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## Quantum confinement in PbI2 nanodisks prepared with cucurbit[7]uril

Fonte: Sociedade Brasileira de Química
Publicador: Sociedade Brasileira de Química

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

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This work presents an alternative route for the preparation of heavy metal iodide nanoparticles, particularly lead iodide nanodisks (ca. 50-340 × 7 Å, diameter × thickness), using the macrocycle cucurbit[7]uril as a synthetic template and stabilizing agent. These nanoparticles exhibit an optical-gap blue shift consistent with their small size and 1D quantum confinement. Their thicknesses are compatible with an exfoliated single layer of lead iodide, indicating that cucurbit[7]uril, preventing the stacking and formation of tactoids, thus limiting nanoparticles growth in the z direction. The structure, morphology and properties of these disks were analyzed by X-ray powder diffractometry (XRD), UV-Visible spectroscopy, atomic force microscopy (AFM), scanning electron microscopy with analysis of energy dispersive X-ray fluorescence (SEM-EDS) and high resolution transmission electron microscopy (HRTEM).; Este trabalho apresenta uma rota alternativa para a preparação de nanodiscos de iodeto de chumbo (ca. 50-340 × 7Å, diâmetro × espessura) utilizando o macrocíclico cucurbit[7]urila como molde de síntese e agente estabilizante. Estas nanopartículas apresentam um deslocamento para o azul de gap óptico consistente com seu tamanho reduzido e confinamento quântico 1D. Suas espessuras são compatíveis com a de uma camada de iodeto de chumbo esfoliado...

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## Quantum confinement in PbI2 nanodisks prepared with cucurbit[7]uril

Fonte: Sociedade Brasileira de Química
Publicador: Sociedade Brasileira de Química

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/08/2011
EN

Relevância na Pesquisa

67.269463%

This work presents an alternative route for the preparation of heavy metal iodide nanoparticles, particularly lead iodide nanodisks (ca. 50-340 × 7 Å, diameter × thickness), using the macrocycle cucurbit[7]uril as a synthetic template and stabilizing agent. These nanoparticles exhibit an optical-gap blue shift consistent with their small size and 1D quantum confinement. Their thicknesses are compatible with an exfoliated single layer of lead iodide, indicating that cucurbit[7]uril, preventing the stacking and formation of tactoids, thus limiting nanoparticles growth in the z direction. The structure, morphology and properties of these disks were analyzed by X-ray powder diffractometry (XRD), UV-Visible spectroscopy, atomic force microscopy (AFM), scanning electron microscopy with analysis of energy dispersive X-ray fluorescence (SEM-EDS) and high resolution transmission electron microscopy (HRTEM).

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## Quantum confinement in hydrogen bond

Fonte: Wiley-Blackwell
Publicador: Wiley-Blackwell

Tipo: Artigo de Revista Científica
Formato: 765-770

ENG

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67.48558%

#quantum confinement#hydrogen bond#supersymmetric quantum mechanics#variational method#NH and OH molecular groups

In this work, the quantum confinement effect is proposed as the cause of the displacement of the vibrational spectrum of molecular groups that involve hydrogen bonds. In this approach, the hydrogen bond imposes a space barrier to hydrogen and constrains its oscillatory motion. We studied the vibrational transitions through the Morse potential, for the NH and OH molecular groups inside macromolecules in situation of confinement (when hydrogen bonding is formed) and nonconfinement (when there is no hydrogen bonding). The energies were obtained through the variational method with the trial wave functions obtained from supersymmetric quantum mechanics formalism. The results indicate that it is possible to distinguish the emission peaks related to the existence of the hydrogen bonds. These analytical results were satisfactorily compared with experimental results obtained from infrared spectroscopy. (c) 2015 Wiley Periodicals, Inc.

