New opportunities for energy harvesting can be found in a century-old thought experiment known as Maxwell's demon, which suggests that energy can be extracted from information. Although systems resembling Maxwell's demon have been experimentally realized, scalability remains a challenge.
In the quantum battery team, our goal is to use the information encoded in nuclear or magnetic impurity spins for energy harvesting.
The current research mostly focuses on the interfacial states of topological insulators, in which the electron spin is locked to its momentum direction: upon driving a current through the material, spin can be transferred for electrons to nuclei via spin-flip interactions, generating a finite nuclear spin polarization. When this polarization thermally relaxes to a disordered state, these spin-flip interactions will drive a finite charge current, which can be used to extract electronic work.
- Theory
Using theoretical analysis, we explore which systems can be suitable quantum batteries. For example, the current-voltage relation on the surface of a three-dimensional topological insulator is expected to gain an inductive component, due to the coupling between electron- and nuclear spins [1]. However, the inductive effect is accompanied by resistive components, which reduce the efficiency of work extraction in these systems. These losses can be avoided in alternative setups, such as by coupling two quantum anomalous Hall states via a junction with nuclear spins [2]. This design not only enables energy storage at the thermodynamic limit but also allows the device to function as a memristor.
Left panel: Schematic description of the transport setup involving the top surface of a 3DTI connected to metallic leads. In response to a charge current flowing through each surface, the charge carriers for top and bottom surfaces are spin-polarized in the opposite direction. Nuclear spins (black/grey arrows) on the top/bottom surface are polarized through spin-flip interactions with spin-polarized charge carriers. Image from [1].
Right panel: Topological information device. The left lead is a quantum anomalous Hall insulator with spin-up electrons propagating in counterclockwise direction, while the right lead is another quantum anomalous Hall insulator with spin-down electrons propagating in clockwise direction. The central region contains nuclear spins and/or magnetic impurities that allow electrons to transmit from one lead to the other lead via spin-flip process. Image from [2].
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[1] A.M. Bozkurt, A. Brinkman, I. Adagideli, Phys. Rev. B 108, 235428 (2023)
[2] A.M. Bozkurt, S. Kölling, A. Brinkman, I. Adagideli, Scipost Phys. Core 8, 023 (2025)
- Experiments
Of course, the burning question remains: does it work? Our experiments pave the way for a proof-of-principle of the quantum battery [1]. The work includes depositing topological insulator thin films, fabricating devices using electron beam lithography, followed by low-temperature transport experiments.
In the three-dimensional topological insulator (Bi1-xSbx)2Te3 (BST), we found signatures of a steady-state nuclear polarization upon applying a DC current. One of the next steps will be to investigate on what timescale this polarization evolves. Furthermore, we add vanadium as a magnetic dopant to BST to investigate whether these impurities can take over the role of nuclear spins in the quantum battery effect.
In collaboration with our theorists and colleagues from our group working on other systems such as Weyl semimetals, we are continuously looking for new systems to experimentally verify the quantum battery effect.
Left panel: Atomic force microscopy image of ultrathin BST (nominal thickness 6 nm) deposited on Al2O3. Holes in the film reach the substrate surface. The graph inset shows the height profile and the scale bar corresponds to 1 micrometer.
Right panel: Measurement geometry where IDC induces a nonequilibrium nuclear polarization. The resultant Overhauser field adds to the external magnetic field, causing an offset in the measured magnetoresistance.
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[1] S. Kölling, PhD thesis (2025)