393 research outputs found
Ballistic charge transport in chiral-symmetric few-layer graphene
A transfer matrix approach to study ballistic charge transport in few-layer
graphene with chiral-symmetric stacking configurations is developed. We
demonstrate that the chiral symmetry justifies a non-Abelian gauge
transformation at the spectral degeneracy point (zero energy). This
transformation proves the equivalence of zero-energy transport properties of
the multilayer to those of the system of uncoupled monolayers. Similar
transformation can be applied in order to gauge away an arbitrary magnetic
field, weak strain, and hopping disorder in the bulk of the sample. Finally, we
calculate the full-counting statistics at arbitrary energy for different
stacking configurations. The predicted gate-voltage dependence of conductance
and noise can be measured in clean multilayer samples with generic metallic
leads.Comment: 6 pages, 5 figures; EPL published versio
Electron transport in disordered graphene
We study electron transport properties of a monoatomic graphite layer
(graphene) with different types of disorder. We show that the transport
properties of the system depend strongly on the character of disorder. Away
from half filling, the concentration dependence of conductivity is linear in
the case of strong scatterers, in line with recent experimental observations,
and logarithmic for weak scatterers. At half filling the conductivity is of the
order of e^2/h if the randomness preserves one of the chiral symmetries of the
clean Hamiltonian; otherwise, the conductivity is strongly affected by
localization effects.Comment: 21 pages, 9 figure
Ballistic transport in disordered graphene
An analytic theory of electron transport in disordered graphene in a
ballistic geometry is developed. We consider a sample of a large width W and
analyze the evolution of the conductance, the shot noise, and the full
statistics of the charge transfer with increasing length L, both at the Dirac
point and at a finite gate voltage. The transfer matrix approach combined with
the disorder perturbation theory and the renormalization group is used. We also
discuss the crossover to the diffusive regime and construct a ``phase diagram''
of various transport regimes in graphene.Comment: 23 pages, 10 figure
Resonant-state expansion of the Green's function of open quantum systems
Our series of recent work on the transmission coefficient of open quantum
systems in one dimension will be reviewed. The transmission coefficient is
equivalent to the conductance of a quantum dot connected to leads of quantum
wires. We will show that the transmission coefficient is given by a sum over
all discrete eigenstates without a background integral. An apparent
"background" is in fact not a background but generated by tails of various
resonance peaks. By using the expression, we will show that the Fano asymmetry
of a resonance peak is caused by the interference between various discrete
eigenstates. In particular, an unstable resonance can strongly skew the peak of
a nearby resonance.Comment: 7 pages, 7 figures. Submitted to International Journal of Theoretical
Physics as an article in the Proceedings for PHHQP 2010
(http://www.math.zju.edu.cn/wjd/
Optimization of Generalized Multichannel Quantum Defect reference functions for Feshbach resonance characterization
This work stresses the importance of the choice of the set of reference
functions in the Generalized Multichannel Quantum Defect Theory to analyze the
location and the width of Feshbach resonance occurring in collisional
cross-sections. This is illustrated on the photoassociation of cold rubidium
atom pairs, which is also modeled using the Mapped Fourier Grid Hamiltonian
method combined with an optical potential. The specificity of the present
example lies in a high density of quasi-bound states (closed channel)
interacting with a dissociation continuum (open channel). We demonstrate that
the optimization of the reference functions leads to quantum defects with a
weak energy dependence across the relevant energy threshold. The main result of
our paper is that the agreement between the both theoretical approaches is
achieved only if optimized reference functions are used.Comment: submitte to Journal of Physics
Subcritical multiplicative chaos for regularized counting statistics from random matrix theory
