Introducing superconductivity (SC) or magnetism into topological insulators (TIs) can give rise to novel quantum states and exotic physical phenomena. Here, we report a high-pressure transport study on the TI Ge2Bi2Te5 and its Mn-doped counterparts. The application of pressure induces a SC in Ge2Bi2Te5, which shows a dome-shape phase diagram with the maximum Tc of 7.6 K at 23 GPa. Doping Mn into Ge2Bi2Te5 introduces an antiferromagnetic order at ambient pressure and strongly weakens the pressure-induced SC, demonstrating that magnetism and SC compete in this material system. Present study provides a new platform for investigating the interplay among band topology, magnetism, and SC.

The exploration of novel topological insulators (TIs) beyond binary chalcogenides has been accelerated in pursuit of exotic quantum states and device applications. Here, the layered ternary chalcogenide Ge2Bi2Te5 is identified as a three-dimensional TI. The bulk electronic structure of Ge2Bi2Te5 features a hole-type Fermi surface at Fermi level EF, which dominates the transport properties. Moreover, an unoccupied topological surface state with a Dirac point located at 290 meV above EF has been observed. Theoretical calculations confirm a bulk bandgap and a nontrivial Z2 topological invariant (000;1). The present study demonstrates that the material family of layered tetradymite-like ternary compounds is an important platform to explore exotic topological phenomena.

Flat-band (FB) systems originating from special lattice geometry like in kagome metals as well as localized orbitals in the materials such as heavy-fermion (HF) compounds have induced intensive interest due to their band topology and strong electron correlation effects, leading to emergent quantum states of matter. However, the question of how these two distinct FBs coexist and interact remains unsettled. Here, we report that YbCr6Ge6 hosting both Cr-kagome lattice and Yb-4f electrons exhibits HF behaviors and a robust antiferromagnetic ground state with transition temperature TN = 3 K, significantly higher than other similar kagome metals with Yb ions. Angle-resolved photoemission spectroscopy measurements reveal the coexistence of FBs originating from both Cr-kagome lattice and localized Yb-4f electrons near Fermi energy level EF. More importantly, the clear spectroscopic signatures of a hybridization of Yb-4f FB with kagome-lattice-derived conduction bands and the high density of states of Cr-kagome FB near EF provide the underlying microscopic mechanisms of HF behaviors and enhanced antiferromagnetism in YbCr6Ge6. Our findings demonstrate that the novel kagome HF metals can not only host the cooperative coexistence of two different types of FBs, but also provide a paradigm material platform to explore the exotic correlated topological quantum phenomena.

The interplay among electronic nematicity, charge density wave, and superconductivity in correlated electronic systems has induced extensive research interest. Here, we discover the existence of nematic fluctuations in TiSe2 single crystal and investigate its evolution with Cu intercalation. It is observed that the elastoresistivity coefficient mEg exhibits a divergent temperature dependence following a Curie-Weiss law at high temperature. Upon Cu intercalation, the characteristic temperature T* of nematic fluctuation is progressively suppressed and becomes near zero when the superconductivity is optimized. Further intercalation of Cu leads to the sign change of T* and the suppression of superconductivity. These results strongly indicate that nematic phase transition may play a vital role in enhancing superconductivity in CuxTiSe2. Therefore, CuxTiSe2 provides a unique material platform to explore the nematic-fluctuation-mediated superconductivity.

Abstract The chiral cubic B20 phase RhGe has recently attracted considerable interest as a candidate topological semimetal, predicted to host high Chern number multifold fermions analogous to those in CoSi. However, its synthesis under ambient pressure remains a challenge. Here, a systematic study of Ru 1− x Rh x Ge ( x = 0–1) polycrystals synthesized under ambient pressure is presented. It is found that with Rh doping the cubic B20 phase is suppressed, accompanied by the appearance of orthorhombic phase. Electrical transport measurements reveal a semiconductor-to-metal transition and a complex evolution of carrier type in Ru 1− x Rh x Ge with the increase of x, which can be mainly ascribed to the band filling effects across this series.

Transition-metal monosilicide RhGe has been reported to exhibit weak itinerant ferromagnetism, superconductivity,and topological properties. In this study, we report the high-pressure growth of high-quality RhGe single crystals up to millimeter size using a flux method. Transport measurements reveal metallic behavior in Rh Ge from 2 K to 300 K with Fermi liquid behavior at low temperatures. However, no superconductivity was observed with variations in the Ge composition. Magnetic characterizations indicate that RhGe exhibits paramagnetic behavior between 2 K and 300 K. The high-quality and large-size RhGe single crystals pave the way for further investigation of their topological properties using spectroscopic techniques.

