Zhongxian Zhao

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (113)244.57 Total impact

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    ABSTRACT: The complexity in AyFe2-xSe2 (A = metal ions) superconductors has brought much controversy regarding whether a common underlying physics may govern both iron selenide and arsenide high-temperature superconductors. The newly synthesized (Li1-xFex)OHFe1-ySe superconductor exhibiting similar physical properties to the iron arsenide superconductors provides a new perspective on the debated issue. However, in-depth investigations on its intrinsic electronic properties are still lacking because the large single crystals are not available yet. Here we report that, by a novel hydrothermal ion-exchange technique with big insulating K0.8Fe1.6Se2 crystal as a matrix, a high-quality (Li0.84Fe0.16)OHFe0.98Se single crystal over 10 mm in length is successfully synthesized. A superconducting transition at 42 K is confirmed through electric resistivity and magnetic susceptibility measurements. Hall coefficient reveals that electron carriers dominate, but its relative contribution is gradually reduced below ~ 120 K. Further lowering temperature, it is remarkable that a linear temperature dependence of the in-plane electric resistivity is observed, a key feature of the anomalous normal state properties of both optimally doped iron arsenide and copper-oxide high-temperature superconductors9-15. Our results indicate that (Li0.84Fe0.16)OHFe0.98Se falls under the same universality class, where the two dimensional antiferromagnetic spin fluctuations play a key role in electron pairing.
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    ABSTRACT: In-situ hydrostatic and uniaxial high pressure studies were performed on recently discovered CrAs-based qausi-one-dimensional superconductors A2Cr3As3 (A=K and Rb). The established Pressure-Temperature phase diagram in this study clearly demonstrates that either hydrostatic pressure or uniaxial pressure globally suppresses the superconducting transition temperature (Tc), and the latter is more effective than the former. Interestingly, in the same hydrostatic pressure environment, the suppressing rate of Tc in Rb2Cr3As3 is nearly twice as that of K2Cr3As3. Significantly, the reduced Tc in these superconductors can fully recover to its ambient-pressure value after the applied pressure is entirely released. Our results suggest that the bonding distance and angle between Cr-Cr in the Cr3As3 chains are the key factor in determining Tc and that the optimal lattice for superconductivity is hosted in the pristine K2Cr3As3.
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    ABSTRACT: The recent discovery of large and non-saturating magnetoresistance (LMR) in WTe2 provides a unique playground to find new phenomena and significant perspective for potential applications. Here we report the first observation of superconductivity near the proximity of suppressed LMR state in pressurized WTe2 through high-pressure synchrotron X-ray diffraction, electrical resistance, magnetoresistance, and ac magnetic susceptibility measurements. It is found that the positive magnetoresistance effect can be turned off at a critical pressure of 10.5 GPa without crystal structure change and superconductivity emerges simultaneously. The maximum superconducting transition temperature can be reached to 6.5 K at ~15 GPa and it decreases down to 2.6 K at ~25 GPa. In-situ high pressure Hall coefficient measurements at 10 K demonstrate that elevating pressure decreases hole carrier's population but increases electron carrier's population. Significantly, at the critical pressure, we observed a sign change in the Hall coefficient, indicating a possible Lifshitz-type quantum phase transition in WTe2.
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    ABSTRACT: Topological insulators (TIs) containing 4f electrons have recently attracted intensive interests due to the possible interplay of their non-trivial topological properties and strong electronic correlations. YbB6 and SmB6 are the prototypical systems with such unusual properties, which may be tuned by external pressure to give rise to new emergent phenomena. Here, we report the first observation, through in-situ high pressure resistance, Hall, X-ray diffraction and X-ray absorption measurements, of two pressure-induced quantum phase transitions (QPTs) in YbB6. Our data revealthat the two insulating phases are separated by a metallic phase due to the pressure-driven valence change of Yb f-orbitals. In combination with previous studies, our results suggest that the two insulating states may be topologically different in nature and originate from the d-p and d-f hybridization, respectively. The tunable topological properties of YbB6 revealed in this study may shed light on the intriguing correlation between the topology and the 4f electrons from the perspective of pressure dependent studies.
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    ABSTRACT: The high density (2 km × 6 km), high resolution (19 sequence boundaries) seismic reflection profiles and 42 industrial wells (including VSP data, gamma ray, sonic and density logs) are now available in Qiongdongnan Basin to the northwest of South China Sea. Then we explored the time-depth relationships of strata, obtained the compaction curves of shale and sand, and recovered the original sediment thickness. Furthermore, we calculated the sediment budget and analyzed the deepwater sedimentation processes.
