What is special about strongly correlated superconductivity
What is special about strongly correlated superconductivity
A.-M.S. TREMBLAY1,2, Giovanni. SORDI3, Patrick SÉMON1, Kristjan HAULE4, David SÉNÉCHAL1, Alexandre DAY1, Vincent BOULIANE1
1Département de physique and Regroupement québécois sur les
matériaux de pointe, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1
2Canadian Institute for Advanced Research, Toronto, Ontario, Canada, M5G 1Z8
3SEPnet and Hubbard Theory Consortium, Department of Physics,
Royal Holloway, University of London, Egham, Surrey, UK, TW20 0EX
4Department of Physics, & Astronomy, Rutgers University, Piscataway, New Jersey 08854-8019, USA
When repulsive interactions are strong enough to lead to a Mott insulator at half-filling, the superconducting phase that appears at low temperature upon doping is in some ways quite different from what one expects in theories based on exchange of spin waves, even though superexchange J controls the magnitude of the order parameter.
First, using Cellular Dynamical Mean-Field theory with an exact diagonalization solver for the extended Hubbard model,[1] we show that for large U, pairing is resilient to near-neighbor repulsion V even when V>>J, as long as V<U/2. While at weak coupling V always reduces the spin fluctuations and hence d-wave pairing, at strong coupling, in the underdoped regime, the increase of J caused by V (J=4t2/(U-V)) increases binding at low frequency while the pair-breaking effect of V is pushed to high frequency. These two effects compensate in the underdoped regime, in the presence of a pseudogap. Clearly, retardation is important here. The resilience to V cannot be accounted for by simple mean-field theories. While the pseudogap competes with superconductivity, retardation effects and the proximity to the Mott transition that leads to the pseudogap protect d-wave superconductivity from V.
Second, using a continuous-time quantum Monte Carlo solver this time, we obtain the whole phase diagram as a function of temperature, doping and interaction strength U. We find that, contrary to the weak-coupling case, a correlation driven pseudogap appears along the Widom line of a first-order transition without the need for competing order.[2] The dynamical mean-field superconducting transition temperature Tcd crosses the pseudogap temperature where Tcd is maximal.[3-5] When the pseudogap appears, it seems to stop Tcd from increasing towards half-filling, suggesting that pseudogap and superconductivity are different phenomena and that they compete. In addition, Tcd does not scale with the superconducting order parameter when there is a normal-state pseudogap. Tcd corresponds to the local pair formation temperature observed in tunneling experiments.
[1] D. Sénéchal, A. Day, V. Bouliane, and A.-M. S. Tremblay, Phys. Rev. B, 87, 075123 (2013).
[2] G. Sordi, P. Sémon, K. Haule, and A.-M. S. TREMBLAY Scientific Reports, 2, 547 (2012).
[3] G. Sordi, P. Sémon, K. Haule, and A.-M. S. TREMBLAY, Phys. Rev. B 87, 041101(R) (2013).
[4] G. Sordi, P. Sémon, K. Haule, and A.-M. S. TREMBLAY, Phys. Rev. Lett. 108, 216401 (2012).
[5] P. Sémon, G. Sordi, and A.-M. S. TREMBLAY, arXiv Feb. 2014.
E-mail for corresponding author: tremblay@physique.usherbrooke.ca