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Specific heat in superconductors

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Chinese Physics B 2020年第1期29卷 24-39页

作者： hai-hu wen School of Physics Nanjing UniversityNanjing 210093China

Specific heat is a powerful tool to investigate the physical properties of condensed *** state is achieved through the condensation of paired electrons,namely,the Cooper *** condensed Cooper pairs have lower entropy compared with that of electrons in normal metal,thus specific heat is very useful in detecting the low lying quasiparticle excitations of the superconducting condensate and the pairing symmetry of the superconducting *** this brief overview,we will give an introduction to the specific heat investigation of the physical properties of *** show the data obtained in cuprate and iron based superconductors to reveal the pairing symmetry of the order parameter.

关键词： specific heat gap symmetry low lying quasiparticle excitations cuprates iron based superconductors

Comparative study of vortex dynamics in CaKFe_4As_4 and Ba_(0.6)K_(0.4)Fe_2As_2 single crystals

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Science Bulletin 2019年第2期64卷 81-90页

作者： Wang Cheng hai Lin Bing Shen hai-hu wen Center for Superconducting Physics and Materials National Laboratory of Solid State Microstructures and Department of Physics National Center of Microstructures and Quantum Manipulation Nanjing University School of Physics Sun Yat-sen University

We investigate the vortex dynamics in two typical hole doped iron based superconductors CaKFe_4As_4(CaK1144) and Ba_(0.6)K_(0.4)Fe_2As_2(BaK122) with similar superconducting transition temperatures. It is found that the magnetization hysteresis loop exhibits a clear second peak effect in BaK122 in wide temperature region while it is absent in CaK1144. However, a second peak effect of critical current density versus temperature is observed in CaK1144, which is however absent in BaK122. The different behaviors of second peak effect in BaK122 and CaK1144 may suggest distinct origins of vortex pinning in different systems. Magnetization and its relaxation have also been measured by using dynamical and conventional relaxation methods for both systems. Analysis and comparison of the two distinct systems show that the vortex pinning is stronger and the critical current density is higher in BaK122 system. It is found that the Maley's method can be used and thus the activation energy can be determined in BaK122 by using the time dependent magnetization in wide temperature region, but this is not applicable in CaK1144 *** we present the different regimes with distinct vortex dynamics in the field-temperature diagram for the two systems.

关键词： CaKFe4As4 Ba0.6K0.4Fe2As2 Magnetization hysteresis loop Vortex pinning Second peak effect Vortex dynamics

Superconductivity in nickel-based 112 systems

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The Innovation 2022年第1期3卷 108-121页

作者： Qiangqiang Gu hai-hu wen National Laboratory of Solid State Microstructures and Department of Physics Collaborative Innovation Center of Advanced MicrostructuresNanjing UniversityNanjing 210093China

Superconductivity has been discovered recently in infinite-layer nickel-based 112 thin films R_(1-x)A_(x)NiO_(2)(R=La,Nd,Pr and A=Sr,Ca).They are isostructural to the infinite-layer cuprate(Ca,Sr)CuO_(2)and are supposed to have a formal Ni 3d9 valence,thus providing a new platform to study the unconventional pairing mechanismof high-temperature *** important discovery immediately triggers a huge amount of innovative scientific curiosity in the *** this paper,we try to give an overview of the recent research progress on the newly found superconducting nickelate systems,both from experimental and theoretical *** mainly focus on the electronic structures,magnetic excitations,phase diagrams and superconducting gaps,and finally make some open discussions for possible pairing symmetries in Ni-based 112 systems.