In magnetic topological materials, the interplay between magnetism and nontrivial topology gives rise to exotic quantum transport phenomena, including the anomalous Hall effect and anomalous Nernst effect. Here,we report the observation of intrinsic topological Hall and topological Nernst effects below the Néel temperature（T N = 25 K） in the antiferromagnetic（AFM） topological insulator Mn Bi 2 Te 4 . The maximum of topological Hall resistivity reaches approximately 9 μΩ·cm at 2 K, while the topological Nernst signal attains a peak value of0.1 μV/K near 10 K. These anomalous transport behaviors originate from the net Berry curvature induced by the non-collinear spin structure in the canted AFM state. Our results suggest a close connection between the topological thermoelectric effect and non-collinear AFM order in AFM topological insulators.

Chiral topological semimetals hosting multifold fermions and exotic surface states represent a frontier in topological materials research.Among them,noncentrosymmetric cubic B20 compounds-notably transition-metal silicides and germanides—offer a unique platform for realizing symmetry-protected topological phases and unconventional optoelectronic responses.Here,we report the physical properties of RhGe and CoGe single crystals with B20 structure in detail.Transport measurements revea metallic behavior with characteristic Fermi-liquid scaling at low temperatures,while magnetization results confirm paramagnetism in both compounds.In addition,both materials exhibit low carrier concentrations with small electronic specific heat coefficients,indicating their semimetal feature with weak electronic correlations.Such high-quality CoGe and RhGe single crystals provide a material platform to explore the evolution of multifold fermions and the instability of helicoid-arc surface states with spin-orbit coupling and surface environment in B20 material systems.

The correlation of topology and disorder has attracted great intention due to appropriate disorder could induce the phase transition between trivial and nontrivial topological states. While it is widely recognized that strong disorder can produce rich phase diagrams in topological nontrivial states, moderate disorder has been proposed to induce transitions into topologically nontrivial phases counter-intuitively, leading to the concept of topological Anderson insulators. This phenomenon has been theoretically explored and simulated in various systems, yet experimental realization in solid state systems has remained elusive due to challenges in controlling disorder. Here, we report the experimental observation of Chern insulator state signed by the coexistence of quantized Hall plateau and zero longitudinal resistance in monolayer MnBi_4Te_7 Hall bar device, which originally hosts a trivial insulating state with Chern number C = 0 in clean limit. We demonstrate that the observed trivial to nontrivial transition in this monolayer device can be attributed to disorder, evidenced by universal conductance fluctuations. Our findings substantiate the existence of a long-sought topological Anderson Chern insulator in real materials, a unique variant of the topological Anderson insulator characterized by broken time-reversal-symmetry.

Layered ordered multianion materials exhibit remarkable structural flexibility and unique chemical and physical properties, which arise from the interplay of intralayer and interlayer interactions, as well as distinct local chemical environments originating from different anionic sublattices. Here, we report a novel layered quaternary compound, Bi18O21.6Se1.8Cl7.2, which features three different anionic sublattices. Bi18O21.6Se1.8Cl7.2 consists of [Bi6O9.6Cl6] and [Bi12O12Se1.8Cl1.2] slabs that stack along the c axis alternatively. Comprehensive physical properties and electronic properties of Bi18O21.6Se1.8Cl7.2 single crystals reveal semiconducting behavior with an indirect band gap of ∼1.51 eV and the dominant electron-type carriers. Notably, Bi18O21.6Se1.8Cl7.2 exhibits exceptionally low c-axial thermal conductivity κc (∼0.261-0.307 W m-1 K-1) at room temperature, significantly expanding the phase space of the ultralow-thermal-conductivity Bi-O-Se-Cl system. Our findings highlight that the strategic combination of distinct two-dimensional building blocks with varied structural and anionic coordination environments offers an effective approach for designing new layered materials with tunable physical properties.