    Marine Geology 01/2015; 361. DOI:10.1016/j.margeo.2015.01.002 · 2.20 Impact Factor
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    ABSTRACT: Previous experimental results have shown important differences between iron selenide and arsenide superconductors, which seem to suggest that the high temperature superconductivity in these two subgroups of iron-based family may arise from different electronic ground states. Here, we report the complete phase diagram of a newly synthesized superconducting (SC) system (Li1-xFex)OHFeSe with a similar structure to FeAs-based superconductors. In the non-SC samples, an antiferromagnetic (AFM) spin-density-wave (SDW) transition occurs at ~127 K. This is the first example to demonstrate such an SDW phase in FeSe-based superconductor system. Transmission electron microscopy (TEM) shows that a well-known sqrr(5) x sqrr(5) iron vacancy ordered state, resulting in an AFM order at ~ 500K in AyFe2-xSe2 (A = metal ions) superconductor system, is absent in both non-SC and SC samples, but a unique superstructure with a modulation wave vector q=1/2(1, 1, 0), identical to that seen in SC phase of KyFe2-xSe2, is dominant in the optimal SC sample (with an SC transition temperature Tc = 40 K). Hence, we conclude that the high-Tc superconductivity in (Li1-xFex)OHFeSe stems from the similarly weak AFM fluctuations as FeAs-based superconductors, suggesting a universal physical picture for both iron selenide and arsenide superconductors.
    Journal of the American Chemical Society 12/2014; 137(1). DOI:10.1021/ja511292f · 11.44 Impact Factor
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    ABSTRACT: The central depression of the Qiongdongnan Basin can be divided into the eastern and western sub-basins by the Lingshui–Songnan paleo-uplift. To the northwest, the orientation of the faults turns from NE, to EW, and later to NW; In the southwest, the orientation of the faults turns from NE, to NNE, and then to NW, making the central depression much wider towards the west. In the eastern sub-basin, the NE-striking faults and the EW-striking faults made up an echelon, making the central depression turn wider towards the east. Fault activity rates indicate that faulting spreads gradually from both the east and west sides to the middle of the basin. Hence, extensional stress in the eastern sub-basin may be related to the South China Sea spreading system, whereas the western sub-basin was more under the effect of the activity of the Red River Fault. The extreme crustal stretching in the eastern sub-basin was probably related to magmatic setting. It seems that there are three periods of magmatic events that occurred in the eastern sub-basin. In the eastern part of the southern depression, the deformed strata indicate that the magma may have intruded into the strata along faults around T60 (23.3 Ma). The second magmatic event occurred earlier than 10.5 Ma, which induced the accelerated subsidence. The final magmatic event commenced later than 10 Ma, which led to today’s high heat flow. As for the western sub-basin, the crust thickened southward, and there seemed to be a southeastward lower crustal flow, which happened during continental breakup which was possibly superimposed by a later lower crustal flow induced by the isostatic compensation of massive sedimentation caused by the right lateral slipping of the Red River Fault. Under the huge thick sediment, super pressure developed in the western sub-basin. In summary, the eastern sub-basin was mainly affected by the South China Sea spreading system and a magma setting, whereas the western sub-basin had a closer relationship with the Indo-China extrusion system.
    Marine Geophysical Researches 12/2014; 36(1). DOI:10.1007/s11001-014-9247-3 · 0.76 Impact Factor
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    ABSTRACT: Qiongdongnan Basin (QB) experienced three main tectonic stages in the Cenozoic: rifting, thermal subsidence, and accelerated subsidence. Corresponding to these stages, the slope breaks also underwent three different evolutionary stages, which differed in space and time between the east and west of QB. Structural slope breaks developed during the rifting stage in the Paleocene. Transitional sedimentary strata without obvious slope break developed in the neritic environment during the thermal subsidence stage in the Neocene. Sedimentary slope breaks and gentle slope zone without slope break developed during the accelerated subsidence stage. The sedimentary slope breaks could be further classified into progradational and aggradational types, the starting points of which varied in space and time. Spatially, the progradational sequences in the Ledong and Lingshui sags started at the north of today’s deep central basin, distant from the basin edge. In the Songnan and Baodao sags, the aggradational sequences were close to the sag edge and essentially controlled by the underlying major boundary faults. Temporally, sedimentary slope breaks developed early in the east and late in the west and were initially partitioned and eventually unified. Fault activity controlled the types and ending time of structural slope breaks during the rifting stage, while tectonic subsidence controlled the time and places of progradational slope breaks during the accelerated subsidence stage. Sediment supply controlled the superposition patterns of the sedimentary sequences of the sedimentary slope breaks. It is suggested that the evolutionary history of the slope breaks has been primarily affected by the southward transition of the South China Sea ocean ridge, the westward collision of the Philippine Sea Plate, and the dextral strike-slipping of the Red River Fault.
