IQIM Postdoctoral and Graduate Student Seminar
Special IQIM seminar
Feng Chen
Title: D-wave and Pair Density Wave Superconductivity in Doped Square-Lattice Mott Insulators
Abstract: Widely regarded as a minimum model for high-temperature superconductivity in cuprates, the t-J model has been intensely studied for over 30 years. Recent advanced numerical simulations have found convincing evidence for a d-wave superconducting ground state in the extended t-J model with a positive next-nearest-neighbor hopping t' corresponding to electron-doped cuprates. I will present our latest density matrix renormalization group calculations on large 8-leg cylinders approximating two-dimensional systems, and demonstrate that the pure t-J model with only nearest-neighbor hopping t and superexchange interaction J, for a wide range of hole doping (δ = 0.1 − 0.2), hosts an exotic SC state where d-wave SC coexists with unidirectional pair density wave. Furthermore, a small t' suppresses the pair density wave, leading to a uniform d-wave SC phase in both electron-doped (t'>0) and hole-doped (t'<0) cuprate model systems.
- X. Lu * , F. Chen * , W. Zhu, D. N. Sheng, S. S. Gong. Phys. Rev. Lett. 132, 066002 (2024)
- F. Chen, F. D. M. Haldane, and D. N. Sheng. arXiv:2311.15092 (2024)
* Equal contribution
Jinwoong Kim
Title: Bismuth antiphase domain wall: A three-dimensional manifestation of the Su-Schrieffer-Heeger model
Abstract: The Su, Schrieffer, and Heeger (SSH) model, describing the soliton excitations in polyacetylene due to the formation of antiphase domain walls (DW) from the alternating bond pattern, has served as a paradigmatic example of one-dimensional (1D) chiral topological insulators. While the SSH model has been realized in photonic and plasmonic systems, there have been limited analogs in three-dimensional (3D) electronic systems, especially regarding the formation of antiphase DWs. Here, we propose[1] that pristine bulk Bi, in which the dimerization of (111) atomic layers renders alternating covalent and van der Waals bonding within and between successive (111) bilayers, respectively, serves as a 3D analog of the SSH model. First, we confirm that the two dimerized Bi structures belong to different Zak phases of 0 and π by considering the parity eigenvalues and Wannier charge centers. Next, we demonstrate the existence of topologically nontrivial (111) DW in which the number of in-gap DW states (ignoring spin) is odd and show how this controls the interlinking of the Zak phases of the two adjacent domains. Finally, we derive general criteria specifying when a DW of arbitrary orientation exhibits a π Zak phase based on the flip of parity eigenvalues.
[1] PRB 107, 045135 (2023)
Lunch will be provided, following the talk, on the lawn north of the Bridge Building.