We report a new kagome quantum spin liquid candidate CuaZn（OH）6FBr, which does not experience any phase transition down to 50inK, more than three orders lower than the antiferromagnetic Curie-Weiss temperature （-20...We report a new kagome quantum spin liquid candidate CuaZn（OH）6FBr, which does not experience any phase transition down to 50inK, more than three orders lower than the antiferromagnetic Curie-Weiss temperature （-200 K）. A clear gap opening at low temperature is observed in the uniform spin susceptibility obtained from 19F nuclear magnetic resonance measurements. We observe the characteristic magnetic field dependence of the gap as expected for fractionalized spin-1/2 spinon excitations. Our experimental results provide firm evidence for spin fractionalization in a topologically ordered spin system, resembling charge fraetionalization in the fractional quantum Hall state.展开更多
The search for quantum spin liquid(QSL) materials has attracted significant attention in the field of condensed matter physics in recent years, however so far only a handful of them are considered as candidates hostin...The search for quantum spin liquid(QSL) materials has attracted significant attention in the field of condensed matter physics in recent years, however so far only a handful of them are considered as candidates hosting QSL ground state. Owning to their geometrically frustrated structures, Kagome materials are ideal systems to realize QSL. We synthesize the kagome structured material claringbullite(Cu_4(OH)_6FCl) and then replace inter-layer Cu with Zn to form Cu_3Zn(OH)_6FCl. Comprehensive measurements reveal that doping Zn^(2+) ions transforms magnetically ordered Cu_4(OH)_6FCl into a non-magnetic QSL candidate Cu_3Zn(OH)_6FCl. Therefore,the successful syntheses of Cu_4(OH)_6FCl and Cu_3Zn(OH)_6FCl provide not only a new platform for the study of QSL but also a novel pathway of investigating the transition between QSL and magnetically ordered systems.展开更多
Interface can be a fertile ground for exotic quantum states,including topological superconductivity,Majorana mode,fractal quantum Hall effect,unconventional superconductivity,Mott insulator,etc.Here we grow single-uni...Interface can be a fertile ground for exotic quantum states,including topological superconductivity,Majorana mode,fractal quantum Hall effect,unconventional superconductivity,Mott insulator,etc.Here we grow single-unit-cell(1UC)FeTe film on NbSe_(2)single crystal by molecular beam epitaxy(MBE)and investigate the film in-situ with a home-made cryogenic scanning tunneling microscopy(STM)and non-contact atomic force microscopy(AFM)combined system.We find different stripe-like superlattice modulations on grown FeTe film with different misorientation angles with respect to NbSe_(2)substrate.We show that these stripe-like superlattice modulations can be understood as moirépattern forming between FeTe film and NbSe_(2)substrate.Our results indicate that the interface between Fe Te and NbSe2 is atomically sharp.By STM-AFM combined measurement,we suggest that the moirésuperlattice modulations have an electronic origin when the misorientation angle is relatively small(≤3°)and have structural relaxation when the misorientation angle is relatively large(≥10°).展开更多
Growth of high-quality single crystals is of great significance for research of condensed matter physics. The exploration of suitable growing conditions for single crystals is expensive and time-consuming, especially ...Growth of high-quality single crystals is of great significance for research of condensed matter physics. The exploration of suitable growing conditions for single crystals is expensive and time-consuming, especially for ternary compounds because of the lack of ternary phase diagram. Here we use machine learning(ML) trained on our experimental data to predict and instruct the growth. Four kinds of ML methods, including support vector machine(SVM), decision tree, random forest and gradient boosting decision tree, are adopted. The SVM method is relatively stable and works well, with an accuracy of 81% in predicting experimental results. By comparison,the accuracy of laboratory reaches 36%. The decision tree model is also used to reveal which features will take critical roles in growing processes.展开更多
We systematically study the low-temperature specific heats for the two-dimensional kagome antiferromagnet,Cu_(3)Zn(OH)_(6)FBr.The specific heat exhibits a T1.7 dependence at low temperatures and a shoulder-like featur...We systematically study the low-temperature specific heats for the two-dimensional kagome antiferromagnet,Cu_(3)Zn(OH)_(6)FBr.The specific heat exhibits a T1.7 dependence at low temperatures and a shoulder-like feature above it.We construct a microscopic lattice model of Z_(2) quantum spin liquid and perform large-scale quantum Monte Carlo simulations to show that the above behaviors come from the contributions from gapped anyons and magnetic impurities.Surprisingly,we find the entropy associated with the shoulder decreases quickly with grain size d,although the system is paramagnetic to the lowest temperature.While this can be simply explained by a core-shell picture in that the contribution from the interior state disappears near the surface,the 5.9-nm shell width precludes any trivial explanations.Such a large length scale signifies the coherence length of the nonlocality of the quantum entangled excitations in quantum spin liquid candidate,similar to Pippard’s coherence length in superconductors.Our approach therefore offers a new experimental probe of the intangible quantum state of matter with topological order.展开更多
