Strong Correlation to Weak Correlation Phase Transition in Bilayer Quantum Hall Systems

At small layer separations, the ground state of a nu=1 bilayer quantum Hall system exhibits spontaneous interlayer phase coherence and has a charged-excitation gap E_g. The evolution of this state with increasing layer separation d has been a matter of controversy. In this letter we report on small system exact diagonalization calculations which suggest that a single phase transition, likely of first order, separates coherent incompressible (E_g >0) states with strong interlayer correlations from incoherent compressible states with weak interlayer correlations. We find a dependence of the phase boundary on d and interlayer tunneling amplitude that is in very good agreement with recent experiments.Comment: 4 pages, 4 figures included, version to appear in Phys. Rev. Let

Quasiparticles in the 111 state and its compressible ancestors

We investigate the relationship of the spontaneously inter-layer coherent ``111''state of quantum Hall bilayers at total filling factor \nu=1 to ``mutual'' composite fermions, in which vortices in one layer are bound to electrons in the other. Pairing of the mutual composite fermions leads to the low-energy properties of the 111 state, as we explicitly demonstrate using field-theoretic techniques. Interpreting this relationship as a mechanism for inter-layer coherence leads naturally to two candidate states with non-quantized Hall conductance: the mutual composite Fermi liquid, and an inter-layer coherent charge e Wigner crystal. The experimental behavior of the interlayer tunneling conductance and resistivity tensors are discussed for these states.Comment: 4 Pages, RevTe

Dynamical Properties in the Bilayer Quantum Hall Ferromagnet

The spectral functions of the pseudospin correlation functions in the bilayer quantum Hall system at \nu=1 are investigated numerically, where the pseudospin describes the layer degrees of freedom. In the pseudospin-ferromagnetic phase, the lowest-energy excitation branch is closely connected with the ground state through the fluctuations of pseudospin S_y and S_z, and it plays a significant role on the tunneling properties in this system. For the system with very small tunneling amplitude and layer separation smaller than the critical one, the system-size dependence of calculated spectral function A_{y z} suggests the superfluidity on the tunneling current in the absence of impurities.Comment: 4 pages, 1 Postscript figur

Composite Fermion Pairing in Bilayer Quantum Hall Systems

We derive the effective Hamiltonian for the composite fermion in double-layer quantum Hall systems with inter-layer tunneling at total Landau-level filling factor $\nu=1/m$, where $m$ is an integer. We find that the ground state is the triplet p-wave BCS pairing state of the composite fermions. At $\nu=1/2$, the ground state of the system evolves from the Halperin $(3,3,1)$-state toward the Pfaffian-state with increasing the tunneling amplitude. On the other hand, at $\nu=1$, the pairing state is uniquely determined independent of tunneling amplitude.Comment: 13 pages, 2 figure

Entanglement entropy in aperiodic singlet phases

We study the average entanglement entropy of blocks of contiguous spins in aperiodic XXZ chains which possess an aperiodic singlet phase at least in a certain limit of the coupling ratios. In this phase, where the ground state constructed by a real space renormalization group method, consists (asymptotically) of independent singlet pairs, the average entanglement entropy is found to be a piecewise linear function of the block size. The enveloping curve of this function is growing logarithmically with the block size, with an effective central charge in front of the logarithm which is characteristic for the underlying aperiodic sequence. The aperiodic sequence producing the largest effective central charge is identified, and the latter is found to exceed the central charge of the corresponding homogeneous model. For marginal aperiodic modulations, numerical investigations performed for the XX model show a logarithmic dependence, as well, with an effective central charge varying continuously with the coupling ratio.Comment: 18 pages, 9 figure