51,750 research outputs found
Numerical Study of Universal Conductance Fluctuation in Three-dimensional Topological Semimetals
We study the conductance fluctuation in topological semimetals. Through
statistic distribution of energy levels of topological semimetals, we determine
the dominant parameters of universal conductance fluctuation (UCF), i.e., the
number of uncorrelated bands , the level degeneracy , and the symmetry
parameter . These parameters allow us to predict the zero-temperature
intrinsic UCF of topological semimetals by the Altshuler-Lee-Stone theory.
Then, we obtain numerically the conductance fluctuations for topological
semimetals of quasi-1D geometry. We find that for Dirac/Weyl semimetals, the
theoretical prediction coincides with the numerical results. However, a
non-universal conductance fluctuation behavior is found for topological nodal
line semimetals, i.e., the conductance fluctuation amplitude increases with the
enlargement of SOC strength. We find that such unexpected parameter-dependent
phenomena of conductance fluctuation are related to Fermi surface shape of 3D
topological semimetals. These results will help us to understand the existing
and future experimental results of UCF in 3D topological semimetals.Comment: 9 pages, 8 figure
Coherent population trapping in a dressed two-level atom via a bichromatic field
We show theoretically that by applying a bichromatic electromagnetic field,
the dressed states of a monochromatically driven two-level atom can be pumped
into a coherent superposition termed as dressed-state coherent population
trapping. Such effect can be viewed as a new doorknob to manipulate a two-level
system via its control over dressed-state populations. Application of this
effect in the precision measurement of Rabi frequency, the unexpected
population inversion and lasing without inversion are discussed to demonstrate
such controllability.Comment: 14 pages, 6 figure
Instabilities at [110] Surfaces of d_{x^2-y^2} Superconductors
We compare different scenarios for the low temperature splitting of the
zero-energy peak in the local density of states at (110) surfaces of
d_{x^2-y^2}-wave superconductors, observed by Covington et al.
(Phys.Rev.Lett.79 (1997), 277). Using a tight binding model in the
Bogolyubov-de Gennes treatment we find a surface phase transition towards a
time-reversal symmetry breaking surface state carrying spontaneous currents and
an s+id-wave state. Alternatively, we show that electron correlation leads to a
surface phase transition towards a magnetic state corresponding to a local spin
density wave state.Comment: 4 pages, 5 figure
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