14,749 research outputs found
Scaling test of fermion actions in the Schwinger model
We discuss the scaling behaviour of different fermion actions in dynamical
simulations of the 2-dimensional massive Schwinger model. We have chosen
Wilson, hypercube, twisted mass and overlap fermion actions. As physical
observables, the pion mass and the scalar condensate are computed for the above
mentioned actions at a number of coupling values and fermion masses. We also
discuss possibilities to simulate overlap fermions dynamically avoiding
problems with low-lying eigenvalues of the overlap kernel
Time-reversal symmetry breaking and gapped surface states due to spontaneous emergence of new order in -wave nanoislands
We solve the Bogoliubov-de Gennes equations self-consistently for the
-wave order parameter in nanoscale -wave systems with [110] surfaces and
show that spontaneous time-reversal symmetry (TRS) breaking occurs at low
temperatures due to a spontaneously induced complex order parameter of extended
-wave symmetry. The Andreev surface bound states, which are protected by a
one-dimensional (1D) topological invariant in the presence of TRS, are gapped
by the emergence of this new order parameter. The extended -wave order
parameter is localized within a narrow region near the surfaces, which is
consistent with the fact that topological protection of the gapless Andreev
surface states is characterized by the 1D topological invariant. In this
TRS-breaking phase, not only is the complex order parameter induced, but also
the -wave order parameter itself becomes complex. Furthermore, the
disappearance of topological protection brings about novel vortex phenomena
near the surfaces. We show that vortex-antivortex pairs are formed in the
extended -wave order parameter along the surfaces if the side length of a
nanoisland or the width of an infinitely long nanoribbon is relatively large.Comment: 6 pages, 4 figures + 6 pages (supplemental material), to be published
in Phys. Rev. B Rapid communicatio
Inhomogeneous Ferromagnetism and Unconventional Charge Dynamics in Disordered Double Exchange Magnets
We solve the double exchange model in the presence of arbitrary
substitutional disorder by using a self consistently generated effective
Hamiltonian for the spin degrees of freedom. The magnetic properties are
studied through classical Monte Carlo while the effective exchange, ,
are calculated by solving the disordered fermion problem, and renormalised
self-consistently with increasing temperature. We present exact results on the
conductivity, magnetoresistance, optical response and `real space' structure of
the inhomogeneous ferromagnetic state, and compare our results with charge
dynamics in disordered La_{1-x}Sr_xMnO_3. The large sizes, ,
accessible within our method allows a complete, controlled calculation on the
disordered strongly interacting problem.Comment: 4 pages, 2 column revtex, 5 embedded figure
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