The structures and stabilization of three crystal surfaces of TCNQ-based charge transfer complexes（CTCs） including PrQ（TCNQ） 2,MPM（TCNQ） 2,and MEM（TCNQ） 2,have been investigated by scanning tunneling microscop...The structures and stabilization of three crystal surfaces of TCNQ-based charge transfer complexes（CTCs） including PrQ（TCNQ） 2,MPM（TCNQ） 2,and MEM（TCNQ） 2,have been investigated by scanning tunneling microscopy（STM）.The three bulk-truncated surfaces are all ac-surface,which are terminated with TCNQ molecular arrays.On the ac-surface of PrQ（TCNQ） 2,the TCNQ molecules form a tetramer structure with a wavelike row behavior and a 纬 angle of about 18掳 between adjacent molecules.Moreover,the dimer structures are resolved on both ac-surfaces of MPM（TCNQ） 2 and MEM（TCNQ） 2.In addition,the tetramer structure is the most stable structure,while the dimer structures are unstable and easily subject to the STM tip disturbance,which results in changeable unit cells.The main reasons for the surface stabilization variation among the three ac-surfaces are provided by using the ＇蟺-atom model＇.展开更多
High mobility quasi two-dimensional electron gas(2DEG)found at the CaZrO_(3)/SrTiO_(3) nonpolar heterointerface is attractive and provides a platform for the development of functional devices and nanoelectronics.Here ...High mobility quasi two-dimensional electron gas(2DEG)found at the CaZrO_(3)/SrTiO_(3) nonpolar heterointerface is attractive and provides a platform for the development of functional devices and nanoelectronics.Here we report that the carrier density and mobility at low temperature can be tuned by gate voltage at the CaZrO_(3)/SrTiO_(3) interface.Furthermore,the magnitude of Rashba spin-orbit interaction can be modulated and increases with the gate voltage.Remarkably,the diffusion constant and the spin-orbit relaxation time can be strongly tuned by gate voltage.The diffusion constant increases by a factor of~19.98 and the relaxation time is reduced by a factor of over three orders of magnitude while the gate voltage is swept from-50 V to 100 V.These findings not only lay a foundation for further understanding the underlying mechanism of Rashba spin-orbit coupling,but also have great significance in developing various oxide functional devices.展开更多
We study systematically the negative magnetoresistance(MR)effect in WTe_(2±α)flakes with different thicknesses and doping concentrations.The negative MR is sensitive to the relative orientation between electrica...We study systematically the negative magnetoresistance(MR)effect in WTe_(2±α)flakes with different thicknesses and doping concentrations.The negative MR is sensitive to the relative orientation between electrical-/magnetic-field and crystallographic orientation of WTe_(2±α).The analysis proves that the negative MR originates from chiral anomaly and is anisotropic.Maximum entropy mobility spectrum is used to analyze the electron and hole concentrations in the flake samples.It is found that the negative MR observed in WTe_(2±α)flakes with low doping concentration is small,and the high doping concentration is large.The doping-induced disorder obviously inhibits the positive MR,so the negative MR can be more easily observed.In a word,we introduce disorder to suppress positive MR by doping,and successfully obtain the negative MR in WTe_(2±α)flakes with different thicknesses and doping concentrations,which indicates that the chiral anomaly effect in WTe_(2)is robust.展开更多
High-quality Sr_(2)CrWO_(6)(SCWO) films have been grown on SrTiO_(3)(STO) substrate by pulsed laser deposition under low oxygen pressure. With decrease of the film thickness, a drastic conductivity increase is observe...High-quality Sr_(2)CrWO_(6)(SCWO) films have been grown on SrTiO_(3)(STO) substrate by pulsed laser deposition under low oxygen pressure. With decrease of the film thickness, a drastic conductivity increase is observed. The Hall measurements show that the thicker the film, the lower the carrier density. An extrinsic mechanism of charge doping due to the dominance of oxygen vacancies at SCWO/STO interfaces is proposed. The distribution and gradient of carrier concentration in SCWO films are considered to be related to this phenomenon. Resistivity behavior observed in these films is found to follow the variable range hopping model. It is