Polymer-derived ceramics(PDCs)is a promising way to prepare ceramic-based electromagnetic functional materials,which can conveniently modulate the composition and dielectric properties of the ceramics.In this paper,Si...Polymer-derived ceramics(PDCs)is a promising way to prepare ceramic-based electromagnetic functional materials,which can conveniently modulate the composition and dielectric properties of the ceramics.In this paper,SiBCN ceramic matrix composites with excellent high-temperature wave-transparent performance were prepared through PDC method.Three hyperbranched polyborosilazanes(PBSZs)were prepared by adjusting the type of chlorosilane monomers containing different numbers of methyl groups.The carbon element of pyrolytic ceramics was tuned by adjusting the molecular structure of the precursor and the pyrolysis temperature.The lower the methyl number and pyrolysis temperature,the lower the dielectric constant of the polymer-derived SiBCN ceramics,which is favorable for electromagnetic wave(EMW)transmittance.The average EMW transmittance of SiBCN-C pyrolyzed from hyperbranched PBSZ using trichlorosilane at 1000℃ was 90.56%at room temperature.More excitingly,the excellent wave-transparent performance was also maintained in the temperature range of 100-800℃.At the test temperature of 800℃,SiBCN-C-1000 still had excellent wave-transparent performance with minimum and average EMW transmittance of 76.13%and 88.96%,respectively.This paper provided a new idea for the preparation of high-temperature wave-transparent SiBCN composite ceramics.展开更多
In this work,zeolitic imidazolate framework-8(ZIF-8)with yolk-shell and hollow structures were pre-pared by a convenient chemical etching method.A subsequent pyrolysis of ZIF-8 enabled one to pro-duce ZnO/nitrogen-dop...In this work,zeolitic imidazolate framework-8(ZIF-8)with yolk-shell and hollow structures were pre-pared by a convenient chemical etching method.A subsequent pyrolysis of ZIF-8 enabled one to pro-duce ZnO/nitrogen-doped carbon nanocomplexes with original ZIF-8 morphology,where hollow struc-ture showed superior electromagnetic wave absorption capacity and was responsible for matching the impedance of free space.The minimum reflection coefficients of hollow ZnO/nitrogen-doped carbon nanocomplexes were-51.2 dB(700℃)and-52.4 dB(800℃),respectively,whereas the effective ab-sorption band width was as large as 4 GHz and the content of pyrolyzed hollow ZIF-8 was 15 wt%,which was inferior to the level among similar electromagnetic wave(EMW)absorption materials.The conve-nient and facile strategy paves the way toward designing hierarchical structures for highly efficient and light-weight electromagnetic wave absorbers.展开更多
The angular-dependent magnetoresistance(AMR)of the ab plane is measured on the single crystals of ironchalcogenide FeSe_(1-x)S_(x)(x=0,0.07,0.13 and 1)and FeSe_(1-y)Te_(y)(y=0.06,0.61 and 1)at various temperatures und...The angular-dependent magnetoresistance(AMR)of the ab plane is measured on the single crystals of ironchalcogenide FeSe_(1-x)S_(x)(x=0,0.07,0.13 and 1)and FeSe_(1-y)Te_(y)(y=0.06,0.61 and 1)at various temperatures under fields up to 9 T.A pronounced twofold-anisotropic carrier-scattering effect is identified by AMR,and attributed to a magnetic-field-induced spin nematicity that emerges from the tetragonal normal-state regime below a characteristic temperature Tsn.This magnetically polarized spin nematicity is found to be ubiquitous in the isoelectronic FeSe_(1-x)S_(x)and FeSe_(1-y)Te_(y)systems,no matter whether the sample shows an electronic nematic order at T_(s)≤T_(sn),or an antiferromagnetic order at TN<T_(sn),or neither order.Importantly,we find that the induced spin nematicity shows a very different response to sulfur substitution from the spontaneous electronic nematicity:The spin-nematic T_(sn)is not suppressed but even enhanced by the substitution,whereas the electronicnematic T_(s)is rapidly suppressed,in the FeSe_(1-x)S_(x)system.Furthermore,we find that the superconductivity is significantly suppressed with the enhancement of the induced spin nematicity in both FeSe_(1-x)S_(x)and FeSe_(1-y)Te_(y)samples.展开更多
