Growth of monocrystals of prototype CdI2 dicalcogens and investigation of superconducting properties

Author(s)

Lucas Eduardo Corrêa

• Document type: Doctoral Thesis
• Press: Lorena.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de Lorena (EEL/ASDI)
• Defense date: 2022-12-16

Examining board members

Antonio Jefferson da Silva Machado; José Albino Oliveira de Aguiar; Enzo Granato; Iakov Veniaminovitch Kopelevitch

• Advisor: Antonio Jefferson da Silva Machado

Abstract

This work systematically explores the intercalation of rare earth atoms as well as transition metals in the ZrTe2 compounds. ZrTe2 is a material with a non-trivial topology today called a Dirac semimetal. In this sense, the superconductivity that emerges from these compounds may show an unconventional behavior. The results presented here reveal that defects at the Te sites in ZrTe2 induce superconductivity at about 3.2 K. Therefore, this is a result that reveals for the first time that this Dirac semimetal can exhibit superconducting behavior. Nickel intercalations are capable of inducing superconductivity in the host material with a critical temperature onset of 4.5 K. It is unambiguously demonstrated that a coexistence between superconductivity and Charge Density Wave (CDW) instability exists in the single crystal of general composition Ni0.04ZrTe2 being, therefore, a rare example of the two competitive phenomena surviving in the same material. The cobalt intercalation reveals, in addition to a superconducting behavior near 3.5 K, a material with a reentrant behavior in high applied magnetic fields. Although we do not have a clear explanation for this effect, the results suggest an unconventional, magnetic fieldcatalyzed superconductivity, where Cooper pairs do not show phase coherence at a temperature close to 15.0 K. When dysprosium is intercalated in the material (ZrTe2), a dome-like superconducting behavior appears, indicating an unconventional superconductivity. Cooper pairs appear to be mediated by some kind of magnetic fluctuation. All superconducting results are best explained within a multiband material scenario. This multiband behavior seems to be related as an intrinsic property of ZrTe2. These results were obtained in single crystals of high chemical and crystallographic quality. In this sense, this thesis contributed to the creation of a new growth method that we call ICVT from the English acronym Isothermal Chemical Vapor Transport. The interpretations in this thesis are supported by measurements of: X-ray diffraction, thermoelectric measurements, specific heat, resistivity, magnetization, microanalysis by Energy Dispersive Spectroscopy - EDS and Induced Coupled Plasma - ICP. (AU)

• FAPESP's process: 18/08819-2 - Growth of single crystals of CdI2 prototype dicalcogens and investigation of superconducting properties
• Grantee: Lucas Eduardo Corrêa
• Support Opportunities: Scholarships in Brazil - Doctorate