اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدTwo-Impurity Anderson model in an Antiferromagnetic metal: zero-bandwidth limit
135
0
0.0
(
0
)
تأليف
R. Allub
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We study the zero-bandwidth limit of the two-impurity Anderson model in an antiferromagnetic (AF) metal. We calculate, for different values of the model parameters, the lowest excitation energy, the magnetic correlation $<mathbf{S}_{1}mathbf{S}_{2}>$ between the impurities, and the magnetic moment at each impurity site, as a function of the distance between the impurities and the temperature. At zero temperature, in the region of parameters corresponding to the Kondo regime of the impurities, we observe an interesting competition between the AF gap and the Kondo physics of the two impurities. When the impurities are close enough, the AF splitting governs the physics of the system and the local moments of the impurities are frozen, in a state with very strong ferromagnetic correlation between the impurities and roughly independent of the distance. On the contrary, when the impurities are sufficiently far apart and the AF gap is not too large, the scenario of the Kondo physics take place: non-magnetic ground state and the possibility of spin-flip excitation emerges and the ferromagnetic $<mathbf{S}_{1}mathbf{S}_{2}>$ decreases as the distance increases, but the complete decoupling of the impurities never occurs. In adition, the presence of the AF gap gives a non-zero magnetic moment at each impurity site, showing a non complete Kondo screening of the impurities in the system. We observe that the residual magnetic moment decreases when the distance between the impurities is increased.
قيم البحث
اقرأ أيضاً
A central feature of the Periodic Anderson Model is the competition between antiferromagnetism, mediated by the Ruderman-Kittel-Kasuya-Yosida interaction at small conduction electron-local electron hybridization $V$, and singlet formation at large $V
$. At zero temperature, and in dimension $d>1$, these two phases are separated by a quantum critical point $V_c$. We use Quantum Monte Carlo simulations to explore the effect of impurities which have a local hybridization $V_{*} < V_c$ in the AF regime which are embedded in a bulk singlet phase with $V > V_c$. We measure the suppression of singlet correlations and the antiferromagnetic correlations which form around the impurity, as well as the size of the resulting domain. Our calculations agree qualitatively with NMR measurements in CeCoIn$_{5-x}$Cd$_x$.
We investigate static and dynamical ground-state properties of the two-impurity Anderson model at half filling in the limit of vanishing impurity separation using the dynamical density-matrix renormalization group method. In the weak-coupling regime,
we find a quantum phase transition as function of inter-impurity hopping driven by the charge degrees of freedom. For large values of the local Coulomb repulsion, the transition is driven instead by a competition between local and non-local magnetic correlations. We find evidence that, in contrast to the usual phenomenological picture, it seems to be the bare effective exchange interactions which trigger the observed transition.
We study the two-impurity Anderson model on finite chains using numerical techniques. We discuss the departure of magnetic correlations as a function of the interimpurity distance from a pure 2k_F oscillation due to open boundary conditions. We obser
ve qualitatively different behaviors in the interimpurity spin correlations and in transport properties at different values of the impurity couplings. We relate these different behaviors to a change in the relative dominance between the Kondo effect and the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction. We also observe that when RKKY dominates there is a definite relation between interimpurity magnetic correlations and transport properties. In this case, there is a recovery of 2k_F periodicity when the on-site Coulomb repulsion on the chain is increased at quarter-filling. The present results could be relevant for electronic nanodevices implementing a non-local control between two quantum dots that could be located at variable distance along a wire.
Using non-equilibrium renormalized perturbation theory, we calculate the conductance G as a function of temperature T and bias voltage V for an Anderson model, suitable for describing transport properties through a quantum dot. For renormalized param
eters that correspond to the extreme Kondo limit, we do not find a simple scaling formula beyond a quadratic dependence in T and V. However, if valence fluctuations are allowed, we find agreement with recent experiments.
We study Gutzwiller-correlated wave functions as variational ground states for the two-impurity Anderson model (TIAM) at particle-hole symmetry as a function of the impurity separation ${bf R}$. Our variational state is obtained by applying the Gutzw
iller many-particle correlator to a single-particle product state. We determine the optimal single-particle product state fully variationally from an effective non-interacting TIAM that contains a direct electron transfer between the impurities as variational degree of freedom. For a large Hubbard interaction $U$ between the electrons on the impurities, the impurity spins experience a Heisenberg coupling proportional to $V^2/U$ where $V$ parameterizes the strength of the on-site hybridization. For small Hubbard interactions we observe weakly coupled impurities. In general, for a three-dimensional simple cubic lattice we find discontinuous quantum phase transitions that separate weakly interacting impurities for small interactions from singlet pairs for large interactions.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
