Showing 1–50 of 214 results for author: Shen, B

Macroscopic wall pressure and microscopic contact load in crowds without egress: social-group cohesion and boundary buffering

Authors: Bo-Shiun Shen, Son-Hsien Chen

Abstract: Crowd safety in confined venues is usually evaluated through evacuation performance or pre-collision avoidance, while direct mechanical hazards in dense gatherings without egress remain poorly understood. We study an Elastic Reorientation Model (ERM), a Social Force Model (SFM), and their coupled dynamics. Post-collision behavior is represented by social-group cohesion ($γ_g$) and wall buffering (… ▽ More Crowd safety in confined venues is usually evaluated through evacuation performance or pre-collision avoidance, while direct mechanical hazards in dense gatherings without egress remain poorly understood. We study an Elastic Reorientation Model (ERM), a Social Force Model (SFM), and their coupled dynamics. Post-collision behavior is represented by social-group cohesion ($γ_g$) and wall buffering ($γ_w$), while risk is quantified by the macroscopic wall line pressure ($P_{\text{wall}}$) and the microscopic maximum per-agent collision impulse ($δp_{\text{max}}$). In the ERM, cohesion and wall buffering generally reduce $P_{\text{wall}}$ by retaining agents in the bulk, but large groups exhibit a high-$δp_{\text{max}}$ hazard window at intermediate cohesion. As $γ_g\rightarrow1$, local pairing suppresses cluster growth and shifts kinetic energy from relative to center-of-mass motion, reducing $δp_{\text{max}}$. SFM pushing and sliding amplify $δp_{\text{max}}$, especially when agent-agent and agent-wall interactions coexist, while active driving raises $P_{\text{wall}}$ through near-wall accumulation. The coupled dynamics produces a wall-pressure/contact-load ($P$-$p$) trade-off. Finite-size scaling reveals an independent-agent-induced phase boundary at $γ_w=0.5$, characterized by a susceptibility discontinuity, and a grouped-agent-induced continuous phase boundary along a finite segment of $(1-γ_w)(1-γ_g)=0.5$, characterized by divergent susceptibility and terminating at a critical point. Both disappear in the social-force-free ERM, showing that they emerge from the coupled ERM+SFM dynamics. These results provide mechanistic guidance for crowd-risk mitigation and safety planning in high-density venues without egress. △ Less

Submitted 28 July, 2026; originally announced July 2026.

Comments: 16 pages, 8 figures

Modulation of anomalous Hall angle in a magnetic topological semimetal

Authors: Jinying Yang, Yanxing Shang, Xingchen Liu, Yibo Wang, Xuebin Dong, Qingqi Zeng, Meng Lv, Shen Zhang, Yang Liu, Binbin Wang, Hongxiang Wei, Yizheng Wu, Stuart Parkin, Gangqin Liu, Claudia Felser, Enke Liu, Baogen Shen

Abstract: The anomalous Hall angle (θA) is a measure of the efficiency of converting a longitudinal driving current to a transverse spin-polarized Hall current. For anomalous Hall sensing, a large anomalous Hall angle can improve the sensitivity of magnetic field detection. However, modulation of this angle is challenging and magnetic materials typically have low angles of 0.1 to 3°. Here, we report modulat… ▽ More The anomalous Hall angle (θA) is a measure of the efficiency of converting a longitudinal driving current to a transverse spin-polarized Hall current. For anomalous Hall sensing, a large anomalous Hall angle can improve the sensitivity of magnetic field detection. However, modulation of this angle is challenging and magnetic materials typically have low angles of 0.1 to 3°. Here, we report modulation of the anomalous Hall angle in the magnetic Weyl semimetal Co3Sn2S2. We propose that the angle parameter tanθA can be formulated as a function of the product of electrical resistivity and anomalous Hall conductivity. Our scheme was utilized to demonstrate the modulation of tanθA up to a magnitude of 0.46, corresponding to an angle of around 25°. Microfabricated anomalous Hall devices using Fe-doped Co3Sn2S2 single-crystalline nanoflakes exhibit a high Hall sensitivity of 7028 μΩucm/T and a magnetic field detectability of 23.5 nT/Hz0.5 at 1 Hz. △ Less

Submitted 30 June, 2026; originally announced July 2026.

Journal ref: Nature Electronics 8, 386-393 (2025)

Kinetically Controlled Condensation Boundary Governing Indium Incorporation in InGaN Metal Organic Vapor Phase Epitaxy

Authors: Qihui Lin, Junlin Wu, Erqi Xu, Jiaqing Yue, Jiale Wang, Zihao Xu, Haixin Qi, Liyi Luo, Haitao Wang, Jia Wang, Hiroshi Amano, Bo Shen, Guangxu Ju

Abstract: We combine in situ synchrotron X-ray crystal truncation rod measurements with a binary Burton-Cabrera-Frank model to quantify indium incorporation during InGaN growth by metal-organic vapor phase epitaxy (MOVPE) on GaN(0001). By distinguishing In adatoms from condensed droplets and incorporating coupled Ga-In incorporation kinetics, the model captures the intrinsically nonlinear dependence of indi… ▽ More We combine in situ synchrotron X-ray crystal truncation rod measurements with a binary Burton-Cabrera-Frank model to quantify indium incorporation during InGaN growth by metal-organic vapor phase epitaxy (MOVPE) on GaN(0001). By distinguishing In adatoms from condensed droplets and incorporating coupled Ga-In incorporation kinetics, the model captures the intrinsically nonlinear dependence of indium composition on precursor flux and growth temperature. The critical In coverage corresponding to the maximum attainable In composition at a given temperature is determined by a kinetic balance between In adatom supply and incorporation capacity, defining a kinetically controlled condensation boundary that shifts with temperature and Ga flux. The model quantitatively predicts this boundary, in agreement with independent measurements, and provides a predictive framework for optimizing high-In-content InGaN growth while avoiding droplet formation. △ Less

Submitted 27 June, 2026; originally announced June 2026.

Comments: 6 pages, 4 figures, 1 table

Complex Magnetic Behavior of the Ce sawtooth chains in CeRhSn$_2$

Authors: P. Opletal, J. Fikáček, E. Duverger-Nédellec, A. Thamizhavel, Z. Hossain, R. Tarasenko, V. Tkáč, D. Legut, Bin Shen, P. Gegenwart, J. Custers

Abstract: Conflicting reports exist on the ground state of the intermetallic compound CeRhSn$_2$. This can be rooted in the sawtooth-like arrangement of two inequivalent Ce sites in the unit cell, which suggests potential geometric magnetic frustration. To resolve, we conducted a comprehensive study on high-quality single crystals of CeRhSn$_2$ by means of magnetization ($M$), specific heat ($C_p/T$), and r… ▽ More Conflicting reports exist on the ground state of the intermetallic compound CeRhSn$_2$. This can be rooted in the sawtooth-like arrangement of two inequivalent Ce sites in the unit cell, which suggests potential geometric magnetic frustration. To resolve, we conducted a comprehensive study on high-quality single crystals of CeRhSn$_2$ by means of magnetization ($M$), specific heat ($C_p/T$), and resistivity ($ρ$). The system exhibits strong magnetic anisotropy, confirming the $b$-axis as the easy magnetic axis. We establish three successive transitions, an AFM order at $T_{N} = 3.65$K, a first-order FM order at $T_{C} = 1.7$K and final transition, at $T = 1.5$K. The transition temperatures are highly field-directional dependent: in a magnetic field, the lowest transition is immediately suppressed while $\mathbf{H} \parallel b$ rapidly merges $T_{C}$ and $T_{N}$ into a single second-order transition. Conversely, $\mathbf{H}\parallel c$ suppresses the FM order and reduces $T_{N}$. Additional ab initio calculations affirm the FM ground state of CeRhSn$_2$. The observation of an enhancement of the Sommerfeld coefficient ($γ= 76.5$mJ/mol$\cdot$K$^2$) may arise from geometric frustration, but it is most consistently attributed to weak Kondo hybridization as frustration cannot be conclusively established through our data. △ Less

Submitted 29 May, 2026; originally announced May 2026.