We report the observation for the pz electron band and the band inversion in Fe1+yTexSe1-xwith angleresolved photoemission spectroscopy. Furthermore, we found that excess Fe(y>0) inhibits the topological band inver...We report the observation for the pz electron band and the band inversion in Fe1+yTexSe1-xwith angleresolved photoemission spectroscopy. Furthermore, we found that excess Fe(y>0) inhibits the topological band inversion in Fe1+yTexSe1-x,which explains the absence of Majorana zero modes in previous reports for Fe1+yTexSe1-xwith excess Fe. Based on our analysis of different amounts of Te doping and excess Fe, we propose a delicate topological phase in this material. Thanks to this delicate phase, one may be able to tune the topological transition via applying lattice strain or carrier doping.展开更多
The phenomenon of phase separation into antiferromagnetic（AFM） and superconducting（SC） or normal-state regions has great implication for the origin of high-temperature（high-T_c） superconductivity. However, the o...The phenomenon of phase separation into antiferromagnetic（AFM） and superconducting（SC） or normal-state regions has great implication for the origin of high-temperature（high-T_c） superconductivity. However, the occurrence of an intrinsic antiferromagnetism above the T_c of（Li,Fe）OHFe Se superconductor is questioned. Here we report a systematic study on a series of（Li,Fe）OHFe Se single crystal samples with T_c up to ～41 K. We observe an evident drop in the static magnetization at T_（afm） ～ 125 K, in some of the SC（T_c 38 K, cell parameter c■9.27 ？） and non-SC samples. We verify that this AFM signal is intrinsic to（Li,Fe）OHFe Se. Thus, our observations indicate mesoscopic-to-macroscopic coexistence of an AFM state with the normal（below T_（afm）） or SC（below T_c） state in（Li,Fe）OHFe Se. We explain such coexistence by electronic phase separation, similar to that in high-T_c cuprates and iron arsenides. However, such an AFM signal can be absent in some other samples of（Li,Fe）OHFe Se, particularly it is never observed in the SC samples of T_c 38 K, owing to a spatial scale of the phase separation too small for the macroscopic magnetic probe. For this case, we propose a microscopic electronic phase separation. The occurrence of two-dimensional AFM spin fluctuations below nearly the same temperature as T_（afm）, reported previously for a（Li,Fe）OHFe Se（T_c ～ 42 K） single crystal, suggests that the microscopic static phase separation reaches vanishing point in high T_c（Li,Fe）OHFe Se. A complete phase diagram is thus established. Our study provides key information of the underlying physics for high-T_c superconductivity.展开更多
We synthesize a series of Mn substituted （Li, Fe）OHFeSe superconductor single crystals via a modified ion-exchange method, with the Mn concentration z （the atomic ratio of Mn：Se） ranging from 0 to 0.07. The distr...We synthesize a series of Mn substituted （Li, Fe）OHFeSe superconductor single crystals via a modified ion-exchange method, with the Mn concentration z （the atomic ratio of Mn：Se） ranging from 0 to 0.07. The distribution homogeneity of the Mn element incorporated into the lattice of （Li, Fe）OHFeSe is checked by combined measurements of high-angle- annular-dark-field （HAADF） imaging and electron energy-loss spectroscopy （EELS）. Interestingly, we find that the superconducting transition temperature Tc and unit cell parameter c of the Mn-doped （Li, Fe）OHFeSe samples display similar V-shaped evolutions with the increasing dopant concentration z. We propose that, with increasing doping level, the Mn dopant first occupies the tetrahedral sites in the （Li, Fe）OH layers before starting to substitute the Fe element in the su- perconducting FeSe layers, which accounts for the V-shaped change in cell parameter c. The observed positive correlation between the Tc and lattice parameter c, regardless of the Mn doping level z, indicates that a larger interlayer separation, or a weaker interlayer coupling, is essential for the high-Tc superconductivity in （Li, Fe）OHFeSe. This agrees with our previous observations on powder, single crystal, and film samples of （Li, Fe）OHFeSe superconductors.展开更多