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## Anisotropic Quantum Confinement Effect and Electric Control of Surface States in Dirac Semimetal Nanostructures

Fonte: Nature Publishing Group
Publicador: Nature Publishing Group

Tipo: Artigo de Revista Científica

Publicado em 20/01/2015
EN

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The recent discovery of Dirac semimetals represents a new achievement in our fundamental understanding of topological states of matter. Due to their topological surface states, high mobility, and exotic properties associated with bulk Dirac points, these new materials have attracted significant attention and are believed to hold great promise for fabricating novel topological devices. For nanoscale device applications, effects from finite size usually play an important role. In this report, we theoretically investigate the electronic properties of Dirac semimetal nanostructures. Quantum confinement generally opens a bulk band gap at the Dirac points. We find that confinement along different directions shows strong anisotropic effects. In particular, the gap due to confinement along vertical c-axis shows a periodic modulation, which is absent for confinement along horizontal directions. We demonstrate that the topological surface states could be controlled by lateral electrostatic gating. It is possible to generate Rashba-like spin splitting for the surface states and to shift them relative to the confinement-induced bulk gap. These results will not only facilitate our fundamental understanding of Dirac semimetal nanostructures, but also provide useful guidance for designing all-electrical topological spintronics devices.

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## Highly efficient luminescence from a hybrid state found in strongle quantum confined PbS nanocrystals

Fonte: Institute of Physics Publishing
Publicador: Institute of Physics Publishing

Tipo: Artigo de Revista Científica

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#Keywords: Charge carriers#Lead compounds#Light emission#Mathematical models#Nanostructured materials#Passivation#Quantum efficiency#Bandgaps#Monodisperse size distribution#Quantum confinement#Stokes shift

We report that high quality PbS nanocrystals, synthesized in the strong quantum confinement regime, have quantum yields as high as 70% at room temperature. We use a combination of modelling and photoluminescence up-conversion to show that we obtain a near

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## Quantum Confinement in Si and Ge Nanostructures

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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We apply perturbative effective mass theory as a broadly applicable
theoretical model for quantum confinement (QC) in all Si and Ge nanostructures
including quantum wells (QWs), wires (Q-wires) and dots (QDs). Within the
limits of strong, medium, and weak QC, valence and conduction band edge energy
levels (VBM and CBM) were calculated as a function of QD diameters, QW
thicknesses and Q-wire diameters. Crystalline and amorphous quantum systems
were considered separately. Calculated band edge levels with strong, medium and
weak QC models were compared with experimental VBM and CBM reported from X-ray
photoemission spectroscopy (XPS), X-ray absorption spectroscopy (XAS) or
photoluminescence (PL). Experimentally, the dimensions of the nanostructures
were determined directly, by transmission electron microscopy (TEM), or
indirectly, by x-ray diffraction (XRD) or by XPS. We found that crystalline
materials are best described by a medium confinement model, while amorphous
materials exhibit strong confinement regardless of the dimensionality of the
system. Our results indicate that spatial delocalization of the hole in
amorphous versus crystalline nanostructures is the important parameter
determining the magnitude of the band gap expansion...

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## N Identical Particles Under Quantum Confinement: A Many-Body Dimensional Perturbation Theory Approach II, The Lowest-Order Wave Function I

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 17/03/2006

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In this paper we continue our development of a dimensional perturbation
theory (DPT) treatment of N identical particles under quantum confinement. DPT
is a beyond-mean-field method which is applicable to both weakly and
strongly-interacting systems and can be used to connect both limits. In a
previous paper we developed the formalism for low-order energies and excitation
frequencies. This formalism has been applied to atoms, Bose-Einstein
condensates and quantum dots. One major advantage of the method is that N
appears as a parameter in the analytical expressions for the energy and so
results for N up to a few thousand are easy to obtain. Other properties
however, are also of interest, for example the density profile in the case of a
BEC,and larger N results are desirable as well. The latter case requires us to
go to higher orders in DPT. These calculations require as input zeroth-order
wave functions and this paper, along with a subsequent paper, addresses this
issue.; Comment: 52 pages

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## Quantum Confinement in Hydrogen Bond

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 09/02/2015

Relevância na Pesquisa

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In this work, the quantum confinement effect is proposed as the cause of the
displacement of the vibrational spectrum of molecular groups that involve
hydrogen bonds. In this approach the hydrogen bond imposes a space barrier to
hydrogen and constrains its oscillatory motion. We studied the vibrational
transitions through the Morse potential, for the NH and OH molecular groups
inside macromolecules in situation of confinement (when hydrogen bonding is
formed) and non-confinement (when there is no hydrogen bonding). The energies
were obtained through the variational method with the trial wave functions
obtained from Supersymmetric Quantum Mechanics (SQM) formalism. The results
indicate that it is possible to distinguish the emission peaks related to the
existence of the hydrogen bonds. These analytical results were satisfactorily
compared with experimental results obtained from infrared spectroscopy.; Comment: 20 pages, 2 figures. To appear in Int.J.Quantum Chem

