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Tao Li

Publications and source records attributed to Tao Li.

609 records · Page 34Linked to original sources
arXiv2006

On the Origin of the Tunneling Asymmetry in the Cuprate Superconductors: a variational perspective

Through variational Monte Carlo calculation on Gutzwiller projected wave functions, we study the quasiparticle(qp) weight for adding and removing an electron from a high temperature superconductor. We find the qp weight is particle-hole symmetric at sufficiently low energy. We propose to use the tunneling asymmetry as a tool to study the mechanism of electron incoherence in high temperature superconductors.

cond-mat.supr-con↗
arXiv2006

Why a local moment induces an antiferromagnetic ordering: An RVB picture

Based on a Gutzwiller projected BCS wavefunction, it is shown that a local S=1/2 moment is present around a vacancy site (zinc impurity) in a form of staggered magnetic moments, which is a direct consequence of the short-ranged resonating-valence-bond (RVB) pairing in the spin background.

cond-mat.str-el↗
arXiv2005

Spin Charge Recombination in Projected Wave Functions

We find spin charge recombination is a generic feature of projected wave functions. We find this effect is responsible for a series of differences between mean field theory prediction and the result from projected wave functions. We also find spin charge recombination plays an important role in determining the dissipation of supercurrent, the quasiparticle properties and the hole - hole correlation.

cond-mat.supr-con↗
arXiv2004

On the Origin of the Tunneling Asymmetry in the Cuprate Superconductors

We argue the coherent part of the spectral weight always contribute symmetrically to the STM spectrum at sufficiently low energy and the tunneling asymmetry is a manifestation of the incoherent part of the electron spectrum. By subtracting the particle side spectrum from the hole side spectrum in the published STM data of Pan \textit{et al} on $BSCCO_{2212}(T_{c}=84K)$, we find the difference spectrum show a well defined gap structure at 25 meV. We argue this gap may represent a new energy scale of the system, namely the energy scale for spin-charge recombination in this system.

cond-mat.supr-con↗
arXiv2004

Magnetic phases of $t-J$ model on triangular lattice

We study the magnetic properties of the $t-J$ model on triangular lattice in light of the recently discovered superconductivity in Na$_{x}$CoO$_{2}$ system. We formulate the problem in the Schwinger Boson - slave Fermion scheme and proposed a sound mean field ansatz(canting ansatz) for the RVB order parameters. Working with the canting ansatz, we map out the temperature-doping phase diagram of the model for both sign of the hopping term. We find the prediction of the $t-J$ model differ drastically from that of earlier LSDA calculation and there is large doping range in which the system show zero net magnetization, rather than saturated magnetization as predicted in the LSDA calculation. We show the result of LSDA is unreliable in the strong coupling regime due to its neglect of electron correlation. We find the spin Berry phase play a vital role in this geometrically frustrated system and the various states in the phases diagram are characterized(and distinguished) by their respective spin Berry phase, rather than any Landau-like order parameter related to broken symmetry. We find the spin Berry phase is responsible for the qualitative difference in the low energy excitation spectrum of the various states of the phase diagram. We argue the phase boundary in the mean field phase diagram may serve as the first explicit and realistic example for phase transition between states with different quantum orders which in our case is nothing but the spin Berry phase. We also find an exotic state with nonzero spin chirality but no spin ordering is stable in a large temperature and doping range and find.......

cond-mat.supr-con↗
arXiv2004

Pseudogap Phase: Exchange Energy Driven vs. Kinetic Energy Driven

We show that both kinetic and superexchange energies of the t-J model may be read off from the optical data, based on an optical sum rule for the Hubbard model. Then we comparatively study two mean-field theories of pseudogap phase based on the t-J model. We find that while the pseudogap phase is superexchange-energy-driven in the slave-boson resonating-valence-bond (RVB) state, it is kinetic-energy-driven in the bosonic RVB state. The sharp contrast in the mechanisms of the pseudogap phases can be attributed to the fact that the antiferromagnetic (AF) correlations behave quite differently in two mean-field states, which in turn distinctly influence the kinetic energy of charge carriers. We elaborate this based on some detailed studies of the superexchange energy, kinetic energy, uniform spin susceptibility, equal-time spin correlations, dynamic spin susceptibility, as well as the optical conductivity. The results provide a consistent picture and understanding on two physically opposite origins of pseudogap phase. In comparison with experimental measurements, we are led to conclude that the pseudogap phase in the cuprates should be kinetic-energy-driven in nature.

