17,449 research outputs found
Interacting topological phases in multiband nanowires
We show that semiconductor nanowires coupled to an s-wave superconductor
provide a playground to study effects of interactions between different
topological superconducting phases supporting Majorana zero-energy modes. We
consider quasi-one dimensional system where the topological phases emerge from
different transverse subbands in the nanowire. In a certain parameter space, we
show that there is a multicritical point in the phase diagram where the
low-energy theory is equivalent to the one describing two coupled Majorana
chains. We study effect of interactions as well as symmetry-breaking
perturbations on the topological phase diagram in the vicinity of this
multicritical point. Our results shed light on the stability of the topological
phase around the multicritical point and have important implications for the
experiments on Majorana nanowires.Comment: 8 pages, 2 figures; final version to appear in PR
The Matrix Product Approach to Quantum Spin Ladders
We present a manifestly rotational invariant formulation of the matrix
product method valid for spin chains and ladders. We apply it to 2 legged spin
ladders with spins 1/2, 1 and 3/2 and different magnetic structures labelled by
the exchange coupling constants, which can be ferromagnetic or
antiferromagnetic along the legs and the rungs of the ladder We compute ground
state energy densities, correlation lengths and string order parameters. We
present numerical evidence of the duality properties of the 3 different non
ferromagnetic spin 1/2 ladders. We show that the long range topological order
characteristic of isolated spin 1 chains is broken by the interchain coupling.
The string order correlation function decays exponentially with a finite
correlation length that we compute. A physical picture of the spin 1 ladder is
given in terms of a collection of resonating spin 1 chains. Finally for ladders
with spin equal or greater than 3/2 we define a class of AKLT states whose
matrix product coefficients are given by 9-j symbols.Comment: REVTEX file, 16 pages, 12 figures, 6 Table
Adsorption desorption processes on mesoscopic pores conected to microscopic pores of complex geometry using the Ising model
In this work we report studies of nitrogen adsorption and desorption onto
solid surfaces using computer simulations of the three dimensional Ising model,
for systems with complex porous structures at the mesoscopic and microscopic
levels. A hysteresis cycle between the adsorption and desorption processes
appears and we find that its characteristics are dependent on the geometry of
the pore and on the strength of the surface fluid interaction. We obtained also
an average adsorption isotherm, which represents a combination of differently
shaped pores, and shows robust jumps at certain values of the chemical
potential as a consequence of the structures of the pores. Lastly, we compare
our results with experimental data and also report the filling process of
microscopic pores connected with mesopores. It is argued that these predictions
are useful for researchers working on the enhanced recovery of oil and for the
design of new nanomaterials, among others
Managerial Organization of U.S. Farms: Importance for Classifying Farms and Evaluating the Distribution of Farm Payments
A new typology of U.S. farms is constructed focusing on the managerial organization of farms. Single operator farms are distinguished from those with multiple operators which are divided into four classes: (single generation farms with 1) operators of the same sex, 2) operators of opposite sex, and multiple generation farms with 3) an elder primary operator, and 4) an younger primary operator). The utility of this classification scheme for understanding farm structure is analyzed and findings show that the managerial organization represents an important classification for understanding the distribution of farm payments.Farm Household, Government Policy, Agricultural and Food Policy,
The many levels pairing Hamiltonian for two pairs
We address the problem of two pairs of fermions living on an arbitrary number
of single particle levels of a potential well (mean field) and interacting
through a pairing force. The associated solutions of the Richardson's equations
are classified in terms of a number , which reduces to the seniority
in the limit of large values of the pairing strength and yields the number
of pairs not developing a collective behaviour, their energy remaining finite
in the limit. We express analytically, through the moments of the
single particle levels distribution, the collective mode energy and the two
critical values and of the coupling which can
exist on a single particle level with no pair degeneracy. Notably and merge when the number of single particle levels
goes to infinity, where they coincide with the (when it exists) of
a one pair system, not envisioned by the Richardson theory. In correspondence
of the system undergoes a transition from a mean field to a
pairing dominated regime. We finally explore the behaviour of the excitation
energies, wave functions and pair transfer amplitudes finding out that the
former, for , come close to the BCS predictions, whereas the
latter display a divergence at , signaling the onset of a long
range off-diagonal order in the system.Comment: 35 pages, 6 figures, 2 tables, to be published in EPJ
Entry into Winner-Take-All and Proportional-Prize Contests: An Experimental Study
This experiment compares the performance of two contest designs: a standard winnertake- all tournament with a single fixed prize, and a novel proportional-payment design in which that same prize is divided among contestants by their share of total achievement. We find that proportional prizes elicit more entry and more total achievement than the winner-take-all tournament. The proportional-prize contest performs better by limiting the degree to which heterogeneity among contestants discourages weaker entrants, without altering the performance of stronger entrants. These findings could inform the design of contests for technological and other improvements, which are widely used by governments and philanthropic donors to elicit more effort on targeted economic and technological development activities.performance pay, tournament, piece rate, tournament design, contest, experiments, risk aversion, feedback, gender
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