We used first-principles calculations to conduct a comparative study of the structure and the electronic and magnetic properties of SrTiO3 doped with a transition metal(TM), namely, Cr, Mn, Fe, Co, or Ni. The calcul...We used first-principles calculations to conduct a comparative study of the structure and the electronic and magnetic properties of SrTiO3 doped with a transition metal(TM), namely, Cr, Mn, Fe, Co, or Ni. The calculated formation energies indicate that compared with Sr, Ti can be substituted more easily by the TM ions. The band structures show that SrTi0.875Cr0.125O3 and SrTi0.875Co0.125O3 are half metals, SrTio.sTDFe0.125O3 is a metal, and SrTi0.875Mn0.125O3 is a semiconductor. The 3d TM-doped SrTiO3 exhibits various magnetic properties, ranging from ferromagnetism (Cr-, Fe-, and Co-doped SrTiO3) to antiferromagnetism (Mn-doped SrTiO3) and nonmagnetism (Ni-doped SrTiO3). The total magnetic moments are 4.0#8, 6.23μ8, and 2.0μ8 for SrTi0.75Cr0.25O3, SrTi0.75Fe0.25O3, and SrTi0.75Co0.25O3, respectively. Room-temperature ferromagnetism can be expected in Cr-, Fe-, and Co-doped SrTiO3, which agrees with the experimental observations. The electronic structure calculations show that the spin polarizations of the 3d states of the TM atoms are responsible for the ferromagnetism in these compounds. The magnetism of TM-doped SrTiO3 is explained by the hybridization between the TM-3d states and the O-2p states.展开更多
Optical emission efficiency of two-dimensional layered transition metal dichalcogenides (TMDs) is one of the most important parameters affecting their optoelectronic performance. The optimization of the growth param...Optical emission efficiency of two-dimensional layered transition metal dichalcogenides (TMDs) is one of the most important parameters affecting their optoelectronic performance. The optimization of the growth parameters by chemical vapor deposition (CVD) to achieve optoelectronic-grade quality TMDs is, therefore, highly desirable. Here, we present a systematic photoluminescence (PL) spectroscopic approach to assess the intrinsic optical and crystalline quality of CVD grown MoS2 (CVD MoS2). We propose the use of the intensity ratio between the PL measured in air and vacuum as an effective way to monitor the intrinsic optical quality of CVD MoS2. Low-temperature PL measurements are also used to evaluate the structural defects in MoS2, via defect-associated bound exciton emission, which well correlates with the field-effect carrier mobility of MoS2 grown at different temperatures. This work therefore provides a sensitive, noninvasive method to characterize the optical properties of TMDs, allowing the tuning of the growth parameters for the development of optoelectronic devices.展开更多
The effects of isovalent Sb substitution on the superconducting properties of the Ca0.88La0.12Fe2(As1-ySby)2 system have been studied through electrical resistivity measure- ments. It is seen that the antiferromagne...The effects of isovalent Sb substitution on the superconducting properties of the Ca0.88La0.12Fe2(As1-ySby)2 system have been studied through electrical resistivity measure- ments. It is seen that the antiferromagnetic or structural transition is suppressed with Sb content, and a high-To superconducting phase, accompanied by a low-Tc phase, emerges at 0.02 ≤y ≤ 0.06. In this intermediate-doping regime, normal-state transport shows non-Fermi-liquid-like behaviors with nearly T-linear resistivity above the high-Tc phase. With further Sb doping, this high-Tc phase abruptly vanishes for y 〉 0.06 and the conventional Fermi liquid is restored, while the low-T,, phase remains robust against Sb inlpurities. The coincidence of the high-Tc phase and non-Fermi liquid transport behaviors in the intermediate Sb-doping regime suggests that AFM fluctuations play an important role in the observed non-Fermi liquid behaviors, which may be intimately related to the unusual nonbulk high-Tc phase in this system.展开更多
