We have studied the quasiparticle transport in quantum-wire /ferromagnetic-insulator/d wave super- conductor Junction （q/FI/d） in the framework of the Blonder-Tinkham-Klapwijk model. We calculate the tunneling condu...We have studied the quasiparticle transport in quantum-wire /ferromagnetic-insulator/d wave super- conductor Junction （q/FI/d） in the framework of the Blonder-Tinkham-Klapwijk model. We calculate the tunneling conductance in q/FI/d as a function of the bias voltage at zero temperature and finite temperature based on Bogoliubov- de Gennes equations. Different from the case in normal-metal/insulator/d wave superconductor Junctions, the zero-bias conductance peaks vanish for the single-mode case. The tunneling conductance spectra depend on the magnitude of the exchange interaction at the ferromagnetic-insulator.展开更多
The Josephson currents in s-wave superconductor/ferromagnet insulator/p-wave superconductor（s/FI/p） junctions are calculated as a function of temperature and the phase taking into account the roughness scattering ef...The Josephson currents in s-wave superconductor/ferromagnet insulator/p-wave superconductor（s/FI/p） junctions are calculated as a function of temperature and the phase taking into account the roughness scattering effect at interface. The phase dependence of the Josephson current I （φ） between s-wave and px-wave superconductor is predicted to be sin（2φ）. The ferromagnet scattering effect, the barrier strength, and the roughness strength at interface suppress the dc currents in s/FI/p junction.展开更多
Nonequilibrium effect due to the imbalance in the number of the ? and ? spin electrons has been studied for the tunneling currents in the ferromagnet-insulator-superconductor (FIS) tunneling junctions within a phenome...Nonequilibrium effect due to the imbalance in the number of the ? and ? spin electrons has been studied for the tunneling currents in the ferromagnet-insulator-superconductor (FIS) tunneling junctions within a phenomenological manner. It has been stated how the nonequilibrium effect should be observed in the spin-polarized quasiparticle tunneling currents, and pointed out that the detectable nonequilibrium effect could be found in the FIS tunneling junction at 77 K using HgBa2Ca2Cu3O8+? (Hg-1223) high-Tc superconductor rather than Bi2Sr2CaCu2O8+? (Bi-2212) one.展开更多
Superconductivity beyond electron-phonon mechanism is always twisted with magnetism. Based on a new field-effect transistor with solid ion conductor as the gate dielectric(SIC-FET), we successfully achieve an electric...Superconductivity beyond electron-phonon mechanism is always twisted with magnetism. Based on a new field-effect transistor with solid ion conductor as the gate dielectric(SIC-FET), we successfully achieve an electric-field-controlled phase transition between superconductor and ferromagnetic insulator in(Li,Fe)OHFeSe. A dome-shaped superconducting phase with optimal T_c of 43K is continuously tuned into a ferromagnetic insulating phase, which exhibits an electric-field-controlled quantum critical behavior. The origin of the ferromagnetism is ascribed to the order of the interstitial Fe ions expelled from the(Li,Fe)OH layers by gating-controlled Li injection. These surprising findings offer a unique platform to study the relationship between superconductivity and ferromagnetism in Fe-based superconductors. This work also demonstrates the superior performance of the SIC-FET in regulating physical properties of layered unconventional superconductors.展开更多
