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Are hydrides under high-pressure-high-temperature superconductors?

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National Science Review 2024年第7期11卷 9-12页

作者： J.E.Hirsch department of physics University of California

Contrary to the current consensus, I argue that the existing evidence for high-temperature superconductivity in hydrides under high pressure is not compelling. I suggest that the focus of the field should urgently shift to establish unequivocally experimentally whether or not superconductivity in pressurized hydrides exists, instead of continuing to search for new materials that might show elusive signals of unproven superconductivity at ever higher temperatures. The implications of a negative finding for the theoretical understanding of superconductivity are discussed.

关键词： Hydrides

Effects of Rattling Behavior of K and Cd Atoms along Different Directions in Anisotropic KCdAs on Lattice Thermal Transport and Thermoelectric Properties

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Energy & Environmental Materials 2024年第6期7卷 388-398页

作者： Yue Wang Yinchang Zhao Jun Ni Zhenhong Dai department of physics Yantai UniversityYantai 264005China State Key Laboratory of Low-Dimensional Quantum physics Department of PhysicsTsinghua UniversityBeijing 100084China

We employ advanced first principles methodology,merging self-consistent phonon theory and the Boltzmann transport equation,to comprehensively explore the thermal transport and thermoelectric properties of ***,the study accounts for the impact of quartic anharmonicity on phonon group velocities in the pursuit of lattice thermal conductivity and investigates 3ph and 4ph scattering processes on phonon *** various methodologies,including examining atomic vibrational modes and analyzing 3ph and 4ph scattering processes,the article unveils microphysical mechanisms contributing to the lowκL within *** features include significant anisotropy in Cd atoms,pronounced anharmonicity in K atoms,and relative vibrations in non-equivalent As atomic *** atoms,situated between As layers,exhibit rattling modes and strong lattice anharmonicity,contributing to the observed lowκ*** flat bands near the valence band maximum translate into high PF,aligning with ultralowκL for exceptional thermoelectric *** optimal temperature and carrier concentration doping,outstanding ZT values are achieved:4.25(a(b)-axis,p-type,3×10^(19)cm^(−3),500 K),0.90(c-axis,p-type,5×10^(20)cm^(−3),700 K),1.61(a(b)-axis,n-type,2×10^(18)cm^(−3),700 K),and 3.06(c-axis,n-type,9×10^(17)cm^(−3),700 K).

关键词： anharmonic lattice dynamics electron transport characteristics first principles calculation lattice thermal transport octahedron thermoelectric properties

Consistency between domain wall oscillation modes and spin wave modes in nanostrips

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Chinese physics B 2024年第6期33卷 511-516页

作者：董新伟吴振江 department of physics and Institute of Theoretical physics and Astrophysics Xiamen UniversityXiamen 361005China

Investigations on domain wall(DW) and spin wave(SW) modes in a series of nanostrips with different widths and thicknesses have been carried out using micromagnetic simulation. The simulation results show that the frequencies of SW modes and the corresponding DW modes are consistent with each other if they have the same node number along the width direction. This consistency is more pronounced in wide and thin nanostrips, favoring the DW motion driven by *** analysis of the moving behavior of a DW driven by SWs is also carried out. The average DW speed can reach a larger value of ~ 140 m/s under two different SW sources. We argue that this study is very meaningful for the potential application of DW motion driven by SWs.

关键词： micromagnetic simulation domain wall spin wave

On the half-quantized Hall conductance of massive surface electrons in magnetic topological insulator films

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Science China(physics,Mechanics & Astronomy) 2024年第6期67卷 127-136页

作者： Rui Chen Shun-Qing Shen department of physics The University of Hong KongHong Kong 999077China department of physics Hubei UniversityWuhan 430062China

In topological insulators,massive surface states resulting from local symmetry breaking were thought to exhibit a half-quantized Hall conductance,obtained from the low-energy effective model in an infinite Brillouin *** a lattice model,the surface band is composed of a combination of surface states and bulk *** massive surface states alone may not be enough to support an exact one-half quantized surface Hall conductance in a finite Brillouin zone and the whole surface band always gives an integer quantized Hall conductance as enforced by the TKNN *** explore this,we investigate the band structures of a lattice model describing the magnetic topological insulator film that supports the axion insulator,Chern insulator,and semi-magnetic topological insulator *** reveal that the gapped and gapless surface bands in the three phases are characterized by an integer-quantized Hall conductance and a half-quantized Hall conductance,*** propose an effective model to describe the three phases and show that the low-energy dispersion of the surface bands inherits from the surface Dirac *** gapped surface band manifests a nearly half-quantized Hall conductance at low energy near the center of Brillouin zone,but is compensated by another nearly half-quantized Hall conductance at high energy near the boundary of Brillouin zone because a single band can only have an integer-quantized Hall *** gapless band hosts a zero Hall conductance at low energy but is compensated by another half-quantized Hall conductance at high energy,and thus the half-quantized Hall conductance can only originate from the gapless ***,we calculate the layer-resolved Hall conductance of the *** conclusion suggests that the individual gapped surface band alone does not support the half-quantized surface Hall effect in a lattice model.