Comments: 10 pages, 8 figures, accepted for publication in Phys. Rev. B

Stacking-order-dependent electronic properties of MoTe2/WSe2 moiré bilayers

Authors: Zhongdong Han, Wenjin Zhao, Eegene Clara Chung, Chia-Hao Lee, Zui Tao, Zhengchao Xia, Yichi Zhang, Yiyu Xia, Jekwan Lee, Bowen Shen, Ariana Ray, Yu-Tsun Shao, Tingxin Li, Shengwei Jiang, Yihang Zeng, Kenji Watanabe, Takashi Taniguchi, David Muller, Kin Fai Mak, Jie Shan

Abstract: Transition metal dichalcogenide (TMD) moiré bilayers have realized a wide range of strongly correlated and topological phenomena. The physics in these materials is often sensitive to the interlayer stacking order. Polarization-resolved optical second harmonic generation (SHG) is the most used technique for stacking order characterization but unverified for most heterobilayers. Here we calibrate th… ▽ More Transition metal dichalcogenide (TMD) moiré bilayers have realized a wide range of strongly correlated and topological phenomena. The physics in these materials is often sensitive to the interlayer stacking order. Polarization-resolved optical second harmonic generation (SHG) is the most used technique for stacking order characterization but unverified for most heterobilayers. Here we calibrate the optical SHG for angle-aligned MoTe2/WSe2 bilayers by the scanning transmission electron microscopy (STEM). We directly compare the transport and magnetic properties and the electronic phase diagram for two distinct stacking orders. With the calibrated stacking order assignment, we clarify the interpretation of earlier results, including the nature of the Chern insulator, mechanism of an electric-field-tuned metal-insulator transition at half band filling, and the Kondo lattice physics. Our work provides a consistent picture of the relation between the stacking order and the electronic properties of MoTe2/WSe2 moiré bilayers. △ Less

Submitted 20 May, 2026; originally announced May 2026.

Thermoviscoelasticity of polydomain liquid crystal elastomers regulated by soft elasticity

Authors: Zhengxuan Wei, Beijun Shen, Zumrat Usmanova, Umme Hani Bootwala, Ruobing Bai

Abstract: Liquid crystal elastomers (LCEs) are elastomeric networks with rod-like mesogens that reorient under load. In polydomain LCEs, this reorientation drives a polydomain-to-monodomain transition that produces a soft-elastic plateau. Coupling between this soft elasticity and polymer-network viscoelasticity yields a path-dependent thermoviscoelastic response, central to applications in damping, impact p… ▽ More Liquid crystal elastomers (LCEs) are elastomeric networks with rod-like mesogens that reorient under load. In polydomain LCEs, this reorientation drives a polydomain-to-monodomain transition that produces a soft-elastic plateau. Coupling between this soft elasticity and polymer-network viscoelasticity yields a path-dependent thermoviscoelastic response, central to applications in damping, impact protection, and tough adhesives. However, the physics governing this response under complex thermomechanical histories remains insufficiently studied. We present a combined experimental and theoretical study of polydomain LCEs under three uniaxial protocols: single-cycle loading-unloading, stress-free recovery from various pre-stretches, and multi-cycle loading with progressively increasing amplitude. We develop a finite-deformation constitutive model combining two parallel mechanisms: rate-independent, temperature-dependent soft elasticity from mesogen reorientation, and time- and temperature-dependent viscoelasticity. With a single parameter set, the model quantitatively reproduces all three protocols and resolves each mechanism's contribution. A temperature-dependent soft-elastic limit governs the low-rate response and the long-time recovered stretch, while viscoelasticity controls the rate-dependent deviation and the cycle-wise accumulation of residual stretch away from this limit. A thermal recovery test above the nematic-isotropic transition confirms that all hysteresis and residual deformation are reversible, ruling out irreversible damage. The framework provides mechanistic understanding and a predictive basis for designing polydomain LCE components under complex thermomechanical histories. △ Less

Submitted 11 May, 2026; originally announced May 2026.

Comments: submitted manuscript

Directional selection of field-induced phases by weak anisotropy in triangular-lattice K$_2$Mn(SeO$_3$)$_2$

Authors: Bin Wang, Yantao Cao, Andi Liu, Guoliang Wu, Jin Zhou, Xiaobai Ma, Wenyun Yang, Takashi Ohhara, Akiko Nakao, Koji Munakata, Bing Shen, Zhendong Fu, Zhaoming Tian, Qian Tao, Zhu-an Xu, Wei Li, Jinkui Zhao, Hanjie Guo

Abstract: Triangular-lattice systems host a variety of ground states, ranging from quantum spin liquids to magnetically ordered phases, the latter of which can exhibit a sequence of magnetic phase transitions under applied magnetic fields. Here, we report magnetic and thermodynamic measurements, combined with powder and single-crystal neutron diffraction, on a high-spin, nearly isotropic Mn$^{2+}$ triangula… ▽ More Triangular-lattice systems host a variety of ground states, ranging from quantum spin liquids to magnetically ordered phases, the latter of which can exhibit a sequence of magnetic phase transitions under applied magnetic fields. Here, we report magnetic and thermodynamic measurements, combined with powder and single-crystal neutron diffraction, on a high-spin, nearly isotropic Mn$^{2+}$ triangular-lattice system K$_2$Mn(SeO$_3$)$_2$. The compound undergoes long-range magnetic ordering below $T_\mathrm{N} \sim 4$~K in zero field. Contrary to expectations for an ideal Heisenberg system, the compound adopts an up-down-zero (UD0) magnetic structure down to the lowest temperature (0.05 K), rather than the commonly expected Y-type structure. This UD0 state is, however, highly sensitive to external magnetic fields. For fields applied along the $c$ axis, it is readily destabilized and replaced by the Y-type structure, followed by an up-up-down (UUD) phase corresponding to the 1/3 magnetization plateau. In contrast, when the field is applied within the triangular plane, the system evolves into a canted Y state at a higher critical field. These results reveal that weak anisotropy, though small in magnitude, exerts a strongly orientation-dependent influence, playing a key role in selecting the field-induced phases in this frustrated magnet. △ Less

Submitted 14 April, 2026; originally announced April 2026.

Comments: 9 pages, 5 figures

Magnetic and electric properties of the metallic kagome antiferromagnet CrRhAs

Authors: Franziska Breitner, Bin Shen, Anton Jesche, Alexander A. Tsirlin, Philipp Gegenwart

Abstract: CrRhAs is an antiferromagnetic kagome metal predicted to host a nontrivial spin texture with vector spin chirality [Huang \textit{et al.}, \textit{npj Quantum Mater.} \textbf{8}, 32 (2023)]. We report the synthesis and basic characterization of CrRhAs single crystals, which exhibit an antiferromagnetic transition with $T_{\rm N}$ = 150~K, evidenced by electrical transport, heat capacity, and magne… ▽ More CrRhAs is an antiferromagnetic kagome metal predicted to host a nontrivial spin texture with vector spin chirality [Huang \textit{et al.}, \textit{npj Quantum Mater.} \textbf{8}, 32 (2023)]. We report the synthesis and basic characterization of CrRhAs single crystals, which exhibit an antiferromagnetic transition with $T_{\rm N}$ = 150~K, evidenced by electrical transport, heat capacity, and magnetization measurements. Hall resistivity varies linearly with magnetic field, i.e., there is no nonlinear Hall contribution. Intriguingly, the Hall coefficient changes sign between the configurations of $j \parallel ab, H \perp ab$ and $j \parallel c, H \perp c$, which is likely connected to a peculiar topology of the Fermi surface. Furthermore, for $j \parallel ab$, the Hall coefficient shows a pronounced and continuous enhancement below $T_{\rm N}$, signaling a significant reconstruction of the Fermi surface or an extra scattering from the magnons. Our results offer guidance for exploring anomalous electric transport phenomena in exotic magnetic systems. △ Less

Submitted 1 July, 2026; v1 submitted 20 March, 2026; originally announced March 2026.

Comments: 8 pages, 8 figures

Journal ref: Phys. Rev. Materials 10, 064204 (2026)

Emergence of a symmetry-broken Chern insulator near a moiré Kondo breakdown

Authors: Wanghao Tian, Bowen Shen, Lizhong Li, Mingjie Zhang, Feng Liu, Chushan Li, Yaotian Liu, Fan Xu, Kenji Watanabe, Takashi Taniguchi, Peiling Li, Li Lu, Yang Xu, Shengwei Jiang, Tingxin Li, Jie Shan, Kin Fai Mak

Abstract: Moiré semiconductors built on angle-aligned transition metal dichalcogenide (TMD) heterobilayers provide a physical realization of the Kondo lattice model, in which one TMD layer is prepared in a Mott insulating state supporting a lattice of local magnetic moments and the other layer in a metallic state supporting itinerant carriers. The artificial Kondo lattice enables the exploration of exotic s… ▽ More Moiré semiconductors built on angle-aligned transition metal dichalcogenide (TMD) heterobilayers provide a physical realization of the Kondo lattice model, in which one TMD layer is prepared in a Mott insulating state supporting a lattice of local magnetic moments and the other layer in a metallic state supporting itinerant carriers. The artificial Kondo lattice enables the exploration of exotic states of matter near a continuously tunable Kondo breakdown. Here we report the emergence of a symmetry-broken Chern insulator at a moiré hole filling factor 4/3 in angle-aligned MoTe2/WSe2 moiré bilayers, which realize a chiral Kondo lattice. The symmetry-broken Chern insulator, which exhibits integer quantized Hall conductance at a fractional moiré filling, breaks the translational symmetry of the lattice spontaneously; it also appears only near a magnetic field-induced Kondo breakdown in the mixed-valence regime of the material. We further demonstrate that the magnetic field required to induce the Kondo breakdown and to stabilize the symmetry-broken Chern insulator is twist angle dependent. The results present new opportunities for exploring the subtle interplay between topology and Kondo interactions in moiré semiconductors. △ Less

Submitted 19 February, 2026; originally announced February 2026.

