Spin susceptibility of disordered Fermi systems

Paul B. Wiegmann

The behaviour of correlation functions of the one-dimensional Fermi system at large distances has been investigated by reducing it to the Sine-Gordon model. The latter is dual to the low-temperature phase of a plane xy model. In this case the fermion operator is the product of the order and disorder parameters. The transitions to the coupling constants between different states of the Fermi system states of the Fermi system may be considered as phase transitions equivalent to xy models. The elasticity modulus and spin susceptibility serves as superfluid density. The question on the phase transition of the xy model is discussed.

A. R. P. Rau, A. K. Rajagopal

A. Barış Özgüler, Canran Xu, Maxim Vavilov

We consider a one-dimensional spin chain system with quenched disorder and in the presence of a local periodic drive. We study the time evolution of the system in the Floquet basis and evaluate the fidelity susceptibility, which is a measure of how a given state changes under a small perturbation, of states to a weak periodic drive. We demonstrate that the statistical properties of the fidelity susceptibility over different disorder realizations can be used to identify two phases of the system: (1) the many-body localized phase, in which the susceptibility exhibits long tails while its average value decreases rapidly as disorder increases, and (2) the ergodic phase, in which the susceptibility distribution is narrow and its average value weakly depends on disorder. This distinction in the average value of the susceptibility between the two phases develops readily for systems with ten or more spins. Therefore, recently built networks of qubits subject to a local drive can simulate dynamics of a system in the many-body localization regime. We also show that the spin accumulation speed is correlated with the fidelity susceptibility and can also be used to distinguish the two phases.

Edward Su, Christian Sanner, Aviv Keshet +3 more

A. J. Leggett

Lubo Zhou, T. R. Kirkpatrick

A comprehensive field theory is developed for superconductors with quenched disorder. We first show that the matrix field theory, used previously to describe a disordered Fermi liquid and a disordered itinerant ferromagnet, also has a saddle-point solution that describes a disordered superconductor. A general gap equation is obtained. We then expand about the saddle point to Gaussian order to explicitly obtain the physical correlation functions. The ultrasonic attenuation, number density susceptibility, spin-density susceptibility, and the electrical conductivity are used as examples. Results in the clean limit and in the disordered case are discussed, respectively. This formalism is expected to be a powerful tool to study the quantum phase transitions between the normal-metal state and the superconductor state.