Spectral function of Mott-insulating Hubbard ladders: From fractionalized excitations to coherent quasiparticles

Abstract

We study the spectral function of two-leg Hubbard ladders with the time-dependent density matrix renormalization group method (tDMRG). The high-resolution spectrum displays features of spin-charge separation and a scattering continuum of excitations with coherent bands of bound states "leaking" from it. As the inter-leg hopping is increased, the continuum in the bonding channel moves to higher energies and spinon and holon branches merge into a single coherent quasi-particle band. Simultaneously, the spectrum undergoes a crossover from a regime with two minima at incommensurate values of kx (a Mott insulator), to one with a single minimum at kx = π (a band insulator). We identify the presence of a continuum of scattering states consisting of a triplon and a polaron. We analyze the processes leading to quasiparticle formation by studying the time evolution of charge and spin degrees of freedom in real space after the hole is created. At short times, incoherent holons and spinons are emitted but after a characteristic time τ charge and spin form polarons that propagate coherently.

Emergence and spectral-weight transfer of electronic states in the Hubbard ladder

“…We consider the case of 0 ≤ n ≤ 1 without loss of generality because A(k, ω) for 1 < n ≤ 2 can be obtained as A(k + π, −ω) at the electron density 2 − n by using the particle-hole transformation. The Hubbard ladder has been studied primarily on the ground-state properties [8][9][10][11][12], spin and charge excitations [13][14][15], spectral function around half-filling [10,15,16], charge and photo dynamics [17,18], and ferromagnetism [19][20][21]. In this paper, to clarify the evolution of electronic states as a function of the electron density, we investigate the spectral function in the overall electron-density regime primarily for U ≫ t ⊥ ≫ t > 0 (U t /t 2 ⊥ is not too large for the ground state to have spin 0 or 1/2 [19,20]) based on the numerical results for U/t = 16 and t ⊥ /t = 2 obtained using the non-Abelian dynamical density-matrix renormalizationgroup (DDMRG) method [5,[22][23][24][25][26][27].…”

The fate of pairing and spin-charge separation in the presence of long-range antiferromagnetism

“…We point out that one-dimensional metals with fermionic quasi-particles are indeed possible, but this typically occurs in gapped systems, such as ladders. [114][115][116] In these systems the spin and charge gap may survive at finite doping [117]. However, our model Eq.…”

Matrix product state recursion methods for strongly correlated quantum systems

“…The next set of figures (Figs. 9,10,11) shows the spectral functions for several values of U and several different doping. The main features have mostly been seen before in other (mostly lower resolution) studies 9,11 .…”

“…9,10,11) shows the spectral functions for several values of U and several different doping. The main features have mostly been seen before in other (mostly lower resolution) studies 9,11 . Note that to more clearly show the particle-hole symmetry, we have used a different k x range in plotting the two different k y modes, but no alterations were made to the data itself.…”

“…The half-filled ladder was studied using quantum Monte Carlo and maximum entropy methods two decades ago. 8 Previous work on spectral functions of this model includes a tDMRG study 9 , and a dynamical DMRG study 10 . Also related is a Lanczos study of the t-J ladder 11 .…”