    Marine Geophysical Researches 12/2014; DOI:10.1007/s11001-014-9246-4 · 0.76 Impact Factor
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    ABSTRACT: The Qiongdongnan Basin, located off Hainan Island, South China, is a petroliferous basin containing what is currently the largest offshore-producing gas field in China (YA13–1). This paper evaluated the potential of CO2 storage in the Qiongdongnan Basin to provide background data on CO2 storage capacities for regional planning purposes. Four regional seals and high-quality reservoirs exists in the basin, in mostly marine sequences. The estimated mean effective CO2 storage capacity of the basin is 41 GtCO2, determined from published data and the Carbon Sequestration Leadership Forum methodology for assessing oil and gas storage capacity; the majority of the storage capacity is in saline formations and oil and gas field (15 MtCO2 and 832 MtCO2, respectively). The prospective areas for CO2 storage in the Qiongdongnan Basin are in the belts of the Northern Depression and the Central Uplift. The Yacheng Uplift, as the most favorable area for CO2 storage, contains the YA13–1 gas field, which has an estimated mean effective CO2 storage capacity of 73 MtCO2. The Qiongdongnan Basin may provide storage sites for CO2 stripped from the CO2-enriched gas from the basin itself, or from the emission sources in Hong Kong and Guangdong Province. However, industrial development on Hainan Island is weak, as the island was defined as an ‘island for international tourism’ by the Chinese government in 2009. The feasibility of transporting CO2 to storage sites in the Qiongdongnan Basin using the pipeline now transporting gas from the YA13–1 gas field to Hong Kong should be explored.
    Greenhouse Gases: Science and Technology 12/2014; 4(6). DOI:10.1002/ghg.1430 · 2.92 Impact Factor
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    ABSTRACT: We report the first observation of a pressure-induced breakdown of the 3D-DSM state in Cd3As2, evidenced by a series of in-situ high-pressure synchrotron X-ray diffraction (XRD) and single crystal transport measurements. We find that Cd3As2 undergoes a structural phase transition from a metallic tetragonal (T) phase in space group I41/acd to a semiconducting monoclinic (M) phase in space group P21/c at critical pressure 2.57 GPa, above this pressure, an activation energy gap appears, accompanied by distinct switches in Hall resistivity slope and electron mobility. These changes of crystal symmetry and corresponding transport properties manifest the breakdown of the 3D-DSM state in pressurized Cd3As2.
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    ABSTRACT: Post-rift fault activities were often observed in deepwater basins, which have great contributions to oil and gas migration and accumulation. The main causes for post-rift fault activities include tectonic events, mud or salt diapirs, and gravitational collapse. In the South China Sea continental margin, post-rift fault activities are widely distributed, especially in Baiyun sag, one of the largest deepwater sag with its main body located beneath present continental slope. During the post-rift stage, large population of faults kept active for a long time from 32 Ma (T70) till 5.5 Ma (T10). Seismic interpretation, fault analysis and analogue modeling experiments indicate that the post-rift fault activities in Baiyun sag between 32 Ma (T70) and 13.8 Ma (T30) was mainly controlled by gravity pointing to the Main Baiyun sag, which caused the faults extensive on the side facing Main Baiyun sag and the back side compressive. Around 32 Ma (T70), the breakup of the continental margin and the spreading of the South China Sea shed a combined effect of weak compression toward Baiyun sag. The gravity during post-rift stage might be caused by discrepant subsidence and sedimentation between strongly thinned sag center and wing areas. This is supported by positive relationship between sedimentation rate and fault growth index. After 13.8 Ma (T30), fault activity shows negative relationship with sedimentation rate. Compressive uplift and erosion in seismic profiles as well as negative tectonic subsiding rates suggest that the fault activity from 13.8 Ma (T30) to 5.5 Ma (T10) might be controlled by the subductive compression from the Philippine plate in the east.
