Localized dynamic perturbations in metals: Fermion versus boson description

Kurt Schönhammer, O. Gunnarsson

O. Gunnarsson, Kurt Schönhammer

Recently we proposed two boson approximations to describe the creation of electronhole---pair excitations by a localized time-dependent perturbation. These boson approximations were shown to be exact in certain limiting cases. In this paper we compare the results in these approximations with exact calculations where the electrons are treated as fermions. We show that the validity of the approximations is broader than had earlier been proven.

Eugeniu Plamadeala, Michael Mulligan, Chetan Nayak

We show that a one-dimensional quantum wire with 23 channels of interacting fermions has a perfect metal phase in which all weak perturbations that could destabilize this phase are irrelevant. Consequently, weak disorder does not localize it, a weak periodic potential does not open a gap, and contact with a superconductor also fails to open a gap. Similar phases occur for $N\ensuremath{\ge}24$ channels of fermions, except for $N=25$, and for $8k$ channels of interacting bosons, with $k\ensuremath{\ge}3$. Arrays of perfect metallic wires form higher-dimensional fermionic or bosonic perfect metals, albeit highly anisotropic ones.

Alessio Recati, Jean-Noël Fuchs, Claudia S. Peça +1 more

We discuss the effective interactions between two localized perturbations in one-dimensional quantum liquids. For noninteracting fermions, the interactions exhibit Friedel oscillations, giving rise to a Ruderman-Kittel-Kasuya-Yosida-type interaction familiar from impurity spins in metals. In the interacting case, at low energies, a Luttinger-liquid description applies. In the case of repulsive fermions, the Friedel oscillations of the interacting system are replaced, at long distances, by a universal Casimir-type interaction which depends only on the sound velocity and decays inversely with the separation. The Casimir-type interaction between localized perturbations embedded in a fermionic environment gives rise to a long-range coupling between quantum dots in ultracold Fermi gases, opening an alternative to couple qubits with neutral atoms. We also briefly discuss the case of bosonic quantum liquids in which the interaction between weak impurities turns out to be short ranged, decaying exponentially on the scale of the healing length.

Krutik Patel, Geyue Cai, B. J. DeSalvo +1 more