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| 1 | Temperature-induced Lifshitz transition in topological insulator candidate HfTe_5显示文摘The ongoing discoveries and studies of novel topological quantum materials have become an emergent and important field of condensed matter physics.Recently,HfTe_5 ignited renewed interest as a candidate of a novel topological material.The single-layer HfTe_5 is predicted to be a two-dimensional large band gap topological insulator and can be stacked into a bulk that may host a temperature-driven topological phase transition.Historically,HfTe_5 attracted considerable interest for its anomalous transport properties characterized by a peculiar resistivity peak accompanied by a sign reversal carrier type.The origin of the transport anomaly remains under a hot debate.Here we report the first high-resolution laser-based angle-resolved photoemission measurements on the temperature-dependent electronic structure in HfTe_5.Our results indicated that a temperature-induced Lifshitz transition occurs in HfTe_5,which provides a natural understanding on the origin of the transport anomaly in HfTe_5.In addition,our observations suggest that HfTe_5 is a weak topological insulator that is located at the phase boundary between weak and strong topological insulators at very low temperature. | Yan Zhang Chenlu Wang Guodong Liu Aiji Liang Lingxiao Zhao Jianwei Huang Qiang Gao Bing Shen Jing Liu Cheng Hu Wenjuan Zhao Genfu Chen Xiaowen Jia Li Yu Lin Zhao Shaolong He Fengfeng Zhang Shenjin Zhang Feng Yang Zhimin Wang Qinjun Peng Zuyan Xu Chuangtian Chen Xingjiang Zhou | 2017 | Science Bulletin2017，62，13： | 4 |
| 2 | Very high upper critical fields of F-doped Fe-based layered superconductors NdO_(0.88)F_(0.12)FeAs and CeO_(0.88)F_(0.12)FeAs显示文摘Using the solid state reaction method, we have synthesized the polycrystalline F-doped NdO0.88F0.12FeAs and CeO0.88F0.12FeAs with the superconducting transition temperatures at about 48 and 40 K, respectively. To obtain the upper critical field Hc2 of Nd(Ce)O0.88F0.12FeAs samples, we measured the electrical resistivity under magnetic field up to 14 T. Based on the Werthamer-Helfand-Hohenberg (WHH) rela-tion together with the Hc2(T) curves in a relatively high field, we estimated that these superconductors have a rather high upper critical field of about 115 T for Nd-based and 107 T for Ce-based samples, indicating the similarities between these ReO1-xFxFeAs (Re = rare earth element) superconductors and high Tc cuprate su-perconductors. | WU Dan, LI Zheng, SU ShaoKui, DONG Jing, LI Gang, HU WanZheng, ZHENG Ping, CHEN GenFu, LUO JianLin & WANG NanLin Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China | 2008 | Science China(Physics,Mechanics & Astronomy)2008，51，6： | 2 |
| 3 | Large transverse thermoelectric figure of merit in a topological Dirac semimetal显示文摘The Seebeck effect encounters a few fundamental constraints hindering its thermoelectric(TE)conversion efficiency.Most notably,there are the charge compensation of electrons and holes that diminishes this effect,and the Wiedemann-Franz(WF)law that makes independent optimization of the corresponding electrical and thermal conductivities impossible.Here,we demonstrate that in the topological Dirac semimetal Cd3As2 the Nernst effect,i.e.,the transverse counterpart of the Seebeck effect,can generate a large TE figure of merit zNT.At room temperature,zNT≈0.5 in a small field of 2 T and it significantly surmounts its longitudinal counterpart for any field.A large Nernst effect is generically expected in topological semimetals,benefiting from both the bipolar transport of compensated electrons and holes and their high mobilities.In this case,heat and charge transport are orthogonal,i.e.,not intertwined by the WF law anymore.More importantly,further optimization of zNT by tuning the Fermi level to the Dirac node can be anticipated due to not only the enhanced bipolar transport,but also the anomalous Nernst effect arising from a pronounced Berry curvature.A combination of the topologically trivial and nontrivial advantages promises to open a new avenue towards high-efficient transverse thermoelectricity. | JunSen Xiang SiLe Hu Meng Lyu WenLiang Zhu ChaoYang Ma ZiYu Chen Frank Steglich GenFu Chen PeiJie Sun | 2020 | Science China(Physics,Mechanics & Astronomy)2020，63，3： | 0 |
| 4 | Recycling valuable cobalt from spent lithium ion batteries for controllably designing a novel sea-urchin-like cobalt nitride-graphene hybrid catalyst: Towards efficient overall water splitting显示文摘Along with the continuous consumption in lithium-ion batteries (LIBs), the price of cobalt is inevitably going up in recent years. Therefore, recycling valuable Co element from spent devices, and boosting its service efficiency are becoming two indispensable approaches to promote the utilization of Co in various energy conversion/storage devices. Herein, we realize the recovery of Co from spent LIBs and synthesize a three–dimensional (3D) sea-urchin-like cobalt nitride composite material (labeled as CoN-Gr-2), which is used as a bi-functional catalyst for water splitting. Benefiting from the intrinsic high conductivity, larger surface area and unique 3D sea–urchin–like architecture, CoN-Gr-2 shows an excellent electron transfer efficiency, highly