Since the beginning of the twenty-first century, the rapid developments of condensed-matter physics have deepened our understanding of microscopic electronic behavior in low-dimensional materials and opened new routes toward quantum devices. The conventional quantum Hall effect relies on a strong external magnetic field to quantize electronic states, and the massive magnetic-field apparatus restricts device integration and practical applications. With growing demand for topological quantum computing and low-power chiral electronic devices, quantized transport without an external magnetic field has become an important research focus. Among the various topological phases, the quantum anomalous Hall (QAH) effect has attracted particular attention because it produces a quantized Hall response at zero magnetic field. The effect connects microscopic magnetic order and Berry-curvature topology with macroscopic quantum transport, thereby deepening our understanding of topological phases and providing a basis for topological quantum devices. When current flows through a two-dimensional sample, the transverse deflection of charge carriers produces a Hall voltage across the two sides of the sample. Whereas the conventional quantum Hall effect uses a strong external magnetic field to form quantized electronic states, the QAH effect exploits the intrinsic magnetism, or layer-pseudospin magnetism, and band topology of a material to generate a quantized Hall response without an applied magnetic field. Magnetic order breaks time-reversal symmetry, allowing a net contribution from the Berry curvature over the Brillouin zone, and making a nonzero Chern number and topological transport possible. In many magnetic topological candidates, exchange interactions and spin–orbit coupling jointly reshape the electronic bands and can open a topological gap, producing a magnetic topological-insulator state. When the Fermi level lies within the band gap, bulk conduction is strongly suppressed and current can propagate along the sample boundary in a fixed direction. Ideally, the quantized transverse Hall conductivity satisfies , while the longitudinal conductivity approaches zero. This perspective will follow the route of materials design–magnetic-state control–transport validation, focusing on how magnetic order, the topological gap, and Fermi-level alignment can jointly establish a reproducible and verifiable QAH quantization window.
Figure 1 illustrates the QAH effect in magnetic topological insulators and its prospective applications, ranging from fundamental studies of zero-field quantization and bulk–edge transport to quantum metrology, chirality writing, and topological current routing. Compared with conventional quantum Hall platforms that require strong external magnetic fields, zero-field quantization has a clear metrological value: for Chern number
, the QAH effect can realize the resistance standard
[
1]. In the longer term, magnetization reversal may write nonvolatile Hall states and reverse the chirality of edge currents, while regions with different Chern numbers may be used to construct reconfigurable chiral current channels [
2,
3]. QAH–superconductor heterostructures also provide a platform for investigating chiral Majorana modes and topological quantum computing [
4]. These device concepts require high-quality QAH platforms. Toward this goal, several types of experimental QAH systems have been developed over the past decade [
5], and related experiments have verified the quantized transport mechanism originating from magnetism-band-topology coupling. For example, Cr-doped (Bi, Sb)
2Te
3 exhibited a nearly quantized zero-field Hall plateau at millikelvin temperatures [
5], followed by intrinsic magnetic topological material MnBi
2Te
4 [
6]. Correlated systems such as moiré MoTe
2 and rhombohedral graphene further exhibit gate-tunable electron filling and spontaneous valley polarization [
7–
10]. At the same time, the design of 2D magnetic materials has increasingly considered local Berry curvature, magnetic order, topological gaps, and the influence of Chern states on electrical transport. Strong anomalous Hall responses in 2D ferromagnetic metals verify that magnetism — Berry curvature coupling yields prominent transverse transport [
11,
12]. Multiple candidate materials with global Chern gaps have also been predicted, and tuning knobs of magnetization, electric-field, strain and electronic correlation are pushing these platforms toward quantized switchable insulating states [
13–
17].
From an application perspective, existing QAH states are far from satisfying the demands of stable device operation. Precise quantization is currently observed mainly at low temperatures and within narrow gate-voltage windows [
18–
20]. The theoretically predicted topological gap describes the band separation in an ideal crystal, whereas defect states, charge inhomogeneity, and interface disorder in practical devices can introduce bulk conduction channels within the gap. Experiments confirm that the rise of bulk conductivity with temperature degrades precise quantization long before edge channels vanish. Local current imaging and multiterminal transport measurements further confirm concurrent conduction via bulk states and edge channels [
21–
23]. Under finite bias, localized hot spots near the contacts may trigger QAH breakdown, thereby limiting the current range over which quantized transport can be sustained [
24]. Accordingly, a large topological gap, high magnetic ordering temperature and robust anomalous Hall signal constitute favorable prerequisites for QAH. Nevertheless, conclusive transport evidence demands simultaneous observation of bulk insulation, chiral edge transport and quantized Hall response. The central challenge for applications lies in realizing all these criteria within a single device under realistic operating conditions.
Magnetic-order control, interface engineering, and transport manipulation for tackling these device-level challenges constitute the two-dimensional magnetism research directions summarized in Fig. 2 from
Frontiers of Physics. Research on high-temperature ferromagnetism and anisotropic exchange has extended the accessible temperature window for 2D magnetic order and deepened insights into its microscopic origin [
25]. Crystal-field effects, spin–orbit coupling, and interlayer exchange interactions further elucidate the formation mechanisms of 2D magnetic moments, magnetic anisotropy, and collective excitations [
26,
27]. On this basis, doping, strain, and interface engineering can actively tune interlayer exchange, magnetic configurations, and hysteresis characteristics [
28–
30], while multiferroic coupling further expands the scope for the coordinated control of multiple order parameters [
31]. As research extends from magnetic-state engineering to electronic band topology, valley and Chern degrees of freedom offer an expanded phase space for realizing quantized transverse transport [
14]. Meanwhile, magnetization orientation and electric fields can select topological phases with distinct Chern numbers as well as topologically trivial phases [
32–
34]. These advances progressively establish a mechanism chain from magnetic-order stability and the control of exchange interactions and magnetic configurations, through the formation of Chern gaps and the selection of topological phases, to suppressed bulk conduction and stable edge transport, thereby showing how the tunable degrees of freedom of two-dimensional magnets enter the QAH device problem. However, these control strategies may also have competing effects on transport: doping can introduce disorder and in-gap impurity states, while strain and interface engineering may cause spatial inhomogeneity, charge transfer, and additional scattering. Only when these factors are appropriately coordinated within the same device can such control strategies be converted into a broader and more reproducible operating window for high-precision QAH quantization.
Driven by these advances and practical demands, we propose that the primary goal for future research is to extend the reproducible quantization window and evolve QAH from a low-temperature plateau into a robust device state that can be reliably established and sustained. At the material-design level, the topological gap and magnetic ordering temperature should be co-optimized alongside disorder, interfaces and carrier modulation. At the device-control level, one must distinguish the distinct physical roles of gate-induced Fermi-level shifts, topological-band reconstruction, and magnetic-configuration writing [
2,
34,
35]. These efforts should be combined with Hall and longitudinal transport, multiterminal/nonlocal measurements, bulk conductance, as well as temperature- and bias-dependent breakdown measurements [
18,
24]. Structure–property relationships for QAH should then be established and tested across different material platforms: local spectroscopy can determine how twist angle, strain, and interfaces affect the electronic structure [
30,
36]; the bulk–edge transport can verify the establishment of target Chern topological state. The resulting knowledge can then be fed back into reproducible growth, device contacting, and integration processes [
37], enabling mutual calibration between fabrication parameters and device transport performance. Stable reproduction of 2D magnetic QAH across wider temperature, gate-voltage and current windows establishes an experimental device platform for quantum metrology and topological technology development.
PDF
(2265KB)
