Three-dimensional flux states as a model for the pseudogap phase of transition metal oxides

Abstract

We propose that the pseudogap state observed in the transition metal oxides can be explained by a three-dimensional flux state, which exhibits spontaneously generated currents in its ground state due to electron-electron correlations. We compare the energy of the flux state to other classes of mean field states, and find that it is stabilized over a wide range of t and δ. The signature of the state will be peaks in the neutron diffraction spectra, the location and intensity of which are presented. The dependence of the pseudogap in the optical conductivity is calculated based on the parameters in the model. PACS numbers: 71.10.Fd, 71.30.+h, 75.10.Lp The motivation for this work is the observation of a pseudogap that opens up in optical conductivity measurements of the three-dimensional transition metal oxide SrRuO 3 [1] above its ferromagnetic transition temperature of T C ≈ 150 K. A pseudogap has also recently been seen in BaRuO 3 [2]. In this pseudogapped regime, ρ (T ) increases linearly with temperature, passing through the Ioffe-Regel limit without saturation [3], behavior indicative of a "bad metal" [4]. The optical conductivity in this state is proportional to the non-Fermi liquid behavior of ω −1/2 at high frequency and has a peak at low frequencies [1] at approximately 250 cm −1 , the precise location of the peak being temperature dependent.We propose that this pseudogap state can be understood by considering a ground state with spontaneously generated electronic currents circulating around the plaquettes. The currents arise from electron-electron correlations, due to the bi-quadratic terms in the Hamiltonian. The state which we propose is a generalization of the two-dimensional flux states invented by Affleck and Marston [5], and studied in their chiral extension by Wen, Wilzcek, and Zee [6]. Unlike the two-dimensional case, there is no possibility of fractional statistics in three dimensions. However, the spontaneous generation of gauge fields is a possibility in three dimensions, and these gauge fields can lead to a ground state with circulating electronic currents. Earlier work was done on three-dimensional flux states by Laughlin and coworkers [7,8] and Zee [9].In actuality, SrRuO 3 has 5 bands crossing the Fermi surface formed by hybridizing the Ruthenium d orbitals with the Oxygen p orbitals [10]. The crystal structure is orthorhombic, becoming cubic at temperatures greater than 900 K [11]. Undoubtedly, the actual electronic structure of SrRuO 3 , and particularly the presence of a van Hove singularity near the Fermi surface, influence the material's behavior. The model which we consider is vastly simplified and serves as a starting point for consid- * Electronic address: dfs@Stanford.edu ering the nature of the pseudogapped state in the threedimensional transition metal oxides. A model which incorporates some of these electronic features, but does not focus on the pseudogap regime, has been proposed by . I. MODEL SYSTEMThe Hamiltonian that we consider is the single orbital t-J model given byw...

Current carrying ground state in a bilayer model of strongly correlated systems

“…As expected from our analytical estimates in (6), if ∆U or t ⊥ gets too large, long-range order disappear as shown on Fig. 5.…”

“…the orbital antiferromagnetic phase (OAF), the staggered flux (SF) or the D-density wave (DDW) phase. In the context of high Tc superconductivity, these current carrying ground states have been proposed as competing states for the pseudogap phase [1,2,3,4,5,6]. The SF or the DDW phase has the attractive feature that the nodal quasi-particles have an energy spectrum similar to that of the d−wave superconducting state.…”

Large-Nlimit of a magnetic impurity in unconventional density waves

“…This causes the lack of periodic modulation of the spin and charge density. Such states have been proposed to describe the pseudogap phase of high T c superconductors 16,17,18 , the low temperature phase of α-(BEDT-TTF) 2 KHg(SCN) 4 19,20 , the antiferromagnetic phase in URu 2 Si 2 21,22 and other heavy fermion materials 23 , the charge density wave in 2H-TaSe 2 24 and the pseudogap phase in transition metal oxides 25 . Due to the wavevector dependence of the gap, the transition to this phase is metal to metal instead of metal to insulator, as in conventional density waves (with constant energy gap).…”

Impurity effects in unconventional density waves in the unitary limit

“…In fact, after the earlier proposals in the context of the excitonic insulator 2,3 , this topic was rediscovered in the early 90's in various dimensions and systems 4,5,6,7,8,9,10 . Since then, the realization of unconventional or nodal density waves 11,12 looks more and more possible: non-superconducting phase transitions without charge or spin ordering have been detected in a number of materials, and one of the possible explanations is provided by the unconventional density wave scenario 13,14,15,16 . One of the main reasons of interest on UDW arises from high T c superconductors, where one of the competing models in the pseudogap phase is the d-density wave state.…”