Search results for "Effective mass"
showing 10 items of 68 documents
Extremely slow Drude relaxation of correlated electrons
2005
The electrical conduction of metals is governed by how freely mobile electrons can move throughout the material. This movement is hampered by scattering with other electrons, as well as with impurities or thermal excitations (phonons). Experimentally, the scattering processes of single electrons are not observed, but rather the overall response of all mobile charge carriers within a sample. The ensemble dynamics can be described by the relaxation rates, which express how fast the system approaches equilibrium after an external perturbation1,2,3. Here we measure the frequency-dependent microwave conductivity of the heavy-fermion metal UPd2Al3 (ref. 4), finding that it is accurately described…
A scenario for critical scalar field collapse in $AdS_3$
2014
We present a family of exact solutions, depending on two parameters $\alpha$ and $b$ (related to the scalar field strength), to the three-dimensional Einstein-scalar field equations with negative cosmological constant $\Lambda$. For $b=0$ these solutions reduce to the static BTZ family of vacuum solutions, with mass $M = -\alpha$. For $b\neq0$, the solutions become dynamical and develop a strong spacelike central singularity. The $\alpha0$ agrees qualitatively with that observed in numerical simulations of subcritical collapse. We analyze the linear perturbations of the threshold solution, $\alpha=0$, in the $\Lambda=0$ approximation, and find that it has only one unstable growing mode, whi…
Geometric aspects of charged black holes in Palatini theories
2015
Charged black holes in gravity theories in the Palatini formalism present a number of unique properties. Their innermost structure is topologically nontrivial, representing a wormhole supported by a sourceless electric flux. For certain values of their effective mass and charge curvature divergences may be absent, and their event horizon may also disappear yielding a remnant. We give an overview of the mathematical derivation of these solutions and discuss their geodesic structure and other geometric properties.
Polarons in thet-J model
1991
A convenient form of the Peierls-Hubbard Hamiltonian is obtained for the case when the Hubbard repulsion is the largest energy parameter. It allows to consider in the spin-wave approximation the properties of the one-hole low-lying excitations of a 2d lattice. For the parameters approximately corresponding to La2CuO4 it is shown that the hole polarons in the CuO2 planes of lightly doped samples are of large size with a solitonlike-shaped highly asymmetric wave function oriented along the diagonals of the planes or of small size depending on the value of the electron-phonon coupling. In both cases the cooperative effect of the electron-phonon and electron-magnon interactions leads to a large…
Chiral excitations of magnetic droplet solitons driven by their own inertia
2019
The inertial effects of magnetic solitons play a crucial role in their dynamics and stability. Yet governing their inertial effects is a challenge for their use in real devices. Here, we show how to control the inertial effects of magnetic droplet solitons. Magnetic droplets are strongly nonlinear and localized autosolitons than can form in current-driven nanocontacts. Droplets can be considered as dynamical particles with an effective mass. We show that the dynamical droplet bears a second excitation under its own inertia. These excitations comprise a chiral profile, and appear when the droplet resists the force induced by the Oersted field of the current injected into the nanocontact. We …
Temperature-Dependent Change of the Electronic Structure in the Kondo Lattice System $YbRh_{2}Si_{2}$
2021
Seminar, Deutschland; Journal of physics / Condensed matter 00(00), 1-20 (2021). doi:10.1088/1361-648X/abe479
The Statistical Description of de Haas—van Alphen Oscillations in Silicon Nanosandwich
2020
Here, we present room temperature de Haas—van Alphen oscillations measured in silicon nanosandwich in a weak magnetic field. Our results demonstrate a decrease of the oscillation magnitude with increasing magnetic field strength. This behavior is drastically different from the results reported earlier and it is attributed to the low-dimensionality of the studied structure, which enables room temperature observation of the de Haas—van Alphen effect in moderate magnetic fields up to 1000 Oe. We employ the classic Lifshitz-Kosevich formalism based on the dependence of the carrier effective mass on the applied magnetic field, to statistically describe this effect. We note that the statistical a…
Two-body contributions to the effective mass in nuclear effective interactions
2018
Starting from general expressions of well-chosen symmetric nuclear matter quantities derived for both zero- and finite-range effective theories, we derive the contributions to the effective mass. We first show that, independently of the range, the two-body contribution is enough to describe correctly the saturation mechanism but gives an effective mass value around $m^*/m \simeq 0.4$. Then, we show that the full interaction (by instance, an effective two-body density-dependent term on top of the pure two-body term) is needed to reach the accepted value $m^*/m \simeq 0.7-0.8$.
Predicting Neutrinoless Double Beta Decay
2005
We give predictions for the neutrinoless double beta decay rate in a simple variant of the A_4 family symmetry model. We show that there is a lower bound for the neutrinoless double beta decay amplitude even in the case of normal hierarchical neutrino masses, corresponding to an effective mass parameter |m_{ee}| >= 0.17 \sqrt{\Delta m^2_{ATM}}. This result holds both for the CP conserving and CP violating cases. In the latter case we show explicitly that the lower bound on |m_{ee}| is sensitive to the value of the Majorana phase. We conclude therefore that in our scheme, neutrinoless double beta decay may be accessible to the next generation of high sensitivity experiments.
Double beta decay versus cosmology: Majorana CP phases and nuclear matrix elements
2004
We discuss the relation between the absolute neutrino mass scale, the effective mass measured in neutrinoless double beta decay, and the Majorana CP phases. Emphasis is placed on estimating the upper bound on the nuclear matrix element entering calculations of the double beta decay half life. Consequently, one of the Majorana CP phases can be constrained when combining the claimed evidence for neutrinoless double beta decay with the neutrino mass bound from cosmology.