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Data-Based Optimal Bandwidth for Kernel Density Estimation of statistical Samples

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Communications in theoretical physics 2018年第12期69卷 728-734页

作者： Zhen-Wei Li Ping He center for theoretical physics and College of physics Jilin University Changchun Observatory National Astronomical ObservatoriesCAS center for High Energy physics Peking University

It is a common practice to evaluate probability density function or matter spatial density function from statistical samples. Kernel density estimation is a frequently used method, but to select an optimal bandwidth of kernel estimation, which is completely based on data samples, is a long-term issue that has not been well settled so far. There exist analytic formulae of optimal kernel bandwidth, but they cannot be applied directly to data samples,since they depend on the unknown underlying density functions from which the samples are drawn. In this work, we devise an approach to pick out the totally data-based optimal bandwidth. First, we derive correction formulae for the analytic formulae of optimal bandwidth to compute the roughness of the sample's density function. Then substitute the correction formulae into the analytic formulae for optimal bandwidth, and through iteration we obtain the sample's optimal bandwidth. Compared with analytic formulae, our approach gives very good results, with relative differences from the analytic formulae being only 2%～3% for sample size larger than 10~4. This approach can also be generalized easily to cases of variable kernel estimations.

关键词： numerical methods kernel density estimation optimal bandwidth large-scale structure of Universe

Identification of Topological Surface State in PdTe2 Superconductor by Angle-Resolved Photoemission Spectroscopy

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Chinese physics Letters 2015年第6期32卷 136-140页

作者：刘艳赵建洲俞理林成天梁爱基胡成丁颖徐煜何少龙赵林刘国东董晓莉张君陈创天许祖彦翁红明戴希方忠周兴江 Beijing National Laboratory for condensed matter physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 Max-Planck-Institut fur Festkorperforschung Heisenbergstrasse 170569 StuttgartGermany Technical Institute of physics and Chemistry Chinese Academy Of Sciences Beijing 100190 Collaborative Innovation center of Quantum matter Beijing 100871

High-resolution angle-resolved photoemission measurements are carried out on transition metal dichalcogenide PdTe2 that is a superconductor with a Tc at 1.7K. Combined with theoretical calculations, we discover for the first time the existence of topologically nontrivial surface state with Dirac cone in PbTe2 superconductor. It is located at the Brillouin zone center and possesses helical spin texture. Distinct from the usual three-dimensional topological insulators where the Dirac cone of the surface state lies at the Fermi level, the Dirac point of the surface state in PdTe2 lies deeply below the Fermi level at - 1.75 eV binding energy and is well separated from the bulk states. The identification of topological surface state in PdTe2 superconductor deeply below the Fermi level provides a unique system to explore new phenomena and properties and opens a door for finding new topological materials in transition metal ehalcogenides.

关键词： Identification of Topological Surface State in PdTe2 Superconductor by Angle-Resolved Photoemission Spectroscopy ARPES

Exact surface energy and elementary excitations of the XXX spin-1/2 chain with arbitrary non-diagonal boundary fields

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Chinese physics B 2023年第1期32卷 483-492页

作者：董家生路鹏程孙佩乔艺曹俊鹏郝昆杨文力 Institute of Modern physics Northwest UniversityXi'an 710127China Beijing National Laboratory for condensed matter physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China School of physics Northwest UniversityXi'an 710127China Peng Huanwu center for Fundamental Theory Xi'an 710127China Shaanxi Key Laboratory for theoretical physics Frontiers Xi'an 710127China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100049China Songshan Lake Materials Laboratory Dongguan 523808China

We study the physical properties of the XXX spin-1/2 chain with arbitrary non-diagonal boundary fields. By using a combination of numerical analysis and analytical method, we obtain the surface energy and elementary excitations of the model. It shows that the contributions of the two boundary fields to the surface energy are additive. We also find that there exists a kind of excitations related to the boundary string.