Chemical substitution during growth is a well-established method to manipulate electronic states of quantum materials, and leads to rich spectra of phase diagrams in cuprate and iron-based superconductors. Here we rep...Chemical substitution during growth is a well-established method to manipulate electronic states of quantum materials, and leads to rich spectra of phase diagrams in cuprate and iron-based superconductors. Here we report a novel and generic strategy to achieve nonvolatile electron doping in series of(i.e.11 and 122 structures) Fe-based superconductors by ionic liquid gating induced protonation at room temperature. Accumulation of protons in bulk compounds induces superconductivity in the parent compounds, and enhances the Tclargely in some superconducting ones. Furthermore, the existence of proton in the lattice enables the first proton nuclear magnetic resonance(NMR) study to probe directly superconductivity. Using Fe S as a model system, our NMR study reveals an emergent high-Tcphase with no coherence peak which is hard to measure by NMR with other isotopes. This novel electric-fieldinduced proton evolution opens up an avenue for manipulation of competing electronic states(e.g.Mott insulators), and may provide an innovative way for a broad perspective of NMR measurements with greatly enhanced detecting resolution.展开更多
Objective:To clarify the length and volume reduction of seminal vesicles(SVs)after neo-adjuvant hormonal therapy(NHT),in order to help contour the optimal SV included into high-dose clinical target volume(CTV)for radi...Objective:To clarify the length and volume reduction of seminal vesicles(SVs)after neo-adjuvant hormonal therapy(NHT),in order to help contour the optimal SV included into high-dose clinical target volume(CTV)for radiotherapy in intermediate-and high-risk patients.Methods:MR images both before and after NHT(5.3±2.2 months)were collected from thirty-one patients with cT2-4N0M0 prostate cancer.SV volume was measured in axial T1WI,while SV length was obtained in a reconstructed oblique coronary plane through its long axial from a 3D sequence.Results:SVs showed evident reduction both in length and volume(length:median 12.1%,range 4.0%–28.0%;volume:median 39.9%,range 9.4%–66.2%).For SVs with and without MR detected involvement,length shortening were(16.7±4.8)%and(11.1±4.4)%(P<0.001);for involved SVs and lesions,volume reduction were(41.0±16.0)%and(66.3±14.4)%,respectively(P<0.001),both indicating a more sensitive response to NHT of the involved portion than normal SV.Conclusions:Both volume and length of the SV will be reduced after receiving NHT.Besides,the invaded segments shrink more than normal SV tissue,indicating that SV portion included within the CTV can be reduced.展开更多
The iron-based nontoxic chalcogenide superconductor Fe(Te,Se)has great potential for high magnetic field applications while it lacks a reliable method to produce bulk superconductor so far.Here we report a one-step sy...The iron-based nontoxic chalcogenide superconductor Fe(Te,Se)has great potential for high magnetic field applications while it lacks a reliable method to produce bulk superconductor so far.Here we report a one-step synthesis method to grow high-quality Fe(Te,Se)single crystals free of interstitial iron atoms through minor Mn doping.Bulk superconductivity is revealed in the as-grown centimetersized crystals with the optimal doping level of 1% Fe atoms substituted by Mn,which is systematically demonstrated by sharp electrical resistivity and magnetic susceptibility transitions,and large specific heat jumps.Compared with the undoped sample,the optimally doped one shows a significantly enhanced upper critical field,and a large self-field critical current density J_(c) of 4.5×10^(5)A cm^(-2) at 2 K(calculated by the Bean model),which maintains large values under high fields.The absence of interstitial iron atoms is testified by the scanning tunneling microscopy,and the effect of Mn doping is discussed.Our results provide a practical method by minor Mn doping to directly synthesize high-performance Fe(Te,Se)bulks that allow for future high-field superconducting applications.展开更多
基金financially supported by the National Science Fund for Distinguished Young Scholars(No.52025034)the Na-tional Key Research and Development Program of China(No.2022YFB3807100/2022YFB3807101)+1 种基金the National Natural Sci-ence Foundation of China(No.22005039)the Polymer Elec-tromagnetic Functional Materials Innovation Team of Shaanxi San-qin Scholars.
