We investigate a system of three tunnel-coupled semiconductor quantum dots in a triangular geometry, one of which is connected to a metallic lead, in the regime where each dot is essentially singly occupied. Both ferromagnetic and antiferromagnetic spin- $\frac{1}{2}$ Kondo regimes, separated by a quantum phase transition, are shown to arise on tuning the interdot tunnel couplings and should be accessible experimentally. Even in the ferromagnetically-coupled local moment phase, the Kondo effect emerges in the vicinity of the transition at finite temperatures. Physical arguments and numerical renormalization group techniques are used to obtain a detailed understanding of the problem.We investigate a system of three tunnel-coupled semiconductor quantum dots in a triangular geometry, one of which is connected to a metallic lead, in the regime where each dot is essentially singly occupied. Both ferromagnetic and antiferromagnetic spin-$\frac{1}{2}$ Kondo regimes, separated by a quantum phase transition, are shown to arise on tuning the interdot tunnel couplings and should be accessible experimentally. Even in the ferromagnetically-coupled local moment phase, the Kondo effect emerges in the vicinity of the transition at finite temperatures. Physical arguments and numerical renormalization group techniques are used to obtain a detailed understanding of the problem.

arXiv:0902.4816Physical Review BFeb 26, 200976 citations

Quantum phase transitions in magnetic systems

Omid Nohadani

Jan 1, 20140 citations

Quantum phase transitions in frustrated ferro- and ferrimagnets

Johannes Richter, Ulrich Schollwöck, Nedko B. Ivanov

Physica B Condensed MatterJun 1, 20005 citations

Interaction effects on the itinerant ferromagnetism phase transition

Jordi Pera, J. Casulleras, Jordi Boronat

Itinerant ferromagnetism is one of the most-studied quantum phase transitions, the transition point and the nature of this phase transition being widely discussed. In dilute Fermi liquids, this analysis has been carried out up to second order in the gas parameter, where the results for any spin degeneracy are universal in terms of only the s -wave scattering length a 0 . We extend this analysis to third order, where energies depend not only on a 0 , but also on the s -wave effective range r 0 and the p -wave scattering length a 1 . The introduction in the theory of these new parameters changes the transition point, with respect to the second-order estimation, and also can modify the nature of the phase transition itself. We analyze these interaction effects on the phase transition for different spin values. The emerging phase diagram shows that the type of ferromagnetic transition changes dramatically as a function of r 0 and a 1 and, importantly, that this classification is not solely determined by the spin value, as happens at second order.Itinerant ferromagnetism is one of the most-studied quantum phase transitions, the transition point and the nature of this phase transition being widely discussed. In dilute Fermi liquids, this analysis has been carried out up to second order in the gas parameter, where the results for any spin degeneracy are universal in terms of only the s -wave scattering length a 0 . We extend this analysis to third order, where energies depend not only on a 0 , but also on the s -wave effective range r 0 and the p -wave scattering length a 1 . The introduction in the theory of these new parameters changes the transition point, with respect to the second-order estimation, and also can modify the nature of the phase transition itself. We analyze these interaction effects on the phase transition for different spin values. The emerging phase diagram shows that the type of ferromagnetic transition changes dramatically as a function of r 0 and a 1 and, importantly, that this classification is not solely determined by the spin value, as happens at second order.

arXiv:2407.14137Physical Review ResearchFeb 14, 20250 citations

Constraints on the merging of the transition lines at the tricritical point in a wing-structure phase diagram

Valentin Taufour, Udhara S. Kaluarachchi, V. G. Kogan

We consider the phase diagram of a ferromagnetic system driven to a quantum phase transition with a tuning parameter $p$ . Before being suppressed, the transition becomes of the first order at a tricritical point, from which wings emerge under application of the magnetic field $H$ in the $T\ensuremath{-}p\ensuremath{-}H$ phase diagram. We show that the edge of the wings merge with tangent slopes at the tricritical point.We consider the phase diagram of a ferromagnetic system driven to a quantum phase transition with a tuning parameter $p$. Before being suppressed, the transition becomes of the first order at a tricritical point, from which wings emerge under application of the magnetic field $H$ in the $T\ensuremath{-}p\ensuremath{-}H$ phase diagram. We show that the edge of the wings merge with tangent slopes at the tricritical point.

arXiv:1608.04424Physical review. B./Physical review. BAug 19, 201611 citations

\frac{1}{2}

Kondo regimes, separated by a quantum phase transition, are shown to arise on tuning the interdot tunnel couplings and should be accessible experimentally. Even in the ferromagnetically-coupled local moment phase, the Kondo effect emerges in the vicinity of the transition at finite temperatures. Physical arguments and numerical renormalization group techniques are used to obtain a detailed understanding of the problem.

We consider the phase diagram of a ferromagnetic system driven to a quantum phase transition with a tuning parameter

p

. Before being suppressed, the transition becomes of the first order at a tricritical point, from which wings emerge under application of the magnetic field

H

in the $T\ensuremath{-}p\ensuremath{-}H$ phase diagram. We show that the edge of the wings merge with tangent slopes at the tricritical point.