    Journal of Asian Earth Sciences 08/2014; 89:76–87. DOI:10.1016/j.jseaes.2014.02.018 · 2.83 Impact Factor
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    ABSTRACT: A unique platform for investigating the correlation between the antiferromagnetic (AFM) and superconducting (SC) states in high temperature superconductors is created by the discovery of alkaline iron selenide superconductors which are composed of an AFM insulating phase and a SC phase separated spatially. Our previous studies showed that pressure can fully suppress the superconductivity of ambient-pressure superconducting phase (SC-I) and AFM order simultaneously, then induce another superconducting phase (SC-II) at higher pressure. Consequently, the connection between the two superconducting phases becomes an intriguing issue. In this study, on the basis of observing pressure-induced reemergence of superconductivity in Rb0.8Fe2-ySe2-xTex (x=0, 0.19 and 0.28) superconductors, we find that the superconductivity of the SC-I and SC-II phases as well as the AFM ordered state can be synchronously tuned by Te doping and disappear together at the doping level of x=0.4. We propose that the two superconducting phases are connected by the AFM phase, in other words, the state of long-ranged AFM order plays a role in giving rise to superconductivity of the SC-I phase, while the fluctuation state of the suppressed AFM phase drives the emergence of SC-II phase. These results comprehensively demonstrate the versatile roles of AFM states in stabilizing and developing superconductivity in the alkaline iron selenide superconductors.
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    ABSTRACT: Here, we report that K-doped BaMn2Bi2 shows no experimental evidence of superconductivity down to 1.5 K under pressures up to 35.6 GPa, however, a tetragonal to an orthorhombic phase transition is observed at pressure of 20 GPa. Theoretical calculations for the tetragonal and orthorhombic phases, on basis of our high-pressure XRD data, find that the AFM order is robust in both of the phases in pressurized Ba0.61K0.39Mn2Bi2. Our experimental and theoretical results suggest that the K-doped BaMn2Bi2 belongs to a strong Hunds AFM metal with a hybridization of localized spin electrons and itinerant electrons, and that its robust AFM order essentially prevents the emergence of superconductivity.
    Scientific Reports 04/2014; 4. DOI:10.1038/srep07342 · 5.08 Impact Factor
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    ABSTRACT: Pressure-induced superconductivity is oberserved in Ca10 (Pt3 As8 )(Fe2 As2 )5 by in situ high-pressure resistance and magnetic susceptibility measurements. Scaling of the pressure-induced and doping-induced superconductivity shows that the electronic phase diagrams of the pressurized and chemically doped 10-3-8 compound are similar in the moderate pressure and doping range but are disparate at higher pressure and heavy doping.
    Advanced Materials 04/2014; 26(15). DOI:10.1002/adma.201305154 · 15.41 Impact Factor
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    ABSTRACT: Here, we report that K-doped BaMn2Bi2 shows no experimental evidence of superconductivity down to 1.5 K under pressures up to 35.6 GPa, however, a tetragonal to an orthorhombic phase transition is observed at pressure of 20 GPa. Theoretical calculations for the tetragonal and orthorhombic phases, on basis of our high-pressure XRD data, find that the AFM order is robust in both of the phases in pressurized Ba0.61K0.39Mn2Bi2. Our experimental and theoretical results suggest that the K-doped BaMn2Bi2 belongs to a strong Hunds AFM metal with a hybridization of localized spin electrons and itinerant electrons, and that its robust AFM order essentially prevents the emergence of superconductivity.
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    ABSTRACT: There is considerable interest in uncovering the physics of iron-based superconductivity from the alkaline iron selenides, a materials class containing an insulating phase (245 phase) and a superconducting (SC) phase. Due to the microstructural complexity of these superconductors, the role of the 245 phase in the development of the superconductivity has been a puzzle. Here we demonstrate a comprehensive high-pressure study on the insulating samples with pure 245 phase and biphasic SC samples. We find that the insulating behavior can be completely suppressed by pressure in the insulating samples and also identify an intermediate metallic (M') state. The Mott insulating (MI) state of the 245 phase and the M' state coexist over a significant range of pressure up to ̃10 GPa, the same pressure at which the superconductivity of the SC samples vanishes. Our results reveal the M' state as a pathway that connects the insulating and SC phases of the alkaline iron selenides and indicate that the coexistence and interplay between the MI and M' states is a necessary condition for superconductivity. Finally, we interpret the M' state in terms of an orbital selectivity of the correlated 3d electrons.
