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arXiv:cond-mat/0101249 · Physical review. B, Condensed matter

Electron spectral function in two-dimensional fractionalized phases

Courtney Lannert, Matthew P. A. Fisher, T. Senthil

Published Jun 15, 2001• 13 citations
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Abstract

We study the electron spectral function of various zero-temperature spin-charge separated phases in two dimensions. In these phases, the electron is not a fundamental excitation of the system, but rather ``decays'' into a spin-1/2 chargeless fermion (the spinon) and a spinless charge e boson (the chargon). Using low-energy effective theories for the spinons (d-wave pairing plus possible N\'eel order) and the chargons (condensed or quantum-disordered bosons), we explore three phases of possible relevance to the cuprate superconductors: (1) ${\mathrm{AF}}^{*},$ a fractionalized antiferromagnet where the spinons are paired into a state with long-ranged N\'eel order and the chargons are 1/2-filled and (Mott) insulating; (2) the nodal liquid, a fractionalized insulator where the spinons are d-wave paired and the chargons are uncondensed; and (3) the d-wave superconductor, where the chargons are condensed and the spinons retain a d-wave gap. Working within the ${Z}_{2}$ gauge theory of such fractionalized phases, our results should be valid at scales below the energy gap of the vison---the basic vortex excitation in the theory. However, on a phenomenological level, our results should apply to any spin-charge separated system where the excitations have these low-energy effective forms. Comparison with angle-resolved photoemission spectroscopy data in the undoped, pseudogapped, and superconducting regions is made.

DOI
10.1103/physrevb.64.014518

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Spin and charge are two fundamental degrees of freedom in strongly correlated electron systems. In this thesis we study low-energy effective theory and phase transitions of spin and charge in a variety of strongly correlated systems. First, we study effective theory of magnetic phase transition in Sp(4) spin system and iron-based superconductors. Quantum phase transitions beyond Landau paradigm has been proposed in SU(2) spill model. We generalize this paradigm to Sp(4) model, which can be realized using spin-[special characters omitted] cold atoms on optical lattice. In iron-based superconductors, we study low-energy effective theory for magnetic and structural phase transitions, and present a global phase diagram of the two phase transitions. Second, we study spin and charge fluctuations on triangular lattice, and compare our results with experiments on organic Mott insulator κ-(ET) 2(CN)2. We show that the spin liquid state observed in experiments can be explained by Z2 spin liquid theory which contains spin-½ spinon and Z2 vison excitations. We also argue that near the Mott-insulator-to-metal transition there are fractionalized spinless charge excitations, which form exciton bound states near the transition. At last, we study spin and charge excitations in high-T c cuprates. We describe fluctuating two-dimensional metallic antiferromagnets by a gauge-theoretic description of an 'algebraic charge liquid' involving spinless fermions and a spin S = 1/2 complex scalar. We propose a phenomenological effective lattice Hamiltonian which describes the binding of these particles into gauge-neutral, electron-like excitations, and describe its implications for the electron spectral function across the entire Brillouin zone. We discuss connections of our results to photoemission experiments in the pseudogap regime of the cuprate superconductors.
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