The Kondo lattice, describing a grid of the local magnetic moments coupling to itinerant electrons, is a fertile ground of strongly correlated states in condensed matter physics. While the Kagome lattice has long been predicted to host Kondo physics with exotic magnetism and nontrivial topology, no experimental realization has been achieved. Here, we report the discovery of CsCr6Sb6, a van der Waals-like Kagome Kondo lattice featuring extremely flat, isolated bands at the Fermi level (EF) that composed entirely of Cr-3d electrons. We observe heavy fermions with the effective mass over 100 times greater than those of its vanadium counterpart. We also observe Kondo insulating behavior in an ultra-low carrier density of 1019 cm-3 and dimensionality-induced Kondo breakdown. More interestingly, the frustrated magnetism observed in the bulk give way to a hidden A-type antiferromagnetic ordering in few layers, in sharp contrast to the common sense of weakened magnetism with thinning. The realization of Kondo physics in Kagome lattice opens avenues for exploring diverse quantum criticalities in a strongly-correlated frustrated system.

Itinerant ferromagnetism at room temperature is a key ingredient for spin transport and manipulation. Here, we report the realization of nearly-room-temperature itinerant ferromagnetism in Co doped Fe5GeTe2 thin flakes. The ferromagnetic transition temperature TC ( 323 K - 337 K) is almost unchanged when thickness is down to 12 nm and is still about 284 K at 2 nm (bilayer thickness). Theoretical calculations further indicate that the ferromagnetism persists in monolayer Fe4CoGeTe2. In addition to the robust ferromagnetism down to the ultrathin limit, Fe4CoGeTe2 exhibits an unusual temperature- and thickness-dependent intrinsic anomalous Hall effect. We propose that it could be ascribed to the dependence of band structure on thickness that changes the Berry curvature near the Fermi energy level subtly. The nearly-room-temperature ferromagnetism and tunable anomalous Hall effect in atomically thin Fe4CoGeTe2 provide opportunities to understand the exotic transport properties of two-dimensional van der Waals magnetic materials and explore their potential applications in spintronics.

Abstract Various noncollinear spin textures and magnetic phases have been predicted in twisted two-dimensional CrI3 due to competing ferromagnetic (FM) and antiferromagnetic (AFM) interlayer exchange from moiré stacking—with potential spintronic applications even when the underlying material possesses a negligible Dzyaloshinskii–Moriya or dipole–dipole interaction. Recent measurements have shown evidence of coexisting FM and AFM layer order in small-twist-angle CrI3 bilayers and double bilayers. Yet, the nature of the magnetic textures remains unresolved and possibilities for their manipulation and electrical readout are unexplored. Here, we use tunneling magnetoresistance to investigate the collective spin states of twisted double-bilayer CrI3 under both out-of-plane and in-plane magnetic fields together with detailed micromagnetic simulations of domain dynamics based on magnetic circular dichroism. Our results capture hysteretic and anisotropic field evolutions of the magnetic states and we further uncover two distinct non-volatile spin textures (out-of-plane and in-plane domains) at ≈1° twist angle, with a different global tunneling resistance that can be switched by magnetic field.

We report the detailed crystal structures and physical properties of Ru 1-x Mo x alloys in the solid solution range of x=0.1-0.9.Structure characterizations indicate that the crystal structure changes from the hcp-Mg-type,to β-CrFe-type,and then bcc-W-type.The measurements of physical properties show that the Ru 1-x Mo x samples with x≥0.2are superconductors and the superconducting transition temperature T c as a function of Mo content exhibits a dome-like behavior.

Transition metal disulfides 4 H b -Ta(S, Se) 2 with natural heterostructure of 1 T - and 1 H -Ta(S, Se) 2 layers have became the focus of correlated materials their unique combinations of Mott physics and possible topological superconductivity. In this work, we study the upper critical fields mu 0 H c 2 of 4 H b -TaS 2 and 4 H b - TaS 1 . 99 Se 0 . 01 single crystals systematically. Transport measurements up to 35 T show that both of ab -plane and c -axis upper critical fields ( mu 0 H c 2 , ab and mu 0 H c 2 , c ) for 4 H b -TaS 2 and 4 H b -TaS 1 . 99 Se 0 . 01 exhibit a linear temperature dependent behavior down to 0.3 K, suggesting the three-dimensional superconductivity with dominant orbital depairing mechanism in bulk 4 H b -Ta(S, Se) 2 . However, the zero -temperature mu 0 H c 2 , ab (0) for both crystals are far beyond the Pauli paramagnetic limit mu 0 H P . It could be explained by the effects of spin -momentum locking in 1 H -Ta(S, Se) 2 layers with local inversion symmetry broken and the relatively weak intersublattice interaction between 1 H layers due to the existence of 1 T layers.

