Sharp peaks in the conductance of a double quantum dot and a quantum-dot spin valve at high temperatures: A hierarchical quantum master equation approach

Abstract

We study sharp peaks in the conductance-voltage characteristics of a double quantum dot and a quantum dot spin-valve that are located around zero bias. The peaks share similarities with a Kondo peak but can be clearly distinguished, in particular as they occur at high temperatures.The underlying physical mechanism is a strong current suppression that is quenched in bias-voltage dependent ways by exchange interactions. Our theoretical results are based on the quantum master equation methodology, including the Born-Markov approximation and a numerically exact, hierarchical scheme, which we extend here to the spin-valve case. The comparison of exact and approximate results allows us to reveal the underlying physical mechanisms, the role of first-, second-and beyond-second-order processes and the robustness of the effect.

Transport mirages in single-molecule devices

“…In the SET regime, such effects can lead to a nearly 100% modulation of the transport current 214,215 due to quantum interference. This emphasises that 216 SET-the first order approximation in Γ-is not "incoherent" or "classical" as some of the nomenclature in Table I seems to imply. Similar coherence effects can arise from orbital polarization in QDs [217][218][219][220][221] and STM configurations 222 , from an interplay between spin and orbital coherence 78,223,224 , or from charge superpositions of electron pairs. Finally, for high-spin systems coherence effects of tensorial character can arise.…”

Nonequilibrium open quantum systems with multiple bosonic and fermionic environments: A hierarchical equations of motion approach

“…For this purpose previous works have introduced an importance criterion for pure fermionic environments, which estimates the importance of an ADO to the dynamics of the system. 40,45,63 If the importance I assigned to an ADO is below a given threshold value θ, it is neglected. This reduces the numerical complexity to a manageable level and allows for a systematic convergence.…”

“…Later it was extended by several groups for the investigation of charge and energy transport caused by fermionic environments. [38][39][40][41][42][43][44][45][46][47] As summarized by Tanimura, 48 so far studies using the HQME approach have focused on either bosonic or fermionic environments. In this work, we formulate the HQME method for more general models, depicted in Fig.…”

Interaction-induced current asymmetries in resonant transport through interacting quantum-dot spin valves revealed by iterative summation of path integrals

“…By treating electron-electron interactions in Hartree-Fock approximation, the TMR and the accumulated spin were examined for a quantum-dot spin valve in a noncollinear setup 13 . In the high-temperature limit, several peaks in the quantum-dot spin valve's conductance were discussed using a hierarchical quantum master equation approach 14 . Within a weak-tunneling approximation in a wide range of bias and gate voltages, characteristics of the exchange field for a quantum-dot spin valve have been discussed 12,15 .…”