Class of variational Ansätze for the spin-incoherent ground state of a Luttinger liquid coupled to a spin bath

Interacting one-dimensional electron systems are generally referred to as “Luttinger liquids”, after the effective low-energy theory in which spin and charge behave as separate degrees of freedom with independent energy scales. The “spin-incoherent Luttinger liquid” describes a finite-temperature regime that is realized when the temperature is very small relative to the Fermi energy, but larger than the characteristic spin energy scale. Similar physics can take place in the ground-state, when a Luttinger Liquid is coupled to a spin bath, which effectively introduces a “spin temperature”through its entanglement with the spin degree of freedom. We show that the spin-incoherent state can be exactly written as a factorized wave-function, with a spin wave-function that can be described within a valence bond formalism. This enables us to calculate exact expressions for the momentum distribution function and the entanglement entropy. This picture holds not only for two antiferromagnetically coupled t−J chains, but also for the t−J-Kondo chain with strongly interacting conduction electrons. We argue that this theory is quite universal and may describe a family of problems that could be dubbed “spin-incoherent”.Accepted manuscrip

Spectral function of the U→∞U \rightarrow \infty one dimensional Hubbard model at finite temperature and the crossover to the spin incoherent regime

The physics of the strongly interacting Hubbard chain (with $t/U \ll 1$) at finite temperatures undergoes a crossover to a spin incoherent regime when the temperature is very small relative to the Fermi energy, but larger than the characteristic spin energy scale. This crossover can be understood by means of Ogata and Shiba's factorized wave function, where charge and spin are totally decoupled, and assuming that the charge remains in the ground state, while the spin is thermally excited and at an effective "spin temperature". We use the time-dependent density matrix renormalization group method (tDMRG) to calculate the dynamical contributions of the spin, to reconstruct the single-particle spectral function of the electrons. The crossover is characterized by a redistribution of spectral weight both in frequency and momentum, with an apparent shift by $k_F$ of the minimum of the dispersion.Comment: 4+pages, 3 fig

Unconventional fermionic pairing states in a monochromatically tilted optical lattice

We study the one-dimensional attractive fermionic Hubbard model under the influence of periodic driving with the time-dependent density matrix renormalization group method. We show that the system can be driven into an unconventional pairing state characterized by a condensate made of Cooper pairs with a finite center-of-mass momentum similar to a Fulde-Ferrell state. We obtain results both in the laboratory and the rotating reference frames demonstrating that the momentum of the condensate can be finely tuned by changing the ratio between the amplitude and the frequency of the driving. In particular, by quenching this ratio to the value corresponding to suppression of the tunneling and the Coulomb interaction strength to zero, we are able to “freeze” the condensate. We finally study the effects of different initial conditions and compare our numerical results to those obtained from a time-independent Floquet theory in the large frequency regime. Our work offers the possibility of engineering and controlling unconventional pairing states in fermionic condensates.This work was conducted at the Center for Nanophase Materials Sciences, sponsored by the Scientific User Facilities Division (SUFD), Basic Energy Sciences (BES), U.S. Department of Energy (DOE), under contract with UT-Battelle. A.N. acknowledges support by the Center for Nanophase Materials Sciences and by the Early Career Research program, SUFD, BES, DOE. A.E.F. acknowledges the DOE, Office of Basic Energy Sciences, for support under Grant No. DE-SC0014407. A.P. was supported by NSF DMR-1506340, ARO W911NF1410540, and AFOSR FA9550-16-1-0334. (Scientific User Facilities Division (SUFD); Basic Energy Sciences (BES); U.S. Department of Energy (DOE); UT-Battelle; Center for Nanophase Materials Sciences; Early Career Research program; SUFD; BES; DOE; DE-SC0014407 - DOE, Office of Basic Energy Sciences; NSF DMR-1506340; ARO W911NF1410540; AFOSR FA9550-16-1-0334)Published versio