    Physical Review B 02/2014; 89(9). DOI:10.1103/PhysRevB.89.094514 · 3.66 Impact Factor
  • Zhongxian Zhao, Zhen Sun, Zhenfeng Wang, Zhipeng Sun
    Marine Geophysical Researches 01/2014; DOI:10.1007/s11001-014-9238-4 · 0.76 Impact Factor
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    ABSTRACT: A 1-D unloaded tectonic subsidence (air-loaded tectonic subsidence) model is proposed and applied to the Qiongdongnan Basin. Results show that three episodes of subsidence exist in Cenozoic, that is, syn-rift rapid subsidence (Eocene-Oligocene) with subsidence rate at 20-100 m/m.y., post-rift slow thermal subsidence (early-middle Miocene) around 40 m/m.y., and post-rift accelerated subsidence (since late Miocene) 40-140 m/m.y., which is substantially deviated from the exponentially decayed thermal subsidence model. For exploring the mechanism of post-rift accelerated subsidence, the faulting analyses are conducted and results show that there is a dramatically decrease in the numbers of active faults and fault growth rate since 21 Ma, which indicates that no active brittle crust extension occurred during post-rift period. Furthermore, previous studies have demonstrated that the stretching of the upper crust is far less than that affecting the whole crust. Therefore, we infer that the lower crust thinned during the post-rift period and a new model of basin development and evolution is put forward to explain the post-rift accelerated subsidence and depth-dependent crust thinning in the Qiongdongnan Basin, which is supported by gravity data.
    Marine Geophysical Researches 11/2013; 34(3-4). DOI:10.1007/s11001-013-9188-2 · 0.76 Impact Factor
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    ABSTRACT: The emergence of superconductivity in the iron pnictide or cuprate high temperature superconductors usually accompanies the suppression of a long-ranged antiferromagnetic (AFM) order state in a corresponding parent compound by doping or pressurizing. A great deal of effort by doping has been made to find superconductivity in Mn-based compounds, which are thought to bridge the gap between the two families of high temperature superconductors, but the AFM order was not successfully suppressed. Here we report the first observations of the pressure-induced elimination of long-ranged AFM order at ~ 34 GPa and a crossover from an AFM insulating to an AFM metallic state at ~ 20 GPa in LaMnPO single crystals that are iso-structural to the LaFeAsO superconductor by in-situ high pressure resistance and ac susceptibility measurements. These findings are of importance to explore potential superconductivity in Mn-based compounds and to shed new light on the underlying mechanism of high temperature superconductivity.
    Scientific Reports 08/2013; 3:2555. DOI:10.1038/srep02555 · 5.08 Impact Factor
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    ABSTRACT: The Ca10(PtnAs8)(Fe2As2)5 (n=3,4) compounds are a new type of iron pnictide superconductor whose structures consist of stacking Ca-PtnAs8-Ca-Fe2As2 layers in a unit cell. When n=3 (the 10-3-8 phase), the undoped compound is an antiferromagnetic (AFM) semiconductor, while, when n=4 (the 10-4-8 phase), the undoped compound is a superconductor (Tc=26K), a difference that has been attributed to the electronic character of the PtnAs8 intermediary layers. Here we report high-pressure studies on 10-3-8 and 10-4-8, using a combination of in-situ resistance, magnetic susceptibility, Hall coefficient and X-ray diffraction measurements. We find that the AFM order in undoped 10-3-8 is suppressed completely at 3.5 GPa and that superconductivity then appears in the 3.5-7 GPa pressure range with a classic dome-like behavior. In contrast, Tc in the 10-4-8 phase displays a monotonic decrease with increasing pressure. Our results allow for the establishment of a unique correspondence between pressure-induced and doping-induced superconductivity in the high-Tc iron pnictides, and also points the way to an effective strategy for finding new high-Tc superconductors.

Publication Stats

887 Citations
244.57 Total Impact Points

Institutions

  • 1993–2015
    • Chinese Academy of Sciences
      • • Institute of Physics
      • • Laboratory of Theoretical Condensed Matter Physics and Computational Materials Physics
      Peping, Beijing, China
    • Tokyo Metropolitan Institute of Medical Science
      Edo, Tōkyō, Japan
    • Academia Sinica
      • Institute of Physics
      T’ai-pei, Taipei, Taiwan
  • 2014
    • Shanghai Institute of Applied Physics
      Shanghai, Shanghai Shi, China
  • 1988–2014
    • Technical Institute of Physics and Chemistry
      Peping, Beijing, China
  • 1998
    • Institute of physics china
      Peping, Beijing, China
  • 1996
    • Hefei Institute of Physical Sciences, Chinese Academy of Sciences
      Luchow, Anhui Sheng, China
  • 1989
    • Nanjing University
      • Department of Physics
      Nan-ching, Jiangsu Sheng, China