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| Author(s): |
Igor Cesar de Almeida
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Carlos. |
| Institution: | Universidade de São Paulo (USP). Instituto de Física de São Carlos (IFSC/BT) |
| Defense date: | 2023-10-11 |
| Examining board members: |
Eric de Castro e Andrade;
Natanael de Carvalho Costa;
Ricardo Luis Doretto;
Paulo Eduardo Fornasari Farinas;
Carlos Eduardo Fiore dos Santos
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| Advisor: | Eric de Castro e Andrade |
| Abstract | |
Correlated materials present an enormity of phases of matter, stabilized by a non-trivial competition between interactions and fluctuations. An important ingredient to take into account in real materials is the deviation of the lattice periodicity , or disorder. In this work, we will investigate properties and emergent phases in the absence of the translational invariance of crystals. In particular, we seek to understand the effects of disorder on frustrated and strongly correlated systems. In the first part of this work, we analyze the effects caused by the dilution of bonds and sites in a Mott insulator with frustrated antiferromagnetic interactions, specially regarding the survival of long-range order. We modeled this system using a semiclassical antiferromagnetic Heisenberg model, and found that any finite dilution in the bonds and/or sites destroys, due to a induced non-trivial spin texture, any long-range order at T = 0. This is an important result for understanding the low temperature properties of quasi-two-dimensional magnets, as in the case of van der Waals materials, and illustrates that the combined presence of disorder and frustration leads to non-trivial effective models. In the second part, we build a minimal model, the so-called two-site Kondo-Heisenberg model, for the Si:P doped semiconductor (phosphorusdoped silicon), in which, in the vicinity of the metal-insulator transition, localized magnetic impurities coexist with conduction electrons. The disorder here is due to the random position of the impurities, which constitute the effective lattice in which the electrons will hop with a hopping constant that is exponentially suppressed with distance.We then sought to analyze the competition between the Kondo coupling, which induces a screening of the impurities, below a temperature TK , by the electronic bath, and the antiferromagnetic interaction between the localized moments, which tend, through this interaction, to form singlets. Our results demonstrate the appearance of a Kondo temperature distribution, P (TK), which is singular, P (TK) α T -α K , with exponent α < 1. This exponent depends very little on the metal-insulator transition, but depends on the Kondo coupling, as well as on the antiferromagnetic coupling between impurities. We show that P (TK) becomes less singular in the presence of antiferromagnetic interaction, correcting a pathology of singlesite theories. However, our simple model is still not able to reproduce all the experimental results for Si:P and, therefore, we point out future directions that will be implemented to advance in this important problem. (AU) | |
| FAPESP's process: | 19/17645-0 - Magnetic excitations in inhomogeneous frustrated magnets |
| Grantee: | Igor César de Almeida |
| Support Opportunities: | Scholarships in Brazil - Doctorate |