文摘Polymer-derived ceramics(PDCs)is a promising way to prepare ceramic-based electromagnetic functional materials,which can conveniently modulate the composition and dielectric properties of the ceramics.In this paper,SiBCN ceramic matrix composites with excellent high-temperature wave-transparent performance were prepared through PDC method.Three hyperbranched polyborosilazanes(PBSZs)were prepared by adjusting the type of chlorosilane monomers containing different numbers of methyl groups.The carbon element of pyrolytic ceramics was tuned by adjusting the molecular structure of the precursor and the pyrolysis temperature.The lower the methyl number and pyrolysis temperature,the lower the dielectric constant of the polymer-derived SiBCN ceramics,which is favorable for electromagnetic wave(EMW)transmittance.The average EMW transmittance of SiBCN-C pyrolyzed from hyperbranched PBSZ using trichlorosilane at 1000℃ was 90.56%at room temperature.More excitingly,the excellent wave-transparent performance was also maintained in the temperature range of 100-800℃.At the test temperature of 800℃,SiBCN-C-1000 still had excellent wave-transparent performance with minimum and average EMW transmittance of 76.13%and 88.96%,respectively.This paper provided a new idea for the preparation of high-temperature wave-transparent SiBCN composite ceramics.
基金financially supported by the National Natural Science Foundation of China (No. 21875190)the National Science Fund for Distinguished Young Scholars (No. 52025034)the Analytical & Testing Center of NPU for support
文摘In this work,zeolitic imidazolate framework-8(ZIF-8)with yolk-shell and hollow structures were pre-pared by a convenient chemical etching method.A subsequent pyrolysis of ZIF-8 enabled one to pro-duce ZnO/nitrogen-doped carbon nanocomplexes with original ZIF-8 morphology,where hollow struc-ture showed superior electromagnetic wave absorption capacity and was responsible for matching the impedance of free space.The minimum reflection coefficients of hollow ZnO/nitrogen-doped carbon nanocomplexes were-51.2 dB(700℃)and-52.4 dB(800℃),respectively,whereas the effective ab-sorption band width was as large as 4 GHz and the content of pyrolyzed hollow ZIF-8 was 15 wt%,which was inferior to the level among similar electromagnetic wave(EMW)absorption materials.The conve-nient and facile strategy paves the way toward designing hierarchical structures for highly efficient and light-weight electromagnetic wave absorbers.
基金the National Key Research and Development Program of China(Grant Nos.2016YFA0300300 and 2017YFA0303003)the National Natural Science Foundation of China(Grant Nos.12061131005,11834016,and 11888101)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB25000000)the Strategic Priority Research Program and Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(Grant Nos.QYZDY-SSW-SLH001)。
文摘The angular-dependent magnetoresistance(AMR)of the ab plane is measured on the single crystals of ironchalcogenide FeSe_(1-x)S_(x)(x=0,0.07,0.13 and 1)and FeSe_(1-y)Te_(y)(y=0.06,0.61 and 1)at various temperatures under fields up to 9 T.A pronounced twofold-anisotropic carrier-scattering effect is identified by AMR,and attributed to a magnetic-field-induced spin nematicity that emerges from the tetragonal normal-state regime below a characteristic temperature Tsn.This magnetically polarized spin nematicity is found to be ubiquitous in the isoelectronic FeSe_(1-x)S_(x)and FeSe_(1-y)Te_(y)systems,no matter whether the sample shows an electronic nematic order at T_(s)≤T_(sn),or an antiferromagnetic order at TN<T_(sn),or neither order.Importantly,we find that the induced spin nematicity shows a very different response to sulfur substitution from the spontaneous electronic nematicity:The spin-nematic T_(sn)is not suppressed but even enhanced by the substitution,whereas the electronicnematic T_(s)is rapidly suppressed,in the FeSe_(1-x)S_(x)system.Furthermore,we find that the superconductivity is significantly suppressed with the enhancement of the induced spin nematicity in both FeSe_(1-x)S_(x)and FeSe_(1-y)Te_(y)samples.