revealed that with increase of the film thickness, the extent of disorder in the lattice increases, which gives a clear evidence of disorder-induced localization charge carriers in these films.Magnetoresistance measurements show that there is a negative magnetoresistance in SCWO films, which is considered to be caused by the magnetic scattering of magnetic elements Cr^(3+) and W^(5+). In addition, a sign reversal of anisotropic magnetoresistance(AMR) in SCWO film is observed for the first time, when the temperature varies across a characteristic value, T_(M). Magnetization-temperature measurements demonstrate that this AMR sign reversal is caused by the direction transition of easy axis of magnetization from the in-plane ferromagnetic order at T > T_(M) to the out-of-plane at T < T_(M).展开更多
In this work,we investigate the electrical transport property and electronic structure of oxide heterostructure LaCrO3/SrTiO3（111）.The interface grown under relatively low oxygen partial pressure is found to be meta...In this work,we investigate the electrical transport property and electronic structure of oxide heterostructure LaCrO3/SrTiO3（111）.The interface grown under relatively low oxygen partial pressure is found to be metallic with a conducting critical thickness of 11 unit cells of LaCrO3.This criticality is also observed by x-ray photoelectron spectroscopy,in which the Ti^3＋ signal intensity at the spectrum edge of the Ti-2p（3/2） core level increases rapidly when the critical thickness is reached.The variations of the valence band offset and full width at half maximum of the core-level spectrum with LaCrO3 thickness suggest that the built-in fields exist both in LaCrO3 and in SrTiO3.Two possible origins are proposed：the charge transfer from LaCrO3 and the formation of a quantum well in SrTiO3.Our results shed light on the understanding of the doping mechanism at the polar/non-polar oxide interface.Moreover,due to the interesting lattice and spin structure of LCO in the（111） direction,our work provides a basis for further exploring the novel topological quantum phenomena in this system.展开更多
The origin of the quantum superconductor to metal transition at zero temperature in two-dimensional superconductors is still an open problem,which has caused intensely discussion.Here,we report the observation of a qu...The origin of the quantum superconductor to metal transition at zero temperature in two-dimensional superconductors is still an open problem,which has caused intensely discussion.Here,we report the observation of a quantum superconductor-to-metal transition in La Al O_(3)/KTa O_(3)(111)interface,driven by magnetic field.When a small magnetic field perpendicular to the film plane is applied,the residual saturated resistance is observed,indicating the emergence of an anomalous metallic state associated with a failed superconductor.The dependence of saturated resistance on magnetic field at low temperature indicates that the observed metal state is a Bose metal state.From our findings,magnetic field regulating La Al O_(3)/KTa O_(3)(111)interface emerges as a platform to scrutinize the details of the anomalous metallic state in a controllable way.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.10804010,50772015,60977015,and 10974019)the National Basic Research Program of China(Grant No.2006CB932301)the Scientific Research Foundation for the Returned Overseas Chinese Scholars of Ministry of Education
文摘The structures and stabilization of three crystal surfaces of TCNQ-based charge transfer complexes（CTCs） including PrQ（TCNQ） 2,MPM（TCNQ） 2,and MEM（TCNQ） 2,have been investigated by scanning tunneling microscopy（STM）.The three bulk-truncated surfaces are all ac-surface,which are terminated with TCNQ molecular arrays.On the ac-surface of PrQ（TCNQ） 2,the TCNQ molecules form a tetramer structure with a wavelike row behavior and a 纬 angle of about 18掳 between adjacent molecules.Moreover,the dimer structures are resolved on both ac-surfaces of MPM（TCNQ） 2 and MEM（TCNQ） 2.In addition,the tetramer structure is the most stable structure,while the dimer structures are unstable and easily subject to the STM tip disturbance,which results in changeable unit cells.The main reasons for the surface stabilization variation among the three ac-surfaces are provided by using the ＇蟺-atom model＇.
