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Journal of Physics: Condensed Matter - latest papers
Latest articles for Journal of Physics: Condensed Matter
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Manipulation of waves in polariton topological insulators
As a frontier in condensed matter physics, the concept of topological insulators has been successfully extended from electronic systems to photonic systems and even to structured microcavities, where strong photon–exciton coupling gives rise to hybrid part-light, part-matter exciton–polaritons quasiparticles. Polaritons inherit the low-loss, tunable characteristics of photons while retaining strong excitonic nonlinear interactions, offering an ideal nonequilibrium platform for exploring topological states. This review systematically surveys the progress of topological insulators in exciton–polariton systems, with emphasis on their underlying physical mechanisms, exotic quantum phenomena induced by various strategies, and the impact of nonlinear effects on topological states. Finally, we discuss the key challenges currently facing this field and provide an outlook on future research directions.
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Lateral finite-size effect of flat-band spectral weight in Kagome metal CoSn
Driven by their unique lattice structure, Kagome systems exhibit fascinating properties, prominent among which is the emergence of flat bands. Here we report a scanning tunneling microscopy and spectroscopy study on the lateral finite-size effect of flat-band spectral weight in the Kagome metal CoSn. We identify two distinct cleaved surfaces: Co3Sn and Sn2. On the Co3Sn surface, we detect two electronic peaks located at 70 and 250 mV below the Fermi level, which correspond to the flat bands originating from Co d orbitals. Notably, the flat-band intensity exhibits a strong dependence on the lateral size of the Kagome islands. The flat bands start to emerge in Co3Sn islands consisting of only a half-unit-wide Kagome chain. As the island width increases, the flat-band intensity rises exponentially and reaches saturation when the island width reaches four-unit cells or larger. By analyzing the size-dependent intensity data, we extract the characteristic length scale for this saturation behavior. Furthermore, on the large Co3Sn surface, we observe a broad and non-dispersive wavevector with a periodicity close to √3×√3 in the Fourier-transformed differential conductance maps. These results not only reveal the novel lateral finite-size effect of flat-band spectral weight at the atomic scale, but also pave the way for a deeper understanding of the complex electronic structures in Kagome materials.
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Classifying coherent peaks in nanoelectronic devices by the presence or absence of spin exchange
Coherent peaks appearing in the differential conductance of quantum-dot single-electron transistors (QDSETs) and quantum point contact (QPC) devices are classified into two categories according to the scaling function onto which the temperature-scaled differential-conductance maxima collapse and the underlying spin dynamics. The zero-bias peaks (ZBPs) observed in QPCs and in the triplet state of the even-particle sector of QDSETs belong to the same category, whereas the ZBP in the odd-particle sector of a QDSET belongs to a different category together with all finite-bias coherent peaks observed in QPCs and in the even-particle sector of QDSETs. The spin dynamics of the former category involve spin exchange, a hallmark of Kondo dynamics, whereas those of the latter category involve only cotunneling of an up–down spin pair. Furthermore, for the former type of ZBP, the scaling temperature coincides with one-half of the full width at half maximum (FWHM), which corresponds to the Kondo temperature. In contrast, for the latter type, the scaling temperature does not coincide with the (1/2)FWHM-derived energy scale. To support these findings, the gate-voltage-dependent differential-conductance line shapes measured in the odd-particle sector of a QDSET are theoretically reproduced. The results demonstrate that the observed ZBP is a merging of two coherent side peaks generated solely by the cotunneling of up–down spin pairs.
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Spin segregation of nonrelativistic charged particles by a helical magnetic field slab
We study a beam of nonrelativistic spin- charge carriers incident normally on a finite slab of helical magnetic field aligned along the beam axis. Starting from the Pauli–Schrödinger equation, we apply a unitary transformation expressed in terms of Pauli matrices to map the system to a spatially independent eigenvalue problem, from which the energy band structure is obtained analytically. Our results reveal two types of bandgap controlled by the field strength: a partial bandgap present for all field values, in which only one spin channel propagates, and a total bandgap that opens above a threshold field strength, in which both channels are evanescent. Using the eigenvectors and a transfer matrix approach, we solve the boundary value problem at the vacuum-magnetic interface and obtain spin-preserving and spin-flip transmittances and reflectances as functions of field strength and energy. The spin-filtering properties are discussed in terms of the alignment of the spin eigenstates with the effective field in spin space, with the Bloch sphere providing a geometric picture of the spin-channel selection mechanism.
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Magnetic ordering in VI 3 ...
Among magnetic van der Waals materials, the vanadium trihalide family exhibits unique features. In particular, can contain two types of V atoms because two electronic occupations are energetically close and may coexist in real samples. These types have strikingly different magnetic anisotropies, predicted to differ by more than an order of magnitude. also shows an unusual thickness dependence: the reported monolayer Curie temperature, , is higher than that of the bulk, contrary to the usual expectation that interlayer coupling reinforces magnetic order. Here, we use atomistic spin-dynamics simulations to study critical temperatures in from the combined perspective of single-ion anisotropy and exchange interactions, aiming to identify the microscopic origin of the bulk–monolayer anomaly. We consider a system composed of two V types with properties predicted by first-principles calculations. The anisotropy contrast strongly affects thermal stability: increasing the fraction of high-anisotropy sites raises the energy cost of transverse spin fluctuations and increases . At the same time, the interlayer super-superexchange network is modified by the inhomogeneous V environment. It becomes spatially non-uniform and can contain competing exchange pathways, weakening coherent interlayer magnetic order while preserving robust intralayer ferromagnetic correlations. Our results show that changing the ratio of the two V types can cause a substantial shift in . The experimental bulk value is reproduced when the ratio is close to 1:1, consistent with two experimental indications of coexisting V configurations. Thus, the finite-temperature magnetization behavior provides further support for the coexistence of two V configurations in . The experimentally observed monolayer is obtained for a slightly modified ratio, which may be related to the polaron concentration. The sensitivity of to the HO/LO ratio suggests that the ordering temperature of could be tuned over a broad range by controlling the relative occupation of the two vanadium configurations.