4,988 research outputs found
Lattice field theory simulations of Dirac semimetals
In this paper the observed Dirac semimetals NaBi and CdAs are
studied within lattice simulation. We formulate lattice field theory with
rooted staggered fermions on anisotropic lattice. It is shown that in the limit
of zero temporal lattice spacing this theory reproduces low energy effective
theory of Dirac semimetals. Using this lattice theory we study the phase
diagram of Dirac semimetals in the plane effective coupling constant--Fermi
velocity anisotropy. Within the formulated theory the results are practically
volume independent in contrast with our previous study. Our results confirm our
previous finding that within the Dirac model with bare Coulomb interaction both
NaBi and CdAs lie deep in the insulator phase.Comment: 11 pages, 5 figures, 2 tables, typo in Eq. (20) corrected, Appendix
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Theory of incommensurate magnetic correlations across the insulator-superconductor transition in underdoped La_{2-x}Sr_xCuO_4
The main feature in the elastic neutron scattering of La_{2-x}Sr_xCuO_4 is
the existence of incommensurate peaks with positions that jump from 45 to 0
degrees at 5% doping. We show that the spiral state of the t-t'-t''-J model
with realistic parameters describes this data perfectly. We explain why in the
insulator the peak is at 45 degrees while it switches to 0 degrees precisely at
the insulator-metal transition. The calculated positions of the peaks are in
agreement with the data in both phases.Comment: 5 pages, 1 figure; minor change
Catalysis of Dynamical Chiral Symmetry Breaking by Chiral Chemical Potential in Dirac semimetals
In this paper we study how dynamical chiral symmetry breaking is affected by
nonzero chiral chemical potential in Dirac semimetals. To perform this study we
applied lattice quantum Monte Carlo simulations of Dirac semimetals. Within
lattice simulation we calculated the chiral condensate for various fermion
masses, the chiral chemical potentials and effective coupling constants. For
all parameters under consideration we have found that the chiral condensate is
enhanced by chiral chemical potential. Thus our results confirms that in Dirac
semimetals the chiral chemical potential plays a role of the catalyst of the
dynamical chiral symmetry breaking.Comment: 11 pages, 3 figure
Lattice Quantum Monte Carlo Study of Chiral Magnetic Effect in Dirac Semimetals
In this paper Chiral Magnetic Effect (CME) in Dirac semimetals is studied by
means of lattice Monte Carlo simulation. We measure conductivity of Dirac
semimetals as a function of external magnetic field in parallel
and perpendicular to the external field
directions. The simulations are carried out in three regimes: semimetal phase,
onset of the insulator phase and deep in the insulator phase. In the semimetal
phase grows whereas drops with magnetic
field. Similar behaviour was observed in the onset of the insulator phase but
conductivity is smaller and its dependence on magnetic field is weaker. Finally
in the insulator phase conductivities are close to
zero and do not depend on magnetic field. In other words, we observe
manifestation of the CME current in the semimetal phase, weaker manifestation
of the CME in the onset of the insulator phase. We do not observe signatures of
CME in the insulator phase. We believe that the suppression of the CME current
in the insulator phase is connected to chiral symmetry breaking and generation
of dynamical fermion mass which take place in this phase.Comment: 6 pages, 4 figure
Screening of Coulomb Impurities in Graphene
We calculate exactly the vacuum polarization charge density in the field of a
subcritical Coulomb impurity, , in graphene. Our analysis is based on
the exact electron Green's function, obtained by using the operator method, and
leads to results that are exact in the parameter , where is
the "fine structure constant" of graphene. Taking into account also
electron-electron interactions in the Hartree approximation, we solve the
problem self-consistently in the subcritical regime, where the impurity has an
effective charge , determined by the localized induced charge. We find
that an impurity with bare charge Z=1 remains subcritical, , for any , while impurities with and higher can become
supercritical at certain values of .Comment: 4 pages, 2 figure
AC Hopping Magnetotransport Across the Spin Flop Transition in Lightly Doped La_2CuO_4
The weak ferromagnetism present in insulating La_{2}CuO_4 at low doping leads
to a spin flop transition, and to transverse (interplane) hopping of holes in a
strong external magnetic field. This results in a dimensional crossover 2D
3D for the in-plane transport, which in turn leads to an increase of the
hole's localization length and increased conduction. We demonstrate
theoretically that as a consequence of this mechanism, a frequency-dependent
jump of the in-plane ac hopping conductivity occurs at the spin flop
transition. We predict the value and the frequency dependence of the jump.
Experimental studies of this effect would provide important confirmation of the
emerging understanding of lightly doped insulating La_{2-x}Sr_xCuO_4.Comment: 4 pages, 1 figur
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