基金supported by the National Natural Science Foundation of China(Grants Nos.92065110,11974048,and 12074334)。
文摘High mobility quasi two-dimensional electron gas(2DEG)found at the CaZrO_(3)/SrTiO_(3) nonpolar heterointerface is attractive and provides a platform for the development of functional devices and nanoelectronics.Here we report that the carrier density and mobility at low temperature can be tuned by gate voltage at the CaZrO_(3)/SrTiO_(3) interface.Furthermore,the magnitude of Rashba spin-orbit interaction can be modulated and increases with the gate voltage.Remarkably,the diffusion constant and the spin-orbit relaxation time can be strongly tuned by gate voltage.The diffusion constant increases by a factor of~19.98 and the relaxation time is reduced by a factor of over three orders of magnitude while the gate voltage is swept from-50 V to 100 V.These findings not only lay a foundation for further understanding the underlying mechanism of Rashba spin-orbit coupling,but also have great significance in developing various oxide functional devices.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.92065110,11674031,11974048,12074334)the National Basic Research Program of China(Grant Nos.2014CB920903 and 2013CB921701)。
文摘We study systematically the negative magnetoresistance(MR)effect in WTe_(2±α)flakes with different thicknesses and doping concentrations.The negative MR is sensitive to the relative orientation between electrical-/magnetic-field and crystallographic orientation of WTe_(2±α).The analysis proves that the negative MR originates from chiral anomaly and is anisotropic.Maximum entropy mobility spectrum is used to analyze the electron and hole concentrations in the flake samples.It is found that the negative MR observed in WTe_(2±α)flakes with low doping concentration is small,and the high doping concentration is large.The doping-induced disorder obviously inhibits the positive MR,so the negative MR can be more easily observed.In a word,we introduce disorder to suppress positive MR by doping,and successfully obtain the negative MR in WTe_(2±α)flakes with different thicknesses and doping concentrations,which indicates that the chiral anomaly effect in WTe_(2)is robust.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 92065110, 11974048, and 12074334)。
文摘High-quality Sr_(2)CrWO_(6)(SCWO) films have been grown on SrTiO_(3)(STO) substrate by pulsed laser deposition under low oxygen pressure. With decrease of the film thickness, a drastic conductivity increase is observed. The Hall measurements show that the thicker the film, the lower the carrier density. An extrinsic mechanism of charge doping due to the dominance of oxygen vacancies at SCWO/STO interfaces is proposed. The distribution and gradient of carrier concentration in SCWO films are considered to be related to this phenomenon. Resistivity behavior observed in these films is found to follow the variable range hopping model. It is revealed that with increase of the film thickness, the extent of disorder in the lattice increases, which gives a clear evidence of disorder-induced localization charge carriers in these films.Magnetoresistance measurements show that there is a negative magnetoresistance in SCWO films, which is considered to be caused by the magnetic scattering of magnetic elements Cr^(3+) and W^(5+). In addition, a sign reversal of anisotropic magnetoresistance(AMR) in SCWO film is observed for the first time, when the temperature varies across a characteristic value, T_(M). Magnetization-temperature measurements demonstrate that this AMR sign reversal is caused by the direction transition of easy axis of magnetization from the in-plane ferromagnetic order at T > T_(M) to the out-of-plane at T < T_(M).
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11674031,11474022 11474024,11422430,and 11374035)the National Basic Research Program of China(Grant Nos.2014CB920903,2013CB921701,and 2013CBA01603)
文摘In this work,we investigate the electrical transport property and electronic structure of oxide heterostructure LaCrO3/SrTiO3（111）.The interface grown under relatively low oxygen partial pressure is found to be metallic with a conducting critical thickness of 11 unit cells of LaCrO3.This criticality is also observed by x-ray photoelectron spectroscopy,in which the Ti^3＋ signal intensity at the spectrum edge of the Ti-2p（3/2） core level increases rapidly when the critical thickness is reached.The variations of the valence band offset and full width at half maximum of the core-level spectrum with LaCrO3 thickness suggest that the built-in fields exist both in LaCrO3 and in SrTiO3.Two possible origins are proposed：the charge transfer from LaCrO3 and the formation of a quantum well in SrTiO3.Our results shed light on the understanding of the doping mechanism at the polar/non-polar oxide interface.Moreover,due to the interesting lattice and spin structure of LCO in the（111） direction,our work provides a basis for further exploring the novel topological quantum phenomena in this system.
基金the National Natural Science Foundation of China(Grant Nos.92065110,11974048,and 12074334)the National Basic Research Program of China(Grant Nos.2014CB920903 and 2013CB921701)。
文摘The origin of the quantum superconductor to metal transition at zero temperature in two-dimensional superconductors is still an open problem,which has caused intensely discussion.Here,we report the observation of a quantum superconductor-to-metal transition in La Al O_(3)/KTa O_(3)(111)interface,driven by magnetic field.When a small magnetic field perpendicular to the film plane is applied,the residual saturated resistance is observed,indicating the emergence of an anomalous metallic state associated with a failed superconductor.The dependence of saturated resistance on magnetic field at low temperature indicates that the observed metal state is a Bose metal state.From our findings,magnetic field regulating La Al O_(3)/KTa O_(3)(111)interface emerges as a platform to scrutinize the details of the anomalous metallic state in a controllable way.
