and high-temperature electronic devices such as metal oxide semiconductor field effect transistors in which many junctions or interfaces are involved. The work function(WF) plays an essential role in these devices. However, studies of the effect of conductive type and polar surfaces on the WF of SiC are limited. Here, we report the measurement of WFs of Si-and C-terminated polar surfaces for both p-type and n-type conductive 4H-SiC single crystals by scanning Kelvin probe microscopy(SKPFM). The results show that p-type SiC exhibits a higher WF than n-type SiC.The WF of a C-terminated polar surface is higher than that of a Si-terminated polar surface, which is further confirmed by first-principles calculations. By revealing this long-standing knowledge gap, our work facilitates the fabrication and development of SiC-based electronic devices, which have tremendous potential applications in electric vehicles, photovoltaics, and so on. This work also shows that SKPFM is a good method for identifying polar surfaces of SiC and other polar materials nondestructively, quickly and conveniently.

Flat Band and Z_(2)Topology of Kagome Metal CsTi_(3)Bi_(5)

The simple kagome-lattice band structure possesses Dirac cones,flat band,and saddle point with van Hove singularities in the electronic density of states,facilitating the emergence of various electronic orders.Here we report a titanium-based kagome metal CsTi_(3)Bi_(5)where titanium atoms form a kagome network,resembling its isostructural compound CsV_3Sb_5.Thermodynamic properties including the magnetization,resistance,and heat capacity reveal the conventional Fermi liquid behavior in the kagome metal CsTi_(3)Bi_(5)and no signature of superconducting or charge density wave(CDW)transition anomaly down to 85 m K.Systematic angle-resolved photoemission spectroscopy measurements reveal multiple bands crossing the Fermi level,consistent with the first-principles calculations.The flat band formed by the destructive interference of hopping in the kagome lattice is observed directly.Compared to Cs V_(3)Sb_(5),the van Hove singularities are pushed far away above the Fermi level in CsTi_(3)Bi_(5),in line with the absence of CDW.Furthermore,the first-principles calculations identify the nontrivial Z_(2)topological properties for those bands crossing the Fermi level,accompanied by several local band inversions.Our results suppose CsTi_(3)Bi_(5)as a complementary platform to explore the superconductivity and nontrivial band topology.

Erratum:Flat Band and Z_(2) Topology of Kagome Metal CsTi_(3)Bi_(5)[Chin.Phys.Lett.40,037102(2023)]

In our most recently published article,[1]an important reference[2]predicting CsTi_(3)Bi_(5) is missing and should be added,along with Ref.[3](originally Ref.[28]),to the introduction section.

Energy Landscape and Phase Competition of CsV_(3)Sb_(5),CsV_(6)Sb_(6)and TbMn_(6)Sn_(6)-Type Kagome Materials

Finding viable Kagome lattices is vital for materializing novel phenomena in quantum materials.In this study,we performed element substitutions on CsV_(3)Sb_(5)with space group P 6/mmm,TbMn_(6)Sn_(6)with space group P 6/mmm,and CsV_(6)Sb_(6)with space group R3m,as the parent compounds.Totally 4158 materials were obtained through element substitutions,and these materials were then calculated via density functional theory in high-throughput mode.Afterwards,48 materials were identified with high thermodynamic stability(E_(hull)<5 meV/atom).Furthermore,we compared the thermodynamic stability of three different phases with the same elemental composition and predicted some competing phases that may arise during material synthesis.Finally,by calculating the electronic structures of these materials,we attempted to identify patterns in the electronic structure variations as the elements change.This study provides guidance for discovering promising AM_(3)X_(5)/AM_(6)X_(6)Kagome materials from a vast phase space.

Anisotropic s-Wave Gap in the Vicinity of a Quantum Critical Point in Superconducting BaFe_(2)(As_(1-x)P_(x))_(2) Single Crystals:A Study of Point-Contact Spectroscopy

We report on soft c-axis point-contact Andreev reflection(PCAR)spectroscopy combining with resistivity measurements on BaFe_(2)(As_(0.7)P_(0.3))_(2),to elucidate the superconducting gap structure in the vicinity of the quantum critical point.A double peak at the gap edge plus a dip feature at zero-bias has been observed on the PCAR spectra,indicative of the presence of a nodeless gap in BaFe_(2)(As_(0.7)P_(0.3))_(2).Detailed analysis within a sophisticated theoretical model reveals an anisotropic gap with deep gap minima.The PCARs also feature additional structures related to the electron-bosonic coupling mode.Using the extracted superconducting energy gap value,a characteristic bosonic energy Ω_(b) and its temperature dependence are obtained,comparable with the spin-resonance energy observed in neutron scattering experiment.These results indicate a magnetism-driven quantum critical point in the BaFe_(2)(As_(1-x)P_(x))_(2) system.

Distinct behavior of electronic structure under uniaxial strain in BaFe_(2)As_(2)

We report a study of the electronic structure of BaFe_(2)As_(2) under uniaxial strains using angle-resolved photoemission spectroscopy and transport measurements. Two electron bands at the MY point, with an energy splitting of 50 meV in the strain-free sample, shift downward and merge into each other under a large uniaxial strain, while three hole bands at theГ point shift downward together. However, we also observed an enhancement of the resistance anisotropy under uniaxial strains by electrical transport measurements, implying that the applied strains strengthen the electronic nematic order in BaFe_(2)As_(2). These observations suggest that the splitting of these two electron bands at the MY point is not caused by the nematic order in BaFe_(2)As_(2).

