Seminário de Matéria Condensada - 17/05/2018, 11:00, Sala 426 (Torre Nova)

The effects of phonon dispersion on pairing and charge ordering

Natanael Costa (UFRJ)

The Holstein Model (HLM) describes the interaction between fermions and a collection of local (dispersionless) phonon modes. In the dilute limit, the phonon degrees of freedom dress the fermions, giving rise to polaron and bipolaron formation. At higher densities, the phonons mediate collective superconducting (SC) and charge-density wave (CDW) phases. Quantum Monte Carlo (QMC) simulations have considered both these limits, but have not yet focused on the physics of more general phonon spectra. Here we present QMC studies of the role of phonon dispersion on SC and CDW order in an extended HLM. We quantify the effect of finite phonon bandwidth and its shape on the critical temperature TCDW for CDW order, and also uncover several novel features of diagonal long-range order, including a competition between a staggered and a striped CDW, breaking down the standard scenario of Peierls instability of the relationship between Fermi Surface Nesting and CDW formation. We also provide evidence of SC order at half-filling in situations where nonzero bandwidth sufficiently suppresses TCDW. These results provide further insight into the (complex) nature of CDW formation in quasi-2D materials, such as NbSe2, exhibiting a new avenue to understand and, ultimately, to control it.

natanael-costa2018.txt · Last modified: 2018/05/11 14:37 by caio
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