关键词： field nickel infinite

Ferromagnetism and insulating behavior with a logarithmic temperature dependence of resistivity in Pb_(10-x)Cux(PO_(4))_(6)O

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Science China(Physics,Mechanics & Astronomy) 2024年第1期67卷 106-111页

作者： Yuhang Zhang Cong Liu Xiyu Zhu hai-hu wen Center for Superconducting Physics and Materials National Laboratory of Solid State Microstructures and Department of PhysicsNational Collaborative Innovation Center of Advanced MicrostructuresNanjing UniversityNanjing 210093China

Recent claim of discovering above-room-temperature superconductivity(Tc≈400 K)at ambient pressure in copper doped apatite Pb10(PO_(4))_(6)O has stimulated world-wide enthusiasm and impulse of motion.A lot of follow-up works have been carried out with controversial *** check whether superconductivity is really present or absent in the material,we need samples which should have a rather pure phase of Pb_(10-x)Cux(PO_(4))_(6)*** we report the characterization results from the Pb_(10-x)Cux(PO_(4))_(6)O with a fraction of about 97 wt.%inferred from the fitting to the X-ray diffraction pattern,if assuming Cu2S as the only *** resistivity measurements show that it is a semiconductor characterized roughly by a ln(1/T)temperature dependence in wide temperature region without trace of *** measurements show that it has a general ferromagnetic signal with a weak superparamagnetic *** grains of the sample show clear interactions with a Nb Fe B *** detected Cu concentration is much lower than the expected nominal *** results show the absence of metallicity and superconductivity in Pb_(10-x)Cux(PO_(4))_(6)O at ambient pressure,and suggest the presence of strong correlation effect.

关键词： superconductivity Pb10(PO4)6O ferromagnetic correlation effect

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Superconductivity in Li OHFe S single crystals with a shrunk c-axis lattice constant

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Science China(Physics,Mechanics & Astronomy) 2017年第2期Mechanics & Astronomy) .卷 50-54页

作者： hai Lin Rui Zhe Kang Lu Kong XiYu Zhu hai-hu wen Center for Superconducting Physics and Materials National Laboratory of Solid State Microstructures and Department of PhysicsNational Collaborative Innovation Center of Advanced Microstructures Nanjing University

By using a hydrothermal ion-exchange method, we have successfully grown superconducting crystals of Li OHFe S with Tcof about 2.8 K. Being different from the sister sample(Li1-xFex)OHFe Se, the energy dispersion spectrum analysis on Li OHFe S shows that the Fe/S ratio is very close to 1:1, suggesting an almost charge neutrality and less electron doping in the Fe S planes of the system. Comparing with the non superconducting Li OHFe S crystal, each peak of the X-ray diffraction pattern of the superconducting crystal splits into two, and the diffraction peaks locating at lower reflection angles are consistent with that of non-superconducting ones. The rest set of diffraction peaks with higher reflection angles is corresponding to the superconducting phase, suggesting that the superconducting phase may has a shrunk c-axis lattice constant. Magnetization measurements indicate that the magnetic shielding due to superconductivity can be quite high under a weak magnetic field. The resistivity measurements under various magnetic fields show that the upper critical field is quite low, which is similar to the tetragonal Fe S superconductor.

关键词： iron chalcogenides magnetic properties transport properties

Robust superconductivity and transport properties in (Li_(1-x)Fe_x)OHFeSe single crystals

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Science China(Physics,Mechanics & Astronomy) 2016年第5期59卷 11-15页

作者： hai Lin Jie Xing Xi Yu Zhu huan Yang hai-hu wen Center for Superconducting Physics and Materials National Laboratory of Solid State Microstructures and Department of PhysicsNational Collaborative Innovation Center of Advanced Microstructures Nanjing University

The recently discovered(Li_(1-x) Fe_x)OHFe Se superconductor with T c about 40 K provides a good platform for investigating the magnetization and electrical transport properties of Fe Se-based superconductors. By using a hydrothermal ion-exchange method,we have successfully grown crystals of(Li_(1-x) Fe_x)OHFe Se. X-ray diffraction on the sample shows the single crystalline Pb O-type structure with the c-axis preferential orientation. Magnetic susceptibility and resistive measurements show an onset superconducting transition at around T c=38.3 K. Using the magnetization hysteresis loops and Bean critical state model, a large critical current J s is observed in low temperature region. The critical current density is suppressed exponentially with increasing magnetic *** dependencies of resistivity under various currents and fields are measured, revealing a robust superconducting current density and bulk superconductivity.

