Previously, the Jian Wang group and collaborators discovered zero-energy excitations at both ends of 1D atomic line defects in 1-UC Fe(Te,Se)/STO, which are found to be consistent with the Majorana zero modes interpretation (Nat. Their paper is published in the journal Nature.īy using molecular beam epitaxy (MBE) technique, Jian Wang's group successfully grew large-area and high-quality one-unit-cell-thick Fe(Te,Se) films on SrTiO 3(001) substrates (1-UC Fe(Te,Se)/STO), which show superconducting gap as large as 18 meV, much higher than that (~1.8 meV) in bulk Fe(Te,Se), a promising topological superconductor candidate. Yi Zhang at Shanghai University, discovered the primary pair density wave state in a 2D iron-based high-Tc superconductor, which provides a new 2D high-Tc platform to investigate the PDW in unconventional superconductors. Jian Wang's group at Peking University, in collaboration with Prof. Furthermore, early theoretical studies of cuprates proposed the PDW is a low-dimensional stripe order in 2D systems, but no compelling experimental evidences of the PDW in 2D systems have been reported so far.
The existence of PDW state in iron-based superconductors, another high-Tc superconductor family, has never been experimentally detected. However, experimental evidences of the PDW state in high-temperature (high-Tc) superconductors have only been observed in some cuprates. Moreover, according to some theoretical proposals, the enigmatic pseudogap phase of cuprates can be attributed to the PDW state, further indicating the potential importance of PDW.
This extraordinary superconducting state, referred to as the pair density wave (PDW), has sparked numerous theoretical investigations due to the potential connection between the PDW and unconventional superconductivity.Īmong various theoretical hypotheses, the most intriguing one is that the PDW is another principal state along with d-wave superconductivity in the phase diagram of cuprates, which provides new insights into the complex intertwined orders of the cuprates showing high-temperature superconductivity. To understand the observed two-dimensional (2D) superconducting properties in cuprates, some theoretical works predicted that the finite-momentum Cooper pairs can exist in strong-coupling systems without breaking time-reversal symmetry and show the spatial modulation of Cooper-pair density. To date, direct evidences of the FFLO state, such as the modulation of the superconducting order parameter in real space, have not been detected experimentally. Although the FFLO state was theoretically proposed in 1964, it has proven challenging to observe the FFLO state due to the stringent requirement for materials.
Theoretically, when time-reversal symmetry is broken, Cooper pairs may acquire a finite momentum and exhibit a spatially modulated superconducting order parameter, which is known as the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. According to the BCS (Bardeen-Cooper-Schrieffer) microscopic theory, superconductivity arises from the condensation of coherent Cooper pairs, and each Cooper pair is formed by two electrons with opposite spins and momenta. Credit: Peking UniversityĪs a macroscopic quantum state of matter, superconductivity has attracted tremendous attention in the field of scientific research and industry over the past century. (h) Spatial distribution of the LDOS modulation phase, showing uniform phases within the domain wall area. (g) Spatial distribution of the LDOS modulation amplitude calculated by the 2D lock-in method, showing the LDOS modulations at Q characterized by higher amplitude (red region) mainly exist within the domain wall region. The modulation wavevector Q circled in blue reveals a spatial modulation of LDOS along the direction of the domain wall. (f) The magnitude of the Fourier transform of e. (e) Zero-bias conductance (ZBC) map g(r, V = 0 mV) taken at the same area in c at 4.3 K, which shows an emergent electronic modulation along the domain wall. Bragg peaks of the Te/Se lattice are circled in red. (d) The magnitude of the Fourier transform of c. (c) Zoom-in image of a, clearly showing the topography of the domain wall D1. (b) The schematic of the domain wall in 1-UC Fe(Te,Se)/STO, illustrating the compression across the domain wall. Figure 1 (a) An STM topographic image of the domain wall structure (bright line) in 1-UC Fe(Te,Se)/STO.
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