-
Revealing the Microscopic Mechanism of Elementary Vortex Pinning in Superconductors
Authors:
C. Chen,
Y. Liu,
Y. Chen,
Y. N. Hu,
T. Z. Zhang,
D. Li,
X. Wang,
C. X. Wang,
Z. Y. W. Lu,
Y. H. Zhang,
Q. L. Zhang,
X. L. Dong,
R. Wang,
D. L. Feng,
T. Zhang
Abstract:
Vortex pinning is a crucial factor that determines the critical current of practical superconductors and enables their diverse applications. However, the underlying mechanism of vortex pinning has long been elusive, lacking a clear microscopic explanation. Here using high-resolution scanning tunneling microscopy, we studied single vortex pinning induced by point defect in layered FeSe-based superc…
▽ More
Vortex pinning is a crucial factor that determines the critical current of practical superconductors and enables their diverse applications. However, the underlying mechanism of vortex pinning has long been elusive, lacking a clear microscopic explanation. Here using high-resolution scanning tunneling microscopy, we studied single vortex pinning induced by point defect in layered FeSe-based superconductors. We found the defect-vortex interaction drives low-energy vortex bound states away from EF, creating a "mini" gap that effectively lowers the system energy and enhances pinning. By measuring the local density-of-states, we directly obtained the elementary pinning energy and estimated the pinning force via the spatial gradient of pinning energy. The results are consistent with bulk critical current measurement. Furthermore, we show that a general microscopic quantum model incorporating defect-vortex interaction can naturally capture our observation. It suggests that the local pairing near pinned vortex core is actually enhanced compared to unpinned vortex, which is beyond the traditional understanding that non-superconducting regions pin vortices. Our study thus unveils a general microscopic mechanism of vortex pinning in superconductors, and provides insights for enhancing the critical current of practical superconductors.
△ Less
Submitted 27 September, 2024; v1 submitted 26 March, 2024;
originally announced March 2024.
-
Superconductivity mediated by the antiferromagnetic spin-wave in chalcogenide iron-base superconductors
Authors:
G. M. Zhang,
Z. Y. Lu,
T. Xiang
Abstract:
The ground state of K$_{0.8+x}$Fe$_{1.6+y}$Se$_2$ and other iron-based selenide superconductors are doped antiferromagnetic semiconductors. There are well defined iron local moments whose energies are separated from those of conduction electrons by a large band gap in these materials. We propose that the low energy physics of this system is governed by a model Hamiltonian of interacting electrons…
▽ More
The ground state of K$_{0.8+x}$Fe$_{1.6+y}$Se$_2$ and other iron-based selenide superconductors are doped antiferromagnetic semiconductors. There are well defined iron local moments whose energies are separated from those of conduction electrons by a large band gap in these materials. We propose that the low energy physics of this system is governed by a model Hamiltonian of interacting electrons with on-site ferromagnetic exchange interactions and inter-site superexchange interactions. We have derived the effective pairing potential of electrons under the linear spin-wave approximation and shown that the superconductivity can be driven by mediating coherent spin wave excitations in these materials. Our work provides a natural account for the coexistence of superconducting and antiferromagnetic long range orders observed by neutron scattering and other experiments.
△ Less
Submitted 22 February, 2011;
originally announced February 2011.
-
Surface and bulk electronic structures of LaOFeAs studied by angle resolved photoemission spectroscopy
Authors:
L. X. Yang,
B. P. Xie,
Y. Zhang,
C. He,
Q. Q. Ge,
X. F. Wang,
X. H. Chen,
M. Arita,
J. Jiang,
K. Shimada,
M. Taniguchi,
I. Vobornik,
G. Rossi,
J. P. Hu,
D. H. Lu,
Z. X. Shen,
Z. Y. Lu,
D. L. Feng
Abstract:
The electronic structure of LaOFeAs, a parent compound of iron-arsenic superconductors, is studied by angleresolved photoemission spectroscopy. By examining its dependence on photon energy, polarization, sodium dosing and the counting of Fermi surface volume, both the bulk and the surface contributions are identified. We find that a bulk band moves toward high binding energies below structural tra…
▽ More
The electronic structure of LaOFeAs, a parent compound of iron-arsenic superconductors, is studied by angleresolved photoemission spectroscopy. By examining its dependence on photon energy, polarization, sodium dosing and the counting of Fermi surface volume, both the bulk and the surface contributions are identified. We find that a bulk band moves toward high binding energies below structural transition, and shifts smoothly across the spin density wave transition by about 25 meV. Our data suggest the band reconstruction may play a crucial role in the spin density wave transition, and the structural transition is driven by the short range magnetic order. For the surface states, both the LaO-terminated and FeAs-terminated components are revealed. Certain small band shifts are verified for the FeAs-terminated surface states in the spin density wave state, which is a reflection of the bulk electronic structure reconstruction. Moreover, sharp quasiparticle peaks quickly rise at low temperatures, indicating of drastic reduction of the scattering rate. A kink structure in one of the surface band is shown to be possibly related to the electron-phonon interactions.
