Quasiparticle collapsing in an anisotropict−Jladder

Abstract

Quasiparticle collapsing is a central issue in the study of strongly correlated electron systems. In the onedimensional case, the quasiparticle collapsing in a form of spin-charge separation has been well established, but the problem remains elusive in dimensions higher than one. By using density matrix renormalization group (DMRG) algorithm, we show that in an anisotropic two-leg t-J ladder, an injected single hole behaves like a well-defined quasiparticle in the strong rung limit, but undergoes a "phase transition" with the effective mass diverging at a quantum critical point (QCP) towards the isotropic limit. After the transition, the quasiparticle collapses into a loosely bound object of a charge (holon) and a spin-1/2 (spinon), accompanied by an unscreened phase string as well as a substantially enhanced binding energy between two doped holes. A phase diagram of multi-leg ladders is further obtained, which extrapolates the QCP towards the two-dimensional limit. The underlying novel mechanism generic for any dimensions is also discussed. The Landau's Fermi liquid theory is characterized by the low-lying quasiparticle excitation that carries well-defined momentum, charge, spin, and a renormalized effective mass.The collapse of such a quasiparticle excitation will be a hallmark of a non-Fermi-liquid state. In particular, the breakdown of the quasiparticle in a form of spin-charge separation has been conjectured in the study of doped Mott insulators, notably the high-T c cuprates 1-8 . However, no consensus has been reached yet on how a quasiparticle precisely falls into parts in such strongly correlated electron systems.A t-J square ladder as a quasi one-dimensional (1D) doped Mott insulator system has been intensively investigated [9][10][11][12][13][14][15][16][17][18][19][20][21] . Such systems are beyond a purely 1D system due to the presence of closed loops of various sizes, and can be accurately studied by the DMRG numerical method 22 . Experimentally, there are also several available materials with the ladder structure 23 . Because of the peculiar quantum destructive interference in the closed paths, a DMRG study has recently revealed 20 a generic self-localization of a single hole injected into the spin ladders in the isotropic limit. It implies the failure of a conventional quasiparticle picture in a way very distinct from a purely 1D system 24 .In this Letter, we focus on a two-leg t-J ladder system in which the undoped spin background remains gapped. By using DMRG, we find that for an injected hole, the quasiparticle description is restored if the ladder is in an anisotropic (strong rung) regime. Then, as the ladder anisotropic parameter is continuously tuned from strong rung coupling towards the isotropic limit, there exists a QCP, at which the quasiparticle collapses with its effective mass diverges. Subsequently the doped hole fractionalizes into a composite structure as a bound state of an incoherent holon and a deconfined spinon. The momentum distribution of the hole also exhibits a qualitative...

Spin and charge modulations in a single-hole-doped Hubbard ladder: Verification with optical lattice experiments

“…Such a total S z = 1/2 is found to distribute around the hole at a given site with an alternative distribution of up (red circle) and down (blue circle) spins (with the magnitude represented by the size of each full circle as determined by the hole-spin correlation function [14]). At α = 0.4, the doped charge is tightly bound with a spin-1/2; in contrast, the hole and the spin-1/2 are loosely bound at α = 1, where the phase string becomes unscreened as previously discussed in the context of the t-J ladder [12] (see text).…”

Nature of a single doped hole in two-leg Hubbard and t−J ladders

“…Previous studies [16][17][18][19] of the two-leg anisotropic t-J ladder show that a nontrivial charge modulation appears in the hole density profile in the isotropic limit α = 1, which is sharply different than the strong-rung limit α < α c , where α c = 0.68 at t/J = 3.…”

“…Spin-charge correlation: Previous studies show that there is no spin-charge separation in the two-leg t-J ladder for 0 ≤ α ≤ 1 18,19 . In this section, we show that this is also true for the two-leg Hubbard ladder.…”

“…22,23 We have carried out systematic DMRG 24 simulations to extract the ground state properties of ladders of length up to L = 300 and elementary excitations of a single doped hole to obtain unprecedentedly complete information. Following previous studies [16][17][18][19] , we have considered a range of values of the parameter α, the ratio of the hopping matrix elements and the spin exchange couplings on the legs and the rungs of the ladders of the Hubbard and t-J models, see Fig. 1.…”

Ultrafast Atomic Scale Dynamics Using X-ray Free Electron Laser

“…PAL-XFEL은 세 계에서 세 번째로 가동된 경 X-선 영역(파장이 1나노미터 이 하)의 XFEL이며, 2009년 미국의 Linac Coherent Light Source(LCLS) [2] 에서 성공적으로 발진된 이후, 2011년 일본의 SPring-8 Angstrom Compact free electron LAser(SACLA) [3] 에 이은 쾌거이다. Germanium에 대한 연구 결과를 보여주며, [6] 최근 시간동기화 에 대한 최적화 후의 결과를 그림 3 [7] 에서 보여주고 있다. 또 한 PbTe에 적용한 결과는 optical phonon과 acoustic phonon의 합과 차가 보이는 overtone도 관찰이 가능함을 보여주 [10]…”