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## Quantum Confinement in Hydrogen Bond of DNA and RNA

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 09/02/2015

Relevância na Pesquisa

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The hydrogen bond is a fundamental ingredient to stabilize the DNA and RNA
macromolecules. The main contribution of this work is to describe
quantitatively this interaction as a consequence of the quantum confinement of
the hydrogen. The results for the free and confined system are compared with
experimental data. The formalism to compute the energy gap of the vibration
motion used to identify the spectrum lines is the Variational Method allied to
Supersymmetric Quantum Mechanics.; Comment: 8 pages, 3 figures. To appear in The Proceedings of the 30th
International Colloquium on Group Theoretical Methods in Physics (Group30),
Ghent, Belgium

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## Spatial confinement effects on quantum field theory using nonlinear coherent states approach

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 10/10/2007

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We study some basic quantum confinement effects through investigation a
deformed harmonic oscillator algebra. We show that spatial confinement effects
on a quantum harmonic oscillator can be represented by a deformation function
within the framework of nonlinear coherent states theory. Using the deformed
algebra, we construct a quantum field theory in confined space. In particular,
we find that the confinement influences on some physical properties of the
electromagnetic field and it gives rise to nonlinear interaction. Furthermore,
we propose a physical scheme to generate the nonlinear coherent states
associated with the electromagnetic field in a confined region.

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## Quantum confinement in Si and Ge nanostructures: Effect of crystallinity

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 09/12/2013

Relevância na Pesquisa

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We look at the relationship between the preparation method of Si and Ge
nanostructures (NSs) and the structural, electronic, and optical properties in
terms of quantum confinement (QC). QC in NSs causes a blue shift of the gap
energy with decreasing NS dimension. Directly measuring the effect of QC is
complicated by additional parameters, such as stress, interface and defect
states. In addition, differences in NS preparation lead to differences in the
relevant parameter set. A relatively simple model of QC, using a
`particle-in-a-box'-type perturbation to the effective mass theory, was applied
to Si and Ge quantum wells, wires and dots across a variety of preparation
methods. The choice of the model was made in order to distinguish contributions
that are solely due to the effects of QC, where the only varied experimental
parameter was the crystallinity. It was found that the hole becomes
de-localized in the case of amorphous materials, which leads to stronger
confinement effects. The origin of this result was partly attributed to
differences in the effective mass between the amorphous and crystalline NS as
well as between the electron and hole. Corrections to our QC model take into
account a position dependent effective mass. This term includes an inverse
length scale dependent on the displacement from the origin. Thus...

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## Spatial confinement effects on quantum harmonic oscillator I: Nonlinear coherent state approach

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 11/12/2011

Relevância na Pesquisa

47.402344%

In this paper we study some basic quantum confinement effects through
investigation of a deformed harmonic oscillator algebra. We show that spatial
confinement effects on a quantum harmonic oscillator can be represented by a
deformation function within the framework of nonlinear coherent states theory.
We construct the coherent states associated with the spatially confined quantum
harmonic oscillator in a one-dimensional infinite well and examine some of
their quantum statistical properties, including sub-poissonian statistics and
quadrature squeezing.; Comment: arXiv admin note: substantial text overlap with arXiv:0710.1942

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## Metallic nanograins: spatially nonuniform pairing induced by quantum confinement

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 19/11/2010

Relevância na Pesquisa

47.44404%

It is well-known that the formation of discrete electron levels strongly
influences the pairing in metallic nanograins. Here we focus on another effect
of quantum confinement in superconducting grains that was not studied
previously, i.e., spatially nonuniform pairing. This effect is very significant
when single-electron levels form bunches and/or a kind of shell structure: in
highly symmetric grains the order parameter can exhibit variations with
position by an order of magnitude. Nonuniform pairing is closely related to a
quantum-confinement induced modification of the pairing-interaction matrix
elements and size-dependent pinning of the chemical potential to groups of
degenerate or nearly degenerate levels. For illustration we consider spherical
metallic nanograins. We show that the relevant matrix elements are as a rule
enhanced in the presence of quantum confinement, which favors spatial
variations of the order parameter, compensating the corresponding energy cost.
The size-dependent pinning of the chemical potential further increases the
spatial variation of the pair condensate. The role of nonuniform pairing is
smaller in less symmetric confining geometries and/or in the presence of
disorder. However, it always remains of importance when the energy spacing
between discrete electron levels $\delta$ is approaching the scale of the bulk
gap $\Delta_B$...

