Gate-tunable Intrinsic Anomalous Hall Effect in Epitaxial MnBi2Te4 Films.

The anomalous Hall effect (AHE) is an important transport signature revealing topological properties of magnetic materials and their spin textures. Recently, MnBi2Te4 has been demonstrated to be an intrinsic magnetic topological insulator. However, the origin of its intriguing AHE behaviors remains elusive. Here, we demonstrate the Berry curvature-dominated intrinsic AHE in wafer-scale MnBi2Te4 films. By applying back-gate voltages, we observe an ambipolar conduction and n-p transition in ∼7-layer MnBi2Te4, where a quadratic relation between the AHE resistance and longitudinal resistance suggests its intrinsic AHE nature. In particular, for ∼3-layer MnBi2Te4, the AHE sign can be tuned from pristine negative to positive. First-principles calculations unveil that such an AHE reversal originated from the competing Berry curvature between oppositely polarized spin-minority-dominated surface states and spin-majority-dominated inner bands. Our results shed light on the underlying physical mechanism of the intrinsic AHE and provide new perspectives for the unconventional sign-tunable AHE.

Magnetic-Field-Induced Re-entrance of Superconductivity in Ta2PdS5 Nanostrips.

The motion of Abrikosov vortices is the dominant origin of dissipation in type II superconductors subjected to a magnetic field, which leads to a finite electrical resistance. It is generally believed that the increase in the magnetic field results in the aggravation of energy dissipation through the increase in vortex density. Here, we show a distinctive re-entrance of the dissipationless state in quasi-one-dimensional superconducting Ta2PdS5 nanostrips. Utilizing magnetotransport measurements, we unveil a prominent magnetoresistance drop with the increase in the magnetic field below the superconducting transition temperature, manifesting itself as a giant re-entrance to the superconducting phase. Time-dependent Ginzburg-Landau calculations show that this is originated from the suppression of the vortex motion by the increased energy barrier on the edges. Interestingly, both our experiments and simulations demonstrate that this giant re-entrance of superconductivity occurs only in certain geometrical regimes because of the finite size of the vortex.

Surface photogalvanic effect in Ag2Te.

The bulk photovoltaic effect (BPVE) in non-centrosymmetric materials has attracted significant attention in recent years due to its potential to surpass the Shockley-Queisser limit. Although these materials are strictly constrained by symmetry, progress has been made in artificially reducing symmetry to stimulate BPVE in wider systems. However, the complexity of these techniques has hindered their practical implementation. In this study, we demonstrate a large intrinsic photocurrent response in centrosymmetric topological insulator Ag2Te, attributed to the surface photogalvanic effect (SPGE), which is induced by symmetry reduction of the surface. Through diverse spatially-resolved measurements on specially designed devices, we directly observe that SPGE in Ag2Te arises from the difference between two opposite photocurrent flows generated from the top and bottom surfaces. Acting as an efficient SPGE material, Ag2Te demonstrates robust performance across a wide spectral range from visible to mid-infrared, making it promising for applications in solar cells and mid-infrared detectors. More importantly, SPGE generated on low-symmetric surfaces can potentially be found in various systems, thereby inspiring a broader range of choices for photovoltaic materials.

Observation of Type-II Topological Nodal-Line Fermions in ZrSiSe.

Recently, there has been significant interest in topological nodal-line semimetals due to their linear energy dispersion with one-dimensional nodal lines or loops. These materials exhibit fascinating physical properties, such as drumhead surface states and 3D anisotropic nodal-line structures. Similar to Weyl semimetals, type-II nodal-line semimetals have two crossing bands that are both electron-like or hole-like along a certain direction. However, the direct observation of type-II nodal-line Fermions has been challenging due to the lack of suitable material platforms and the low density of states. Here we present experimental evidence for the coexistence of both type-I and type-II nodal-line Fermions in ZrSiSe, which was obtained through magneto-optical and angle-resolved photoemission spectroscopy (ARPES) measurements. Our density functional theory calculations predict that the type-II nodal-line structure can be developed in the Z-R line of the first Brillouin zone based on the lattice constants of the grown single crystal. Indeed, ARPES measurements reveal the type-II nodal-line band structure. The extracted type-II Landau level transitions from magneto-optical measurements exhibit good agreement with the calculated type-II energy dispersion model based on the band structure. Our experimental results demonstrate that ZrSiSe possesses two types of nodal-line Fermions, distinguishing it from other ZrSiX (X = S, Te) materials and positioning it as an ideal platform for investigating type-II nodal-line semimetals.

The differences between the water- and alkaline-soluble Poria cocos polysaccharide: A review.

