1. Phases of Mott-Hubbard Bilayers Ref: Ribeiro et al, cond-mat/0605284
Jung Hoon Han
Sung Kyun Kwan U.
成均館大
Ref: Ribeiro et al, cond-mat/
Han & Jia, cond-mat/

2. Sharp Interface of Band Insulator and Mott Insulator
H.Y.Hwang, Nature (2002) La Sr
SrTi(d0)O3 and LaTi(d1)O3 interfacial layer with atomic precision was successfully fabricated.

3. Millis-Okamoto Theory
N-layers of Mott insulators are sandwiched between band insulators
Ti t2g orbital states are studied within Hartree-Fock theory
Okamoto & Millis, Nature (2004)

4. Millis-Okamoto Theory
Electron leakage occurs; Spectral function shows metallic behavior

5. Can we do something similar with interface of
two doped Mott insulators?
After all physics of doped Mott insulators is much richer than that of doped band insulator, e.g.
spin liquid, d-wave superconductivity, and antiferromagnetism

6. Sharp Interface of two Mott Insulators
Bozovic, Nature (2003)

7. Layers are oppositely doped with density x of holes(doublons)
Our Model
Ramesh, Science (2004)
Layers are oppositely doped with density x of holes(doublons)
Short-range Coulomb coupling across the layers
Each layer modeled as large-U Hubbard or tJ

8. In this talk we try to answer a naïve question:
What are the possible phases of
coupled doped Mott insulators?

9. Phase Diagram of Hubbard Model – Recent Efforts
Senechal et al, PRL (2005)

10. Single-layer tJ Model – slave boson meanfield theory
Han, Wang, Lee IJMPB (2001)

11. Lessons from 1D Coupled Chains (A. Seidel)
1D constrained hopping model has
(wavefunction) = (charge w.f.) X (spin w.f.)
Inter-layer interaction for the charge sector has effective Hamiltonian given by 1D attractive Hubbard model
Ribeiro et al, cond-mat/

12. Lessons from 1D Coupled Chains (A. Seidel)
1D analog of paired superfluid phase emerges as the ground state; In the original picture this is the holon-doublon exciton
Existence of exciton instability is rigorously established in coupled 1D chains
Ribeiro et al, cond-mat/

13. Phases of Mott-Hubbard Bilayers at T=0
DOPING
INTERLAYER
INTERACTION
Han & Jia, cond-mat/

14. Spin Liquid Insulator – a new phase for bilayers
Exciton pairing acts like a pairing gap for quasiparticles. Single charge excitation has a gap due to excitons: Insulator
It emerges after magnetic order has melted: Spin Liquid

15. Dichotomy of one-particle vs. two-particle responses
In the SLI phase, one-particle Green’s function has a charge gap
Two-particle response function such as conductivity is that of a superfluid due to transport by excitons

16. Other Phases of Bilayer Mott-Hubbard Model
DOPING
INTERLAYER
INTERACTION
AFI: Antiferromagnetic insulator with (,) ordering; Charge gap due both to AFM and exciton gaps; Evolves into SLI when magnetism vanishes; Transport still superfluid-like
m-dSC: Magnetic d-wave Superconductor; Exciton gap has vanished; d-wave pairing of electrons; Evolves into non-magnetic d-wave superconductor upon doping

17. Phases of Mott-Hubbard Bilayers from Berkeley group
Ribeiro et al, cond-mat/
Calculation based on doped carrier formulation
Results are consistent with slave boson theory

18. New Features of Bilayers
Exciton binding is responsible for incoherent quasiparticles and charge gap for small doping
Exciton binding is responsible for in-plane superfluid transport
Easy realization of spin liquid without lattice frustration