Competing Superconducting Orders in Extended Attractive Hubbard Model

Date

Jul 31, 2017

Time

11:00 AM - 12:00 PM

Speaker

Swagatam Nayak

Affiliation

Indian Institute or Science Education and Research (IISER) Mohali

Language

en

Main Topic

Materialien

Other Topics

Materialien, Physik

Host

Grit Rötzer

Description

Superconductivity is a fascinating example of correlated quantum behavior driven by an effective attractive interaction between electrons. It is now well-known that in conventional BCS superconductors the effective attractive interaction is mediated via phonons, and leads to a spin-singlet pairing with s-wave symmetry [1]. Since the discovery of cuprates, heavy-fermion superconductors and iron-pnictides, it has become clear that phonons are not the only possible mediator for the attractive interaction [2-4]. In fact, the most important question that arises along with the discovery of any new superconducting material is: “what is the pairing glue?”. A first step towards answering this question is to understand the symmetries of the superconducting order parameter. Despite a large body of existing work on superconductors with different order parameters, a systematic exploration of the competition between different order parameter symmetries has been lacking [5-9]. In this work we make an effort to fill this gap by studying the competition between different superconducting order parameter symmetries in an electronic system with attractive interactions. As a generic model system we consider an attractive extended Hubbard Hamiltonian defined on a two-dimensional square lattice. In addition to the chemical potential, the model consists of two parameters: the on-site attraction strength U, and the inter-site attraction strength V. The model is well known to lead to an s-wave superconducting state for V=0 and a d-wave superconducting state for U=0. We employ a mean-field decoupling in the pairing channel, allowing for both singlet and triplet states, to write down the Bogoliubov-de Gennes mean-field Hamiltonian [10]. The model is then investigated for the existence of various possible superconducting order parameters using a combination of restricted (momentum-space)and unrestricted(real-space)self-consistent approaches. The parameter space of U, V-n and μ is explored and the competition between s-wave and d-wave superconducting phases is captured in the form of comprehensive U-V-n phase diagrams. Our main results include the possibility of coexistence of s-wave and d-wave superconducting orders in the intermediate density regime. Evolution of quasiparticle dispersion from a swave to d-wave superconducting state is shown below. We uncover an interesting possibility of an s-wave wave order for U=0. The implications for experimentally observable quantities such as the local density of states are discussed. Finally we compare our results with those obtained via the recently proposed static auxiliary-field Monte-Carlo method [11]. The temperature and magnetic field dependence is also discussed.[1] [1] J. Bardeen, L. Cooper, and J. Schrieffer, Phys. Rev, 108, 1175 (1957). [2] J. Bednorz and K. Müller, Zeitschrift für Physik B Condensed Matter, 64, 189 (1986) [3] M. Wu et al.,Phys. Rev. Lett., 58, 908 (1987) [4] Y. Kamihara et al.,J. Am. Chem. Soc., 128, 10012 (2006) [5] A. Ruckenstein, P. Hirschfeld, and J. Appel, Phys. Rev. B, 36, 857 (1987) [6] G. Kotliar, Phys. Rev. B, 37, 3664 (1988) [7] K. Musaelian et al., Phys. Rev. B, 53, 3598 (1996) [8] E. Shapoval, JETP Letters, 64, 625 (1996) [9] D. Scalapino, Physics Reports, 250, 329 (1995) [10] P. G. de Gennes, Superconductivity of Metals and Alloys, Benjamin, New York (1966) [11] A. Erez and Y. Meir, EPL, 91, 47003 (2010)

Links

• Seminars at the IFW

Last modified: Jul 31, 2017, 9:54:52 AM