Poria cocos (PC) refers to a fungal species which is also known as "Fuling" in China. For >2000 years, PC has demonstrated its therapeutic values as a kind of traditional medicine. It is believed that the various biological benefits created by PCs highly rely on the Poria cocos polysaccharide (PCP). This review recapitulates the recent progress made in PCP in four aspects: i) the methods of extraction, separation, and purification, ii) structural characterization and identification, iii) the related bioactivities and mechanism of action, and iv) structure-activity relationships. Through discussion about the objective as mentioned above, it can be found out that PCP is categorized into water-soluble polysaccharide (WPCP) and alkaline-soluble polysaccharide (APCP), which are totally different in structure and bioactivity. The structures of WPCP are multiplicity whose backbone can be (1,6)-α-galactan and (1,3)-ß-mannoglucan etc. to perform various bioactivities including anti-tumor effect, anti-depressant effect, anti-Alzheimer effect, anti-atherosclerosis effect, hepatoprotection etc. The structures of APCP are much more single with backbone of (1,3)-ß-D-glucan and the studies of activity concentrate on anti-tumor effect, anti-inflammatory effect and immunomodulation. Besides, the future opportunities of WPCP are primary structure identification. For APCP, scholars can focus on the conformation of polysaccharide and its relationship with activity.

Effect of steam explosion pretreatment on polysaccharide isolated from Poria cocos: Structure and immunostimulatory activity.

This study aimed to examine the effects of steam explosion (SE) pretreatment on the structural characteristics and immunostimulatory activity of polysaccharide from Poria cocos. Results showed that the average molecular weights of native polysaccharide (PCP) and SE-pretreated polysaccharide (SEPCP) were 18.67 and 6.52 kDa, respectively. PCP and SEPCP shared the same profiles of monosaccharides (mannose, glucose, galactose, and fucose) in different composition ratios, that is, PCP in a molar percentage of 13.5:33:40.3:13.2 and SEPCP in a molar percentage of 2.1:90.3:5.8:1.8. The surface structure of PCP showed smooth and densely spherical particles, whereas SEPCP had a rough surface and porous honeycomb structure. The main linkage types of PCP comprised 1,6-α-d-Galp, 1,2,6-α-d-Glcp, and T-α-d-Manp, whereas SEPCP primarily contained 1,3-ß-d-Glcp backbone and T-ß-d-Glcp branches. Compared with PCP, we further revealed that SEPCP had a better immune enhancement on the phagocytic ability, NO production, and the secretion levels of TNF-α and IL-6 in RAW 264.7 cells. Collectively, our observations supported that SE pretreatment could help to change the structure and improve the immunostimulatory activity of polysaccharide from P. cocos. PRACTICAL APPLICATIONS: SE technology is extensively used to extract bioactive components with improved yields owing to this technology's benefits of low energy consumption and high efficiency. SE pretreatment was found to contribute to the destruction of cell-wall structure, which could help to enhance the extraction yields of P. cocos polysaccharide (PCP). Meanwhile, SE pretreatment also could change the structural features and improve the immunostimulatory activity of PCP. This study revealed that more bioactive PCP with strengthened immunoregulatory effect was obtained pretreated by SE. This study was able to provide the effective information on the application of steam explosion technology to promote the further development and utilization of PCP in the pharmaceutical and functional food fields.

Magnetic field-induced non-linear transport in HfTe5.

The interplay of electron correlations and topological phases gives rise to various exotic phenomena including fractionalization, excitonic instability and axionic excitation. Recently discovered transition-metal pentatellurides can reach the ultra-quantum limit in low magnetic fields and serve as good candidates for achieving such a combination. Here, we report evidence of density wave and metal-insulator transition in HfTe5 induced by intense magnetic fields. Using the non-linear transport technique, we detect a distinct non-linear conduction behavior in the longitudinal resistivity within the a-c plane, corresponding to the formation of a density wave induced by magnetic fields. In high fields, the onset of non-linear conduction in the Hall resistivity indicates an impurity-pinned magnetic freeze-out as the possible origin of the insulating behavior. These frozen electrons can be gradually reactivated into mobile states above a threshold of electric field. This experimental evidence calls for further investigation into the underlying mechanism of the bulk quantum Hall effect and field-induced phase transitions in pentatellurides.

Photodetection and Infrared Imaging Based on Cd3As2 Epitaxial Vertical Heterostructures.

Due to the nontrivial electronic structure, Cd3As2 is predicted to possess various transport properties and outstanding photoresponses. Photodetectors based on topological materials are mostly made up of nanoplates, yet monolithic in situ heteroepitaxial Cd3As2 photodetectors are rarely reported to date owing to the crystal mismatch between Cd3As2 and semiconductors. Here, we demonstrate Cd3As2/ZnxCd1-xTe/GaSb vertical heteroepitaxial photodetectors via molecule beam epitaxy. By constructing dual-Schottky junctions, these photodetectors show high responsivity and external quantum efficiency in a broadband spectrum. Based on the strong and fast photoresponse, we achieved visible light to near-infrared imaging using a one-pixel imaging system with a galvo. Our results illustrate that the integration of three-dimensional Dirac semimetal Cd3As2 with semiconductors has potential applications in broadband photodetection and infrared cameras.

