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