Samuele Fraizzoli's research while affiliated with Scuola Normale Superiore di Pisa and other places
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Publications (10)
A comprehensive theory of shallow impurities in quantum wells (QW's) is presented. The energy levels of donor and acceptor impurities are calculated within the effective mass theory including the mismatch of the band parameters and of the dielectric constants between well and barrier materials. The theory also accounts for Coulomb coupling between...
We perform a tight-binding fit of the self-consistent LMTO-LDA electronic structure of CeAg. This allows us to calculate the width DELTA(epsilon) of the Ce 4f-levels due to hybridisation with conduction states. The f-levels are shown to hybridise with p-and d-band states at the Fermi energy.
We calculate energies and oscillator strengths of infrared transitions between ground and excited shallow acceptor states in quantum wells (QW’s) for varying well width. The impurity states are calculated within a four-band effective-mass theory, which accounts for the valence-band mixing as well as for the mismatch of the band parameters and the d...
Self-consistent linear muffin-tin orbital calculations are performed for CeAg. The electronic structure is calculated in the paramagnetic and ferromagnetic phase, for both the cubic and tetragonal symmetry. The presence of hybridization relevant to the Anderson lattice behavior, invoked to interpret the low-temperature properties of this compound,...
We perform self-consistent linear muffin-tin-orbital local-density-approximation (LMTO-LDA) electronic structure calculations for paramagnetic CeAg in the cubic phase to study the hybridization of the Ce f states which is found particularly effective with the Ce d and Ag p states. We also make self-consistent calculations of the electronic structur...
The competition between Kondo effect and RKKY interaction is studied within an exactly solvable model, obtained from the two-impurity Anderson model by replacing the conduction band by two states. Results depend on the ratio between hopping t and Kondo temperature TK: for t ⪡ TK two independent Kondo singlets are formed, while for t ⪢ TK the impuri...
In a recent paper on acceptors in strained quantum wells [J. P. Loehr and J. Singh, Phys. Rev. B 41, 3695 (1990)], a splitting between the two spin states is found when the impurity is placed off center. We point out that this splitting is inconsistent with symmetry and show that the error arises from an incorrect treatment of the transformation pr...
We calculate binding energies of shallow acceptors in GaAs/Ga1-xAlxAs quantum wells (QW’s) for varying well widths. Variational calculations are performed in the framework of a multiband effective-mass theory, which accounts for the mixing between heavy and light holes. The Hamiltonian also takes into account the mismatch between the band parameter...
We present a variational method to compute donor eigenstates in a GaAs-Ga1-xAlxAs quantum well. The effective-mass approximation is used, and the envelope function is expanded in the complete set of the states of the quantum well at k?=0, including the continuum states. The convergence is good; the contribution of the continuum is very small, excep...
Citations
... Fortunately, the synthetic antiferromagnet (SAF) and synthetic ferrimagnet (SFi), consisting of two antiferromagnetically coupled ferromagnetic layers and a nonmagnetic spacer, possess the advantages of reduced stray field and high thermal stability due to the strong interlayer exchange coupling, as well as keeping almost the same manipulation and detection of magnetization as the single ferromagnet layer [8,9]. The interlayer exchange coupling between two magnetic layers adjacent to the same nonmagnetic spacer can be referred to as the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction [10,11]. Based on RKKY interaction theory, this sandwich structure has an oscillatory interlayer exchange coupling as a function of the nonmagnetic spacer layer thickness. ...
... The bulk intermetallic exhibits various stoichiometries as for example CeAg, CeAg 2 , CeAg 3 or Ce 3 Ag as well as a variety of different lattice structures [136][137][138][139][140][141][142]. CeAg for example exhibits a cubic structure with a lattice constant of a = 3.733 Å, but undergoes a transition to a tetragonal symmetry at T s = 16 K [136,137]. ...
... A starting point of our theory is the eight-band Kohn-Luttinger Hamiltonian with boundary conditions previously used to obtain the subband structure in HgTe QWs [13] and the four-band model developed for determining, in the axial approximation, acceptor levels in GaAs QWs [14]. Within that approximation, discussed in Sec. ...
... The presence of the magnetic field breaks the time inversion symmetry in the problem and leads to the disbalance of scattering rates W k,k ′ and W k ′ ,k , which is why a non-zero Hall contribution J k,k ′ emerges. Let us assume that the impurity potential is described by the Coulomb potential [22] V e (r) = −V h (r) = −eq imp /(4πε 0 εr). The Lippmann-Schwinger equation can not be treated perturbatively for such a potential in our system, which is why we solve this integral equation (8) numerically. ...
Reference: Anomalous Exciton Hall Effect
... rity, grown in the 001 direction, which we take as the quantization axis z, the acceptor Hamiltonian is w x given by a 4 = 4 matrix operator[8][9][10][11][12] H sy H kin qH qw qH c .2Fig. 1. a The critical layer thickness CLT of In Ga As Eq. 1 in the text. b The calculated energies of acceptor S-like states on-center impurity in a In Ga AsrGaAs QW structure. ...