Superconducting SnTe-type topological crystalline insulators(TCIs)are predicted to host multiple Majorana zero modes(MZMs)which can coexist in a single vortex.Fermi level(FL)close to the Dirac points of topological su...Superconducting SnTe-type topological crystalline insulators(TCIs)are predicted to host multiple Majorana zero modes(MZMs)which can coexist in a single vortex.Fermi level(FL)close to the Dirac points of topological surface states is helpful for detecting MZMs.However,the TCI SnTe is a heavily p-type semiconductor which is very difficult to modify to n-type via doping or alloying.In this work,we fabricate the atomically flat Sn_(1-x)Pb_(x)Te/Pb heterostructure by molecular beam epitaxy,and make the p-type Sn_(1-x)Pb_(x)Te become n-type through changing the interface roughness.Using scanning tunnelling microscope,we find the Dirac points of Sn_(1-x)Pb_(x)Te/Pb heterostructure are always above the FL due to the Fermi level pinning(FLP)induced by topological surface states at atomically flat interface.After increasing the interface roughness,the FLP effect is suppressed and then the Dirac points of p-type Sn_(1-x)Pb_(x)Te can be tuned very close to or even below the FL.Our work provides a new method for tuning the FL of SnTe-type TCI which has potential application in novel topological superconductor device.展开更多
Majorana fermions have been observed in topological insulator/s-wave superconductor heterostructures. To manipulate Majorana fermions, superconducting materials should be deposited on the surfaces of topological insul...Majorana fermions have been observed in topological insulator/s-wave superconductor heterostructures. To manipulate Majorana fermions, superconducting materials should be deposited on the surfaces of topological insulators. In this study, highquality superconducting PdTe_2 films are deposited on the topological insulator Bi_2Te_3 surface using molecular beam epitaxy. The surface topography and electronic properties of PdTe_2/Bi_2Te_3 heterostructures are investigated via in situ scanning tunneling microscopy/spectroscopy. Under Te-rich conditions, the Pd atoms presumably form PdTe_2 film on Bi_2Te_3 surface rather than diffuse into Bi_2Te_3. The superconductivity of the PdTe_2/Bi_2Te_3 heterostructure is detected at a transition temperature of ～1.4 K using the two-coil mutual inductance technique. This study proposes a method for fabricating superconducting materials on topological insulator surfaces at low doping levels, paving ways for designing nanodevices that can manipulate Majorana fermions.展开更多
基金The project supported by the Natural Science Foundation of the Education Committee of Jiangsu Province of China under Grant No.06KJB140009
文摘We have studied the quasiparticle transport in quantum-wire /ferromagnetic-insulator/d wave super- conductor Junction （q/FI/d） in the framework of the Blonder-Tinkham-Klapwijk model. We calculate the tunneling conductance in q/FI/d as a function of the bias voltage at zero temperature and finite temperature based on Bogoliubov- de Gennes equations. Different from the case in normal-metal/insulator/d wave superconductor Junctions, the zero-bias conductance peaks vanish for the single-mode case. The tunneling conductance spectra depend on the magnitude of the exchange interaction at the ferromagnetic-insulator.
基金The project supported by the Natural Science Foundation of the Education Commission 0f Jiangsu Province of China under Grant No. 06KJB140009
文摘The Josephson currents in s-wave superconductor/ferromagnet insulator/p-wave superconductor（s/FI/p） junctions are calculated as a function of temperature and the phase taking into account the roughness scattering effect at interface. The phase dependence of the Josephson current I （φ） between s-wave and px-wave superconductor is predicted to be sin（2φ）. The ferromagnet scattering effect, the barrier strength, and the roughness strength at interface suppress the dc currents in s/FI/p junction.
文摘Nonequilibrium effect due to the imbalance in the number of the ? and ? spin electrons has been studied for the tunneling currents in the ferromagnet-insulator-superconductor (FIS) tunneling junctions within a phenomenological manner. It has been stated how the nonequilibrium effect should be observed in the spin-polarized quasiparticle tunneling currents, and pointed out that the detectable nonequilibrium effect could be found in the FIS tunneling junction at 77 K using HgBa2Ca2Cu3O8+? (Hg-1223) high-Tc superconductor rather than Bi2Sr2CaCu2O8+? (Bi-2212) one.
