13,177 research outputs found
Plaquette order and deconfined quantum critical point in the spin-1 bilinear-biquadratic Heisenberg model on the honeycomb lattice
We have precisely determined the ground state phase diagram of the quantum
spin-1 bilinear-biquadratic Heisenberg model on the honeycomb lattice using the
tensor renormalization group method. We find that the ferromagnetic,
ferroquadrupolar, and a large part of the antiferromagnetic phases are stable
against quantum fluctuations. However, around the phase where the ground state
is antiferroquadrupolar ordered in the classical limit, quantum fluctuations
suppress completely all magnetic orders, leading to a plaquette order phase
which breaks the lattice symmetry but preserves the spin SU(2) symmetry. On the
evidence of our numerical results, the quantum phase transition between the
antiferromagnetic phase and the plaquette phase is found to be either a direct
second order or a very weak first order transition.Comment: 6 pages, 9 figures, published versio
Coherent laser control of the current through molecular junctions
The electron tunneling through a molecular junction modeled by a single site
weakly coupled to two leads is studied in the presence of a time-dependent
external field using a master equation approach. In the case of small bias
voltages and high carrier frequencies of the external field, we observe the
phenomenon of coherent destruction of tunneling, i.e. the current through the
molecular junction vanishes completely for certain parameters of the external
field. In previous studies the tunneling within isolated and open multi-site
systems was suppressed; it is shown here that the tunneling between a single
site and electronic reservoirs, i.e. the leads, can be suppressed as well. For
larger bias voltages the current does not vanish any more since further
tunneling channels participate in the electron conduction and we also observe
photon-assisted tunneling which leads to steps in the current-voltage
characteristics. The described phenomena are demonstrated not only for
monochromatic fields but also for laser pulses and therefore could be used for
ultrafast optical switching of the current through molecular junctions.Comment: 6 pages and 4 figure
Improved lattice QCD with quarks: the 2 dimensional case
QCD in two dimensions is investigated using the improved fermionic lattice
Hamiltonian proposed by Luo, Chen, Xu, and Jiang. We show that the improved
theory leads to a significant reduction of the finite lattice spacing errors.
The quark condensate and the mass of lightest quark and anti-quark bound state
in the strong coupling phase (different from t'Hooft phase) are computed. We
find agreement between our results and the analytical ones in the continuum.Comment: LaTeX file (including text + 10 figures
Two Kinds of Iterative Solutions for Generalized Sombrero-shaped Potential in -dimensional Space
Based on two different iteration procedures the groundstate wave functions
and energies for N-dimensional generalized Sombrero-shaped potentials are
solved. Two kinds of trial functions for the iteration procedure are defined.
The iterative solutions are convergent nicely to consistent results for
different choices of iteration procedures and trial functions.Comment: 16 pages, 3 figure
Deeply buried ancient volcanoes control hydrocarbon migration in the South China Sea
Seismic reflection data image nowâburied and inactive volcanoes, both onshore and along the submarine portions of continental margins. However, the impact that these volcanoes have on later, postâeruption fluid flow events (e.g., hydrocarbon migration and accumulation) is poorly understood. Determining how buried volcanoes and their underlying plumbing systems influence subsurface fluid or gas flow, or form traps for hydrocarbon accumulations, is critical to deârisk hydrocarbon exploration and production. Here, we focus on evaluating how buried volcanoes affect the bulk permeability of hydrocarbon seals, and channel and focus hydrocarbons. We use highâresolution 3D seismic reflection and borehole data from the northern South China Sea to show how ca. <10 km wide, ca. <590 m high Miocene volcanoes, buried several kilometres (ca. 1.9 km) below the seabed and fed by a subâvolcanic plumbing system that exploited riftârelated faults: (i) acted as longâlived migration pathways, and perhaps reservoirs, for hydrocarbons generated from even more deeply buried (ca. 8â10 km) source rocks; and (ii) instigated differential compaction and doming of the overburden during subsequent burial, producing extensional faults that breached regional seal rocks. Considering that volcanism and related deformation are both common on many magmaârich passive margins, the interplay between the magmatic products and hydrocarbon migration documented here may be more common than currently thought. Our results demonstrate that nowâburied and inactive volcanoes can locally degrade hydrocarbon reservoir seals and control the migration of hydrocarbonârich fluids and gas. These fluids and gases can migrate into and be stored in shallower reservoirs, where they may then represent geohazards to drilling and impact slope stability
- âŠ