41 research outputs found
Orbital Magnetism of 2D Chaotic Lattices
We study the orbital magnetism of 2D lattices with chaotic motion of
electrons withing a primitive cell. Using the temperature diagrammatic
technique we evaluate the averaged value and rms fluctuation of magnetic
response in the diffusive regime withing the model of non-interacting
electrons. The fluctuations of magnetic susceptibility turn out to be large and
at low temperature can be of the order of , where
is the Fermi wavevector, is the mean free path, and is
the Landau susceptibility. In the certain region of magnetic fields the
paramagnetic contribution to the averaged response is field independent and
larger than the absolute value of Landau response.Comment: 6 pages, Latex file, figures available upon reques
Thermodynamics of Finite Quantum Systems: Application to Spin Magnetism II
We extend our study of thermodynamics of a Kubo particle to temperatures
smaller than the interlevel spacing. We obtain the distribution functions of
spin susceptibility and heat capacity for Poisson and Wigner-Dyson level
statistics. We evaluate the line shape of the Knight shift due to spin effects
both in a single particle and for the ensemble average and compare it with
orbital and spin-orbit contributions.Comment: 20 pages (16 text, 4 figures) uu-encoded, z-compressed PostScript.
Latest versions of manuscripts available at
http://physuna.phs.uc.edu/professors/serota.html or by e-mail, by request
from [email protected]
Orbital Magnetism and Current Distribution of Two-Dimensional Electrons under Confining Potential
The spatial distribution of electric current under magnetic field and the
resultant orbital magnetism have been studied for two-dimensional electrons
under a harmonic confining potential V(\vecvar{r})=m \omega_0^2 r^2/2 in
various regimes of temperature and magnetic field, and the microscopic
conditions for the validity of Landau diamagnetism are clarified. Under a weak
magnetic field (\omega_c\lsim\omega_0, \omega_c being a cyclotron frequency)
and at low temperature (T\lsim\hbar\omega_0), where the orbital magnetic
moment fluctuates as a function of the field, the currents are irregularly
distributed paramagnetically or diamagnetically inside the bulk region. As the
temperature is raised under such a weak field, however, the currents in the
bulk region are immediately reduced and finally there only remains the
diamagnetic current flowing along the edge. At the same time, the usual Landau
diamagnetism results for the total magnetic moment. The origin of this dramatic
temperature dependence is seen to be in the multiple reflection of electron
waves by the boundary confining potential, which becomes important once the
coherence length of electrons gets longer than the system length. Under a
stronger field (\omega_c\gsim\omega_0), on the other hand, the currents in
the bulk region cause de Haas-van Alphen effect at low temperature as
T\lsim\hbar\omega_c. As the temperature gets higher (T\gsim\hbar\omega_c)
under such a strong field, the bulk currents are reduced and the Landau
diamagnetism by the edge current is recovered.Comment: 15 pages, 11 figure
Electron-Assisted Hopping in Two Dimensions
We have studied the non-ohmic effects in the conductivity of a
two-dimensional system which undergoes the crossover from weak to strong
localization with decreasing electron concentration. When the electrons are
removed from equilibrium with phonons, the hopping conductivity depends only on
the electron temperature. This indicates that the hopping transport in a system
with a large localization length is assisted by electron-electron interactions
rather than by the phonons.Comment: 5 pages, 4 figure
Effect of dephasing on mesoscopic conductance fluctuations in quantum dots with single channel leads
We consider the distribution of conductance fluctuations in disordered
quantum dots with single channel leads. Using a perturbative diagrammatic
approach, valid for continuous level spectra, we describe dephasing due to
processes within the dot by considering two different contributions to the
level broadening, thus satisfying particle number conservation. Instead of a
completely non-Gaussian distribution, which occurs for zero dephasing, we find
for strong dephasing that the distribution is mainly Gaussian with
non-universal variance and non-Gaussian tails.Comment: 11 pages in REVTeX two-column format; 6 eps figures included;
submitted to Phys. Rev.
Strong localization of electrons in quasi-one-dimensional conductors
We report on the experimental study of electron transport in sub-micron-wide
''wires'' fabricated from Si -doped GaAs. These quasi-one-dimensional
(Q1D) conductors demonstrate the crossover from weak to strong localization
with decreasing the temperature. On the insulating side of the crossover, the
resistance has been measured as a function of temperature, magnetic field, and
applied voltage for different values of the electron concentration, which was
varied by applying the gate voltage. The activation temperature dependence of
the resistance has been observed with the activation energy close to the mean
energy spacing of electron states within the localization domain. The study of
non-linearity of the current-voltage characteristics provides information on
the distance between the critical hops which govern the resistance of Q1D
conductors in the strong localization (SL) regime. We observe the exponentially
strong negative magnetoresistance; this orbital magnetoresistance is due to the
universal magnetic-field dependence of the localization length in Q1D
conductors. The method of measuring of the single-particle density of states
(DoS) in the SL regime has been suggested. Our data indicate that there is a
minimum of DoS at the Fermi level due to the long-range Coulomb interaction.Comment: 12 pages, 11 figures; the final version to appear in Phys. Rev.
Magnetolocalization in disordered quantum wires
The magnetic field dependent localization in a disordered quantum wire is
considered nonperturbatively.
An increase of an averaged localization length with the magnetic field is
found, saturating at twice its value without magnetic field.
The crossover behavior is shown to be governed both in the weak and strong
localization regime by the magnetic diffusion length L_B. This function is
derived analytically in closed form as a function of the ratio of the mean free
path l, the wire thickness W, and the magnetic length l_B for a two-dimensional
wire with specular boundary conditions, as well as for a parabolic wire. The
applicability of the analytical formulas to resistance measurements in the
strong localization regime is discussed. A comparison with recent experimental
results on magnetolocalization is included.Comment: 22 pages, RevTe
Predictors of pain-related functional impairment among people living with HIV on long-term opioid therapy
People living with HIV (PLWH) have high levels of functional impairment due to pain, also called pain interference. Long-term opioid therapy (LTOT) is commonly prescribed for chronic pain among PLWH. We sought to better understand the predictors of pain interference, measured with the Brief Pain Inventory Interference subscale (BPI-I), among PLWH with chronic pain on LTOT. Using a prospective cohort of PLWH on LTOT we developed a model to identify predictors of increased pain interference over 1 year of follow up. Participants (n = 166) were 34% female, 72% African American with a median age of 55 years, and 40% had severe pain interference (BPI-I ≥ 7). In multivariable models, substance use disorder, depressive symptoms, PTSD symptoms, financial instability, and higher opioid doses were associated with increased pain interference. Measures of behavioral health and socioeconomic status had the most consistent association with pain interference. In contrast, the biomedical aspects of chronic pain and LTOT - comorbidities, duration of pain - were not predictive of pain interference. PLWH with chronic pain on LTOT with lower socioeconomic status and behavioral health symptoms have higher risk of pain interference. Addressing the social determinants of health and providing access to behavioral health services could improve patients' pain-related functional status