exposed active sites as well as the superior mass transport capacity. The CoN-Gr-2 catalyst exhibits low overpotentials of 128.9 mV and 280 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), which are comparable to the commercial 20 wt% Pt/C and RuO_(2) catalysts. Moreover, when adopting CoN-Gr-2 as both anode and cathode materials for overall water splitting (in 1.0 M KOH electrolyte), the assembled cell achieves a current density of 10 mA cm^(−2) at 1.61 V, which almost close to that of Pt/C||RuO_(2) benchmark (1.60 V), demonstrating its superior water-splitting efficiency. Meanwhile, the CoN catalysts exhibit strong chemical interaction with the Gr support, suppressing the aggregation of CoN catalysts and maintains their high activity during HER and OER reactions. So, the cell exhibits a high current retention of 97.3% after 40 h. This work successfully develops an industrial chain from recycling Co wastes in spent energy devices to controllably designing 3D sea-urchin-like CoN-Gr with high water splitting efficiency. Therefore, it could further promote the efficient utilization of valuable Co element in various energy devices. | Tingting Liu Sheng Cai Genfu Zhao Zhihui Gao Shuming Liu Huani Li Lijuan Chen Mian Li Xiaofei Yang Hong Guo | 2021 | Journal of Energy Chemistry2021，30，11： | 0 |
| 5 | Structural phase transition, antiferromagnetism and two superconducting domes in LaFeAsO_(1-x)F_x(0显示文摘We report^(75) As nuclear magnetic resonance(NMR)/nuclear quadrupole resonance(NQR) and transmission electron microscopy(TEM) studies on LaFeAsO_(1-x)F_x. There are two superconducting domes in this material. The first one appears at 0.03 ≤ x ≤0.2 with T_c^(max) = 27 K, and the second one at 0.25 ≤x≤0.75 with T_c^(max) = 30 K. By NMR and TEM, we demonstrate that a C4-to-C2 structural phase transition(SPT) takes place above both domes, with the transition temperature T_s varying strongly with x. In the first dome, the SPT is followed by an antiferromagnetic(AF) transition, but neither AF order nor low-energy spin fluctuations are found in the second dome. By ^(75) As nuclear spin-lattice relaxation rate(1/T_1) measurements, we find that AF order and superconductivity coexist microscopically in LaFeAsO_(0.97) F_(0.03). In the coexisting region, 1/T_1 decreases at T_c but becomes proportional to T below 0.6 T_c, indicating gapless excitations. Therefore, in contrast to the early reports, the obtained phase diagram for x ≤ 0.2 is quite similar to the doped BaFe_2As_2 system. The electrical resistivity p in the second dome can be fitted by ρ = ρ0 + AT^n with n = 1 and a maximal coefficient A at around xopt = 0.5-0.55 at which T_s extrapolates to zero and Tc is the maximal, which suggests the importance of quantum critical fluctuations associated with the SPT. We have constructed a complete phase diagram of LaFeAsO_(1-x)F_x, which provides insight into the relationship between SPT, antiferromagnetism and superconductivity. | Jie Yang Toshihide Oka Zheng Li HuaiXin Yang JianQi Li GenFu Chen Guo-Qing Zheng | 2018 | Science China(Physics,Mechanics & Astronomy)2018，61，11： | 0 |
| 6 | Highly Anisotropic Magnetism and Nearly Isotropic Magnetocaloric Effect in Mn_(3)Sn_(2)Single Crystals显示文摘Mn_(3)Sn_(2)has been proposed as an ideal material for magnetic refrigeration.It undergoes two successive ferromagnetic transitions(T_(C1)=262 K and T_(C2)=227 K)and one antiferromagnetic transition(TN=192 K).Herein we report,for the first time,the preparation of single crystals of Mn_(3)Sn_(2)from Bi flux.The resultant anisotropic magnetic properties and magnetocaloric effect are investigated along the three principal crystallographic directions of the crystal.Significant anisotropy of magnetic susceptibility and multiple field-induced metamagnetic transitions were found at low fields,whereas the magnetocaloric effect was found to be almost isotropic and larger than that of the polycrystalline one.The maximum magnetic entropy change amounts to-ΔSM=4.01 J·kg^(-1)·K^(-1)near T_(C1)under a magnetic field change of μ_(0)ΔH=5 T along the c-axis,with the corresponding refrigerant capacity of 1750 mJ·cm^(-3).Combined with a much wider cooling temperature span(~80 K),our results demonstrate Mn_(3)Sn_(2)single crystal to be an attractive candidate working material for active magnetic refrigeration at low temperatures. | Jianli Bai Qingxin Dong Libo Zhang Qiaoyu Liu Jingwen Cheng Pinyu Liu Cundong Li Yingrui Sun Yu Huang Zhian Ren Genfu Chen | 2023 | Chinese Physics Letters2023，40，12： | 0 |
| 7 | Superconductivity in LaPd2Bi2 with CaBe2Ge2-type structure显示文摘Since the discovery of superconductivity in LaFeAsO1-xFx, the high-Tc iron-based superconductors have been extensively studied from both experimental and theoretical viewpoints [1-8].However,the mechanism of the unconventional superconductivity is still to be resolved.To address such issues,numerous 3d,4d,5d transition metal pnietide,silicide,germanide,chalcogenide materials crystalizing in the similar crystal structure with iron pnictide/ selenide suoerconductors were studied [9-24]. | QingGe Mu BoJin Pan BinBin Ruan Tong Liu Kang Zhao Lei Shan GenFu Chen ZhiAn Ren | 2018 | Science China(Physics,Mechanics & Astronomy)2018，61，12： | 0 |
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