TR2017-007

The role of local repulsion in superconductivity in the Hubbard-Holstein model


    •  Lin, C., Wang, B., Teo, K.H., "The role of local repulsion in superconductivity in the Hubbard-Holstein model", Physica C, DOI: 10.1016/j.physc.2016.11.011, Vol. 532, pp. 27–32, January 2017.
      BibTeX TR2017-007 PDF
      • @article{Lin2017jan,
      • author = {Lin, Chungwei and Wang, Bingnan and Teo, Koon Hoo},
      • title = {The role of local repulsion in superconductivity in the Hubbard-Holstein model},
      • journal = {Physica C},
      • year = 2017,
      • volume = 532,
      • pages = {27–32},
      • month = jan,
      • doi = {10.1016/j.physc.2016.11.011},
      • url = {https://www.merl.com/publications/TR2017-007}
      • }
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  • Research Area:

    Applied Physics

We examine the superconducting solution in the Hubbard-Holstein model using Dynamical Mean Field Theory. The Holstein term introduces the site-independent Boson fields coupling to local electron density, and has two competing influences on superconductivity: The Boson field mediates the effective electron-electron attraction, which is essential for the S-wave electron pairing; the same coupling to the Boson fields also induces the polaron effect, which makes the system less metallic and thus suppresses superconductivity. The Hubbard term introduces an energy penalty U when two electrons occupy the same site, which is expected to suppress superconductivity. By solving the Hubbard-Holstein model using Dynamical Mean Field theory, we find that the Hubbard U can be beneficial to superconductivity under some circumstances. In particular, we demonstrate that when the Boson energy omega is small, a weak local repulsion actually stabilizes the S-wave superconducting state. This behavior can be understood as an interplay between superconductivity, the polaron effect, and the on-site repulsion: As the polaron effect is strong and suppresses superconductivity in the small omega regime, the weak on-site repulsion reduces the polaron effect and effectively enhances superconductivity. Our calculation elucidates the role of local repulsion in the conventional S-wave superconductors.