We systematically investigate the magnetic properties of Cu4-xZnx(OH)6FBr using the neutron diffraction and muon spin rotation and relaxation(μSR) techniques.Neutron-diffraction measurements suggest that the longrang...We systematically investigate the magnetic properties of Cu4-xZnx(OH)6FBr using the neutron diffraction and muon spin rotation and relaxation(μSR) techniques.Neutron-diffraction measurements suggest that the longrange magnetic order and the orthorhombic nuclear structure in the x=0 sample can persist up to x=0.23 and 0.43,respectively.The temperature dependence of the zero-field μSR spectra provides two characteristic temperatures,TA0 and Tλ,which are associated with the initial drop close to zero time and the long-time exponential decay of the muon relaxation,respectively.Comparison between TA0 and TM from previously reported magnetic-susceptibility measurements suggest that the former comes from the short-range interlayer-spin clusters that persist up to x=0.82.On the other hand,the doping level where Tλ becomes zero is about 0.66,which is much higher than threshold of the long-range order,i.e.,~0.4.Our results suggest that the change in the nuclear structure may alter the spin dynamics of the kagome layers and a gapped quantum-spin-liquid state may exist above x=0.66 with the perfect kagome planes.展开更多
基金Supported by the National Key Research and Development Program of China under Grant Nos 2016YFA0300502,2016YFA0300503,2016YFA0300604,2016YF0300300 and 2016YFA0300802the National Natural Science Foundation of China under Grant Nos 11421092,11474330,11574359,11674406,11374346 and 11674375+3 种基金the National Basic Research Program of China(973 Program)under Grant No 2015CB921304the National Thousand-Young-Talents Program of Chinathe Strategic Priority Research Program(B) of the Chinese Academy of Sciences under Grant Nos XDB07020000,XDB07020200 and XDB07020300supported by DOE-BES under Grant No DE-FG02-04ER46148
文摘We report a new kagome quantum spin liquid candidate CuaZn（OH）6FBr, which does not experience any phase transition down to 50inK, more than three orders lower than the antiferromagnetic Curie-Weiss temperature （-200 K）. A clear gap opening at low temperature is observed in the uniform spin susceptibility obtained from 19F nuclear magnetic resonance measurements. We observe the characteristic magnetic field dependence of the gap as expected for fractionalized spin-1/2 spinon excitations. Our experimental results provide firm evidence for spin fractionalization in a topologically ordered spin system, resembling charge fraetionalization in the fractional quantum Hall state.
基金Supported by the National Key Research and Development Program(2016YFA0300502,2017YFA0302901,2016YFA0300604 and 2016YFA0300501)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB28000000,XDB07020100and QYZDB-SSW-SLH043)the National Natural Science Foundation of China under Grant Nos 11421092,11574359,11674370,11774399,11474330 and U1732154
文摘The search for quantum spin liquid(QSL) materials has attracted significant attention in the field of condensed matter physics in recent years, however so far only a handful of them are considered as candidates hosting QSL ground state. Owning to their geometrically frustrated structures, Kagome materials are ideal systems to realize QSL. We synthesize the kagome structured material claringbullite(Cu_4(OH)_6FCl) and then replace inter-layer Cu with Zn to form Cu_3Zn(OH)_6FCl. Comprehensive measurements reveal that doping Zn^(2+) ions transforms magnetically ordered Cu_4(OH)_6FCl into a non-magnetic QSL candidate Cu_3Zn(OH)_6FCl. Therefore,the successful syntheses of Cu_4(OH)_6FCl and Cu_3Zn(OH)_6FCl provide not only a new platform for the study of QSL but also a novel pathway of investigating the transition between QSL and magnetically ordered systems.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2016YFA0302400,2016YFA0300602,and2017YFA0302903)the National Natural Science Foundation of China(Grant No.11227903)+2 种基金the Beijing Municipal Science and Technology Commission,China(Grant Nos.Z181100004218007 and Z191100007219011)the National Basic Research Program of China(Grant No.2015CB921304)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB07000000,XDB28000000,and XDB33000000)。
文摘Interface can be a fertile ground for exotic quantum states,including topological superconductivity,Majorana mode,fractal quantum Hall effect,unconventional superconductivity,Mott insulator,etc.Here we grow single-unit-cell(1UC)FeTe film on NbSe_(2)single crystal by molecular beam epitaxy(MBE)and investigate the film in-situ with a home-made cryogenic scanning tunneling microscopy(STM)and non-contact atomic force microscopy(AFM)combined system.We find different stripe-like superlattice modulations on grown FeTe film with different misorientation angles with respect to NbSe_(2)substrate.We show that these stripe-like superlattice modulations can be understood as moirépattern forming between FeTe film and NbSe_(2)substrate.Our results indicate that the interface between Fe Te and NbSe2 is atomically sharp.By STM-AFM combined measurement,we suggest that the moirésuperlattice modulations have an electronic origin when the misorientation angle is relatively small(≤3°)and have structural relaxation when the misorientation angle is relatively large(≥10°).