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## Effect of Quantum Confinement on Electron Tunneling through a Quantum Dot

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 13/03/1997

Relevância na Pesquisa

47.37234%

Employing the Anderson impurity model, we study tunneling properties through
an ideal quantum dot near the conductance minima. Considering the Coulomb
blockade and the quantum confinement on an equal footing, we have obtained
current contributions from various types of tunneling processes; inelastic
cotunneling, elastic cotunneling, and resonant tunneling of thermally activated
electrons. We have found that the inelastic cotunneling is suppressed in the
quantum confinement limit, and thus the conductance near its minima is
determined by the elastic cotunneling at low temperature ($k_BT \ll \Gamma$,
$\Gamma$: dot-reservoir coupling constant), or by the resonant tunneling of
single electrons at high temperature ($k_BT \gg \Gamma$).; Comment: 11 pages Revtex, 2 Postscript figures, To appear in Phys.Rev.B

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## Anisotropic Quantum Confinement Effect and Electric Control of Surface States in Dirac Semimetal Nanostructures

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

47.415166%

The recent discovery of Dirac semimetals represents a new achievement in our
fundamental understanding of topological states of matter. Due to their
topological surface states, high mobility, and exotic properties associated
with bulk Dirac points, these new materials have attracted significant
attention and are believed to hold great promise for fabricating novel
topological devices. For nanoscale device applications, effects from finite
size usually play an important role. In this report, we theoretically
investigate the electronic properties of Dirac semimetal nanostructures.
Quantum confinement generally opens a bulk band gap at the Dirac points. We
find that confinement along different directions shows strong
anisotropiceffects. In particular, the gap due to confinement along vertical
c-axis shows a periodic modulation, which is absent for confinement along
horizontal directions. We demonstrate that the topological surface states could
be controlled by lateral electrostatic gating. It is possible to generate
Rashba-like spin splitting for the surface states and to shift them relative to
the confinement-induced bulk gap. These results will not only facilitate our
fundamental understanding of Dirac semimetal nanostructures, but also provide
useful guidance for designing all-electrical topological spintronics devices.; Comment: 23 pages...

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## Quantum confinement effects in InAs-InP core-shell nanowires

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 04/01/2007

Relevância na Pesquisa

47.382705%

We report the detection of quantum confinement in single InAs-InP core-shell
nanowires. The wires having an InAs core with ~25 nm diameter are characterized
by emission spectra in which two peaks are identified under high excitation
intensity conditions. The peaks are caused by emission from the ground and
excited quantized levels, due to the quantum confinement in the plane
perpendicular to the nanowire axis. We have identified in the emission spectra
different energy contributions related to the wurtzite structure of the wires,
the strain between the wurtzite core and shell, and the confinement energy of
the InAs core. Calculations based on 6-band strain-dependent k.p theory allow
the theoretical estimation of the confined energy states in such materials and
we found these results to be in good agreement with those from the
photoluminescence studies.; Comment: 10 pages, 4 figures, accepted to Journal of Physics: Condensed Matter

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## Vortex states in nanoscale superconducting squares: the influence of quantum confinement

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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Bogoliubov-de Gennes theory is used to investigate the effect of the size of
a superconducting square on the vortex states in the quantum confinement
regime. When the superconducting coherence length is comparable to the Fermi
wavelength, the shape resonances of the superconducting order parameter have
strong influence on the vortex configuration. Several unconventional vortex
states, including asymmetric ones, giant multi-vortex combinations, and states
comprising giant antivortex, were found as ground states and their stability
was found to be very sensitive on the value of $k_F\xi_0$, the size of the
sample $W$, and the magnetic flux $\Phi$. By increasing the temperature and/or
enlarging the size of the sample, quantum confinement is suppressed and the
conventional mesoscopic vortex states as predicted by the Ginzburg-Laudau (GL)
theory are recovered. However, contrary to the GL results we found that the
states containing symmetry-induced vortex-antivortex pairs are stable over the
whole temperature range. It turns out that the inhomogeneous order parameter
induced by quantum confinement favors vortex-antivortex molecules, as well as
giant vortices with a rich structure in the vortex core - unattainable in the
GL domain.