Electric-field-tuned consecutive topological phase transitions between distinct correlated insulators in moire MoTe2/WSe2 heterobilayer

Authors: Xumin Chang, Zui Tao, Bowen Shen, Wanghao Tian, Jenny Hu, Kateryna Pistunova, Kenji Watanabe, Takashi Taniguchi, Tony F. Heinz, Tingxin Li, Kin Fai Mak, Jie Shan, Shengwei Jiang

Abstract: Consecutive topological phase transitions (TPTs) between strongly correlated electronic phases that differ simultaneously in symmetry breaking and topological order are of fundamental interest in condensed matter physics, yet are rarely realized experimentally. We report two consecutive electric-field-driven TPTs at half filling (nu = 1) in angle-aligned MoTe2/WSe2 moire heterobilayers. With incre… ▽ More Consecutive topological phase transitions (TPTs) between strongly correlated electronic phases that differ simultaneously in symmetry breaking and topological order are of fundamental interest in condensed matter physics, yet are rarely realized experimentally. We report two consecutive electric-field-driven TPTs at half filling (nu = 1) in angle-aligned MoTe2/WSe2 moire heterobilayers. With increasing out-of-plane displacement field, a geometrically frustrated Mott insulator evolves into a ferromagnetic quantum anomalous Hall (QAH) Mott insulator, i.e., a spin-polarized topological Mott insulator without an observable charge-gap closure, and subsequently into an antiferromagnetic, valley-coherent Mott insulator (VC-AFM) accompanied by a continuous charge-gap collapse and the emergence of a critical metallic state. Layer-resolved magnetic circular dichroism (MCD), magneto-transport, and compressibility measurements jointly determine the phase diagram. The high-field evolution of the antiferromagnetic state reveals a metamagnetic-like transition at a critical field B*, above which a Chern insulating transport response reappears. Our results establish the MoTe2/WSe2 moire platform as a tunable realization of an extended Kane-Mele-Hubbard model hosting sequential correlation-topology-intertwined transitions. △ Less

Submitted 17 February, 2026; originally announced February 2026.

Giant Magnetocaloric Effect in a High-Spin Shastry-Sutherland Dipolar Magnet

Authors: Jianjian Gong, Junsen Wang, Junsen Xiang, Zhaojun Mo, Lei Zhang, Xinyang Liu, Xuetong He, Lu Tian, Zhixing Ye, Huicai Xie, Xucai Kan, Xinqiang Gao, Zhenxing Li, Peijie Sun, Shouguo Wang, Wei Li, Baogen Shen, Jun Shen

Abstract: The Shastry-Sutherland lattice is a prototypical frustrated quantum magnet. It is notable for its exactly solvable dimer-singlet ground state and hosts a wealth of magnetic phenomena under external fields. Here, this work investigates the high-spin (S = 7/2) Eu-based magnet Eu2MgSi2O7 (EMSO) using low-temperature magnetothermal measurements and Monte Carlo simulations, revealing a giant magnetocal… ▽ More The Shastry-Sutherland lattice is a prototypical frustrated quantum magnet. It is notable for its exactly solvable dimer-singlet ground state and hosts a wealth of magnetic phenomena under external fields. Here, this work investigates the high-spin (S = 7/2) Eu-based magnet Eu2MgSi2O7 (EMSO) using low-temperature magnetothermal measurements and Monte Carlo simulations, revealing a giant magnetocaloric effect (MCE) in this Shastry-Sutherland compound. The entropy change peak value is found to be 55.0 J kg-1 K-1 under a field change of B = 0-4 T, approximately 1.5 times larger than the commercial Gd3Ga5O12 (GGG). Adiabatic demagnetization refrigeration achieves a lowest temperature of 151 mK, deeply into the sub-Kelvin regime. Furthermore, a distinctive cooling effect persists below about 1 T, a characteristic absent for conventional magnetic coolants. A dipolar Shastry-Sutherland model is introduced as a minimal model to describe this system; in particular, the experimentally revealed 1/3 magnetization pseudo-plateau can be ascribed to the presence of dipolar couplings between Eu2+ ions, further stabilized by the thermal fluctuations, explaining the persistent cooling effect. This work establishes EMSO as a novel platform for exploring the dipolar Shastry-Sutherland system and for sub-Kelvin adiabatic demagnetization refrigeration. △ Less

Submitted 9 February, 2026; originally announced February 2026.

Magnetic field and pressure tuning of the heavy fermion antiferromagnet CePdIn

Authors: Bin Shen, Feng Du, Rui Li, Hang Su, Yasuyuki Shimura, Takahiro Onimaru, Kazunori Umeo, Xin Lu, Toshiro Takabatake, Michael Smidman, Huiqiu Yuan

Abstract: Frustrated Kondo lattices are ideal platforms for studying how both the Kondo effect and quantum fluctuations compete with the magnetic exchange interactions that drive magnetic ordering. Here, we investigate the effect of tuning the heavy-fermion compound CePdIn, which crystallizes in the geometrically frustrated ZrNiAl-type structure, using applied magnetic fields and hydrostatic pressure. At am… ▽ More Frustrated Kondo lattices are ideal platforms for studying how both the Kondo effect and quantum fluctuations compete with the magnetic exchange interactions that drive magnetic ordering. Here, we investigate the effect of tuning the heavy-fermion compound CePdIn, which crystallizes in the geometrically frustrated ZrNiAl-type structure, using applied magnetic fields and hydrostatic pressure. At ambient pressure, CePdIn exhibits two magnetic transitions, one at $T_{\rm{N}} \approx 1.65$ K and another at $T_{\rm{M}} \approx 1.15$ K, which are both suppressed by applied $c$-axis fields. Upon applying pressure in zero magnetic field, there is a non-monotonic evolution of $T_{\rm{N}}$, which decreases to 0.8 K at 2.3 GPa, before abruptly increasing to 1.5 K at 2.6 GPa. At higher pressures, $T_{\rm{N}}$ has a weak pressure dependence, and vanishes near 5 GPa. Together with the high-pressure phase being more robust to applied fields, these results suggest two distinct antiferromagnetic phases in CePdIn, which are separated near 2.6 GPa, and this change may be driven by the evolution of the underlying electronic structure due to enhanced Kondo hybridization under pressure. △ Less

Submitted 13 March, 2026; v1 submitted 27 December, 2025; originally announced December 2025.

Comments: 9 pages, 11 figures

Journal ref: Phys. Rev. B 113, 115130 (2026)

Microscale selective laser sintering of Cu nanoparticles with a short-wavelength nanosecond laser

Authors: Youwen Liang, Bo Shen, Wan Shou

Abstract: Microscale additive manufacturing of reflective copper is becoming increasingly important for microelectronics and microcomputers, due to its excellent electrical and thermal conductivity. Yet, it remains challenging for state-of-the-art commercial metal 3D printers to achieve sub-100-micron manufacturing. Two aspects are sub-optimal using commercial laser powder bed fusion systems with infrared (… ▽ More Microscale additive manufacturing of reflective copper is becoming increasingly important for microelectronics and microcomputers, due to its excellent electrical and thermal conductivity. Yet, it remains challenging for state-of-the-art commercial metal 3D printers to achieve sub-100-micron manufacturing. Two aspects are sub-optimal using commercial laser powder bed fusion systems with infrared (IR) lasers (wavelength of 1060-1070 nm): (1) IR laser has a low absorption rate for Cu, which is energy-inefficient for manufacturing; (2) short wavelength lasers can potentially offer higher resolution processing due to the diffraction-limited processing. On the other hand, laser sintering or melting typically uses continuous wave (CW) lasers, which may reduce the manufacturing resolution due to a large heat-affected zone. Based on these facts, this study investigates the UV (wavelength of 355 nm) nanosecond (ns) laser sintering of Cu nanoparticles. Different laser processing parameters, as well as different nanoparticle packing densities, are studied. Our results show that a short-wavelength laser can reduce the required energy for sintering with decent morphology, and a densified nanoparticle powder bed favors continuous melting. We further show that sub-20 micron printing can be readily achieved with a UV ns laser. These findings provide new insights into short-wavelength laser-metal nanoparticle interactions, which may pave the way to achieve high-resolution micro and nano-scale additive manufacturing. △ Less

Submitted 28 December, 2025; v1 submitted 20 December, 2025; originally announced December 2025.

