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AIP conference proceedings

Quantum spin pumping for a system with competing exchange interactions.

Sujit Sarkar, Chong Der Hu, Amitabha Ghoshray, Bilwadal Bandyopadhyay

Published Jan 1, 2008• 0 citations
Publisher

Abstract

We study the quantum spin pumping of an antiferromagnetic spin‐1/2 chain with competing exchange interactions. We show that spatially periodic potential modulated in space and time acts as a quantum spin pump. In our model system, an applied electric field causes a spin gap to its critical ground state by introducing bond‐alternation exchange interactions.

DOI
10.1063/1.2928927

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cond-mat.mes-hallCross-listedarXiv:2609.16819•Sep 16, 2026
We study the quantum spin pumping of an antiferromagnetic spin‐1/2 chain with competing exchange interactions. We show that spatially periodic potential modulated in space and time acts as a quantum spin pump. In our model system, an applied electric field causes a spin gap to its critical ground state by introducing bond‐alternation exchange interactions.
We study the quantum spin pumping of an antiferromagnetic spin-1∕21∕21∕2 chain with competing exchange interactions. We show that spatially periodic potential modulated in space and time acts as a quantum spin pump. In our model system, an applied electric field causes a spin gap to its critical ground state by introducing bond-alternation exchange interactions. We study quantum spin pumping at different quantized magnetization states and also explain physically the presence and absence of quantum spin pumping at different fractionally quantized magnetization states.
In this paper, we propose the quantum spin pumping in quantum spin systems where an applied electric field (EEE) and magnetic field (HHH) cause a finite spin gap to its critical ground state. When these systems are subject to alternating electromangetic fields; (E,H)=(sin⁡2πtT,cos⁡2πtT)(E,H)=(\sin\frac{2πt}{T},\cos\frac{2πt}{T})(E,H)=(sinT2πt​,cosT2πt​) and travel along the {\it{loop}} ΓloopΓ_{\rm{loop}}Γloop​ which encloses their critical ground state in this EEE-HHH phase diagram, the locking potential in the sine-Gordon model slides and changes its minimum. As a result, the phase operator acquires 2π2π2π holonomy during one cycle along ΓloopΓ_{\rm{loop}}Γloop​, which means that the quantized spin current has been transported through the bulk systems during this adiabatic process. The relevance to real systems such as Cu-benzoate and Yb4As3{\rm{Yb}}_4{\rm{As}}_3Yb4​As3​ is also discussed.
We propose an exactly solvable quantum spin model, in which the alternation of the exchange interactions between neighboring spins is accompanied by the multiple spin exchange. The model permits us to obtain exactly thermodynamic characteristics of the considered quantum spin chain. In the ground state, depending on the strength of the three-spin coupling, the model manifests either the spin-gapped behavior of low-lying excitations at low magnetic fields, or the ferrimagnetic ordering with the spontaneous magnetization and with gapless low-lying excitations. The system undergoes second order or first order quantum phase transitions, governed by an external magnetic field and the multiple spin exchange coupling strength. Our exactly solvable quantum spin model demonstrates that multispin interactions in a dimerized quantum spin chain can produce a spontaneous magnetization. On the other hand, for quantum spin chains with a spontaneous magnetization, caused by multispin couplings, the alternation of nearest neighbor exchange interactions can be the reason for destroying of that magnetization and the onset of a spin gap for low-lying excitations.
Abstract A quantum spin model of a delta chain with exchange interactions of ferro- (F) and antiferromagnetic (AF) types is studied. The model properties significantly depend on the frustration parameter α (the ratio of the constants of AF and F interactions). When α < 1/2, the ground state is ferromagnetic, and at α = 1/2, a quantum phase transition occurs to another phase. Based on the numerical calculations and analysis of the model at large values of α it is concluded that the ground state at α > 1/2 is magnetically ordered and the total spin of the ground state is half the maximum possible spin. Comparison of the properties of the ground state of the classical and quantum models shows that the considered model is an example of a system in which quantum effects are responsible for the appearance of order from disorder.
The strongest interaction between microscopic spins in magnetic materials is the exchange interaction Jex. Therefore, ultrafast control of Jex holds the promise to control spins on ultimately fast timescales. We demonstrate that time-periodic modulation of the electronic structure by electric fields can be used to reversibly control Jex on ultrafast timescales in extended antiferromagnetic Mott insulators. In the regime of weak driving strength, we find that Jex can be enhanced and reduced for frequencies below and above the Mott gap, respectively. Moreover, for strong driving strength, even the sign of Jex can be reversed and we show that this causes time reversal of the associated quantum spin dynamics. These results suggest wide applications, not only to control magnetism in condensed matter systems, for example, via the excitation of spin resonances, but also to assess fundamental questions concerning the reversibility of the quantum many-body dynamics in cold atom systems.
In this study, quantum spin pumping in an antiferromagnetic chain driven by time-dependent potential is investigated. The aim is to explore the possibility of generating and controlling spin currents in the absence of external bias and to examine the role of exchange field and periodic driving in the separation of spin-up and spin-down currents. The system is described using a tight-binding model, and spin-resolved currents are calculated employing the Keldysh non-equilibrium Green's function formalism. Two time-dependent potentials with a specific phase difference are applied to the two ends of the chain, while the chemical potentials of both electrodes are set equal. The results demonstrate that in the adiabatic regime (low frequencies), the response of the two spin channels is nearly identical. However, as the driving frequency increases and the system enters the nonadiabatic regime, absorption and emission processes of energy quanta become activated, leading to significant differences between spin-up and spin-down currents. The pumped current exhibits strong dependence on the chemical potential, allowing for the control of both magnitude and direction of the spin current through its adjustment. With increasing frequency, the spin current enhances, and parameters can be tuned such that the charge current nearly vanishes while a considerable spin current persists. This finding indicates the feasibility of achieving nearly pure spin pumping without net charge transfer in the antiferromagnetic chain. The results provide a promising perspective for designing spin-pumping devices based on antiferromagnetic systems.