cond-mat.supr-con↗
arXiv2003

The Driving Force of Superconducting Transition in High Temperature Superconductors

We show that both the kinetic energy and the exchange energy of the t-J model can be read off from the optical data. We show that the optical data indicates that the superconducting transition in high temperature superconductors is kinetic energy driven and the exchange energy resist the transition. We also show that kinetic energy may also be the driving force of the pseudogap phenomenon.

cond-mat.supr-con↗
arXiv2003

The Zinc Doping Induced STM Resonance as a Zero Mode

We show that the Zinc doping induced STM resonance in high-Tc cuprates is a zero mode - a d-wave monomer confined in the opposite sublattice of the Zinc site. We propose that the resonance come from the superconducting peak around $(π,0) $ as observed in ARPES experiments. It is predicted that the resonance should vanish in single layer $BSCCO_{2201}$ or in the vortex core of underdoped cuprate where the ARPES peak is absent. We argue that the STM result imply the ARPES peak around $(π,0) $ is the only coherent feature in the whole Brillouin zone.

cond-mat.supr-con↗
arXiv2003

Spin Dynamics of t-J Model on Triangular Lattice

We study the spin dynamics of t-J model on triangular lattice in the Slave-Boson-RPA scheme in light of the newly discovered superconductor Na$_{x}$CoO$_{2}$. We find resonant peak in the dynamic spin susceptibility in the $d+id^{^{\prime}}$-wave superconducting state for both hole and electron doping in large doping range. We find the geometrical frustration inherent of the triangular lattice provide us a unique opportunity to discriminate the SO(5) and RPA-like intepretation of the origin of the resonant peak.

cond-mat.supr-con↗
arXiv2003

Property P for Knots admitting Certain Gabai Disks

We show that if a knot has a minimal spanning surface that admits certain Gabai disks, then this knot has Property P. As one of the applications we extend and simplify a recent result of Menasco and Zhang that closed 3-braid knots have Property P. Other applications are given.

math.GT↗
arXiv2002

Boundary curves of surfaces with the 4-plane property

Let M be an orientable and irreducible 3-manifold whose boundary is an incompressible torus. Suppose that M does not contain any closed nonperipheral embedded incompressible surfaces. We will show in this paper that the immersed surfaces in M with the 4-plane property can realize only finitely many boundary slopes. Moreover, we will show that only finitely many Dehn fillings of M can yield 3-manifolds with nonpositive cubings. This gives the first examples of hyperbolic 3-manifolds that cannot admit any nonpositive cubings.

math.GT↗
arXiv2002

Laminar Branched Surfaces in 3-manifolds

We define a laminar branched surface to be a branched surface satisfying the following conditions: (1) Its horizontal boundary is incompressible; (2) there is no monogon; (3) there is no Reeb component; (4) there is no sink disk (after eliminating trivial bubbles in the branched surface). The first three conditions are standard in the theory of branched surfaces, and a sink disk is a disk branch of the branched surface with all branch directions of its boundary arcs pointing inwards. We will show in this paper that every laminar branched surface carries an essential lamination, and any essential lamination that is not a lamination by planes is carried by a laminar branched surface. This implies that a 3-manifold contains an essential lamination if and only if it contains a laminar branched surface.

math.GT↗
arXiv2000

Theory of Sinusoidal Modulation of the Resonant Neutron Scattering in High Temperature Superconductors

A model with interlayer pairing is proposed to explain the sinusoidal modulation of the resonant neutron scattering in high temperature superconductors. It is found that the interlayer pairing has s-wave symmetry in the CuO$_2$ plane and has comparable magnitude with the d-wave intralayer pairing. It is also found that the interlayer pairing mainly affects momentum close to the hot spots on the Fermi surface while its effect on the gap nodes is negligible. It is pointed out that these characteristics of the interlayer pairing can be understood in a model in which the superconducting pairing originates from the exchange of the antiferromagnetic spin fluctuation.

cond-mat.supr-con↗