ABSTRACT
We introduce in this Letter an exact solvable BCS-Hubbard model in arbitrary dimensions. The model describes a p-wave BCS superconductor with equal spin pairing moving on a bipartite (cubic, square, etc.) lattice with on-site Hubbard interaction U. We show that the model becomes exactly solvable for arbitrary U when the BCS pairing amplitude Δ equals the hopping amplitude t. The nature of the solution is described in detail in this Letter. The construction of the exact solution is parallel to the exactly solvable Kitaev honeycomb model for S=1/2 quantum spins and can be viewed as a generalization of Kitaev's construction to S=1/2 interacting lattice fermions. The BCS-Hubbard model discussed in this Letter is just an example of a large class of exactly solvable lattice fermion models that can be constructed similarly.
ABSTRACT
We extend the idea of quantum phase transitions of light in the photonic Bose-Hubbard model with interactions to two atomic species by a self-consistent mean field theory. The excitation of two-level atoms interacting with a coherent photon field is analyzed with a finite temperature dependence of the order parameters. Four ground states of the system are found, including an isolated Mott-insulator phase and three different superfluid phases. Like two weakly coupled superconductors, our proposed dual-species lattice system shows a photonic analogue of Josephson effect. i.e., the crossovers between two superfluid states. The dynamics of the proposed two species model provides a promising quantum simulator for possible quantum information processes.
ABSTRACT
We report an optical and atomic force microscopic (AFM) study of interactions between weakly charged silica spheres at a water-air interface. Attractive interactions are observed at intermediate interparticle distances and the amplitude of the attraction increases with the amount of salt (NaCl) added into the water phase. AFM images obtained in the salty water show the formation of patchy charge domains of size approximately 100 nm on the silica surface. The experiment suggests that surface heterogeneity produced during ionization plays an important role in the generation of attractions between like-charged particles at the interface.
ABSTRACT
The electronic contribution to thermal conductivity is studied in models of underdoped cuprates where the normal state has a pocketed Fermi surface with circumference â¼x (hole concentration) and the superconducting state is formed by opening a gap in the Fermi pocket. The physical consequences of the Fermi pocket are studied by comparing the thermal conductivity computed in four different models: (1) an ordinary d-wave superconductor with four Dirac Fermi points; (2) a normal metal with a pocketed Fermi surface; (3) a superconductor formed by spinon-holon binding in the t-J model; (4) a phenomenological d-wave Bardeen-Cooper-Schrieffer (BCS) superconductor with superconductivity formed by opening a gap on the pocketed Fermi surface. Our results suggest that thermal conductivity provides useful information to distinguish between different scenarios of the normal-to-superconducting transition in underdoped cuprates.
ABSTRACT
In this Letter, we study the effect of nonmagnetic impurities on two-band superconductors by deriving the corresponding Ginzburg-Landau equation. Depending on the strength of (impurity-induced) interband scattering, we find that there are two distinctive regions where the superconductors behave very differently. In the strong impurity-induced interband scattering regime T(c) << tau(t)(-1), where tau(t) approximately mean lifetime an electron stays in one band, the two-band superconductor behaves as an effective one-band dirty superconductor. In the other limit T(c) > or = tau(t)(-1), the dirty two-band superconductor is described by a network of frustrated two-band superconductor grains connected by Josephson tunneling junctions, and the Anderson theorem breaks down.
ABSTRACT
Spin liquid states for the spin-1/2 antiferromagnetic Heisenberg model on a hyperkagome lattice are studied. We classify and study flux states according to symmetries. Applying this model to Na4Ir3O8, we propose that the high temperature state may be described by a spinon Fermi surface, which forms a paired state with line nodes below 20 K. The possible mixed spin singlet and spin triplet pairing states are discussed according to the lattice symmetry which breaks inversion.
ABSTRACT
The charge dynamics of spin-liquid states described by U(1) gauge theory coupling to fermionic spinons is discussed in this paper. We find that the gapless spinons give rise to a power-law optical conductivity inside the charge gap. The theory is applied to explain the unusual optical conductivity observed recently in the organic compound kappa-(BEDT-TTF)2Cu2(CN){3}. We also propose an optical experiment to search for the in-gap excitations in the kagome spin-liquid insulator.
ABSTRACT
Because of the absence of a center of inversion in some superconducting compounds, a p-wave admixture to the dominant d-wave (or s) order parameter must exist. If time reversal is also violated, an allowed invariant is the product of the d wave (or s wave), p wave, and an appropriately directed current. We show that this leads to a new and remarkable property of the Josephson current for tunneling into a s-wave superconductor along the direction parallel to the axis of the p-wave component. These ideas are applied to the heavy-fermion compounds which lack center of inversion due to crystalline symmetry, as well as time-reversal symmetry, such as CePt(3)Si. They also apply to the superconducting state of the cuprates in the pseudogap region of the phase diagram where in the normal phase some experiments have detected a time-reversal and inversion symmetry broken phase.
ABSTRACT
We report results of a systematic experimental study of interactions between charged polystyrene (PS) latex spheres at a water-air interface. Optical observations of stable bonded particle clusters and formation of circular chainlike structures at the interface demonstrate that the interaction potential is of dipole origin. Atomic force microscopy (AFM) is used to examine the distribution of charge groups on the colloidal surface. AFM phase images show patchy domains of size approximately 100 nm on the particle surface, indicating that the surface charge distribution of the PS spheres is not uniform, as is commonly believed. Such patchy charges can introduce fluctuating in-plane dipoles, leading to an attraction at short interparticle separations. A theoretical analysis is given to explain the mechanism for attractions between like-charged particles at the interface.
ABSTRACT
We report an optical and atomic force microscopic study of interactions between charged polystyrene spheres at a water-air interface. Optical observations of bonded particle clusters and formation of circular chainlike structures at the interface demonstrate that the interaction potential is of dipole origin. Atomic force microscope phase images show patchy domains on the colloidal surface, indicating that the surface charge distribution is not uniform as is commonly believed. Such surface heterogeneity introduces in-plane dipoles, leading to an attraction at short interparticle distances.
