Browsing by Author "Kirchner, Stefan"

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Quantum phase transition in a two-dimensional Kondo-Heisenberg model: A dynamical Schwinger-boson large-N approach
(2020-09-15)
Wang, Jiangfan
;
Chang, Yung-Yeh
;
Mou, Chung-Yu
;
Kirchner, Stefan
;
Chung, Chung-Hou
We generalize the dynamical large-N multichannel Schwinger-boson approach to study the quantum phase transition of a two-dimensional Kondo-Heisenberg model, relevant for heavy electron systems, close to an antiferromagnetic Kondo destruction quantum critical point. By breaking up a Kondo singlet into a charge fermion (holon) and a bosonic spinon, we identify and characterize the quantum phase transition from an antiferromagnetically ordered state to a Kondo-dominated paramagnetic state, and attribute a jump in the holon phase shift to Kondo breakdown. We calculate transport and thermodynamic quantities. The global finite-temperature phase diagram and the critical behavior of various physical observables therein show a close resemblance to experimental observations.
Universal scaling of nonlinear conductance in the two-channel pseudogap Anderson model: Application for gate-tuned Kondo effect in magnetically doped graphene
(2013-08-26)
Lee, Tsung-Han
;
Zhang, Kenneth Yi-Jie
;
Chung, Chung-Hou
;
Kirchner, Stefan
;
電子物理學系
Based on the noncrossing approximation, we calculate both the linear and nonlinear conductance within the two-lead two-channel single-impurity Anderson model where the conduction electron density of states vanishes in a power-law fashion proportional to vertical bar omega - mu(F)vertical bar(r) with r = 1 near the Fermi energy, appropriate for a hexagonal system. For given gate voltage, we address the universal crossover from a two-channel Kondo phase, argued to occur in doped graphene, to an unscreened local moment phase. We extract universal scaling functions in conductance governing charge transfer through the two-channel pseudogap Kondo impurity and discuss our results in the context of a recent scanning tunneling spectroscopy experiment on Co-doped graphene.