关键词： quantum spin chain integrable systems Bethe ansatz

Local high-density distributions of phospholipids induced by the nucleation and growth of smectic liquid crystals at the interface

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Chinese Chemical Letters 2022年第8期33卷 3973-3976页

作者： Chenjing Yang Li Chen Rui Zhang Dong Chen Laura R.Arriaga David A.Weitz College of Energy Engineering and State Key Laboratory of Fluid Power and Mechatronic Systems Zhejiang UniversityHangzhou 310027China Zhejiang Key Laboratory of Smart BioMaterials and center for Bionanoengineering College of Chemical and Biological EngineeringZhejiang UniversityHangzhou 310027China Department of theoretical condensed matter physics Condensed Matter Physics Center and Instituto Nicolás CabreraUniversidad Autónoma de MadridMadrid 28049Spain John A.Paulson School of Engineering and Applied Sciences and Department of physics Harvard UniversityCambridgeMA 02138United States Department of physics The Hong Kong University of Science&TechnologyHong KongChina

Amphiphilic molecules adsorbed at the interface could control the orientation of liquid crystals(LCs)while LCs in turn could influence the distributions of amphiphilic *** studies on the interactions between liquid crystals and amphiphilic molecules at the interface are important for the development of molecular *** this paper,we demonstrate that the development of smectic LC ordering from isotropic at the LC/water interface could induce local high-density distributions of amphiphilic *** of liquid crystals and phospholipids in chloroform are first emulsified in *** fluorescently labeling the phospholipids adsorbed at the interface,their distributions are visualized under fluorescent confocal ***,local high-density distributions of phospholipids showing a high fluorescent intensity are observed on the surface of LC *** on the correlation between phospholipid density,surface tension and smectic LC ordering suggest that when domains of smectic LC layers nucleate and grow from isotropic at the LC/water interface as chloroform slowly evaporates at room temperature,phospholipids transition from liquid-expanded to liquid-condensed phases in response to the smectic ordering,which induces a higher surface tension at the *** results will provide an important insight into the interactions between liquid crystals and amphiphilic molecules at the interface.

关键词： Liquid crystals Phospholipids Droplet Interface Smectic

Exact solution of an integrable quantum spin chain with competing interactions

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Chinese physics B 2021年第11期30卷 558-564页

作者： Jian Wang Yi Qiao Junpeng Cao Wen-Li Yang Beijing National Laboratory for condensed matter physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100190China Songshan Lake Materials Laboratory Dongguan 523808China Peng Huanwu center for Fundamental Theory Xi’an 710127China Institute of Modern physics Northwest UniversityXi’an 710127China Shaanxi Key Laboratory for theoretical physics Frontiers Xi’an 710127China School of physics Northwest UniversityXi’an 710127China

We construct an integrable quantum spin chain that includes the nearest-neighbor,next-nearest-neighbor,chiral threespin couplings,Dzyloshinsky–Moriya interactions and unparallel boundary magnetic *** the interactions in bulk materials are isotropic,the spins nearby the boundary fields are polarized,which induce the anisotropic exchanging interactions of the first and last *** U(1)symmetry of the system is broken because of the off-diagonal boundary *** the off-diagonal Bethe ansatz,we obtain an exact solution to the *** inhomogeneous T–Q relation and Bethe ansatz equations are given *** also calculate the ground state *** method given in this paper provides a general way to construct new integrable models with certain interesting interactions.

关键词： quantum spin chain Bethe ansatz Yang-Baxter equation

Quark confinement and the fractional quantum Hall effect

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Chinese physics C 2008年第9期32卷 705-709页

作者：王海军耿文通 center for theoretical physics Jilin University Department of Materials Science & Engineering and Department of physics University of Science and Technology Beijing

Working in the physics of Wilson factor and Aharonov-Bohm effect, we find in the fluxtubequark system the topology of a baryon consisting of three heavy flavor quarks resembles that of the fractional quantum Hall effect （FQHE） in condensed matter. This similarity yields the result that the constituent quarks of baryon have the ＂filling factor＂ 1/3, thus the previous conjecture that quark confinement is a correlation effect is confirmed. Moreover, by deriving a Hamiltonian of the system analogous to that of FQHE, we predict an energy gap for the ground state of a heavy three-quark system.

