LDOS modulations in cuprate superconductors with competing AF order: the temperature effect

Based upon a phenomenological $t-t'-U-V$ model and using Bogoliubov-de Gennes equations, we found that near the optimal doping $\delta=0.15$ at low temperature ($T$), only the pure d-wave superconductivity (dSC) prevails and the antiferromagnetic (AF) order is completely suppressed. However, at higher $T$ the AF order with stripe modulation and the accompanying charge density wave (CDW) emerge, and they could exist even above the superconducting transition temperature. This implies that the existence of the CDW depends critically on the presence of the AF order, not so much on the dSC. The LDOS (local density of states) image indicates that the stripe modulation has an energy independent spacing of $5a/4a$ spreading over a $24a \times 48a$ lattice, corresponding to an average periodicity $4.8a$. This result may be relevant to the recent STM experiment [Vershinin $et al.$, Science {\bf 303}, 1995 (2004)]

Entropy evolution law in a laser process

For the first time, we obtain the entropy variation law in a laser process after finding the Kraus operator of the master equation describing the laser process with the use of the entangled state representation. The behavior of entropy is determined by the competition of the gain and damping in the laser process. The photon number evolution formula is also obtained

Local Density of States in a d-wave Superconductor with Stripe-Like Modulations and a Strong Impurity

Using an effective Hamiltonian with d-wave superconductivity (dSC) and competing antiferromagnetic (AF) interactions, we show that weak and one-dimensionally modulated dSC, spin density wave (SDW) and charge density wave (CDW) could coexist in the ground state configuration. With proper parameters, the SDW order exhibits a period of 8a, while for dSC and CDW orders the period is 4a. The local density of states (LDOS), which probing the behavior of quasiparticle excitations, is found to have the identical stripe-like structure as those in dSC and CDW orders. We point out that any energy dependent modulations should come from the scatterings of the quasiparticles from weak defects. The LDOS as a function of the bias voltage are showing two small bumps within the superconducting coherence peaks, a signature of presence of the stripes. When a strong impurity like Zn is placed in such a system, the LDOS at its nearest neighboring sites are suppressed at the zero bias by the local AF order and show a double-peak structure

Evolution of physical observables and entropy in laser process studied on the basis of Kraus-form solution of laser's master equation

Though laser physics began at 1960s, its entropy evolution has not been touched until very recently the Kraus-form solution of laser's master equation is reported (Ann. Phys. 334 (2013)). We study the new physics based on the discovery in this paper. We analyze time evolution of physical observables and quantum optical properties in the laser process with arbitrary initial states, such as the photon number, the second degree of coherence, etc. The evolution of entropy of these states is also studied. Our results well conform with the known behaviour of laser, which confirms that the master equation describes laser suitably, and the Kraus-form operator solution is correct, elegant and useful

Quantum mechanical perspectives and generalization of the fractional Fourier Transformation

Fourier and fractional-Fourier transformations are widely used in theoretical physics. In this paper we make quantum perspectives and generalization for the fractional Fourier transformation (FrFT). By virtue of quantum mechanical representation transformation and the method of integration within normal ordered product (IWOP) of operators, we find the key point for composing FrFT, and reveal the structure of FrFT. Following this procedure, a full family of generalized fractional transformations are discovered with the usual FrFT as one special case. The eigen-functions of arbitrary GFrT are derived explicitly

Connecting quantum contextuality and genuine multipartite nonlocality with the quantumness witness

The Clauser-Horne-Shimony-Holt-type noncontextuality inequality and the Svetlichny inequality are derived from the Alicki-Van Ryn quantumness witness. Thus a connection between quantumness and quantum contextuality, and that between quantumness and genuine multipartite nonlocality, are established.Comment: 4 pages. Accpeted in Chin. Phys. Let

Quantum backflow in solutions to the Dirac equation of the spin-1/21/2 free particle

It was known that a free, nonrelativistic particle in a superposition of positive momenta can, in certain cases, bear a negative probability current --- hence termed quantum backflow. Here, it is shown that more variations can be brought about for a free Dirac particle, particularly when negative-energy solutions are taken into account. Since any Dirac particle can be understood as an antiparticle that acts oppositely (and vice versa), quantum backflow is found to arise in the superposition (i) of a well-defined momentum but different signs of energies, or more remarkably (ii) of different signs of both momenta and energies. Neither of these cases has counterpart in nonrelativistic quantum mechanics. A generalization by using the field-theoretic formalism is also presented and discussed.Comment: 5 pages, 1 figur

Conditions for plasma evolution to the\ strong general Woltjer-Taylor state

We find that the proof in the recent paper\textsuperscript{\cite{14}} can not justify the authors' conclusion. We provide a real proof that any state will eventually evolves to the Woltjer-Taylor state exponentially. However, this kind of evolution is is mainly due to Joule heat, which also makes the magnetic field vanishes exponentially. Zero Woltjer-Taylor states are not physically attractive. Instead of examine $\Delta$, we introduce the quantity $\theta_{\nabla \times \vec{B},\vec{B}}$ and $R$ to examine if the plasma reaches to the strong (general) Woltjer-Taylor state, and then derive the condition for the evolution to the strong/general Woltjer-Taylor state

Simulating a two-dimensional frustrated spin system with fermionic resonating-valence-bond states

The frustrated Heisenberg $J_{1}-J_{2}$ model on a square lattice is numerically investigated by variational Monte Carlo simulations. We propose a antiferromagnetic fermion resonating-valence-bond (AF-fRVB) state that has ability to examine the entire phase diagram in the $J_{1}-J_{2}$ model. Two phase transition points, the second order around $J_{2}/J_{1}=0.45$ and the first order around $J_{2}/J_{1}=0.6$, can be extracted more clearly than the conventional bosonic RVB state. At the maximally frustrated point ($J_{2}/J_{1}=0.5$), the AF-fRVB state shows the variational ground-state energy in the thermodynamic limit very close to the one estimated by the projected entangled pair state at the largest bond dimension available. On the other hand, in the frustrated regime $0.4\lesssim J_{2}/J_{1}\leq0.5$, AF-fRVB states with $s_{+-}$ (using the terminology in the field of iron-based superconductors) and $d_{xy}$ pairing symmetries are degenerate in the thermodynamic limit, implying the existence of gapless Dirac excitations in the spinon spectrum.Comment: 5 pages, 4 figure

The Fock-Darwin States of Dirac Electrons in Graphene-based Artificial Atoms

We have investigated the Fock-Darwin states of the massless chiral fermions confined in a graphitic parabolic quantum dot. In the light of the Klein tunneling, we have analyzed the condition for confinement of the Dirac fermions in a cylindrically-symmetric potential. New features of the energy levels of the Dirac electrons as compared to the conventional electronic systems are dicussed. We have also evaluated the dipole-allowed transitions in the energy levels of the dots. We propose that in the high magnetic field limit, the band parameters can be accurately determined from the dipole-allowed transitions.Comment: 4 pages and 3 figure