C-Type Antiferromagnetic Structure of Topological Semimetal CaMnSb_(2)

Determination of the magnetic structure and confirmation of the presence or absence of inversion(P)and time reversal(Τ)symmetry is imperative for correctly understanding the topological magnetic materials.Here highquality single crystals of the layered manganese pnictide CaMnSb_(2)are synthesized using the self-flux method.

Interstitial Doping of SnO_(2) Film with Li for Indium-Free Transparent Conductor

SnO_(2)films exhibit significant potential as cost-effective and high electron mobility substitutes for In_(2)O_(3)films.In this study,Li is incorporated into the interstitial site of the SnO_(2)lattice resulting in an exceptionally low resistivity of 2.028×10^(-3)Ω·cm along with a high carrier concentration of 1.398×10^(20)cm^(-3)and carrier mobility of 22.02 cm^(2)/V·s.

Superconductivity of Lanthanum Superhydride Investigated Using the Standard Four-Probe Configuration under High Pressures

Recently,the theoretically predicted lanthanum superhydride,LaH 10±δ,with a clathrate-like structure was successfully synthesized and found to exhibit a record high superconducting transition temperature T c≈250 K at∼170 GPa,opening a new route for room-temperature superconductivity.However,since in situ experiments at megabar pressures are very challenging,few groups have reported the∼250 K superconducting transition in LaH 10±δ.Here,we establish a simpler sample-loading procedure that allows a relatively large sample size for synthesis and a standard four-probe configuration for resistance measurements.Following this procedure,we successfully synthesized LaH 10±δwith dimensions up to 10×20μm^2 by laser heating a thin La flake and ammonia borane at∼1700 K in a symmetric diamond anvil cell under the pressure of 165 GPa.The superconducting transition at T c≈250 K was confirmed through resistance measurements under various magnetic fields.Our method will facilitate explorations of near-room-temperature superconductors among metal superhydrides.

Absorption Range and Energy Shift of Surface Plasmon in Au Monomer and Dimer

The resonance behaviors of local surface plasmon resonance in Au monomer and dimer are characterized sys- temically by electron energy loss spectroscopy in a scanning transmission electron microscope. The measured absorption range is about 20nm larger than the physical size of the Au nanoparticles and the resonance peak energy shows a red shift when the electron beam passes off the nanoparticles. The Au dimer displays similar behaviors. Numerical simulation also reproduces those experimental results.

Rare-Earth Chalcogenides:A Large Family of Triangular Lattice Spin Liquid Candidates

Frustrated quantum magnets are expected to host many exotic quantum spin states like quantum spin liquid（QSL）, and have attracted numerous interest in modern condensed matter physics. The discovery of the triangular lattice spin liquid candidate YbMgGaO_4 stimulated an increasing attention on the rare-earth-based frustrated magnets with strong spin-orbit coupling. Here we report the synthesis and characterization of a large family of rare-earth chalcogenides AReCh_2（A = alkali or monovalent ions, Re = rare earth, Ch = O,S,Se）. The family compounds share the same structure（R3 m） as YbMgGaO_4,and antiferromagnetically coupled rare-earth ions form perfect triangular layers that are well separated along the c-axis. Specific heat and magnetic susceptibility measurements on NaYbO_2,NaYbS_2 and NaYbSe_2 single crystals and polycrystals, reveal no structural or magnetic transition down to 50 mK. The family, having the simplest structure and chemical formula among the known QSL candidates, removes the issue on possible exchange disorders in YbMgGaO_4. More excitingly, the rich diversity of the family members allows tunable charge gaps, variable exchange coupling, and many other advantages.This makes the family an ideal platform for fundamental research of QSLs and its promising applications.

Random Motion of a Charged Test Particle with a Classical Constant Velocity in Vacuum in a Cylindrical Spacetime

我们与非零检验一个控告的测试粒子的随机的运动在圆柱的 spacetimeand 的电磁的真空变化计算的量驾驶的古典速度测试粒子的速度和职务分散。分散在不同方向显示不同行为，这被发现。这些差别能由于配置和起始的物理条件的拓扑学被理解。

Lorentz Invariance and Brownian Motion of Test Particles with Constant Classical Velocity in Electromagnetic Vacuum

我们证明有古典速度经历 Brownian 运动与飞机边界在一个空格由电磁的真空变化引起了的一个非零常数的一个测试粒子的速度和位置分散能静态的案例 byLorentz 转变从那些被获得。我们明确地导出联系二诉讼的分散的 Lorentz 转变然后与经常的古典速度平行把他们用于一个测试粒子的 Brownian 动议的诉讼到在二之间的边界进行飞机。我们结果表演非零的影响起始的速度为非相对论的测试粒子是可以忽略的。

Dye-sensitized solar cells: Atomic scale investigation of interface structure and dynamics

Recent progress in dye-sensitized solar cells （DSC） research is reviewed, focusing on atomic-scale investigations of the interface electronic structures and dynamical processes, including the structure of dye adsorption onto Ti02, ultrafast electron injection, hot-electron injection, multiple-exciton generation, and electron-hole recombination. Advanced exper- imental techniques and theoretical approaches are briefly summarized, and then progressive achievements in photovoltaic device optimization based on insights from atomic scale investigations are introduced. Finally, some challenges and oppor- tunities for further improvement of dye solar cells are presented.

Random Motion of a Charged Test Particle with a Constant Classical Velocity in a Spacetime with a Plane Boundary

我们学习与非零在一条完美地思考的飞机边界附近联合到电磁的真空变化的一个控告的测试粒子的随机的运动在到飞机的方向平行的古典经常的速度。我们推测平均数在考虑电的波动的两个和磁性的力量的测试粒子的速度和位置摆平变化。我们一般来说，波动的磁场的影响比那具有更高的顺序的结果表演由波动的电场引起了并且因此是可以忽略的。