Electrides are unique materials because of the existence of interstitial anionic electrons (IAEs). Due to these loosely bound IAEs and their strong interaction with the framework of cations, electrides can host superconductivity with rather high Tc, especially under high pressure, as predicted in theory. However, the experimental observations of superconductivity in electrides are very rare, let alone the detailed studies on intrinsic properties of single crystals. Here, we report the superconducting and normal-state properties of electride La3In single crystals. La3In shows a type-II superconductivity with Tc 9.4 K and a T-linear resistivity in a wide temperature range. Experimental measurements and theoretical calculations suggest that the relatively high Tc could be ascribed to the high density of states around the Fermi level caused by short flat bands along R-M direction and the strong electron-phonon coupling, partially derived from the IAEs. Meanwhile, the T-linear resistivity may reflect the significant electronic correlation effect in this material. These findings will shed light on understanding the role of IAEs in superconductivity and open a promising way to explore high-temperature superconductors in electrides.

Transition metal disulfides $4{H}_{b}$-Ta(S, ${\mathrm{Se})}_{2}$ with natural heterostructure of $1T$- and $1H$-Ta(S, ${\mathrm{Se})}_{2}$ layers have became the focus of correlated materials their unique combinations of Mott physics and possible topological superconductivity. In this work, we study the upper critical fields ${\ensuremath{\mu}}_{0}{H}_{c2}$ of $4{H}_{b}\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ and $4{H}_{b}\text{\ensuremath{-}}{\mathrm{TaS}}_{1.99}{\mathrm{Se}}_{0.01}$ single crystals systematically. Transport measurements up to 35 T show that both of $ab$-plane and $c$-axis upper critical fields (${\ensuremath{\mu}}_{0}{H}_{c2,ab}$ and ${\ensuremath{\mu}}_{0}{H}_{c2,c}$) for $4{H}_{b}\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ and $4{H}_{b}\text{\ensuremath{-}}{\mathrm{TaS}}_{1.99}{\mathrm{Se}}_{0.01}$ exhibit a linear temperature dependent behavior down to 0.3 K, suggesting the three-dimensional superconductivity with dominant orbital depairing mechanism in bulk $4{H}_{b}$-Ta(S, ${\mathrm{Se})}_{2}$. However, the zero-temperature ${\ensuremath{\mu}}_{0}{H}_{c2,ab}$(0) for both crystals are far beyond the Pauli paramagnetic limit ${\ensuremath{\mu}}_{0}H{}_{\mathrm{P}}$. It could be explained by the effects of spin-momentum locking in $1H$-Ta(S, ${\mathrm{Se})}_{2}$ layers with local inversion symmetry broken and the relatively weak intersublattice interaction between $1H$ layers due to the existence of $1T$ layers.

Effectively tuning magnetic state by using current is essential for novel spintronic devices. Magnetic van der Waals (vdW) materials have shown superior properties for the applications of magnetic information storage based on the efficient spin torque effect. However, for most of known vdW ferromagnets, the ferromagnetic transition temperatures lower than room temperature strongly impede their applications and the room-temperature vdW spintronic device with low energy consumption is still a long-sought goal. Here, we realize the highly efficient room-temperature nonvolatile magnetic switching by current in a single-material device based on vdW ferromagnet Fe3GaTe2. Moreover, the switching current density and power dissipation are about 300 and 60000 times smaller than conventional spin-orbit-torque devices of magnet/heavymetal heterostructures. These findings make an important progress on the applications of magnetic vdW materials in the fields of spintronics and magnetic information storage.

Topological boundary states emerged at the spatial boundary between topological non-trivial and trivial phases, are usually gapless, or commonly referred as metallic states. For example, the surface state of a topological insulator is a gapless Dirac state. These metallic topological boundary states are typically well described by non-interacting fermions. However, the behavior of topological boundary states with significant electron-electron interactions, which could turn the gapless boundary states into gapped ordered states, e.g., density wave states or superconducting states, is of great interest theoretically, but is still lacking evidence experimentally. Here, we report the observation of incommensurable charge density wave (CDW) formed on the topological boundary states driven by the electron-electron interactions on the (001) surface of CoSi. The wavevector of CDW varies as the temperature changes, which coincides with the evolution of topological surface Fermi arcs with temperature. The orientation of the CDW phase is determined by the chirality of the Fermi arcs, which indicates a direct association between CDW and Fermi arcs. Our finding will stimulate the search of more interactions-driven ordered states, such as superconductivity and magnetism, on the boundaries of topological materials.

A series of “turn-on” type NIR materials are developed with two-stage superlarge redshifted absorption in the first and second NIR window under the stimulation of protonation for smart photothermal conversion.