Ronaldo N. Araújo | Searcharxiv

arXiv2024

Fragile magnetic order in metallic quasicrystals

Inspired by recent experimental studies of local magnetic moments interacting with a metallic quasicrystal, we study the low-temperature fate of spins placed in two-dimensional tilings. In the diluted local moment limit, we calculate the spin relaxation rate $1/T_{1}$, as measured by electron spin resonance, and show that it displays a marked dependence on the system size $N$ and the filing $n$ of the electronic bath. For a finite concentration of spins, we integrate out the conduction electrons and generate an effective magnetic coupling between the local moments, which we treat as Ising spins. Despite the strongly frustrating nature of the magnetic couplings and the lack of periodicity in the problem, we find long-range orders for finite $N$ in our large-scale Monte Carlo simulations. However, the resulting magnetically state is fragile, as clusters of essentially free spins fluctuate down to very low temperatures.

cond-mat.str-el↗

arXiv2019

Conventional superconductivity in quasicrystals

Motivated by a recent experimental observation of superconductivity in the Al-Zn-Mg quasicrystal, we study the low-temperature behavior of electrons moving in the quasiperiodic potential of the Ammann-Beenker tiling in the presence of a local attraction. We employ the Bogoliubov-de Gennes approach for approximants of different sizes and determine the local pairing amplitude $Δ_{i}$ as well its spatial average, $Δ_{0}$, the superconducting order parameter. Due to the lack of periodicity of the octagonal tiling, the resulting superconducting state is inhomogeneous, but we find no evidence of the superconductivity islands, as observed in disordered systems, with $Δ_{i}\rightarrow0$ at $T_{c}$ for all sites. In the weak-coupling regime, we find that the superconducting order parameter depends appreciably on the approximant size only if the Fermi energy sits at a pseudogap in the noninteracting density of states, with $Δ_{0}$ decreasing as the system size increases. These results are in line with the experimental observations for the Al-Zn-Mg quasicrystal, and they suggest that, despite their electronic structure, quasicrystals are prone to display conventional BCS-like superconductivity.

cond-mat.supr-con↗