Exceptional Alkaline Methanol Electrooxidation on Bi-modified Pt3M Intermetallics: Kinetic Origins and an OH Binding Energy Descriptor

Authors: Lecheng Liang, Hengyu Li, Shao Ye, Peng Li, Kaiyang Xu, Jinhui Liang, Binwen Zeng, Bo Shen, Taisuke Ozaki, Zhiming Cui

Abstract: The exploration of advanced CO-free catalysts and clarifying the ambiguous kinetic origins and governing factors would undoubtedly open up opportunities to overcome the sluggish kinetics of methanol electrooxidation and promote the development of direct methanol fuel cells. Herein, we constructed a family of Bi-modified Pt3M intermetallic catalysts (Bi-Pt3M/C, M=Cr, Mn, Co, Zn, In, Ga, and Sn) tha… ▽ More The exploration of advanced CO-free catalysts and clarifying the ambiguous kinetic origins and governing factors would undoubtedly open up opportunities to overcome the sluggish kinetics of methanol electrooxidation and promote the development of direct methanol fuel cells. Herein, we constructed a family of Bi-modified Pt3M intermetallic catalysts (Bi-Pt3M/C, M=Cr, Mn, Co, Zn, In, Ga, and Sn) that follow CO-free dominated pathway and exhibit exceptional catalytic activity. More significantly, leveraging this platform, we have identified the pivotal factor governing the reaction kinetics in CO-free pathway, namely OH binding energy (OHBE). This arises because the rate-determining step (RDS) encompasses both C-H bond activation and water dissociation, whose respective barriers can be reflected by the OHBE. Accordingly, OHBE can act as an activity descriptor. Specifically, Bi-Pt3In/C stands out from other Bi-Pt3M/C and delivers the unprecedented mass activity of 36.7 A mgPt-1 at peak potential, far exceeding state-of-the-art Pt-based catalysts reported to date. Taking Bi-Pt3In/C as a proof of concept, we clearly elucidate the origin of enhanced MOR activity by combining theoretical calculations, kinetic isotope effects, and formaldehyde electrooxidation. Moreover, there exhibits a volcano-type trend between OHBE and the activity of Bi-Pt3M/C. Beyond the discovery of ultrahigh-performance catalysts, these findings provide a detailed mechanistic picture of RDS and offer an innovative design principle for advanced catalysts. △ Less

Submitted 12 December, 2025; originally announced December 2025.

Competition between Weak Localization and Antilocalization of Dirac-like Fermions in a Spin-Polarized Two-Dimensional Electron Gas at KTaO3 (111) Interface

Authors: Hui Zhang, Daming Tian, Xiaobing Chen, Lu Chen, Min Li, Yetong Bai, Fengxia Hu, Baogen Shen, Jirong Sun, Weisheng Zhao

Abstract: Quantum transport phenomena in two-dimensional electron gases (2DEGs) at oxide interfaces have garnered significant interest owing to their potential in spintronic and quantum information technologies. Here, we systematically investigate the quantum conductance corrections of spin-polarized 2DEGs formed at the interfaces between two insulating oxides, ferromagnetic EuTiO3 (ETO) films and (111)-ori… ▽ More Quantum transport phenomena in two-dimensional electron gases (2DEGs) at oxide interfaces have garnered significant interest owing to their potential in spintronic and quantum information technologies. Here, we systematically investigate the quantum conductance corrections of spin-polarized 2DEGs formed at the interfaces between two insulating oxides, ferromagnetic EuTiO3 (ETO) films and (111)-oriented KTaO3 (KTO) substrates. The anomalous Hall effect and hysteretic magnetoresistance provide clear evidence for long-range ferromagnetic order in the 2DEGs, which could be attributed to interfacial Eu doping in combination with the magnetic proximity effect of the ETO layer. The breaking of time-reversal symmetry by ferromagnetism in the 2DEGs, and with the assistance of spin-orbit coupling effect, gives rise to a nontrivial Berry phase. This results in a competition between weak localization (WL) and weak antilocalization (WAL) in the quantum transport of Dirac-like fermions at the KTO (111) interfaces. Notably, this competitive behavior can be effectively tuned by optical gating via a photoexcitation-induced shift of the Fermi level. Our findings demonstrate a controllable platform based on spin-polarized oxide 2DEGs for quantum transport, opening new avenues for spin-orbitronic and topological electronic applications. △ Less

Submitted 13 November, 2025; originally announced November 2025.

Phonon-scattering-induced quantum linear magnetoresistance up to room temperature

Authors: Nannan Tang, Shuai Li, Yanzhao Liu, Jiayi Yang, Huakun Zuo, Gangjian Jin, Yi Ji, Bing Shen, Dingyong Zhong, Donghui Guo, Qizhong Zhu, Zhongbo Yan, Haizhou Lu, Jian Wang, Huichao Wang

Abstract: The realization of quantum transport effects at elevated temperatures has long intrigued researchers due to the implications for unveiling novel physics and developing quantum devices. In this work, we report remarkable quantum linear magnetoresistance (LMR) in the Weyl semiconductor tellurium at high temperatures of 40-300 K under strong magnetic fields up to 60 T. At high fields, the Weyl band f… ▽ More The realization of quantum transport effects at elevated temperatures has long intrigued researchers due to the implications for unveiling novel physics and developing quantum devices. In this work, we report remarkable quantum linear magnetoresistance (LMR) in the Weyl semiconductor tellurium at high temperatures of 40-300 K under strong magnetic fields up to 60 T. At high fields, the Weyl band features a large energy gap between the lowest and first Landau levels, which suppresses thermal excitation and preserves Landau quantization at high temperatures. The LMR is observed as long as majority carriers remain in the lowest Landau level without requiring monochromaticity, allowing it to persist up to room temperature. The inverse relationship between the LMR slope and temperature provides clear evidence that quantum LMR originates from high-temperature phonon scattering in the quantum limit, firstly demonstrating a theoretical prediction made nearly fifty years ago. This study highlights the key role of electron-phonon interaction and reveals an innovative quantum mechanism for achieving high-temperature LMR, fundamentally distinct from previous findings. Our results bridge a gap in the understanding of phonon-mediated quantum-limit physics and establish strong magnetic fields at high temperatures as a promising platform for exploring novel quantum phenomena. △ Less

Submitted 27 August, 2025; originally announced August 2025.

Shubnikov-de Haas oscillations and planar Hall effect in HfTe2

Authors: Qixuan Li, Gangjian Jin, Nannan Tang, Bin Wang, Bing Shen, Donghui Guo, Dingyong Zhong, Huakun Zuo, Huichao Wang

Abstract: Layered transition-metal dichalcogenide (TMD) HfTe2 is a topological semimetal candidate with increasing attentions recently. The map of the Fermi surface is of interest and importance to understand its properties. Here we present a study of Shubnikov-de Haas (SdH) oscillations and planar Hall effect (PHE) in HfTe2. The single crystals grown by flux method show the largest unsaturated magnetoresis… ▽ More Layered transition-metal dichalcogenide (TMD) HfTe2 is a topological semimetal candidate with increasing attentions recently. The map of the Fermi surface is of interest and importance to understand its properties. Here we present a study of Shubnikov-de Haas (SdH) oscillations and planar Hall effect (PHE) in HfTe2. The single crystals grown by flux method show the largest unsaturated magnetoresistance (MR) effect of 1.1*104 % at 14 T and 2 K. The angle-resolved SdH oscillations reveal that the Fermi surface consists of three pockets with different anisotropy. In addition, we observe PHE and anisotropic MR (AMR) effect in the material for a wide temperature range. The effective mass, carrier density and quantum transport mobility are quantified in the system, and the Berry phase is discussed. Our work provides crucial insights into the electronic structure and the Fermi surface of the semimetal. △ Less

Submitted 27 August, 2025; v1 submitted 26 August, 2025; originally announced August 2025.

Journal ref: Phys. Rev. B 108, 235155(2023)

Light-Induced Giant Enhancement of the Nonlinear Hall Effect in Two-Dimensional Electron Gases at KTaO3 (111) Interfaces

Authors: Hui Zhang, Daming Tian, Xiaobing Chen, Weijian Qi, Lu Chen, Min Li, Yetong Bai, Jine Zhang, Furong Han, Huaiwen Yang, Yuansha Chen, Yunzhong Chen, Jing Wu, Yongbing Xu, Fengxia Hu, Baogen Shen, Jirong Sun, Weisheng Zhao

Abstract: The nonlinear Hall effect (NLHE), an emergent phenomenon in noncentrosymmetric systems, enables the generation of a transverse voltage without an external magnetic field through a second-order electrical response. However, achieving a sizable NLHE signal remains a critical challenge for its application in frequency-doubling and rectifying devices. Here, we report a light-induced giant enhancement… ▽ More The nonlinear Hall effect (NLHE), an emergent phenomenon in noncentrosymmetric systems, enables the generation of a transverse voltage without an external magnetic field through a second-order electrical response. However, achieving a sizable NLHE signal remains a critical challenge for its application in frequency-doubling and rectifying devices. Here, we report a light-induced giant enhancement of the NLHE in the two-dimensional electron gas (2DEG) at the CaZrO3/KTaO3 (111) interface. Under light illumination, the second harmonic Hall voltage (V2ω y) increases substantially and undergoes a sign reversal. Correspondingly,the second-order transverse conductivity increases by nearly five orders of magnitude, reaching 2.4 um V-1 omega-1, while also reversing its sign. Scaling analysis indicates that skew scattering is the dominant mechanism underlying the NLHE and is highly tunable via optical gating. Photoexcitation pumps electrons from in-gap states into the higher-lying Ta 5d conduction band, generating high-mobility photocarriers that significantly increase the cubic transport scattering time, thereby driving a dramatic enhancement of σ(2) yxx. First-principles calculations further reveal that the Berry curvature distribution on the Fermi surface strongly depends on band filling. As the Fermi level approaches a band crossing in the Ta 5d subband near the M point, the Berry curvature triple undergoes a sign change, accounting for the experimentally observed sign reversal of the nonlinear Hall response. Our work offers a new strategy to optically boost and tune the nonlinear Hall effect in oxide 2DEG systems, paving the way for applications in light-controlled rectification and nonlinear electronic devices. △ Less

Submitted 19 July, 2025; originally announced July 2025.

