Search results for "Effective mass"
showing 10 items of 68 documents
Nature of Heavy Quasiparticles in Magnetically Ordered Heavy FermionsUPd2Al3andUPt3
2002
The optical conductivity of the heavy fermions $\mathrm{UPd}{}_{2}{\mathrm{Al}}_{3}$ and $\mathrm{UPt}{}_{3}$ has been measured in the energy range from 0.04 to 5 meV. In both compounds a well pronounced pseudogap of less than 1 meV develops in the optical response at low temperatures; we relate this to the antiferromagnetic ordering. From the energy dependence of the effective mass and scattering rate we conclude that the enhancement of the mass mainly occurs below the energy which is related to magnetic correlations between the local magnetic moments and the itinerant electrons. This implies that the magnetic order in these compounds is the prerequisite to the formation of the heavy quasi…
Density-near-zero using the acoustically induced transparency of a Fano acoustic resonator
2016
International audience; We report experimental results of near-zero mass density involving an acoustic metamaterial supporting Fano resonance. For this, we designed and fabricated an acoustic resonator with two closely coupled modes and measured its transmission properties. Our study reveals that the phenomenon of acoustically induced transparency is accompanied by an effect of near-zero density. Indeed, the dynamic effective parameters obtained from experimental data show the presence of a frequency band where the effective mass density is close to zero, with high transmission levels reaching 0.7. Furthermore, we demonstrate that such effective parameters lead to wave guiding in a 90-degre…
Paramagnetic-diamagnetic interplay in quantum dots for non-zero temperatures
2000
In the usual Fock-and Darwin-formalism with parabolic potential characterized by the confining energy $\eps_o := \hbar\omega_o= 3.37$ meV, but including explicitly also the Zeeman coupling between spin and magnetic field, we study the combined orbital and spin magnetic properties of quantum dots in a two-dimensional electron gas with parameters for GaAs, for N =1 and N >> 1 electrons on the dot. For N=1 the magnetization M(T,B) consists of a paramagnetic spin contribution and a diamagnetic orbital contribution, which dominate in a non-trivial way at low temperature and fields rsp. high temperature and fields. For N >> 1, where orbital and spin effects are intrinsically coupled in a subtle w…
Finite amplitude method applied to giant dipole resonance in heavy rare-earth nuclei
2015
Background: The quasiparticle random phase approximation (QRPA), within the framework of the nuclear density functional theory (DFT), has been a standard tool to access the collective excitations of the atomic nuclei. Recently, finite amplitude method (FAM) has been developed, in order to perform the QRPA calculations efficiently without any truncation on the two-quasiparticle model space. Purpose: We discuss the nuclear giant dipole resonance (GDR) in heavy rare-earth isotopes, for which the conventional matrix diagonalization of the QRPA is numerically demanding. A role of the Thomas-Reiche-Kuhn (TRK) sum rule enhancement factor, connected to the isovector effective mass, is also investig…
Size dependent light absorption modulation and enhanced carrier transport in germanium quantum dots devices
2015
Quantum confinement in closely packed arrays of Ge quantum dots (QDs) was studied for energy applications. In this work, we report an efficient tuning mechanism of the light harvesting and detection of Ge QDs. Thin films of SiGeO alloys, produced by rf-magnetron sputtering, were annealed at 600 degrees C in N-2 to induce precipitation of small amorphous Ge QDs into the oxide matrix. Varying the Ge content, the QD size was tailored between 2 and 4 nm, as measured by high resolution transmission electron microscopy. X-ray photoelectron spectroscopy (XPS) measurements indicate the formation of pure SiO2, as well as the presence of a sub-stoichiometric Ge oxide shell at the QD interface. Light …
Gluon mass and freezing of the QCD coupling
2007
Infrared finite solutions for the gluon propagator of pure QCD are obtained from the gauge-invariant non-linear Schwinger-Dyson equation formulated in the Feynman gauge of the background field method. These solutions may be fitted using a massive propagator, with the special characteristic that the effective mass employed drops asymptotically as the inverse square of the momentum transfer, in agreement with general operator-product expansion arguments. Due to the presence of the dynamical gluon mass the strong effective charge extracted from these solutions freezes at a finite value, giving rise to an infrared fixed point for QCD.
Quasi-one-dimensional quantum spin liquid in the $\rm {Cu(C_4H_4N_2)(NO_3)_2}$ insulator
2015
We analyze measurements of the magnetization, differential susceptibility and specific heat of quasi-one dimensional insulator Cu(C$_4$H$_4$N$_2$)(NO$_3$)$_2$ (CuPzN) subjected to magnetic fields. We show that the thermodynamic properties are defined by quantum spin liquid formed with spinons, with the magnetic field tuning the insulator CuPzN towards quantum critical point related to fermion condensation quantum phase transition (FCQPT) at which the spinon effective mass diverges kinematically. We show that the FCQPT concept permits to reveal and explain the scaling behavior of thermodynamic characteristics. For the first time, we construct the schematic $T-H$ (temperature---magnetic field…
Magnetic breakdown and charge density wave formation: a quantum oscillation study of the rare-earth tritellurides
2020
The rare-earth tritellurides ($R$Te$_3$, where $R$ = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Y) form a charge density wave state consisting of a single unidirectional charge density wave for lighter $R$, with a second unidirectional charge density wave, perpendicular and in addition to the first, also present at low temperatures for heavier $R$. We present a quantum oscillation study in magnetic fields up to 65T that compares the single charge density wave state with the double charge density wave state both above and below the magnetic breakdown field of the second charge density wave. In the double charge density wave state it is observed that there remain several small, light pockets…
Magnetic-field-induced reentrance of Fermi-liquid behavior and spin-lattice relaxation rates in
2009
Abstract A strong departure from Landau–Fermi liquid (LFL) behavior have been recently revealed in observed anomalies in both the magnetic susceptibility χ and the muon and 63Cu nuclear spin-lattice relaxation rates 1 / T 1 of YbCu 5 − x Au x ( x = 0.6 ). We show that the above anomalies along with magnetic-field-induced reentrance of LFL properties are indeed determined by the dependence of the quasiparticle effective mass M ∗ on magnetic field B and temperature T and demonstrate that violations of the Korringa law also come from M ∗ ( B , T ) dependence. We obtain this dependence theoretically utilizing our approach based on fermion condensation quantum phase transition (FCQPT) notion. Ou…
Energy scales and magnetoresistance at a quantum critical point
2009
The magnetoresistance (MR) of CeCoIn_5 is notably different from that in many conventional metals. We show that a pronounced crossover from negative to positive MR at elevated temperatures and fixed magnetic fields is determined by the scaling behavior of quasiparticle effective mass. At a quantum critical point (QCP) this dependence generates kinks (crossover points from fast to slow growth) in thermodynamic characteristics (like specific heat, magnetization etc) at some temperatures when a strongly correlated electron system transits from the magnetic field induced Landau Fermi liquid (LFL) regime to the non-Fermi liquid (NFL) one taking place at rising temperatures. We show that the abov…