Marcin Mierzejewski

Snapshots of the retarded interaction of charge carriers with ultrafast fluctuations in cuprates

By pushing both time and frequency resolution in optical spectroscopy it is now possible to resolve antiferromagnetic fluctuations in a copper oxide superconductor, which are believed to mediate the pairing of charge carriers.

The Fulde-Ferrell-Larkin-Ovchinnikov phase in the presence of pair hopping interaction

The recent experimental support for the presence of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase in CeCoIn(5) directed attention towards the mechanisms responsible for this type of superconductivity. We investigate the FFLO state in a model where on-site/inter-site pairing coexists with the repulsive pair hopping interaction. The latter interaction is interesting in that it leads to pairing with non-zero momentum of the Cooper pairs even in the absence of the external magnetic field (the so-called η pairing). It turns out that, depending on the strength of the pair hopping interaction, the magnetic field can induce one of two types of the FFLO phase with different spatial modulations of the order parameter. It is argued that the properties of the FFLO phase may give information about the magnitude of the pair hopping interaction. We also show that η pairing and d-wave superconductivity may coexist in the FFLO state. It holds true also for superconductors which, in the absence of magnetic field, are of pure d-wave type.

Modification of the isotope effect by the van Hove singularity of electrons on a two-dimensional lattice

We discuss the problem of phonon-induced superconductivity of electrons on a two-dimensional lattice. Analytical expressions for the superconducting transition temperature and the isotope coefficient have been derived for the case that the Fermi level is close to the van Hove singularity. We have considered the weak- and strong-coupling cases. Our results show that in the presence of the van Hove singularity the isotope coefficient can take on small values despite the fact that superconductivity originates from phonon-induced pairing.

Breakdown of the generalized Gibbs ensemble for current-generating quenches.

We establish a relation between two hallmarks of integrable systems: the relaxation towards the generalized Gibbs ensemble (GGE) and the dissipationless charge transport. We show that the former one is possible only if the so-called Mazur bound on the charge stiffness is saturated by local conserved quantities. As an example we show how a non-GGE steady state with a current can be generated in the one-dimensional model of interacting spinless fermions with a flux quench. Moreover, an extended GGE involving the quasilocal conserved quantities can be formulated for this case.

Inhomogeneity-induced enhancement of the pairing interaction in cuprate superconductors.

Scanning tunneling spectroscopy has recently discovered a positive correlation between the magnitude of the superconducting gap and positions of dopant oxygen atoms in Bi-based cuprates. We propose a microscopic mechanism that could be responsible for this effect. In particular, we demonstrate that the dopant-induced spatial variation of the atomic levels always enhances the superexchange interaction.

Mechanism of ultrafast relaxation of a photo-carrier in antiferromagnetic spin background

We study the relaxation mechanism of a highly excited charge carrier propagating in the antiferromagnetic background modeled by the

Nonequilibrium dynamics of the Holstein polaron driven by an external electric field

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Coexistence of superconductivity and incommensurate magnetic order

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Critical field in a superconductivity model with local pairs

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Nonequilibrium quantum dynamics of a charge carrier doped into a Mott insulator.

Hamiltonian on a square lattice. We show that the relaxation consists of two distinct stages. The initial ultrafast stage with the relaxation time