We investigated the superconducting properties of Fe_(1+y)Te_(0:6)Se_(0:4) single-crystalline microbridges with a width of 4 m and thicknesses ranging from 20.8 to 136.2 nm. The temperature-dependent in-plane resistan...We investigated the superconducting properties of Fe_(1+y)Te_(0:6)Se_(0:4) single-crystalline microbridges with a width of 4 m and thicknesses ranging from 20.8 to 136.2 nm. The temperature-dependent in-plane resistance of the bridges exhibited a type of metalinsulator transition in the normal state. The critical current density(J_c) of the microbridge with a thickness of 136.2 nm was82.3 kA/cm^2 at 3K and reached 105 kA/cm^2 after extrapolation to T = 0 K. The current versus voltage characteristics of the microbridges showed a Josephson-like behavior with an obvious hysteresis. These results demonstrate the potential application of ultra-thin Fe-based microbridges in superconducting electronic devices such as bolometric detectors.展开更多
Graphene has attracted much attention for the realization of high-speed photodetection for silicon photonics over a wide wavelength range.However,the reported fast graphene photodetectors mainly operate in the 1.55μm...Graphene has attracted much attention for the realization of high-speed photodetection for silicon photonics over a wide wavelength range.However,the reported fast graphene photodetectors mainly operate in the 1.55μm wavelength band.In this work,we propose and realize high-performance waveguide photodetectors based on bolometric/photoconductive effects by introducing an ultrathin wide silicon−graphene hybrid plasmonic waveguide,which enables efficient light absorption in graphene at 1.55μm and beyond.When operating at 2μm,the present photodetector has a responsivity of ~70 mA/W and a setup-limited 3 dB bandwidth of >20 GHz.When operating at 1.55μm,the present photodetector also works very well with a broad 3 dB bandwidth of >40 GHz(setup-limited)and a high responsivity of ~0.4 A/W even with a low bias voltage of−0.3 V.This work paves the way for achieving highresponsivity and high-speed silicon-graphene waveguide photodetection in the near/mid-infrared ranges,which has applications in optical communications,nonlinear photonics,and on-chip sensing.展开更多
基金This work was supported by the National Natural Science Foundation of China (Grant No. 11747124).
文摘We used first-principles calculations to conduct a comparative study of the structure and the electronic and magnetic properties of SrTiO3 doped with a transition metal(TM), namely, Cr, Mn, Fe, Co, or Ni. The calculated formation energies indicate that compared with Sr, Ti can be substituted more easily by the TM ions. The band structures show that SrTi0.875Cr0.125O3 and SrTi0.875Co0.125O3 are half metals, SrTio.sTDFe0.125O3 is a metal, and SrTi0.875Mn0.125O3 is a semiconductor. The 3d TM-doped SrTiO3 exhibits various magnetic properties, ranging from ferromagnetism (Cr-, Fe-, and Co-doped SrTiO3) to antiferromagnetism (Mn-doped SrTiO3) and nonmagnetism (Ni-doped SrTiO3). The total magnetic moments are 4.0#8, 6.23μ8, and 2.0μ8 for SrTi0.75Cr0.25O3, SrTi0.75Fe0.25O3, and SrTi0.75Co0.25O3, respectively. Room-temperature ferromagnetism can be expected in Cr-, Fe-, and Co-doped SrTiO3, which agrees with the experimental observations. The electronic structure calculations show that the spin polarizations of the 3d states of the TM atoms are responsible for the ferromagnetism in these compounds. The magnetism of TM-doped SrTiO3 is explained by the hybridization between the TM-3d states and the O-2p states.
文摘Optical emission efficiency of two-dimensional layered transition metal dichalcogenides (TMDs) is one of the most important parameters affecting their optoelectronic performance. The optimization of the growth parameters by chemical vapor deposition (CVD) to achieve optoelectronic-grade quality TMDs is, therefore, highly desirable. Here, we present a systematic photoluminescence (PL) spectroscopic approach to assess the intrinsic optical and crystalline quality of CVD grown MoS2 (CVD MoS2). We propose the use of the intensity ratio between the PL measured in air and vacuum as an effective way to monitor the intrinsic optical quality of CVD MoS2. Low-temperature PL measurements are also used to evaluate the structural defects in MoS2, via defect-associated bound exciton emission, which well correlates with the field-effect carrier mobility of MoS2 grown at different temperatures. This work therefore provides a sensitive, noninvasive method to characterize the optical properties of TMDs, allowing the tuning of the growth parameters for the development of optoelectronic devices.
