By introducing the possibility of equal- and opposite-spin pairings concurrently, we show that the extended attractive Hubbard model (EAHM) exhibits rich ground state phase diagrams with a variety of singlet, triplet, and mixed parity superconducting
orders. We study the competition between these superconducting pairing symmetries invoking an unrestricted Hartree-Fock- Bogoliubov-de Gennes (HFBdG) mean-field approach, and we use the d-vector formalism to characterize the nature of the stabilized superconducting orders. We discover that, while all other types of orders are suppressed, a non-unitary triplet order dominates the phase space in the presence of an in-plane external magnetic field. We also find a transition between a non-unitary to unitary superconducting phase driven by the change in average electron density. Our results serve as a reference for identifying and understanding the nature of superconductivity based on the symmetries of the pairing correlations. The results further highlight that EAHM is a suitable effective model for describing most of the pairing symmetries discovered in different materials.
Light is known to exert a pushing force through the radiation pressure on any surface it is incident upon, via the transfer of momentum from the light to the surface. For an atom, the interaction with light can lead to both absorption as well as emis
sion of photons, leading to repulsive and attractive forces, respectively. For classical light, these two processes occur at the same rates. Therefore, a thermal ensemble of atoms at a finite temperature always experiences a net pushing force. In this paper, we show that when treated quantum mechanically the pulsed electromagnetic field interacting with the thermal ensemble of atoms leads to unequal transition rates, again resulting in a non-zero net force. However, the signature and the magnitude of the force depends upon the intensity of the light, the number of atoms, and the initial temperature of the ensemble. Thus, even at finite temperature, controlling the parameters of the electromagnetic pulse and the number of particles in the ensemble, the net force can be changed from repulsive to attractive, generating negative radiation pressure in the process. Quite counterintuitively, this negative radiation pressure arising out of pure quantum character of light gets stronger for higher temperatures.
Topological insulators are a new class of materials that have attracted significant attention in contemporary condensed matter physics. They are different from the regular insulators and they display novel quantum properties that also involve the ide
a of `topology, an area of mathematics. Some of the fundamental ideas behind the topological insulators, particularly in low-dimensional condensed matter systems such as poly-acetylene chains, can be understood using a simple one-dimensional toy model popularly known as the Su-Schrieffer-Heeger model or the SSH model. This model can also be used as an introduction to the topological insulators of higher dimensions. Here we give a concise description of the SSH model along with a brief review of the background physics and attempt to understand the ideas of topological invariants, edge states, and bulk-boundary correspondence using the model.
Using a prototype model for proximity induced superconductivity on a bilayer square lattice, we show that interlayer tunneling can drive change in topology of the Bogoliubov quasiparticle bands. Starting with topologically trivial superconductors, tr
ansitions to a non-trivial $p_x + {rm i} p_y$ state and back to another trivial state are discovered. We characterize these phases in terms of edge-state spectra and Chern indices. We show that these transitions can also be controlled by experimentally viable control parameters, the bandwidth of the metallic layer and the gate potential. Insights from our results on a simple model for proximity induced superconductivity may open up a new route to discover topological superconductors.