关键词： magnetic topological insulator Dirac equation half-quantized Hall conductance

Prospects and challenges in electrochemical nitrogen activation for ammonia synthesis

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Science China Chemistry 2024年第11期67卷 3510-3514页

作者： Xianbiao Fu Ib Chorkendorff department of physics Technical University of Denmark

“The fixation of atmospheric nitrogen stands as one of the profound discoveries awaiting the ingenuity of chemists,”proclaimed William Crookes in his 1898 speech [1]. This statement swiftly surged like a colossal wa... 详细信息

关键词： REDUCTION EFFICIENCY N-2

The combined effects of quantum and strong coupling on the nonlinear collective excitation in quantum dusty plasmas

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Communications in Theoretical physics 2024年第10期76卷 137-142页

作者： Chengkai Li Youyou Kang Yunliang Wang department of physics School of Mathematics and Physics University of Science and Technology Beijing

The quantum hydrodynamic model for electrons and ions and the generalized hydrodynamic model for the strongly coupled dust particles are proposed in the strongly coupled quantum dusty plasma, where the combined quantum effects of quantum diffraction, quantum statistic pressure,as well as electron exchange and correlation effects are all considered in the quantum hydrodynamic model. The shear and bulk viscosity effects are included in the viscoelastic relaxation, which leads to the decay of the dust-ion-acoustic waves. The approximate time-dependent solitary solution is obtained by the momentum conservation law in the presence of viscosity.

关键词： dusty plasma quantum plasma strongly coupled plasma

Facile synthesis of samarium and cerium doped double perovskite cobaltite with enhanced dielectric response

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Journal of Rare Earths 2024年第7期42卷 1317-1327,I0005页

作者： Yasir Abbas M.Kamran M.Anis-ur-Rehman Applied Thermal physics Laboratory Department of PhysicsCOMSATS University IslamabadIslamabad 45550Pakistan

The investigation of Sm-Ce doping on structure,conduction,and dielectric response of Bi_(2)Ca_(2-2x)Sm_(x)CexCoO_(6)(x=0.000,0.025,0.050,0.075)(BCSCCO)are *** the specimens were synthesized by a facile synthesis technique named the co-precipitation route.X-ray diffraction(XRD)reveals that BCSCCO crystallizes into one phase with space group P21/*** crystallite size,dislocation density,lattice parameters,lattice strain,unit cell volume,and bulk density were determined using XRD *** structural properties of Bi_(2)Ca_(2)CoO_(6)were examined using calculations based on the density functional *** and experimental values discrepancy is less than 1%.A scanning electron microscope was used for performing a microstructural *** SEM images demonstrate the homogeneous distribution of grains with a range of sizes(0.054-0.090μm).The alternating current(ac)conductivity,dielectric permittivity,and tangent loss were also studied as a function of frequency(20 Hz-3 MHz)at different temperatures(100-500℃).All synthesized samples were examined using non-linear Debye's function to determine their spreading factor and relaxation *** specimen with the lowest crystallite size(∼23 nm)exhibits a high dielectric permittivity(∼3.80×10^(6)).The conduction mechanism was examined in the studied samples with the use of Jonscher's power *** power law indicates that the BCSCCO(x=0.000,0.025)follows correlated barrier hopping,whereas the x=0.050 and 0.075 compositions follow non-overlapping polaron *** studied specimen Bi_(2)Ca_(1.9)0Sm_(0.05)0Ce_(0.05)_(0)CoO_(6)with the highest density(∼5.65 g/cm^(3))displays a high electrical conductivity(∼46.1 S/cm).These findings correspond to those published for ceramics made from calcium cobaltite using solid-state reactions(5.0-26.0 S/cm).

关键词： Bismuth calcium samarium cerium cobaltite (BCSCCO) Spreading factor Conduction mechanism Rare earths

An improved bound on accelerated light dark matter

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Science China(physics,Mechanics & Astronomy) 2024年第2期67卷 105-118页

作者： Liangliang Su Lei Wu Bin Zhu department of physics and Institute of Theoretical physics Nanjing Normal UniversityNanjing 210023China School of physics Yantai UniversityYantai 264005China

Light(sub-GeV)dark matter has gained increasing interest in terms of direct *** dark matter is a promising candidate that can generate detectable nuclear recoil energy within the sub-GeV *** of the large kinetic energy,its interactions with the nucleus are predominantly governed by inelastic scattering,including quasi-elastic and deep inelastic *** this work,we calculated the inelastic effects in dark matter-Earth scattering mediated by a vector *** analysis revealed that the impact of inelastic scattering relies on the mediator mass and the kinetic energy spectrum of dark *** results exhibited considerable disparity:the upper bounds of the exclusion limit for the spin-independent cross-section between accelerated dark matter and nuclei via a heavy mediator differ by several tens of times when inelastic scattering is considered.

关键词： accelerated dark matter inelastic scattering direct detection experiment

Ion-acoustic waves with non-planar wavefronts

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Plasma Science and Technology 2024年第1期26卷 1-7页

作者： Shujaht BUKHARI Muhammad SHAHID Ata-ur RAHMAN department of physics The University of Azad Jummu and KashmirMuzaffarabad 13100Azad Kashmir department of physics Women University of Azad Jammu&KashmirBagh 12500Pakistan department of physics Islamia College PeshawerPeshawar 25120Pakistan

The ion-acoustic(IA) mode exhibiting various orbital angular momentum(OAM) states is examined in a plasma with drifting *** constituent plasma species are modeled with a non-gyrotropic Maxwellian distribution and discussion of dispersion relation and growth rate of twisted IA waves under various conditions is *** the domain of kinetic model,the twisted IA waves are characterized by Laguerre-Gaussian(LG) solutions,where plasma distribution function and electric field are decomposed into axial and azimuthal *** plasma response function is obtained under paraxial approximations and investigated for threshold condition of instability growth rate with helical electric field *** impact of an extra electron specie on the instability is demonstrated through a comparison of twisted waves for single and double electron species.

关键词： instability twist parameter wave excitation orbital angular momentum threshold limit