关键词： QCD confinement Wilson factor Aharonov-Bohm effect fractional quantum Hall effect

High-Temperature Superconductivity in La_(3)Ni_(2)O_(7)

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Chinese physics Letters 2024年第1期41卷 85-91页

作者：蒋坤汪自强张富春 Beijing National Laboratory for condensed matter physics and Institute of PhysicsChinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100190China Department of physics Boston CollegeChestnut HillMA 02467USA Kavli Institute of theoretical Sciences University of Chinese Academy of SciencesBeijing 100190China Collaborative Innovation center of Advanced Microstructures Nanjing UniversityNanjing 210093China

Motivated by the recent discovery of high-temperature superconductivity in bilayer La_(3)Ni_(2)O_(7) under pressure,we study its electronic properties and superconductivity due to strong electron *** the inversion symmetry,we decouple the low-energy electronic structure into block-diagonal symmetric and antisymmetric *** is found that the antisymmetric sector can be reduced to a one-band system near half filling,while the symmetric bands occupied by about two electrons are heavily overdoped *** the strong coupling mean field theory,we obtain strong superconducting pairing with B_(1g)symmetry in the antisymmetric *** propose that due to the spin-orbital exchange coupling between the two sectors,B_(1g)pairing is induced in the symmetric bands,which in turn boosts the pairing gap in the antisymmetric band and enhances the high-temperature superconductivity with a congruent d-wave symmetry in pressurized La_(3)Ni_(2)O_(7).

关键词： symmetry superconductivity symmetric

Measurement of Carrier-Envelope Phase and Field Strength of a Few-Cycle Pulse by Non-sequential Double Ionization

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Chinese physics Letters 2009年第10期26卷 117-120页

作者：李洪云陈京蒋红兵刘杰傅盘铭龚旗煌严宗朝王兵兵 Laboratory of Optical physics Belting National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100080 Department of physics State Key Laboratory for Artificial Microstructures and Mesoscopic Physics Peking University Beijing 100871 center for Nonlinear Studies Institute of Applied Physics and Computational Mathematics Beijing 100088 Department of physics University of New Brunswick PO Box 4400 Fredericton New Brunswick E3B 5A3 Canada center for theoretical Atomic and Molecular physics the Academy of Fundamental and Interdisciplinary Sciences Harbin Institute of Technology Harbin 150080 center for Applied physics and Technology Petting University Beijing 100876

We propose a method to measure the carrier-envelop phase （CEP） and the intensity of a few-cycle pulse by controlling the non-sequentiai double ionization （NSDI） process. By using an additional static electric field, we can change the momentum distribution of the double-charged ions parallel to the laser polarization from an asymmetrical double-hump structure to a nearly symmetrical one. It is found that the ratio between the strength of the static electric field and that of the laser field is sensitive to the CEP but robust against the intensity fluctuation. Therefore we can determine the OEP of a few-cycle pulse precisely by measuring the static electric field. Fhrthermore, if the CEP of the few-cycle pulse is fixed at a certain value, we can also calibrate the intensity of the laser pulse by the static electric field.

关键词： sea surface nonliear interaction numerical method

Superconductivity near the(2+1)-Dimensional Ferromagnetic Quantum Critical Point

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Chinese physics Letters 2022年第9期39卷 47-52页

作者： Yunchao Hao Gaopei Pan Kai Sun Zi Yang Meng Yang Qi State Key Laboratory of Surface physics and Department of physics Fudan UniversityShanghai 200433China Beijing National Laboratory for condensed matter physics and Institute of physics Chinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100190China Department of physics University of MichiganAnn ArborMI 48109USA Department of physics and HKU-UCAS Joint Institute of theoretical and Computational physics The University of Hong KongPokfulam RoadHong KongChina Collaborative Innovation center of Advanced Microstructures Nanjing 210093China

We utilize both analytical and numerical methods to study the superconducting transition temperature Tnear a fermionic quantum critical point(QCP) using a model constructed by Xu et al. [Phys. Rev. X 7, 031059(2017)] as an example. In this model, the bosonic critical fluctuation plays the role of pairing glue for the Cooper pairs, and we use a Bardeen–Cooper–Schrieffer-type mean-field theory to estimate T. We further argue that the Tc computed from the BCS theory approximates a pseudogap temperature TPG, instead of the Berezinskii–Kosterlitz–Thouless transition temperature T, which is confirmed by our determinant quantum Monte Carlo simulation. Moreover, due to the fact that electron density of state starts to deplete at T, the critical scaling of the underlying QCP is also affected below TPG. Thus, when studying the critical behavior of fermionic QCPs, we need to monitor that the temperature is above TPG instead of T. This was often ignored in previous studies.

关键词： critical quantum utilize