?Nondiagonal? magnetic resonance in a two-level spin-system

Marco Frasca

V. Koerting, Jens Paaske, P. Wölfle

The eigenstates of an isolated nanostructure may get mixed by the coupling to external leads. This effect is the stronger, the smaller the level splitting on the dot and the larger the broadening induced by the coupling to the leads. We describe how to calculate the nondiagonal density matrix of the nanostructure efficiently in the cotunneling regime. As an example, we consider a system of two quantum dots in the Kondo regime, the two spins coupled by an antiferromagnetic exchange interaction and each dot tunnel coupled to two leads. Calculating the nonequilibrium density matrix and the corresponding current, we demonstrate the importance of the off-diagonal terms in the presence of an applied magnetic field and a finite bias voltage.

杨宝 Yang Bao, 缪培贤 Miao Peixian, 史彦超 Shi Yanchao +4 more

Finn Lasse Buessen, Vincent Noculak, Simon Trebst +1 more

In the field of quantum magnetism, the advent of numerous spin-orbit assisted Mott insulating compounds, such as the family of Kitaev materials, has led to a growing interest in studying general spin models with nondiagonal interactions that do not retain the SU(2) invariance of the underlying spin degrees of freedom. However, the exchange frustration arising from these nondiagonal and often bond-directional interactions for two- and three-dimensional lattice geometries poses a serious challenge for numerical many-body simulation techniques. In this paper, we present an extended formulation of the pseudofermion functional renormalization group that is capable of capturing the physics of frustrated quantum magnets with generic (diagonal and off-diagonal) two-spin interaction terms. Based on a careful symmetry analysis of the underlying flow equations, we reveal that the computational complexity grows only moderately, as compared to models with only diagonal interaction terms. We apply the formalism to a kagome antiferromagnet which is augmented by general in-plane and out-of-plane Dzyaloshinskii-Moriya (DM) interactions, as argued to be present in the spin liquid candidate material herbertsmithite. We calculate the complete ground state phase diagram in the strength of in-plane and out-of-plane DM couplings, and discuss the extended stability of the spin liquid of the unperturbed kagome antiferromagnet in the presence of these couplings.

С.Д. Петрова, R. M. Umarkhodzhaev

A theoretical and experimental investigation into the motion of the magnetization vector in the presence of two additional circularly-polarized nonresonant rf fields, when these fields rotate in the plane analogous to that of resonant rf fields with the frequency ω, has been performed. The nonresonant fields are equal in magnitude; their frequencies differ from the resonant frequency ω by the value of ±Ω, which essentially exceeds the magnetic resonance line width.

Pietro Bucci, M Martinelli, S. Santucci +1 more