Observation of thickness-tuned universality class in superconducting ß-W thin films.

The interplay between quenched disorder and critical behavior in quantum phase transitions is conceptually fascinating and of fundamental importance for understanding phase transitions. However, it is still unclear whether or not the quenched disorder influences the universality class of quantum phase transitions. More crucially, the absence of superconducting-metal transitions under in-plane magnetic fields in 2D superconductors imposes constraints on the universality of quantum criticality. Here, we observe the thickness-tuned universality class of superconductor-metal transition by changing the disorder strength in ß-W films with varying thickness. The finite-size scaling uncovers the switch of universality class: quantum Griffiths singularity to multiple quantum criticality at a critical thickness of tc⊥1~8nm and then from multiple quantum criticality to single criticality at tc⊥2~16nm. Moreover, the superconducting-metal transition is observed for the first time under in-plane magnetic fields and the universality class is changed at tc‖~8nm. The observation of thickness-tuned universality class under both out-of-plane and in-plane magnetic fields provides broad information for the disorder effect on superconducting-metal transitions and quantum criticality.

The discovery of dynamic chiral anomaly in a Weyl semimetal NbAs.

The experimental discovery of Weyl semimetals offers unprecedented opportunities to study Weyl physics in condensed matters. Unique electromagnetic response of Weyl semimetals such as chiral magnetic effect has been observed and presented by the axial θ E · B term in electromagnetic Lagrangian (E and B are the electric and magnetic field, respectively). But till now, the experimental progress in this direction in Weyl semimetals is restricted to the DC regime. Here we report experimental access to the dynamic regime in Weyl semimetal NbAs by combining the internal deformation potential of coupled phonons with applied static magnetic field. While the dynamic E · B field is realized, it produces an anomalous phonon activity with a characteristic angle-dependence. Our results provide an effective approach to achieve the dynamic regime beyond the widely-investigated DC limit which enables the coupling between the Weyl fermions and the electromagnetic wave for further study of novel light-matter interactions in Weyl semimetals.

Nonreciprocal superconducting NbSe2 antenna.

The rise of two-dimensional (2D) crystalline superconductors has opened a new frontier of investigating unconventional quantum phenomena in low dimensions. However, despite the enormous advances achieved towards understanding the underlying physics, practical device applications like sensors and detectors using 2D superconductors are still lacking. Here, we demonstrate nonreciprocal antenna devices based on atomically thin NbSe2. Reversible nonreciprocal charge transport is unveiled in 2D NbSe2 through multi-reversal antisymmetric second harmonic magnetoresistance isotherms. Based on this nonreciprocity, our NbSe2 antenna devices exhibit a reversible nonreciprocal sensitivity to externally alternating current (AC) electromagnetic waves, which is attributed to the vortex flow in asymmetric pinning potentials driven by the AC driving force. More importantly, a successful control of the nonreciprocal sensitivity of the antenna devices has been achieved by applying electromagnetic waves with different frequencies and amplitudes. The device's response increases with increasing electromagnetic wave amplitude and exhibits prominent broadband sensing from 5 to 900 MHz.

Chiral Landau levels in Weyl semimetal NbAs with multiple topological carriers.

Recently, Weyl semimetals have been experimentally discovered in both inversion-symmetry-breaking and time-reversal-symmetry-breaking crystals. The non-trivial topology in Weyl semimetals can manifest itself with exotic phenomena, which have been extensively investigated by photoemission and transport measurements. Despite the numerous experimental efforts on Fermi arcs and chiral anomaly, the existence of unconventional zeroth Landau levels, as a unique hallmark of Weyl fermions, which is highly related to chiral anomaly, remains elusive owing to the stringent experimental requirements. Here, we report the magneto-optical study of Landau quantization in Weyl semimetal NbAs. High magnetic fields drive the system toward the quantum limit, which leads to the observation of zeroth chiral Landau levels in two inequivalent Weyl nodes. As compared to other Landau levels, the zeroth chiral Landau level exhibits a distinct linear dispersion in magnetic field direction and allows the optical transitions without the limitation of zero z momentum or [Formula: see text] magnetic field evolution. The magnetic field dependence of the zeroth Landau levels further verifies the predicted particle-hole asymmetry of the Weyl cones. Meanwhile, the optical transitions from the normal Landau levels exhibit the coexistence of multiple carriers including an unexpected massive Dirac fermion, pointing to a more complex topological nature in inversion-symmetry-breaking Weyl semimetals. Our results provide insights into the Landau quantization of Weyl fermions and demonstrate an effective tool for studying complex topological systems.