Recently Chakravarty et al. proposed an ordered d-density wave (DDW) state as an explanation of the pseudogap phase in underdoped high-temperature cuprates. We study the competition between the DDW and superconducting ordering based on an effective mean-field Hamiltonian. We are mainly concerned with the effect of the DDW ordering on the electronic state around a single nonmagnetic impurity. We find that a single subgap resonance peak appears in the local density of state around the impurity. In the unitary limit, the position of this resonance peak is always located at Er = −µ with respect to the Fermi energy. This result is dramatically different from the case of the pure superconducting state for which the impurity resonant energy is approximately pinned at the Fermi level. This can be used to probe the existence of the DDW ordering in cuprates.PACS numbers: 74.25Jb, 73.20.Hb Recently a d-density wave (DDW) state was proposed to model the pseudogap in the underdoped high-T c cuprates [1,2]. The key feature of the DDW state is staggered orbital magnetic moments (i.e., staggered currents) which break parity and time-reversal symmetry as well as the translation invariance by one lattice constant and rotation by π/2. This proposal of a new order parameter differs fundamentally from other theoretical ideas [3][4][5] for which the staggered current is a fluctuating rather than a static quantity. Whether such a DDW state really exists in the phase diagram of high-T c cuprates is an interesting theoretical question [6]. More recently, the SU(2) [7] or U(1) [8] mean-field theory of the t-J model predicted that the DDW order could exist in a vortex core.An interesting question is the effect of a single nonmagnetic impurity on the DDW state. The single impurity problem in the superconducting state has been intensively studied both theoretically [9][10][11][12] and experimentally [13][14][15]. However, the same problem has not been well studied in the pseudogap (PG) state, which has been indicated by STM [16] and by ARPES experiments [17]. Currently, the origin of the PG state remains unclear. Experimentally it was also argued [18] that in the underdoped cuprates the superconducting and pseudo gap coexist unlike in the pre-formed pair model [19]. The electronic states around a single impurity may serve as a local probe to distinguish between these scenarios. Within the T -matrix approximation, it was argued [20] that, as long as the band density of states is depleted at the Fermi energy, the existence of impurity resonant states is robust regardless of the microscopic origin of the PG state. Note that, without invoking any particular model, the band density of states was assumed in Ref.[20] to be symmetric with respect to the Fermi energy. This choice corresponds to the chemical potential µ being zero in a two-dimensional tight-binding model with nearest-neighbor hopping. In addition, because of the lack of a specific model, the calculation of the local density of states (LDOS) around an impurity goes beyond the scop...
Quantum transport in a lattice is distinct from its counterpart in continuum media. Even a free wave packet travels differently in a lattice than in the continuum. We describe quantum scattering in a one dimensional lattice using three different formulations and illustrate characteristics of quantum transport such as resonant transmission. We demonstrate the real time propagation of a wave packet and its phase shift due to impurity configurations. Spin-flip scattering is also taken into account in a spin chain system. We show how individual spins in the chain evolve as a result of a spin-flip interaction between an incoming electron and a spin chain.
Considering the spin of a local magnetic atom as a quantum mechanical operator, we illustrate the dynamics of a local spin interacting with a ballistic electron represented by a wave packet. This approach improves the semi-classical approximation and provides a complete quantum mechanical understanding for spin transfer phenomena. Sending spin-polarized electrons towards a local magnetic atom one after another, we estimate the minimum number of electrons needed to flip a local spin.
We study the Wiedemann-Franz (WF) law in the d-density wave (DDW) model. Even though the opening of the DDW gap (W0) profoundly modifies the electronic density of states and makes it dependent on energy, the value of the WF ratio at zero temperature (T = 0) remains unchanged. However, neither electrical nor thermal conductivity display universal behavior. For finite temperature, with T greater than the value of the impurity scattering rate at zero frequency γ(0) i.e. γ(0) < T ≪ W0, the usual WF ratio is obtained only in the weak scattering limit. For strong scattering there are large violations of the WF law.
We calculate the Hall conductivity for a spin-triplet superconductor, using a generalized pairing symmetry dependent on an arbitrary phase, ϕ. A promising candidate for such an order parameter is Sr2RuO4, whose superconducting order parameter symmetry is still subject to investigation. The value of this phase can be determined through Kerr rotation and DC Hall conductivity measurements. Our calculations impose significant constraints on ϕ.
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