△ Less
Submitted 6 June, 2010;
originally announced June 2010.
-
Spin-Peierls-like transition in AFe$_2$As$_2$(A=Ba, Sr)
Authors:
D. Hou,
Q. M. Zhang,
Z. Y. Lu,
J. H. Wei
Abstract:
From first-principles density functional theory calculations combined with varying temperature Raman experiments, we show that AFe$_2$As$_2$ (A=Ba, Sr), the parent compound of the FeAs based superconductors of the new structural family, undergoes a spin-Peierls-like phase transition at low temperature. The coupling between the phonons and frustrated spins is proved to be the main cause of the st…
▽ More
From first-principles density functional theory calculations combined with varying temperature Raman experiments, we show that AFe$_2$As$_2$ (A=Ba, Sr), the parent compound of the FeAs based superconductors of the new structural family, undergoes a spin-Peierls-like phase transition at low temperature. The coupling between the phonons and frustrated spins is proved to be the main cause of the structural transition from the tetragonal to orthorhombic phase. These results well explain the magnetic and structural phase transitions in AFe$_2$As$_2$(A=Ba, Sr) recently observed by neutron scattering.
△ Less
Submitted 12 January, 2009;
originally announced January 2009.
-
Electronic structure and exotic exchange splitting in spin-density-wave states of BaFe$_2$As$_2$
Authors:
L. X. Yang,
Y. Zhang,
H. W. Ou,
J. F. Zhao,
D. W. Shen,
B. Zhou,
J. Wei,
F. Chen,
M. Xu,
C. He,
Y. Chen,
Z. D. Wang,
X. F. Wang,
T. Wu,
G. Wu,
X. H. Chen,
M. Arita,
K. Shimada,
M. Taniguchi,
Z. Y. Lu,
T. Xiang,
D. L. Feng
Abstract:
The magnetic properties in the parent compounds are often intimately related to the microscopic mechanism of superconductivity. Here we report the first direct measurements on the electronic structure of a parent compound of the newly discovered iron-based superconductor, BaFe$_2$As$_2$, which provides a foundation for further studies. We show that the energy of the spin density wave (SDW) in Ba…
▽ More
The magnetic properties in the parent compounds are often intimately related to the microscopic mechanism of superconductivity. Here we report the first direct measurements on the electronic structure of a parent compound of the newly discovered iron-based superconductor, BaFe$_2$As$_2$, which provides a foundation for further studies. We show that the energy of the spin density wave (SDW) in BaFe$_2$As$_2$ is lowered through exotic exchange splitting of the band structure, rather than Fermi surface nesting of itinerant electrons. This clearly demonstrates that a metallic SDW state could be solely induced by interactions of local magnetic moments, resembling the nature of antiferromagnetic order in cuprate parent compounds.
△ Less
Submitted 6 July, 2008; v1 submitted 16 June, 2008;
originally announced June 2008.
-
Raman spectra in iron-based quaternary CeO$_{1-x}$F$_x$FeAs and LaO$_{1-x}$F$_x$FeAs
Authors:
S. C. Zhao,
D. Hou,
Y. Wu,
T. L. Xia,
A. M. Zhang,
G. F. Chen,
J. L. Luo,
N. L. Wang,
J. H. Wei,
Z. Y. Lu,
Q. M. Zhang
Abstract:
Raman spectra have been measured on iron-based quaternary CeO$_{1-x}$F$_x$FeAs and LaO$_{1-x}$F$_x$FeAs with varying fluorine doping at room temperatures. A group analysis has been made to clarify the optical modes. Based on the first principle calculations, the observed phonon modes can be assigned accordingly. In LaO$_{1-x}$F$_x$FeAs, the E$_g$ and A$_{1g}$ modes related to the vibrations of L…
▽ More
Raman spectra have been measured on iron-based quaternary CeO$_{1-x}$F$_x$FeAs and LaO$_{1-x}$F$_x$FeAs with varying fluorine doping at room temperatures. A group analysis has been made to clarify the optical modes. Based on the first principle calculations, the observed phonon modes can be assigned accordingly. In LaO$_{1-x}$F$_x$FeAs, the E$_g$ and A$_{1g}$ modes related to the vibrations of La, are suppressed with increasing F doping. However F doping only has a small effect on the E$_g$ and A$_{1g}$ modes of Fe and As. The Raman modes of La and As are absent in rare-earth substituted CeO$_{1-x}$F$_x$FeAs, and the E$_g$ mode of oxygen, corresponding to the in-plane vibration of oxygen, moves to around 450 cm$^{-1}$ and shows a very sharp peak. Electronic scattering background is low and electron-phonon coupling is not evident for the observed phonon modes. Three features are found above 500 cm$^{-1}$, which may be associated with multi-phonon process. Nevertheless it is also possible that they are related to magnetic fluctuations or interband transitions of d orbitals considering their energies.
△ Less
Submitted 4 June, 2008;
originally announced June 2008.