关键词： iron chalcogenides critical currents magnetic properties transport properties

Preface to the topical issue

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Science China(Physics,Mechanics & Astronomy) 2018年第12期61卷 1-2页

作者： hai-hu wen huiQiu Yuan ShiPing Feng Nanjing University Nanjing 210093China Zhejiang University Hangzhou 310058China Beijing Normal University Beijing 100875China

Transition metals contain d-orbital electrons,and compounds based on transition metals often exhibit a duality of magnetism and *** date,a large number of interesting physics phenomena exhibited by transition-metal compounds have been discovered;for example,high-temperature superconductivity has been found to emerge in compounds such as copper-oxide (cuprate)compounds,iron pnictides/*** the relationship between superconductivity and magnetism is essential for realizing these unconventional superconductors.

关键词： topical issue Preface

Contrasting physical properties of the trilayer nickelates Nd4Ni3O10 and Nd4Ni3O8

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Science China(Physics,Mechanics & Astronomy) 2021年第2期64卷 98-104页

作者： Qing Li ChengPing He XiYu Zhu Jin Si XinWei Fan hai-hu wen Center for Superconducting Physics and Materials National Laboratory of Solid State Microstructures and Department of PhysicsCollaborative Innovation Center of Advanced MicrostructuresNanjing UniversityNanjing210093China

We report the crystal structures and physical properties of trilayer nickelates Nd4Ni3O10and *** of magnetization and electrical resistivity display contrasting behaviors in the two ***4Ni3O10shows a paramagnetic metallic behavior with a metal-to-metal phase transition(T^*)at about 162 K,as revealed by both magnetic susceptibility and *** magnetoresistance and Hall coefficient results show a negative magnetoresistance at low temperatures and the carrier type of Nd4Ni3O10is dominated by hole-type charge *** significant enhancement of Hall coefficient and resistivity below T*suggests that effective charge carrier density decreases when cooling through the transition *** contrast,Nd4Ni3O8 shows an insulating *** addition,this compound shows a paramagnetic behavior with the similar magnetic moment as that of Nd4Ni3O10derived from the Curie-Weiss *** may suggest that the magnetic moments in both systems are contributed by Nd^3+ *** applying pressures up to about 49 GPa,the insulating behavior is still present and becomes even stronger under a high *** results suggest that the different Ni configurations(Ni^1+/2+ or Ni^2+/3+)and the changes of coordination environment of Ni sites may account for the contrasting behaviors in trilayer nickelates Nd4Ni3O10and Nd4Ni3O8.

关键词： trilayer nickelate Nd4Ni3O10 and Nd4Ni3O8 high-pressure study

Preparations of TiO_2 film coated on foam nickel substrate by sol-gel processes and its photocatalytic activity for degradation of acetaldehyde

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Journal of Environmental Sciences 2007年第1期19卷 80-85页

作者： hu hai XIAO wen-jun YUAN Jian SHI Jian-wei CHEN Ming-xia SHANG GUAN wen-feng Research Center for Combustion and Environment Technology Shanghai Jiao Tong University. Shanghai 200030 China

Anatase TiO2 films were successfully prepared on foam nickel substrates by sol-gel technique using tetrabutyl titanate as precursor. The characteristics of the TiO2 films were investigated by XPS, XRD, FE-SEM, TEM and UV-Vis absorption spectra. The photocatalytic activities of TiO2 films were investigated by photocatalytic degradation reactions of gaseous acetaldehyde, an indoor pollutant, under ultraviolet light irradiation. It was found that Ni^2＋ doping into TiO2 films due to the foam nickel substrates resulted in the extension of absorption edges of TiO2 films from UV region to visible light region. The pre-heating for foam nickel substrates resulted in the formation of NiO layer, which prevented effectively the injection of photogenerated electrons from TiO2 films to metal nickel. The TiO2 films displayed high photocatalytic activity for the degradation of acetaldehyde, and were enhanced by calcining the substrates and coating TiO2 films repeatedly. The high activity was mainly attributed to the improvement of the characteristics of substrate surface and the increase of active sites on photocatalyst.

关键词： photocatalyst TiO2 films foam nickel sol-gel acetaldehyde degradation