Study on Phase String Theory­based Variational methods in Doped Mott Insulators (Apr. 23, 2021)

  • Published: 2021-04-21

Time: 10:00am (UTC/GMT+8:00, Beijing/Shanghai), Apr. 23 (Fri.), 2021

Venue: KITS Meeting Room, 4th floor, No. 7 Building, UCAS [View Map]


Speaker: Shuai CHEN (Tsinghua U)


We employ the essential emergent sign structure in the study of doped Mott insulators. The higher temperature superconductivity is generally accepted as a typical problem of doped Mott insulators. t-J model is recognized as one of the simplest models, and the no­double­occupancy constraint on the Hilbert space enforces its nature of strong correlation to be the emergent singular phase­string sign structure. With the help of variational wave functions that satisfy the phase­string sign structure, we systematically investigate the single­hole and two­hole doped Mott insulators in t-J model. A case study on a single­hole problem in two spatial dimensions establishes properties of fundamental excitations. Due to phase­string sign fluctuations, a bare hole twisted by a global phase marks a fundamental quasiparticle. The ground states have four exact degeneracies corresponding to a singular angular momentum quantum number Lz= ±1 and hidden charge/spin currents. At finite size, the momentum distribution of holes possesses four sharp peaks and background broadening, which indicates the breakdown of Landau’s one­to­one principle with two components: the coherent and the incoherent. In the thermodynamics limit, the coherent component vanishes in a pow­law pattern, and only the incoherent remains. By contrast, turning off the phase string induced by the hole hopping in the so­called ? t­-J model, a conventional Bloch­type wave function with a finite quasiparticle weight can be recovered. A case study on a two­hole problem in a ladder system proves the phase­string sign plays a vital role as a pairing glue. Pictorially, the induced phase string signs by the two­hole collaborative hopping cancel each other and thus the they form a stronger Cooper pair. A BCS­type wave function gives a bad variational ground state energy and makes a qualitatively wrong prediction and is incompatible with the fundamental pairing force in the t­-J model. By contrast, a non­BCS­like wave function incorporating such a novel effect will result in substantially enhanced pairing strength and improved ground state energy as compared to the DMRG results. We argue that the non­BCS form of such a new ground state wave function is essential to describe a doped Mott antiferromagnet at finite dopings.


Invited by Prof. Zheng Zhu