Two-Dimensional Superconductivity at the CaZrO3/KTaO3 (001) Heterointerfaces

Authors: Lu Chen, Siyi Zhou, Daming Tian, Yinan Xiao, Qixuan Gao, Yongchao Wang, Yuansha Chen, Fengxia Hu, Baogen Shen, Jirong Sun, Weisheng Zhao, Jinsong Zhang, Hui Zhang

Abstract: Two-dimensional superconductivity at KTaO3 (KTO) heterointerfaces has sparked intensive investigations since its discovery, yet whether the (001)-oriented KTO interface hosts superconductivity remains to be elucidated. Here, we provide unambiguous evidence of superconductivity in two-dimensional electron gases (2DEGs) at CaZrO3/KTO(001) heterointerfaces, with a superconducting transition TC up to… ▽ More Two-dimensional superconductivity at KTaO3 (KTO) heterointerfaces has sparked intensive investigations since its discovery, yet whether the (001)-oriented KTO interface hosts superconductivity remains to be elucidated. Here, we provide unambiguous evidence of superconductivity in two-dimensional electron gases (2DEGs) at CaZrO3/KTO(001) heterointerfaces, with a superconducting transition TC up to ~0.25 K. Notably, TC increases linearly with carrier density nS over the range of 4.5*10^13~10.3*10^13 cm^-2. Furthermore, superconductivity exhibits a pronounced dependence on crystallographic orientation, with TC rising from 0.25 K for (001) to 1.04 K for (110) and 2.22 K for (111), underscoring the crucial role of interfacial symmetry in the CaZrO3/KTO system. The two-dimensional nature of the superconducting state is corroborated by the Berezinskii-Kosterlitz-Thouless (BKT) transition and the large anisotropy of the upper critical field. For the CaZrO3/KTO(001) sample with nS=7.7*10^13 cm^-2, the estimated Ginzburg-Landau coherence length ξGL=146.4 nm is larger than the superconducting layer thickness dSC=10.1 nm by a factor of ~14.5, confirming significant two-dimensional confinement of the CaZrO3/KTO(001) superconductor. In addition, we demonstrate that the two-dimensional superconductivity at the CaZrO3/KTO(001) interface can be effectively tuned by applying a back gate voltage. Our findings reveal the existence of two-dimensional superconductivity at CaZrO3/KTO(001), providing a new platform for exploring two-dimensional superconductivity at oxide interfaces. △ Less

Submitted 9 April, 2026; v1 submitted 2 July, 2025; originally announced July 2025.

Comments: 27 Pages,5 figures

Tension-Induced Soft Stress and Viscoelastic Bending in Liquid Crystal Elastomers for Enhanced Energy Dissipation

Authors: Beijun Shen, Yuefeng Jiang, Christopher M. Yakacki, Sung Hoon Kang, Thao D. Nguyen

Abstract: Architected materials that exploit buckling instabilities to reversibly trap energy have been shown to be effective for impact protection. The energy-absorbing capabilities of these architected materials can be enhanced further by incorporating viscoelastic material behavior into the buckling elements using liquid crystal elastomers (LCE). In addition to conventional viscoelastic behavior, LCEs al… ▽ More Architected materials that exploit buckling instabilities to reversibly trap energy have been shown to be effective for impact protection. The energy-absorbing capabilities of these architected materials can be enhanced further by incorporating viscoelastic material behavior into the buckling elements using liquid crystal elastomers (LCE). In addition to conventional viscoelastic behavior, LCEs also exhibit a highly dissipative rate-dependent soft stress response from mesogen rotation under a mechanical load. However, the buckling elements cannot take advantage of this dissipation mechanism because buckling occurs at strains below the threshold for mesogen rotation. In this study, we investigate tension-induced soft stress behavior as an additional dissipation mechanism in horizontal members of lattice structures composed of tilted LCE beams under compression. Viscoelastic properties of LCEs with two crosslinking densities were characterized experimentally, and a nonlinear viscoelastic model was implemented in Abaqus/Standard as a user-defined element to simulate finite-strain behavior of monodomain LCEs, including soft stress response. Simulations and experiments revealed a non-monotonic dependence of energy dissipation on the thickness ratio between horizontal and tilted LCE members. Optimized structures with stretchable horizontal bars dissipated 2-3 times more energy than rigid-bar counterparts by balancing tension-driven soft stress with viscoelastic beam bending. These findings demonstrate a new design strategy for LCE-based architected materials to enhance energy dissipation. △ Less

Submitted 13 August, 2025; v1 submitted 29 June, 2025; originally announced June 2025.

Comments: in total 39 pages, 11 figures in main text, and 11 figures in appendix

Journal ref: Journal of the Mechanics and Physics of Solids, Volume 209, March 2026, 106497

Emergence of Chern metal in a moiré Kondo lattice

Authors: Wenjin Zhao, Zui Tao, Yichi Zhang, Bowen Shen, Zhongdong Han, Patrick Knüppel, Yihang Zeng, Zhengchao Xia, Kenji Watanabe, Takashi Taniguchi, Jie Shan, Kin Fai Mak

Abstract: A Chern metal is a two-dimensional metallic state of matter carrying chiral edge states. It can emerge as a doped Chern insulator, but theoretical studies have also predicted its emergence near a Kondo breakdown separating a metallic chiral spin liquid and a heavy Fermi liquid in a frustrated lattice. To date, the latter exotic scenario has not been realized. Here, we report the observation of a C… ▽ More A Chern metal is a two-dimensional metallic state of matter carrying chiral edge states. It can emerge as a doped Chern insulator, but theoretical studies have also predicted its emergence near a Kondo breakdown separating a metallic chiral spin liquid and a heavy Fermi liquid in a frustrated lattice. To date, the latter exotic scenario has not been realized. Here, we report the observation of a Chern metal at the onset of the magnetic Kondo breakdown in a frustrated moiré Kondo lattice--angle-aligned MoTe2/WSe2 bilayers. The state is compressible and is manifested by a nearly quantized Hall resistance but a finite longitudinal resistance that arises from a bad metallic bulk. The state also separates an itinerant and a heavy Fermi liquid and appears far away from the band inversion critical point of the material, thus ruling out its origin from simply doping a Chern insulator. We demonstrate the presence of a chiral edge state by nonlocal transport measurements and current-induced quantum anomalous Hall breakdown. Magnetic circular dichroism measurements further reveal a magnetization plateau for the Chern metal before a metamagnetic transition at the Kondo breakdown. Our results open an opportunity for moiré engineering of exotic quantum phases of matter through the close interplay between band topology and Kondo interactions. △ Less

Submitted 16 June, 2025; originally announced June 2025.

Pressure tuning of competing interactions on a honeycomb lattice

Authors: Piyush Sakrikar, Bin Shen, Eduardo H. T. Poldi, Faranak Bahrami, Xiaodong Hu, Eric M. Kenney, Qiaochu Wang, Kyle W. Fruhling, Chennan Wang, Ritu Gupta, Rustem Khasanov, Hubertus Luetkens, Stuart A. Calder, Adam A. Aczel, Gilberto Fabbris, Russell J. Hemley, Kemp W. Plumb, Ying Ran, Philipp Gegenwart, Alexander A. Tsirlin, Daniel Haskel, Michael J. Graf, Fazel Tafti

Abstract: Magnetic exchange interactions are mediated via orbital overlaps across chemical bonds. Thus, modifying the bond angles by physical pressure or strain can tune the relative strength of competing interactions. Here we present a remarkable case of such tuning between the Heisenberg (J) and Kitaev (K) exchange, which respectively establish magnetically ordered and spin liquid phases on a honeycomb la… ▽ More Magnetic exchange interactions are mediated via orbital overlaps across chemical bonds. Thus, modifying the bond angles by physical pressure or strain can tune the relative strength of competing interactions. Here we present a remarkable case of such tuning between the Heisenberg (J) and Kitaev (K) exchange, which respectively establish magnetically ordered and spin liquid phases on a honeycomb lattice. We observe a rapid suppression of the Neel temperature (TN) with pressure in Ag3LiRh2O6, a spin-1/2 honeycomb lattice with both J and K couplings. Using a combined analysis of x-ray data and first-principles calculations, we find that pressure modifies the bond angles in a way that increases the |K/J| ratio and thereby suppresses TN. Consistent with this picture, we observe a spontaneous onset of muon spin relaxation (muSR) oscillations below TN at low pressure, whereas in the high-pressure phase, oscillations appear only when T < TN/2. Unlike other candidate Kitaev materials, Ag3LiRh2O6 is tuned toward a quantum critical point by pressure while avoiding a structural dimerization in the relevant pressure range. △ Less

Submitted 23 May, 2025; originally announced May 2025.