基金Supported by the National Key Research and Development Program of China under Grant Nos 2016YFA0401000 and2017YFA0302901the National Basic Research Program of China under Grant No 2015CB921000+2 种基金the National Natural Science Foundation of China under Grant Nos 11574371,11774399 and 11774398the Beijing Natural Science Foundation(Z180008)the Strategic Priority Research Program of Chinese Academy of Sciences under Grant No XDB28000000
文摘Growth of high-quality single crystals is of great significance for research of condensed matter physics. The exploration of suitable growing conditions for single crystals is expensive and time-consuming, especially for ternary compounds because of the lack of ternary phase diagram. Here we use machine learning(ML) trained on our experimental data to predict and instruct the growth. Four kinds of ML methods, including support vector machine(SVM), decision tree, random forest and gradient boosting decision tree, are adopted. The SVM method is relatively stable and works well, with an accuracy of 81% in predicting experimental results. By comparison,the accuracy of laboratory reaches 36%. The decision tree model is also used to reveal which features will take critical roles in growing processes.
基金Supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0302900,2016YFA0300500,and2020YFA0406003)the National Natural Science Foundation of China(Grant Nos.11874401,11674406,11961160699,11774399+4 种基金11804383)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant Nos.XDB33000000,XDB28000000,XDB25000000XDB07020000)the K.C.Wong Education Foundation(Grant Nos.GJTD-2020-01 and GJTD-2018-01)the Beijing Natural Science Foundation(Grant No.Z180008)。
文摘We systematically study the low-temperature specific heats for the two-dimensional kagome antiferromagnet,Cu_(3)Zn(OH)_(6)FBr.The specific heat exhibits a T1.7 dependence at low temperatures and a shoulder-like feature above it.We construct a microscopic lattice model of Z_(2) quantum spin liquid and perform large-scale quantum Monte Carlo simulations to show that the above behaviors come from the contributions from gapped anyons and magnetic impurities.Surprisingly,we find the entropy associated with the shoulder decreases quickly with grain size d,although the system is paramagnetic to the lowest temperature.While this can be simply explained by a core-shell picture in that the contribution from the interior state disappears near the surface,the 5.9-nm shell width precludes any trivial explanations.Such a large length scale signifies the coherence length of the nonlocality of the quantum entangled excitations in quantum spin liquid candidate,similar to Pippard’s coherence length in superconductors.Our approach therefore offers a new experimental probe of the intangible quantum state of matter with topological order.
基金Supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0302900,2016YFA0300500,2018YFA0704200,2017YFA0303100,and 2016YFA0300600)the National Natural Science Foundation of China(Grant Nos.11874401,11674406,11674372,11961160699,11774399,12061130200,11974392,and 11822411)+4 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant Nos.XDB25000000,XDB07020000,XDB33000000,and XDB28000000)the Beijing Natural Science Foundation(Grant Nos.Z180008 and JQ19002)Guangdong Introducing Innovative and Entrepreneurial Teams(Grant No.2017ZT07C062)the Youth Innovation Promotion Association of CAS(Grant No.2016004)the Royal Society-Newton Advanced Fellowship(Grant No.NAF∖R1∖201248).
文摘We systematically investigate the magnetic properties of Cu4-xZnx(OH)6FBr using the neutron diffraction and muon spin rotation and relaxation(μSR) techniques.Neutron-diffraction measurements suggest that the longrange magnetic order and the orthorhombic nuclear structure in the x=0 sample can persist up to x=0.23 and 0.43,respectively.The temperature dependence of the zero-field μSR spectra provides two characteristic temperatures,TA0 and Tλ,which are associated with the initial drop close to zero time and the long-time exponential decay of the muon relaxation,respectively.Comparison between TA0 and TM from previously reported magnetic-susceptibility measurements suggest that the former comes from the short-range interlayer-spin clusters that persist up to x=0.82.On the other hand,the doping level where Tλ becomes zero is about 0.66,which is much higher than threshold of the long-range order,i.e.,~0.4.Our results suggest that the change in the nuclear structure may alter the spin dynamics of the kagome layers and a gapped quantum-spin-liquid state may exist above x=0.66 with the perfect kagome planes.