基金supported by the National Key R&D Program of China(2017YFA0303001 and 2016YFA0300201)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(XDB25010100)+2 种基金the National Natural Science Foundation of China(11888101 and 11534010)Science Challenge Project(TZ2016004)Hefei Science Center CAS(2016HSC-IU001)
文摘Superconductivity beyond electron-phonon mechanism is always twisted with magnetism. Based on a new field-effect transistor with solid ion conductor as the gate dielectric(SIC-FET), we successfully achieve an electric-field-controlled phase transition between superconductor and ferromagnetic insulator in(Li,Fe)OHFeSe. A dome-shaped superconducting phase with optimal T_c of 43K is continuously tuned into a ferromagnetic insulating phase, which exhibits an electric-field-controlled quantum critical behavior. The origin of the ferromagnetism is ascribed to the order of the interstitial Fe ions expelled from the(Li,Fe)OH layers by gating-controlled Li injection. These surprising findings offer a unique platform to study the relationship between superconductivity and ferromagnetism in Fe-based superconductors. This work also demonstrates the superior performance of the SIC-FET in regulating physical properties of layered unconventional superconductors.
基金the Ministry of Science and Technology of China(Grant Nos.2019YFA0308600,and 2020YFA0309000)the National Natural Science Foundation of China(Grant Nos.11861161003,12104293,92365302,22325203,92265105,92065201,12074247,and 12174252)+3 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000)the Science and Technology Commission of Shanghai Municipality(Grant Nos.2019SHZDZX01,19JC1412701,and 20QA1405100)the Innovation program for Quantum Science and Technology(Grant No.2021ZD0302500)the China National Postdoctoral Program for Innovative Talents(Grant No.BX2021185)。
文摘Superconducting SnTe-type topological crystalline insulators(TCIs)are predicted to host multiple Majorana zero modes(MZMs)which can coexist in a single vortex.Fermi level(FL)close to the Dirac points of topological surface states is helpful for detecting MZMs.However,the TCI SnTe is a heavily p-type semiconductor which is very difficult to modify to n-type via doping or alloying.In this work,we fabricate the atomically flat Sn_(1-x)Pb_(x)Te/Pb heterostructure by molecular beam epitaxy,and make the p-type Sn_(1-x)Pb_(x)Te become n-type through changing the interface roughness.Using scanning tunnelling microscope,we find the Dirac points of Sn_(1-x)Pb_(x)Te/Pb heterostructure are always above the FL due to the Fermi level pinning(FLP)induced by topological surface states at atomically flat interface.After increasing the interface roughness,the FLP effect is suppressed and then the Dirac points of p-type Sn_(1-x)Pb_(x)Te can be tuned very close to or even below the FL.Our work provides a new method for tuning the FL of SnTe-type TCI which has potential application in novel topological superconductor device.
基金supported by the Ministry of Science and Technology of China(Grant Nos.2016YFA0301003,and 2016YFA0300403)the National Natural Science Foundation of China(Grant Nos.11521404,11634009,U1632102,11504230,11674222,11790313,11574202,11674226,11574201,11655002,and U1632272)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000)support from the National Thousand Young Talents Program
文摘Majorana fermions have been observed in topological insulator/s-wave superconductor heterostructures. To manipulate Majorana fermions, superconducting materials should be deposited on the surfaces of topological insulators. In this study, highquality superconducting PdTe_2 films are deposited on the topological insulator Bi_2Te_3 surface using molecular beam epitaxy. The surface topography and electronic properties of PdTe_2/Bi_2Te_3 heterostructures are investigated via in situ scanning tunneling microscopy/spectroscopy. Under Te-rich conditions, the Pd atoms presumably form PdTe_2 film on Bi_2Te_3 surface rather than diffuse into Bi_2Te_3. The superconductivity of the PdTe_2/Bi_2Te_3 heterostructure is detected at a transition temperature of ～1.4 K using the two-coil mutual inductance technique. This study proposes a method for fabricating superconducting materials on topological insulator surfaces at low doping levels, paving ways for designing nanodevices that can manipulate Majorana fermions.