Comments: 1 pdf, 3 figures, 1 table, published

Journal ref: Nature Communications 16, 4712 (2025)

Pressure-tuned spin chains in brochantite, Cu$_4$SO$_4$(OH)$_6$

Authors: Victoria A. Ginga, Bin Shen, Ece Uykur, Nico Giordano, Philipp Gegenwart, Alexander A. Tsirlin

Abstract: Using high-pressure single-crystal x-ray diffraction combined with thermodynamic measurements and density-functional calculations, we uncover the microscopic magnetic model of the mineral brochantite, Cu$_4$SO$_4$(OH)$_6$, and its evolution upon compression. The formation of antiferromagnetic spin chains with the effective intrachain coupling of $J\simeq 100$\,K is attributed to the occurrence of… ▽ More Using high-pressure single-crystal x-ray diffraction combined with thermodynamic measurements and density-functional calculations, we uncover the microscopic magnetic model of the mineral brochantite, Cu$_4$SO$_4$(OH)$_6$, and its evolution upon compression. The formation of antiferromagnetic spin chains with the effective intrachain coupling of $J\simeq 100$\,K is attributed to the occurrence of longer Cu--Cu distances and larger Cu--O--Cu bond angles between the structural chains within the layers of the brochantite structure. These zigzag spin chains are additionally stabilized by ferromagnetic couplings $J_2$ between second neighbors and moderately frustrated by several antiferromagnetic couplings that manifest themselves in the reduced Néel temperature of the material. Pressure tuning of the brochantite structure keeps its monoclinic symmetry unchanged and leads to the growth of antiferromagnetic $J$ with the rate of 3.2\,K/GPa, although this trend is primarily caused by the enhanced ferromagnetic couplings $J_2$. Our results show that the nature of magnetic couplings in brochantite and in other layered Cu$^{2+}$ minerals is controlled by the size of the lattice translation along their structural chains and by the extent of the layer buckling. △ Less

Submitted 16 April, 2025; originally announced April 2025.

Comments: 11 pages, 6 figures

Journal ref: Phys. Rev. Materials 9, 094412 (2025)

Evidence of competing ground states between fractional Chern insulator and antiferromagnetism in moiré MoTe2

Authors: Xumin Chang, Feng Liu, Fan Xu, Cheng Xu, Jiayong Xiao, Zheng Sun, Pengfei Jiao, Yixin Zhang, Shaozheng Wang, Bohan Shen, Renjie He, Kenji Watanabe, Takashi Taniguchi, Ruidan Zhong, Jinfeng Jia, Zhiwen Shi, Xiaoxue Liu, Yang Zhang, Dong Qian, Tingxin Li, Shengwei Jiang

Abstract: Two-dimensional moire materials present unprecedented opportunities to explore quantum phases of matter arising from the interplay of band topology and strong correlations.One of the most striking examples is the recent observation of fractional quantum anomalous Hall (FQAH) effect in twisted bilayer MoTe$_2$ (tMoTe2) with relatively large twist angles(~3.7deg-3.9deg). The electronic ground states… ▽ More Two-dimensional moire materials present unprecedented opportunities to explore quantum phases of matter arising from the interplay of band topology and strong correlations.One of the most striking examples is the recent observation of fractional quantum anomalous Hall (FQAH) effect in twisted bilayer MoTe$_2$ (tMoTe2) with relatively large twist angles(~3.7deg-3.9deg). The electronic ground states are usually expected to be sensitive to the twist angle, as the twist angle determines the electron bandwidth and correlation strength in the moire system. Here, we report the observation of unexpected competing magnetic ground states in tMoTe2 moire superlattice, on which balance can be tipped by both twist angle and electric field (E). Specifically, we observed anomalous antiferromagnetic (AFM) ground states with zero Hall resistance at both v_h=1 and 2/3, at intermediate twist angles ~3deg. The AFM orders are suppressed by applying vertical E, and emergent ferromagnetism accompanied by integer Chern insulator (ICI) or fractional Chern insulator (FCI) states are observed near the critical E (E_c) of moire superlattice symmetry transition. Our results demonstrate tMoTe2 as a fascinating platform for exploring unexpected correlated phases with nontrivial topology and fractional excitations and point to electric-field-controlled ultralow-power spin-valleytronic devices. △ Less

Submitted 15 May, 2025; v1 submitted 17 March, 2025; originally announced March 2025.

Ferromagnetism in LaFeO3/LaNiO3 Superlattices with High Curie Temperature

Authors: Tianlin Zhou, Fei Gao, Qinghua Zhang, Yuansha Chen, Xinzhe Hu, Yuzhou He, Yuchen Zhao, Jianjie Li, Minghang Li, Shaojin Qi, Fengxia Hu, Jirong Sun, Yunzhong Chen, Baogen Shen

Abstract: Interfacing complex oxides in atomically engineered layered structures can give rise to a wealth of exceptional electronic and magnetic properties that surpass those of the individual building blocks. Herein, we demonstrate a ferromagnetic spin order with a high Curie temperature of 608 K in superlattices consisting of otherwise paramagnetic perovskite LaNiO3 (LNO) and antiferromagnetic LaFeO3 (LF… ▽ More Interfacing complex oxides in atomically engineered layered structures can give rise to a wealth of exceptional electronic and magnetic properties that surpass those of the individual building blocks. Herein, we demonstrate a ferromagnetic spin order with a high Curie temperature of 608 K in superlattices consisting of otherwise paramagnetic perovskite LaNiO3 (LNO) and antiferromagnetic LaFeO3 (LFO). The extraordinary ferromagnetism likely results from the covalent exchange due to interfacial charge transfer from Fe to Ni cations. By deliberately controlling the thickness of the LNO sublayers thus the amount of charge transfer, a robust ferromagnetism of 4 uB is realized for a stacking periodicity consisting of one single unit cell of both LNO and LFO, an emergent double perovskite phase of La2FeNiO6 with B-site layered ordering configurations. The ferromagnetic LFO/LNO superlattices offer great potential for the search of emergent magnetodielectric and/or multiferroic properties as well as applications in spintronics and electrocatalysts. △ Less

Submitted 17 March, 2025; originally announced March 2025.

Comments: 4 figures, 1 table.to be appear in Nat. Commun.2025

Antiferromagnetic Spin Fluctuations and Structural Transition in Cluster Mott Insulator Candidate Nb3Cl8 Revealed by 93Nb- and 35Cl-NMR

Authors: Y. Z. Zhou, X. Han, J. Luo, D. T. Wu, A. F. Fang, B. Shen, B. J. Feng, Y. G. Shi, J. Yang, R. Zhou

Abstract: Motivated by recent studies of the cluster Mott insulator candidate compound Nb3Cl8, this study performs 93Nb and 35Cl nuclear magnetic resonance (NMR) measurements to investigate the electron correlations. Below the structural transition temperature Ts ~ 97 K, all satellites of the 93Nb NMR spectra split into three distinct peaks, which suggests symmetry lowering due to the structural transition… ▽ More Motivated by recent studies of the cluster Mott insulator candidate compound Nb3Cl8, this study performs 93Nb and 35Cl nuclear magnetic resonance (NMR) measurements to investigate the electron correlations. Below the structural transition temperature Ts ~ 97 K, all satellites of the 93Nb NMR spectra split into three distinct peaks, which suggests symmetry lowering due to the structural transition and could be attributed to the change in the Nb-Nb bond-lengths of the Nb3 clusters. The spin-lattice relaxation rate 1/T1 divided by the temperature T, 1/T1T, increases upon cooling to Ts for all Cl sites, whereas only the Knight shift K of Cl located at the center of the Nb3 clusters exhibits a temperature dependence similar to that observed in magnetic susceptibility. These findings collectively demonstrate the existence of strong spin correlations between the Nb atoms in Nb3Cl8, which are closely associated with Mottness. △ Less

Submitted 17 March, 2025; originally announced March 2025.

