scholarly journals The Microscopic Mechanisms Involved in Superexchange

2021 ◽  
Vol 8 (1) ◽  
pp. 6
Author(s):  
Jacques Curély

In earlier work, we previously established a formalism that allows to express the exchange energy J vs. fundamental molecular integrals without crystal field, for a fragment A–X–B, where A and B are 3d1 ions and X is a closed-shell diamagnetic ligand. In this article, we recall this formalism and give a physical interpretation: we may rigorously predict the ferromagnetic (J < 0) or antiferromagnetic (J > 0) character of the isotropic (Heisenberg) spin-spin exchange coupling. We generalize our results to ndm ions (3 £ n £ 5, 1 £ m £ 10). By introducing a crystal field we show that, starting from an isotropic (Heisenberg) exchange coupling when there is no crystal field, the appearance of a crystal field induces an anisotropy of exchange coupling, thus leading to a z-z (Ising-like) coupling or a x-y one. Finally, we discuss the effects of a weak crystal field magnitude (3d ions) compared to a stronger (4d ions) and even stronger one (5d ions). In the last step, we are then able to write the corresponding Hamiltonian exchange as a spin-spin one.

Polyhedron ◽  
2017 ◽  
Vol 137 ◽  
pp. 246-255 ◽  
Author(s):  
Evgeniya S. Bazhina ◽  
Grigory G. Aleksandrov ◽  
Mikhail A. Kiskin ◽  
Nikolay N. Efimov ◽  
Elena A. Ugolkova ◽  
...  

2017 ◽  
Vol 8 (9) ◽  
pp. 6207-6217 ◽  
Author(s):  
Benedict M. Gardner ◽  
David M. King ◽  
Floriana Tuna ◽  
Ashley J. Wooles ◽  
Nicholas F. Chilton ◽  
...  

Analysis of UIV–E–UIV (E = S, Se, Te) complexes reveals their behaviour is due to crystal field effects and not exchange coupling.


2020 ◽  
Vol 11 (1) ◽  
Author(s):  
B. Voisin ◽  
J. Bocquel ◽  
A. Tankasala ◽  
M. Usman ◽  
J. Salfi ◽  
...  

AbstractTunneling is a fundamental quantum process with no classical equivalent, which can compete with Coulomb interactions to give rise to complex phenomena. Phosphorus dopants in silicon can be placed with atomic precision to address the different regimes arising from this competition. However, they exploit wavefunctions relying on crystal band symmetries, which tunneling interactions are inherently sensitive to. Here we directly image lattice-aperiodic valley interference between coupled atoms in silicon using scanning tunneling microscopy. Our atomistic analysis unveils the role of envelope anisotropy, valley interference and dopant placement on the Heisenberg spin exchange interaction. We find that the exchange can become immune to valley interference by engineering in-plane dopant placement along specific crystallographic directions. A vacuum-like behaviour is recovered, where the exchange is maximised to the overlap between the donor orbitals, and pair-to-pair variations limited to a factor of less than 10 considering the accuracy in dopant positioning. This robustness remains over a large range of distances, from the strongly Coulomb interacting regime relevant for high-fidelity quantum computation to strongly coupled donor arrays of interest for quantum simulation in silicon.


2015 ◽  
Vol 6 (1) ◽  
Author(s):  
X. Ma ◽  
F. Fang ◽  
Q. Li ◽  
J. Zhu ◽  
Y. Yang ◽  
...  

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