14,652 research outputs found

### Reconstruction of potential energy profiles from multiple rupture time distributions

We explore the mathematical and numerical aspects of reconstructing a
potential energy profile of a molecular bond from its rupture time
distribution. While reliable reconstruction of gross attributes, such as the
height and the width of an energy barrier, can be easily extracted from a
single first passage time (FPT) distribution, the reconstruction of finer
structure is ill-conditioned. More careful analysis shows the existence of
optimal bond potential amplitudes (represented by an effective Peclet number)
and initial bond configurations that yield the most efficient numerical
reconstruction of simple potentials. Furthermore, we show that reconstruction
of more complex potentials containing multiple minima can be achieved by
simultaneously using two or more measured FPT distributions, obtained under
different physical conditions. For example, by changing the effective potential
energy surface by known amounts, additional measured FPT distributions improve
the reconstruction. We demonstrate the possibility of reconstructing potentials
with multiple minima, motivate heuristic rules-of-thumb for optimizing the
reconstruction, and discuss further applications and extensions.Comment: 20 pages, 9 figure

### Reaching optimally oriented molecular states by laser kicks

We present a strategy for post-pulse orientation aiming both at efficiency
and maximal duration within a rotational period. We first identify the
optimally oriented states which fulfill both requirements. We show that a
sequence of half-cycle pulses of moderate intensity can be devised for reaching
these target states.Comment: 4 pages, 3 figure

### Evidence for competition between the superconducting and the pseudogap state in (BiPb)_2(SrLa)_2CuO_{6+\delta} from muon-spin rotation experiments

The in-plane magnetic penetration depth \lambda_{ab} in optimally doped
(BiPb)_2(SrLa)_2CuO_{6+\delta} (OP Bi2201) was studied by means of muon-spin
rotation. The measurements of \lambda_{ab}^{-2}(T) are inconsistent with a
simple model of a d-wave order parameter and a uniform quasiparticle weight
around the Fermi surface. The data are well described assuming the angular gap
symmetry obtained in ARPES experiments [Phys. Rev. Lett {\bf 98}, 267004
(2007)], where it was shown that the superconducting gap in OP Bi2201 exists
only in segments of the Fermi surface near the nodes. We find that the
remaining parts of the Fermi surface, which are strongly affected by the
pseudogap state, do not contribute significantly to the superconducting
condensate. Our data provide evidence that high temperature superconductivity
and pseudogap behavior in cuprates are competing phenomena.Comment: 5 pages, 3 figure

### A Generalization of Mathieu Subspaces to Modules of Associative Algebras

We first propose a generalization of the notion of Mathieu subspaces of
associative algebras $\mathcal A$, which was introduced recently in [Z4] and
[Z6], to $\mathcal A$-modules $\mathcal M$. The newly introduced notion in a
certain sense also generalizes the notion of submodules. Related with this new
notion, we also introduce the sets $\sigma(N)$ and $\tau(N)$ of stable elements
and quasi-stable elements, respectively, for all $R$-subspaces $N$ of $\mathcal
A$-modules $\mathcal M$, where $R$ is the base ring of $\mathcal A$. We then
prove some general properties of the sets $\sigma(N)$ and $\tau(N)$.
Furthermore, examples from certain modules of the quasi-stable algebras [Z6],
matrix algebras over fields and polynomial algebras are also studied.Comment: A new case has been added; some mistakes and misprints have been
corrected. Latex, 31 page

### Observation of plaquette fluctuations in the spin-1/2 honeycomb lattice

Quantum spin liquids are materials that feature quantum entangled spin
correlations and avoid magnetic long-range order at T = 0 K. Particularly
interesting are two-dimensional honeycomb spin lattices where a plethora of
exotic quantum spin liquids have been predicted. Here, we experimentally study
an effective S=1/2 Heisenberg honeycomb lattice with competing nearest and
next-nearest neighbor interactions. We demonstrate that YbBr$_3$ avoids order
down to at least T=100 mK and features a dynamic spin-spin correlation function
with broad continuum scattering typical of quantum spin liquids near a quantum
critical point. The continuum in the spin spectrum is consistent with plaquette
type fluctuations predicted by theory. Our study is the experimental
demonstration that strong quantum fluctuations can exist on the honeycomb
lattice even in the absence of Kitaev-type interactions, and opens a new
perspective on quantum spin liquids.Comment: 32 pages, 7 Figure

### Laser control for the optimal evolution of pure quantum states

Starting from an initial pure quantum state, we present a strategy for
reaching a target state corresponding to the extremum (maximum or minimum) of a
given observable. We show that a sequence of pulses of moderate intensity,
applied at times when the average of the observable reaches its local or global
extremum, constitutes a strategy transferable to different control issues.
Among them, post-pulse molecular alignment and orientation are presented as
examples. The robustness of such strategies with respect to experimentally
relevant parameters is also examined.Comment: 16 pages, 9 figure

### Incommensurate Magnetic Order in TbTe$_3$

We report a neutron diffraction study of the magnetic phase transitions in
the charge-density-wave (CDW) TbTe$_3$ compound. We discover that in the
paramagnetic phase there are strong 2D-like magnetic correlations, consistent
with the pronounced anisotropy of the chemical structure. A long-range
incommensurate magnetic order emerges in TbTe$_3$ at $T_{mag1}$ = 5.78 K as a
result of continuous phase transitions. We observe that near the temperature
$T_{mag1}$ the magnetic Bragg peaks appear around the position (0,0,0.24) (or
its rational multiples), that is fairly close to the propagation vector
$(0,0,0.29)$ associated with the CDW phase transition in TbTe$_3$. This
suggests that correlations leading to the long-range magnetic order in TbTe$_3$
are linked to the modulations that occur in the CDW state

### Continuity of the four-point function of massive $\phi_4^4$-theory above threshold

In this paper we prove that the four-point function of massive
\vp_4^4-theory is continuous as a function of its independent external
momenta when posing the renormalization condition for the (physical) mass
on-shell. The proof is based on integral representations derived inductively
from the perturbative flow equations of the renormalization group. It closes a
longstanding loophole in rigorous renormalization theory in so far as it shows
the feasibility of a physical definition of the renormalized coupling.Comment: 23 pages; to appear in Rev. Math. Physics few corrections, two
explanatory paragraphs adde

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