基金supported by the National Natural Science Foundation of China(Grant Nos.11888101 and U1832202)the Chinese Academy of Sciences(Grant Nos.QYZDB-SSW-SLH043,XDB28000000,and XDB33000000)+3 种基金the K.C.Wong Education Foundation(Grant No.GJTD-2018-01)the Informatization Plan of Chinese Academy of Sciences(Grant No.CAS-WX2021SF-0102)supported by the Synergetic Extreme Condition User Facility(SECUF)supported by US DOE(Grant Nos.DESC0010526 and DE-SC0012704)。
文摘We report the observation for the pz electron band and the band inversion in Fe1+yTexSe1-xwith angleresolved photoemission spectroscopy. Furthermore, we found that excess Fe(y>0) inhibits the topological band inversion in Fe1+yTexSe1-x,which explains the absence of Majorana zero modes in previous reports for Fe1+yTexSe1-xwith excess Fe. Based on our analysis of different amounts of Te doping and excess Fe, we propose a delicate topological phase in this material. Thanks to this delicate phase, one may be able to tune the topological transition via applying lattice strain or carrier doping.
基金Supported by the National Key Research and Development Program of China under Grant Nos 2017YFA0303003,2016YFA0300300 and 2015CB921000the National Natural Science Foundation of China under Grant Nos 11574370,11474338,11674374 and 61501220+1 种基金the Strategic Priority Research Program and Key Research Program of Frontier Sciences of the Chinese Academy of Sciences under Grant Nos QYZDY-SSW-SLH001,QYZDY-SSW-SLH008 and XDB07020100the Beijing Municipal Science and Technology Project under Grant No Z161100002116011
文摘The phenomenon of phase separation into antiferromagnetic（AFM） and superconducting（SC） or normal-state regions has great implication for the origin of high-temperature（high-T_c） superconductivity. However, the occurrence of an intrinsic antiferromagnetism above the T_c of（Li,Fe）OHFe Se superconductor is questioned. Here we report a systematic study on a series of（Li,Fe）OHFe Se single crystal samples with T_c up to ～41 K. We observe an evident drop in the static magnetization at T_（afm） ～ 125 K, in some of the SC（T_c 38 K, cell parameter c■9.27 ？） and non-SC samples. We verify that this AFM signal is intrinsic to（Li,Fe）OHFe Se. Thus, our observations indicate mesoscopic-to-macroscopic coexistence of an AFM state with the normal（below T_（afm）） or SC（below T_c） state in（Li,Fe）OHFe Se. We explain such coexistence by electronic phase separation, similar to that in high-T_c cuprates and iron arsenides. However, such an AFM signal can be absent in some other samples of（Li,Fe）OHFe Se, particularly it is never observed in the SC samples of T_c 38 K, owing to a spatial scale of the phase separation too small for the macroscopic magnetic probe. For this case, we propose a microscopic electronic phase separation. The occurrence of two-dimensional AFM spin fluctuations below nearly the same temperature as T_（afm）, reported previously for a（Li,Fe）OHFe Se（T_c ～ 42 K） single crystal, suggests that the microscopic static phase separation reaches vanishing point in high T_c（Li,Fe）OHFe Se. A complete phase diagram is thus established. Our study provides key information of the underlying physics for high-T_c superconductivity.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0303003 and 2016YFA0300300)the National Natural Science Foundation of China(Grant No.11574370)the Strategic Priority Research Program and Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(Grant Nos.QYZDY-SSW-SLH001,QYZDY-SSW-SLH008,and XDB07020100)
文摘We synthesize a series of Mn substituted （Li, Fe）OHFeSe superconductor single crystals via a modified ion-exchange method, with the Mn concentration z （the atomic ratio of Mn：Se） ranging from 0 to 0.07. The distribution homogeneity of the Mn element incorporated into the lattice of （Li, Fe）OHFeSe is checked by combined measurements of high-angle- annular-dark-field （HAADF） imaging and electron energy-loss spectroscopy （EELS）. Interestingly, we find that the superconducting transition temperature Tc and unit cell parameter c of the Mn-doped （Li, Fe）OHFeSe samples display similar V-shaped evolutions with the increasing dopant concentration z. We propose that, with increasing doping level, the Mn dopant first occupies the tetrahedral sites in the （Li, Fe）OH layers before starting to substitute the Fe element in the su- perconducting FeSe layers, which accounts for the V-shaped change in cell parameter c. The observed positive correlation between the Tc and lattice parameter c, regardless of the Mn doping level z, indicates that a larger interlayer separation, or a weaker interlayer coupling, is essential for the high-Tc superconductivity in （Li, Fe）OHFeSe. This agrees with our previous observations on powder, single crystal, and film samples of （Li, Fe）OHFeSe superconductors.