For an N×N random unitary matrix U_N, we consider the random field defined by counting the number of eigenvalues of U_N in a mesoscopic arc of the unit circle, regularized at an N-dependent scale Ɛ_N>0. We prove that the renormalized exponential of this field converges as N → ∞ to a Gaussian multiplicative chaos measure in the whole subcritical phase. In addition, we show that the moments of the total mass converge to a Selberg-like integral and by taking a further limit as the size of the arc diverges, we establish part of the conjectures in [55]. By an analogous construction, we prove that the multiplicative chaos measure coming from the sine process has the same distribution, which strongly suggests that this limiting object should be universal. The proofs are based on the asymptotic analysis of certain Toeplitz or Fredholm determinants using the Borodin-Okounkov formula or a Riemann-Hilbert problem for integrable operators. Our approach to the L¹-phase is based on a generalization of the construction in Berestycki [5] to random fields which are only asymptotically Gaussian. In particular, our method could have applications to other random fields coming from either random matrix theory or a different context
The differential-algebraic and bi-Hamiltonian integrability analysis of the Riemann type hierarchy revisited
A differential-algebraic approach to studying the Lax type integrability of
the generalized Riemann type hydrodynamic hierarchy is revisited, its new Lax
type representation and Poisson structures constructed in exact form. The
related bi-Hamiltonian integrability and compatible Poissonian structures of
the generalized Riemann type hierarchy are also discussed.Comment: 18 page
From the Mendeleev periodic table to particle physics and back to the periodic table
We briefly describe in this paper the passage from Mendeleev's chemistry
(1869) to atomic physics (in the 1900's), nuclear physics (in the 1932's) and
particle physics (from 1953 to 2006). We show how the consideration of
symmetries, largely used in physics since the end of the 1920's, gave rise to a
new format of the periodic table in the 1970's. More specifically, this paper
is concerned with the application of the group SO(4,2)xSU(2) to the periodic
table of chemical elements. It is shown how the Madelung rule of the atomic
shell model can be used for setting up a periodic table that can be further
rationalized via the group SO(4,2)xSU(2) and some of its subgroups. Qualitative
results are obtained from this nonstandard table.Comment: 15 pages; accepted for publication in Foundations of Chemistry
(special issue to commemorate the one hundredth anniversary of the death of
Mendeleev who died in 1907); version 2: 16 pages; some sentences added;
acknowledgment and references added; misprints correcte
Round-Optimal Secure Two-Party Computation from Trapdoor Permutations
In this work we continue the study on the round complexity of secure two-party computation with black-box simulation. Katz and Ostrovsky in CRYPTO 2004 showed a 5 (optimal) round construction assuming trapdoor permutations for the general case where both players receive the output. They also proved that their result is round optimal. This lower bound has been recently revisited by Garg et al. in Eurocrypt 2016 where a 4 (optimal) round protocol is showed assuming a simultaneous message exchange channel. Unfortunately there is no instantiation of the protocol of Garg et al. under standard polynomial-time hardness assumptions. In this work we close the above gap by showing a 4 (optimal) round construction for secure two-party computation in the simultaneous message channel model with black-box simulation, assuming trapdoor permutations against polynomial-time adversaries. Our construction for secure two-party computation relies on a special 4-round protocol for oblivious transfer that nicely composes with other protocols in parallel. We define and construct such special oblivious transfer protocol from trapdoor permutations. This building block is clearly interesting on its own. Our construction also makes use of a recent advance on non-malleability: a delayed-input 4-round non-malleable zero knowledge argument
Prompt Quark Production by exploding Sphalerons
Following recent works on production and subsequent explosive decay of QCD
sphaleron-like clusters, we discuss the mechanism of quark pair production in
this process. We first show how the gauge field explosive solution of Luscher
and Schechter can be achieved by non-central conformal mapping from the
O(4)-symmetric solution. Our main result is a new solution to the Dirac
equation in real time in this configuration, obtained by the same inversion of
the fermion O(4) zero mode. It explicitly shows how the quark acceleration
occurs, starting from the spherically O(3) symmetric zero energy chiral quark
state to the final spectrum of non-zero energies.
The sphaleron-like clusters with any Chern-Simons number always produce quarks, and the antisphaleron-like clusters the
chirality opposite.
The result are relevant for hadron-hadron and nucleus-nucleus collisions at
large , wherein such clusters can be produced
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