Comments: 13 pages, 4 figures, 1 table. Supplementary materials: 9 pages, 7 figures

Journal ref: Chinese Physics Letters 42, 037303 (2025)

Pressure-induced strange metal phase in a metallic kagome ferromagnet

Authors: Bin Shen, Feng Du, Franziska Breitner, Victoria A. Ginga, Ece Uykur, Alexander A. Tsirlin, Philipp Gegenwart

Abstract: Strange metallicity with $T$-linear electrical resistance preceding high-$T_c$ superconductivity remains an enigmatic, yet crucial, signature of correlation physics. Using electrical transport and magnetization measurements up to 50 GPa, we show that such a strange-metal phase is formed in pressurized kagome ferromagnet CrNiAs. In contrast to other kagome materials, a linear suppression of the Cur… ▽ More Strange metallicity with $T$-linear electrical resistance preceding high-$T_c$ superconductivity remains an enigmatic, yet crucial, signature of correlation physics. Using electrical transport and magnetization measurements up to 50 GPa, we show that such a strange-metal phase is formed in pressurized kagome ferromagnet CrNiAs. In contrast to other kagome materials, a linear suppression of the Curie temperature is found, with the ferromagnetic quantum critical point at $p_{\rm{c}} \approx 12.5$ GPa. Remarkably, from $p_{\rm{c}}$ up to the highest measured pressure, characteristic strange-metal behavior is observed, whereas magnetic field reinstates the Fermi liquid. Electronic structure calculations reveal robust weakly dispersive bands persisting unchanged beyond $p_{\rm{c}}$, possibly at the origin of the $T$-linear electrical resistance. This establishes pressurized kagome ferromagnets as an intriguing platform for strange-metal behavior. △ Less

Submitted 12 March, 2025; originally announced March 2025.

Comments: 7 pages, 4 figures (main text)

Red Emission from Strain-Relaxed Bulk InGaN Active Region

Authors: Zuojian Pan, Zhizhong Chen, Haodong Zhang, Chuhan Deng, Ling Hu, Fei Huang, Qi Wang, Guoyi Zhang, Xiaohang Li, Bo Shen

Abstract: High-In-content InGaN quantum wells (QWs) in red light-emitting diodes (LEDs) are typically grown at low temperatures to ensure effective In incorporation. In this study, red LEDs based on bulk InGaN active region were demonstrated. The growth temperature of bulk InGaN was ~800C, which is over 100C higher than the typical growth temperature of red QWs. By introducing high-density trench structures… ▽ More High-In-content InGaN quantum wells (QWs) in red light-emitting diodes (LEDs) are typically grown at low temperatures to ensure effective In incorporation. In this study, red LEDs based on bulk InGaN active region were demonstrated. The growth temperature of bulk InGaN was ~800C, which is over 100C higher than the typical growth temperature of red QWs. By introducing high-density trench structures in the underlying green multi-quantum wells (MQWs), the compressive strain in bulk InGaN was relaxed by ~96%. With strain relaxation, phase separation occurred in the bulk InGaN, forming low-In-content (blue) and high-In-content (red) phases. The red phase acted as carrier localization centers, enabling red light emission under electrical injection. The red LEDs based on bulk InGaN exhibited a peak wavelength of 645 nm at 20 mA, with on-wafer peak external quantum efficiency of 0.32%. This study presents a new epitaxial strategy for red InGaN LEDs. △ Less

Submitted 6 March, 2025; originally announced March 2025.

Journal ref: Opt. Express 33, 27245-27254 (2025)

Time-reversal symmetry breaking fractional quantum spin Hall insulator in moiré MoTe2

Authors: Kaifei Kang, Yichen Qiu, Bowen Shen, Kihong Lee, Zhengchao Xia, Yihang Zeng, Kenji Watanabe, Takashi Taniguchi, Jie Shan, Kin Fai Mak

Abstract: Twisted bilayer transition metal dichalcogenide semiconductors, which support flat Chern bands with enhanced interaction effects, realize a platform for fractional Chern insulators and fractional quantum spin Hall (FQSH) insulators. A recent experiment has reported the emergence of a FQSH insulator protected by spin-Sz conservation at a moiré lattice filling factor ν=3 in 2.1-degree twisted bilaye… ▽ More Twisted bilayer transition metal dichalcogenide semiconductors, which support flat Chern bands with enhanced interaction effects, realize a platform for fractional Chern insulators and fractional quantum spin Hall (FQSH) insulators. A recent experiment has reported the emergence of a FQSH insulator protected by spin-Sz conservation at a moiré lattice filling factor ν=3 in 2.1-degree twisted bilayer MoTe2. Theoretical studies have proposed both time-reversal symmetric and asymmetric ground states as possible candidates for the observed FQSH insulator, but the nature of the state remains unexplored. Here we report the observation of spontaneous time-reversal symmetry breaking at generic fillings in 2.1-degree twisted bilayer MoTe2 from ν<1 all the way to ν>6 except at ν=2, 4, and 6. Although zero Hall response is observed at ν=3 for magnetic fields higher than 20 mT, a finite anomalous Hall response accompanied by a magnetic hysteresis is observed at lower magnetic fields, demonstrating spontaneous time-reversal symmetry breaking. Our work shows the tendency towards ferromagnetism by doping the first three pairs of conjugate Chern bands in the material; it also sheds light on the nature of the FQSH insulator at ν=3. △ Less

Submitted 12 January, 2025; v1 submitted 5 January, 2025; originally announced January 2025.

Comments: In Supplemental Figure 4, we contrast a 2.6-degree device with a 2.1-degree device

Spectroscopic signatures of magnetization-induced band renormalization and strong spin-charge-lattice coupling in EuZn$_2$As$_2$

Authors: Zhiyu Liao, Boxuan Li, Shaohui Yi, Lincong Zheng, Yubiao Wu, Enkui Yi, Premysl Marsik, Bing Shen, Hongming Weng, Bing Xu, Xianggang Qiu, Christian Bernhard

Abstract: We report an infrared spectroscopy study of the antiferromagnetic (AFM) insulator EuZn$_2$As$_2$ over a broad frequency range, spanning temperatures both above and below the AFM transition $T_{\rm N} \simeq$ 20 K. The optical response reveals an insulating behavior, featuring two prominent infrared-active phonon modes at around 95 and 190 cm$^{-1}$, and two subtle absorption peaks at around 130 (… ▽ More We report an infrared spectroscopy study of the antiferromagnetic (AFM) insulator EuZn$_2$As$_2$ over a broad frequency range, spanning temperatures both above and below the AFM transition $T_{\rm N} \simeq$ 20 K. The optical response reveals an insulating behavior, featuring two prominent infrared-active phonon modes at around 95 and 190 cm$^{-1}$, and two subtle absorption peaks at around 130 ($α$ peak) and 2700 cm$^{-1}$ ($β$ peak), along with a strong absorption edge rising around 9000 cm$^{-1}$ ($γ$ peak). Significantly, the temperature-dependent changes in these peaks show noticeable anomalies across the AFM transition, particularly the emergence of the $α$ peak and an unusual redshift of the $γ$ peak, suggesting a strong interaction between the charge excitations and the AFM order. Band structure calculations reveal that these anomalies arise from magnetization-induced band renormalizations, including shifts and foldings. Additionally, both phonon modes feature asymmetric Fano line shapes at low temperatures, with the 95 cm$^{-1}$ phonon mode exhibiting strong coupling to the fluctuations of Eu spins. These findings highlight a complex interplay of spin, charge, and lattice degrees of freedom in EuZn$_2$As$_2$. △ Less

Submitted 14 April, 2025; v1 submitted 17 December, 2024; originally announced December 2024.

Comments: 6 pages, 4 figures

Journal ref: Phys. Rev. B 111, 155131 (2025)

Unveiling the multiband metallic nature of the normal state in nickelate La3Ni2O7

Authors: Bowen Chen, Hengyuan Zhang, Jingyuan Li, Deyuan Hu, Mengwu Huo, Shuyang Wang, Chuanying Xi, Zhaosheng Wang, Hualei Sun, Meng Wang, Bing Shen

Abstract: The discovery of unconventional superconductivity around 80 K in perovskite nickelates under high pressure has furnished a new platform to explore high-temperature unconventional superconductivity in addition to cuprates. Understanding the normal state of nickelate superconductors is crucial to uncovering the origin of this unconventional superconductivity and gaining further insight into its unde… ▽ More The discovery of unconventional superconductivity around 80 K in perovskite nickelates under high pressure has furnished a new platform to explore high-temperature unconventional superconductivity in addition to cuprates. Understanding the normal state of nickelate superconductors is crucial to uncovering the origin of this unconventional superconductivity and gaining further insight into its underlying mechanism. In this study, we systemically studied the transport properties of La3Ni2O7 by tuning the pressure under high magnetic fields. Magnetoresistance (MR) consistently exhibits a quasi-quadratic dependence on the magnetic field across all measured pressures and temperatures. Increased pressure enhances the metallicity of the system and leads to a monotonic increase in MR, which follows the extended Kohler's rule. These results suggest that the normal state of La3Ni2O7 to be a multiband metallic nature. △ Less

Submitted 27 June, 2025; v1 submitted 12 December, 2024; originally announced December 2024.