基金supported by the Ministry of Science and Technology of China(2015CB921700,2016YFA0300504,2016YFA0301004,2016YFA0300401 and 2017YFA0302903)the National Natural Science Foundation of China(11374364,11522429,11374011 and 11534005)
文摘Chemical substitution during growth is a well-established method to manipulate electronic states of quantum materials, and leads to rich spectra of phase diagrams in cuprate and iron-based superconductors. Here we report a novel and generic strategy to achieve nonvolatile electron doping in series of(i.e.11 and 122 structures) Fe-based superconductors by ionic liquid gating induced protonation at room temperature. Accumulation of protons in bulk compounds induces superconductivity in the parent compounds, and enhances the Tclargely in some superconducting ones. Furthermore, the existence of proton in the lattice enables the first proton nuclear magnetic resonance(NMR) study to probe directly superconductivity. Using Fe S as a model system, our NMR study reveals an emergent high-Tcphase with no coherence peak which is hard to measure by NMR with other isotopes. This novel electric-fieldinduced proton evolution opens up an avenue for manipulation of competing electronic states(e.g.Mott insulators), and may provide an innovative way for a broad perspective of NMR measurements with greatly enhanced detecting resolution.
基金This study was supported by National Natural Science Foundation of China(82271771)National High Level Hospital Clinical Research Funding(Interdepartmental Clinical Research Project of Peking University First Hospital,2022CR29)Beijing Xisike Clinical Oncology Research Foundation(Y-2019AZQN-0003),China.
文摘Objective:To clarify the length and volume reduction of seminal vesicles(SVs)after neo-adjuvant hormonal therapy(NHT),in order to help contour the optimal SV included into high-dose clinical target volume(CTV)for radiotherapy in intermediate-and high-risk patients.Methods:MR images both before and after NHT(5.3±2.2 months)were collected from thirty-one patients with cT2-4N0M0 prostate cancer.SV volume was measured in axial T1WI,while SV length was obtained in a reconstructed oblique coronary plane through its long axial from a 3D sequence.Results:SVs showed evident reduction both in length and volume(length:median 12.1%,range 4.0%–28.0%;volume:median 39.9%,range 9.4%–66.2%).For SVs with and without MR detected involvement,length shortening were(16.7±4.8)%and(11.1±4.4)%(P<0.001);for involved SVs and lesions,volume reduction were(41.0±16.0)%and(66.3±14.4)%,respectively(P<0.001),both indicating a more sensitive response to NHT of the involved portion than normal SV.Conclusions:Both volume and length of the SV will be reduced after receiving NHT.Besides,the invaded segments shrink more than normal SV tissue,indicating that SV portion included within the CTV can be reduced.
基金supported by the National Key Research and Development Program of China(2018YFA0704200,2017YFA0302904,2019YFA0308500,and 2018YFA0305602)the National Natural Science Foundation of China(12074414,12074002,52072401,11804379,and 11774402)+1 种基金the Recruitment Program for Leading Talent Team of Anhui Province(2019-16)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB25000000)。
文摘The iron-based nontoxic chalcogenide superconductor Fe(Te,Se)has great potential for high magnetic field applications while it lacks a reliable method to produce bulk superconductor so far.Here we report a one-step synthesis method to grow high-quality Fe(Te,Se)single crystals free of interstitial iron atoms through minor Mn doping.Bulk superconductivity is revealed in the as-grown centimetersized crystals with the optimal doping level of 1% Fe atoms substituted by Mn,which is systematically demonstrated by sharp electrical resistivity and magnetic susceptibility transitions,and large specific heat jumps.Compared with the undoped sample,the optimally doped one shows a significantly enhanced upper critical field,and a large self-field critical current density J_(c) of 4.5×10^(5)A cm^(-2) at 2 K(calculated by the Bean model),which maintains large values under high fields.The absence of interstitial iron atoms is testified by the scanning tunneling microscopy,and the effect of Mn doping is discussed.Our results provide a practical method by minor Mn doping to directly synthesize high-performance Fe(Te,Se)bulks that allow for future high-field superconducting applications.
