Strain-induced superconductor-insulator transition on a Lieb lattice

Abstract

We report the numerical investigation of strain induced superconductor-insulator quantum phase transition on a Lieb lattice. Based on a non perturbative Monte Carlo technique we show that in two dimensions an s-wave superconductor undergoes transition to a highly correlated Bosonic insulator under the influence of strain, applied as staggered hopping amplitudes. To the best of our knowledge, this is the first work to report theoretical investigation of "disorder free" superconductor-insulator phase transition in systems with Lieb lattice structure. With the recent experimental realization of the Lieb lattice in ultracold atomic gases, photonic lattices as well as in solid state systems, we believe that the results presented in this paper would be of importance to initiate experimental investigation of such novel quantum phase transitions. We further discuss the fate of such systems at finite temperature, highlighting the effect of fluctuations on the superconducting pair formations, thermal scales and quasiparticle behavior. The high temperature quasiparticle signatures discussed in this paper are expected to serve as benchmarks for experiments such as radio frequency and momentum resolved radio frequency spectroscopy measurements carried out on systems such as ultracold atomic gases.

Possible insulator-pseudogap crossover in the attractive Hubbard model on the Lieb lattice

“…A pseudogap was also predicted in the normal state of the Lieb lattice in [16]. In this Monte Carlo study, a metallic state is predicted at low interaction strengths and a pseudogap phase with short-range pairing correlations at intermediate interactions.…”

“…As the band width and kinetic energy are zero, any attractive interaction could be anticipated to cause pairing already in the normal state. Indeed preformed pairs [14,15] and a pseudogap [16][17][18] have been suggested. Here we show that the normal state in a Lieb lattice features, for decreasing interaction, a crossover from a flat-band enhanced pseudogap to a non-Fermi liquid with insulating properties.…”

“…We considered weak and intermediate coupling. In the strong-coupling limit, the normal state is expected to contain bosonic pairs as the Bose-Einstein condensation (BEC) limit of the BCS-BEC crossover is reached [16,47,48].…”

Electron-Phonon Interactions in Flat Band Systems

“…Subsequent work further investigated flat band ferromagnetism [5][6][7][8]. The effect of attractive electron-electron interactions is also of interest [9][10][11][12], especially since the momentum at which Bose-Einstein condensation of fermionic pairs might occur is uncertain in a flat band [13][14][15].…”

Insulator-pseudogap crossover in the Lieb lattice

“…As the band width and kinetic energy are zero, any attractive interaction could be anticipated to cause pairing already in the normal state. Indeed preformed pairs [14,15] and a pseudogap [16,17] have been suggested. Here we show that the normal state in a Lieb lattice features, for decreasing interaction, a crossover from a flat-band enhanced pseudogap to an insulator.…”