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## Using Quantum Confinement to Uniquely Identify Devices

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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#Condensed Matter - Materials Science#Condensed Matter - Mesoscale and Nanoscale Physics#Quantum Physics

Modern technology unintentionally provides resources that enable the trust of
everyday interactions to be undermined. Some authentication schemes address
this issue using devices that give unique outputs in response to a challenge.
These signatures are generated by hard-to-predict physical responses derived
from structural characteristics, which lend themselves to two different
architectures, known as unique objects (UNOs) and physically unclonable
functions (PUFs). The classical design of UNOs and PUFs limits their size and,
in some cases, their security. Here we show that quantum confinement lends
itself to the provision of unique identities at the nanoscale, by using
fluctuations in tunnelling measurements through quantum wells in resonant
tunnelling diodes (RTDs). This provides an uncomplicated measurement of
identity without conventional resource limitations whilst providing robust
security. The confined energy levels are highly sensitive to the specific
nanostructure within each RTD, resulting in a distinct tunnelling spectrum for
every device, as they contain a unique and unpredictable structure that is
presently impossible to clone. This new class of authentication device operates
with few resources in simple electronic structures above room temperature.; Comment: 12 pages...

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## Band formation from coupled quantum dots formed by a nanoporous network on a copper surface

Fonte: American Association for the Advancement of Science
Publicador: American Association for the Advancement of Science

Tipo: Artículo
Formato: 2039679 bytes; application/pdf

ENG

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#Coupled quantum systems#Quantum dots#Quantum confinement#Crystalline solids#Surfaces#Organic nanoporous network#Electronic band structure#Pore states

4 pages, 3 figures.-- Supporting information (Materials and Methods, SOM Text, Suppl. figs. S1-S7, Suppl Refs, 15 pages) available at: http://science-mag.aaas.org/cgi/data/325/5938/300/DC1/1; The properties of crystalline solids can to a large extent be derived from the scale and dimensionality of periodic arrays of coupled quantum systems such as atoms and molecules. Periodic quantum confinement in two dimensions has been elusive on surfaces, mainly because of the challenge to produce regular nanopatterned structures that can trap electronic states. We report that the two-dimensional free electron gas of the Cu(111) surface state can be trapped within the pores of an organic nanoporous network, which can be regarded as a regular array of quantum dots. Moreover, a shallow dispersive electronic band structure is formed, which is indicative of electronic coupling between neighboring pore states.; Supported by the Swiss National Science Foundation, the National Center of Competence in Research "Nanoscale Science", the European Union through the Marie Curie Research Training
Network PRAIRIES, the Wolfermann-Nägeli-Stiftung, the Bundesministerum für Bildung und Forschung (BMBF) Cluster "Forum Organic Electronics" (Heidelberg), and the Swiss Federal Commission for Technology and Innovation (CTI).; Peer reviewed

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## Quantum confinement particle in a 2D quadrupole potential

Fonte: Sociedad Mexicana de Física
Publicador: Sociedad Mexicana de Física

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/06/2010
EN

Relevância na Pesquisa

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We analytically solve the Hamiltonian for a quantum particle confined in a cylindrical hard-wall well, subject to the action of a two-dimensional quadrupolar potential at the well center. The angular part of the wavefunction is expressed by Mathieu functions whose angular eigenenergies take negative values when the quadrupolar momentum is above a certain threshold. We show that in this case, the radial part of the eigenfunctions is expressed in terms of Bessel functions of an imaginary order which are imaginary-value functions whose phases are not well defined at the origin. However, the density of probability is well defined everywhere and the wave function satisfies hard-wall boundary conditions for any value of the parameters involved. We discuss an alternative criterion for determining the eigenenergies of the system based on the expected value of the symmetrized radial momentum.

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