arXiv subjects

Zhao Gong

Publications and source records attributed to Zhao Gong.

5 recordsLinked to original sources

arXiv2026

Cascade of magnetic-field-induced quantum spin states in a spin-1 honeycomb magnet

Quantum fluctuations endow spin systems with surprisingly enriched magnetic phase diagrams. In frustrated magnets, strong quantum fluctuations boosted by either geometrical incompatibility or competitive exchange interactions stabilize cascades of unusual phases of matter. Here we reveal the presence of multiple quantum phases in the honeycomb antiferromagnet Na$_{3}$Ni$_{2}$BiO$_{6}$, both inside and beyond its field-induced one-third magnetization plateau. Comprehensive measurements of thermodynamic quantities demonstrate that the one-third plateau comprises at least three distinct spin states with nearly-degenerate net magnetization, separated by first-order transitions that likely involve sequential spin reconfiguration. Upon further increasing the magnetic field, the system evolves across a myriad of peculiar phases before reaching full polarization; these intermediate phases possess copious low-energy excitations, manifested by anomalous upturns of specific heat at ultralow temperatures -- probably hinting at the development of "hidden" ordered ground states. The complex magnetic phase diagram of Na$_{3}$Ni$_{2}$BiO$_{6}$ underlines the preponderant impact of quantum fluctuations on a honeycomb spin lattice with strong exchange frustration.

cond-mat.str-el↗

arXiv2025

Multiple quantum spin Hall states and topological current divider in Twisted Bilayer WSe$_2$

It has been demonstrated that topological quantum spin Hall (QSH) state exist in twisted bilayers of transition metal dichalcogenides. However, a comprehensive theoretical characterization of the topological edge states remains a topic of interest and an unresolved issue. Here, the topological transport properties of the twisted WSe$_2$ bilayers are investigated. Beyond the conventional single QSH, we identify emergent double and quartuple quantum spin Hall states, hosting two and four pairs of counter-propagating helical edge channels respectively. Furthermore, the charge carriers in these edge states are not localized at edge but rather the high potential point of the moire superlattice boundary, undergoing interlayer transitions and propagating forward continuously. We term these edge states as moire edge states. These edge states can survive in non-magnetic disorder, with the robustness of double QSH states surpassing that of single QSH states. At a twisting angle of 2.45$^\circ$, the transition between the single and double QSH states can be achieved by adjusting the gate on the surface. Based on this, we propose a five-terminal device to as a topological current devider. Our findings provide support for the development of dissipationless spintronics.

cond-mat.mes-hall↗

arXiv2024

Topological Insulator in Twisted Transition Metal Dichalcogenide Heterotrilayers

The quantum spin Hall effect has been predicted in twisted homobilayer transition metal dichalcogenides (TMDs) owing to the layer-pseudospin magnetic field. Recently, experimental observations have also confirmed such topological states of matter. However, the topological electronic properties in multilayer moir\'e superlattices remain to be further explored. In twisted TMDs heterotrilayers, the realization of moir\'e potential with various symmetries becomes feasible. Here, we demonstrate that twisted trilayer TMDs can enter a topological insulator phase under the influence of moir\'e potential with ${C_6}$ symmetry. Specifically, we built two types of trilayer heterostructures, where the low-energy valence band electrons are contributed by the middle layer. In the AA-stacked moir\'e WS$_2$/WSe$_2$/MoS$_2$ heterotrilayers where only the middle layer is twisted, the maxima of the moir\'e potential exhibits an approximate ${C_6}$ symmetry. The $C_6$ symmetry effectively compensates for the spatial inversion symmetry breaking in the WSe$_2$ layer, leading to a twist-angle-dependent topological phase transition. Leveraging a Green's function approach, we calculate the local state density of edge states at topological minigaps, confirming their nature as moir\'e edge states. In the helical twisted AA-stacked moir\'e MoS$_2$/WSe$_2$/MoS$_2$ heterotrilayers, we observed a mosaic pattern of topological and trivial insulators. The emergence of topological mosaic is attributed to the maxima of the local moir\'e potential possessing $C_6$ symmetry. The results provide a new way for the experimental realization of topological phases in TMDs heterojunctions.

cond-mat.mes-hall↗

arXiv2024

Layer-dependent transport properties in the Moiré of strained homobilayer transition metal dichalcogenides

Bilayer moiré structures have attracted significant attention recently due to their spatially modulated layer degrees of freedom. However, the layer-dependent transport mechanism in the moiré structures is still a problem to be explored. Here we investigate the layer-dependent transport properties regulated by the strain, the interlayer bias and the number of moiré periods in a strained moiré homobilayer TMDs nanoribbon based on low-energy efficient models. The charge carriers can pass perfectly through the scattering region with the moiré potential. While, it is noted that the overall transmission coefficient is mainly contributed from either intralayer or interlayer transmissions. The transition of transport mechanism between intralayer and interlayer transmissions can be achieved by adjusting the strain. The intralayer transmissions are suppressed and one of the interlayer transmissions can be selected by a vertical external electric field, which can cause a controllable layer polarization. Moreover, the staggered intralayer and interlayer minigaps are formed as the number of moiré periods increases in the scattering region due to the overlap of the wave functions in two adjacent moiré periods. Our finding points to an opportunity to realize layer functionalities by the strain and electric field.

cond-mat.mes-hall↗

arXiv2023

Spin-polarized transport properties in magnetic moir\'e superlattices

Since the discovery of the fascinating properties in magic-angle graphene, the exploration of moir\'e systems in other two-dimensional materials has garnered significant attention and given rise to a field known as 'moir\'e physics'. Within this realm, magnetic van der Waals heterostructure and the magnetic proximity effect in moir\'e superlattices have also become subjects of great interest. However, the spin-polarized transport property in this moir\'e structures is still a problem to be explored. Here, we investigate the spin-polarized transport properties in a moir\'e superlattices formed by a two-dimensional ferromagnet CrI_3 stacked on a monolayer BAs, where the spin degeneracy is lifted because of the magnetic proximity effect associated with the moir\'e superlattices. We find that the conductance exhibits spin-resolved miniband transport properties at a small twist angle because of the periodic moir\'e superlattices. When the incident energy is in the spin-resolved minigaps, the available states are spin polarized, thus providing a spin-polarized current from the superlattice. Moreover, only a finite number of moir\'e period is required to obtain a net spin polarization of 100\%. In addition, the interlayer distance of the heterojunction is also moir\'e modifiable, so a perpendicular electric field can be applied to modulate the intensity and direction of the spin polarization. Our finding points to an opportunity to realize spin functionalities in magnetic moir\'e superlattices.

cond-mat.mes-hall↗