基金This work was supported by tile National Natural Science Foundation of China (Grant Nos. U1432135, 11674054, 11474080, and 11611140101) and the Scientific Research Foundation of Graduate School of Southeast University (Grant No. YBJJ1621). X. Xu would also like to acknowledge the National Key Basic Research Program of China (Grant No. 2014CB648400) and the support from the Distinguished Young Scientist Funds of Zhejiang Province (No. LR14A040001).
文摘The effects of isovalent Sb substitution on the superconducting properties of the Ca0.88La0.12Fe2(As1-ySby)2 system have been studied through electrical resistivity measure- ments. It is seen that the antiferromagnetic or structural transition is suppressed with Sb content, and a high-To superconducting phase, accompanied by a low-Tc phase, emerges at 0.02 ≤y ≤ 0.06. In this intermediate-doping regime, normal-state transport shows non-Fermi-liquid-like behaviors with nearly T-linear resistivity above the high-Tc phase. With further Sb doping, this high-Tc phase abruptly vanishes for y 〉 0.06 and the conventional Fermi liquid is restored, while the low-T,, phase remains robust against Sb inlpurities. The coincidence of the high-Tc phase and non-Fermi liquid transport behaviors in the intermediate Sb-doping regime suggests that AFM fluctuations play an important role in the observed non-Fermi liquid behaviors, which may be intimately related to the unusual nonbulk high-Tc phase in this system.
基金supported by the National Natural Science Foundation of China(Grant Nos.11234006,61501220,U1432135,11674054,and 11611140101)Jiangsu Provincial Natural Science Fund(Grant No.SBK2015040804)Opening Project of Wuhan National High Magnetic Field Center(Grant No.2015KF19)
文摘We investigated the superconducting properties of Fe_(1+y)Te_(0:6)Se_(0:4) single-crystalline microbridges with a width of 4 m and thicknesses ranging from 20.8 to 136.2 nm. The temperature-dependent in-plane resistance of the bridges exhibited a type of metalinsulator transition in the normal state. The critical current density(J_c) of the microbridge with a thickness of 136.2 nm was82.3 kA/cm^2 at 3K and reached 105 kA/cm^2 after extrapolation to T = 0 K. The current versus voltage characteristics of the microbridges showed a Josephson-like behavior with an obvious hysteresis. These results demonstrate the potential application of ultra-thin Fe-based microbridges in superconducting electronic devices such as bolometric detectors.
基金supported by the National Major Research and Development Program(No.2018YFB2200200)National Science Fund for Distinguished Young Scholars(61725503)+2 种基金National Natural Science Foundation of China(NSFC)(61905210 and 91950205)China Postdoctoral Science Foundation(2019M662041)Zhejiang Provincial Natural Science Foundation(LZ18F050001 and LD19F050001).
文摘Graphene has attracted much attention for the realization of high-speed photodetection for silicon photonics over a wide wavelength range.However,the reported fast graphene photodetectors mainly operate in the 1.55μm wavelength band.In this work,we propose and realize high-performance waveguide photodetectors based on bolometric/photoconductive effects by introducing an ultrathin wide silicon−graphene hybrid plasmonic waveguide,which enables efficient light absorption in graphene at 1.55μm and beyond.When operating at 2μm,the present photodetector has a responsivity of ~70 mA/W and a setup-limited 3 dB bandwidth of >20 GHz.When operating at 1.55μm,the present photodetector also works very well with a broad 3 dB bandwidth of >40 GHz(setup-limited)and a high responsivity of ~0.4 A/W even with a low bias voltage of−0.3 V.This work paves the way for achieving highresponsivity and high-speed silicon-graphene waveguide photodetection in the near/mid-infrared ranges,which has applications in optical communications,nonlinear photonics,and on-chip sensing.