Journal ref: Phys. Rev. B 111. 054519 (2025)

Unambiguous identification of the indirect band nature of atomically thin hexagonal boron nitride

Authors: Lei Fu, Yuqing Hu, Ning Tang, Junxi Duan, Xionghui Jia, Huaiyuan Yang, Zhuoxian Li, Xiangyan Han, Guoping Li, Jianming Lu, Lun Dai, Weikun Ge, Bo Shen

Abstract: Atomically thin hexagonal boron nitride (h-BN), especially monolayer, has garnered increasing attention due to its intriguing optical and light-matter-interaction properties. However, its intrinsic optical properties and electronic band structure, have long remained elusive. In this study, near-resonance excited deep-UV photoluminescence/Raman spectroscopy and deep-UV reflectance contrast spectros… ▽ More Atomically thin hexagonal boron nitride (h-BN), especially monolayer, has garnered increasing attention due to its intriguing optical and light-matter-interaction properties. However, its intrinsic optical properties and electronic band structure, have long remained elusive. In this study, near-resonance excited deep-UV photoluminescence/Raman spectroscopy and deep-UV reflectance contrast spectroscopy are utilized to experimentally investigate the optical properties of atomically thin h-BN across various layer numbers. It is revealed that the absence of luminescence in 1-3 layers h-BN is indicative of their indirect band gap nature, rectifying previously adopted identification of a direct band gap in monolayer BN. Notably, band-edge luminescence signals and indirect bandgap absorption start to appear in 4-layer, and the luminescence intensity increases with the number of layers, suggesting that interlayer interactions and periodicity along the z-axis enhance phonon-assisted indirect bandgap transition, even in the 4-layer case, and furthermore indicating the formation process of flat bands at the K and M valleys as the periodicity along the z direction increases. Additionally, the prominent resonance Raman signals in atomically thin h-BN underscore strong electron-phonon coupling in this material. △ Less

Submitted 16 October, 2024; originally announced October 2024.

Pressure-dependent magnetism of the Kitaev candidate Li$_2$RhO$_3$

Authors: Bin Shen, Efrain Insuasti Pazmino, Ramesh Dhakal, Friedrich Freund, Philipp Gegenwart, Stephen M. Winter, Alexander A. Tsirlin

Abstract: We use magnetization measurements under pressure along with \textit{ab initio} and cluster many-body calculations to investigate magnetism of the Kitaev candidate Li$_2$RhO$_3$. Hydrostatic compression leads to a decrease in the magnitude of the nearest-neighbor ferromagnetic Kitaev coupling $K_1$ and the corresponding increase in the off-diagonal anisotropy $Γ_1$, whereas the experimental Curie-W… ▽ More We use magnetization measurements under pressure along with \textit{ab initio} and cluster many-body calculations to investigate magnetism of the Kitaev candidate Li$_2$RhO$_3$. Hydrostatic compression leads to a decrease in the magnitude of the nearest-neighbor ferromagnetic Kitaev coupling $K_1$ and the corresponding increase in the off-diagonal anisotropy $Γ_1$, whereas the experimental Curie-Weiss temperature changes from negative to positive with the slope of +40~K/GPa. On the other hand, spin freezing persists up to at least 3.46~GPa with the almost constant freezing temperature of 5~K that does not follow the large changes in the exchange couplings and indicates the likely extrinsic origin of spin freezing. Magnetic frustration in Li$_2$RhO$_3$ is mainly related to the interplay between ferromagnetic $K_1$ and antiferromagnetic $Γ_1$, along with the weakness of the third-neighbor coupling $J_3$ that would otherwise stabilize zigzag order. The small $J_3$ distinguishes Li$_2$RhO$_3$ from other Kitaev candidates. △ Less

Submitted 22 January, 2025; v1 submitted 21 September, 2024; originally announced September 2024.

Comments: Main text: 10 pages, 6 figures. Supplemental material: 4 pages, 3 figures

Journal ref: npj Quantum Materials, 10:9 (2025)

Tunable Anomalous Hall Effect in a Kagome Ferromagnetic Weyl Semimetal

Authors: Samuel E. Pate, Bin Wang, Yang Zhang, Bing Shen, Enke Liu, Ivar Martin, J. Samuel Jiang, Xiuquan Zhou, Duck Young Chung, Mercouri G. Kanatzidis, Ulrich Welp, Wai-Kwong Kwok, Zhi-Li Xiao

Abstract: Emerging from the intricate interplay of topology and magnetism, the giant anomalous Hall effect (AHE) is the most known topological property of the recently discovered kagome ferromagnetic Weyl semimetal Co_3Sn_2S_2 with the magnetic Co atoms arranged on a kagome lattice. Here we report that the AHE in Co_3Sn_2S_2 can be fine-tuned by an applied magnetic field orientated within ~2 degrees of the… ▽ More Emerging from the intricate interplay of topology and magnetism, the giant anomalous Hall effect (AHE) is the most known topological property of the recently discovered kagome ferromagnetic Weyl semimetal Co_3Sn_2S_2 with the magnetic Co atoms arranged on a kagome lattice. Here we report that the AHE in Co_3Sn_2S_2 can be fine-tuned by an applied magnetic field orientated within ~2 degrees of the kagome plane, while beyond this regime, it stays unchanged. Particularly, it can vanish in magnetic fields parallel to the kagome plane and even decrease in magnetic fields collinear with the spin direction. This tunable AHE can be attributed to local spin switching enabled by the geometrical frustration of the magnetic kagome lattice, revealing that spins in a kagome ferromagnet change their switching behavior as the magnetic field approaches the kagome plane. Our results also suggest a versatile way to tune the properties of a kagome magnet. △ Less

Submitted 20 September, 2024; originally announced September 2024.

Journal ref: Adv. Sci. 11, 2406882 (2024)

Single-atom-resolved vibrational spectroscopy of a dislocation

Authors: Hailing Jiang, Tao Wang, Zhenyu Zhang, Ruochen Shi, Xifan Xu, Bowen Sheng, Fang Liu, Weikun Ge, Ping Wang, Bo Shen, Peng Gao, Lucas R Lindsay, Xinqiang Wang

Abstract: Phonon resistance from dislocation scattering is often divided into short-range core interactions and long-range strain field interactions. Using electron energy-loss spectroscopy on a GaN dislocation, we report observations of vibrational modes localized at specific core atoms (short-range) and strain-driven phonon energy shifts around the dislocation (long-range). Ab initio calculations support… ▽ More Phonon resistance from dislocation scattering is often divided into short-range core interactions and long-range strain field interactions. Using electron energy-loss spectroscopy on a GaN dislocation, we report observations of vibrational modes localized at specific core atoms (short-range) and strain-driven phonon energy shifts around the dislocation (long-range). Ab initio calculations support these findings and draw out additional details. This study reveals atomically resolved vibrational spectra of dislocations, thus offering insights for engineering improved material functionalities. △ Less

Submitted 16 September, 2024; originally announced September 2024.

Topological Nodal Chains and Transverse Transports in Ferromagnetic Centrosymmetric Semimetal FeIn2S4

Authors: Junyan Liu, Yibo Wang, Xuebin Dong, Jinying Yang, Shen Zhang, Meng Lyu, Binbin Wang, Hongxiang Wei, Shouguo Wang, Enke Liu, Baogen Shen

Abstract: Nodal chain semimetals protected by nonsymmorphic symmetries are distinct from Dirac and Weyl semimetals, featuring unconventional topological surface states and resulting in anomalous magnetotransport properties. Here, we reveal that the ferromagnetic FeIn2S4 is a suitable nodal chain candidate in theory. Centrosymmetric FeIn2S4 with nonsymmorphic symmetries shows half-metallicity and clean band-… ▽ More Nodal chain semimetals protected by nonsymmorphic symmetries are distinct from Dirac and Weyl semimetals, featuring unconventional topological surface states and resulting in anomalous magnetotransport properties. Here, we reveal that the ferromagnetic FeIn2S4 is a suitable nodal chain candidate in theory. Centrosymmetric FeIn2S4 with nonsymmorphic symmetries shows half-metallicity and clean band-crossings with hourglass-type dispersion tracing out nodal lines. Owing to glide mirror symmetries, the nontrivial nodal loops form nodal chain, which is associated with the perpendicular glide mirror planes. These nodal chains are robust against spin-orbital interaction, giving rise to the coexistence of drumhead-type surface states and closed surface Fermi arcs. Moreover, the nodal loops protected by nonsymmorphic symmetry contribute to large anomalous Hall conductivity and the anomalous Nernst conductivity. Our results provide a platform to explore the intriguing topological state and transverse transport properties in magnetic system. △ Less

Submitted 15 September, 2024; originally announced September 2024.

Comments: 7 figs and 1 table

Scaling the topological transport based on an effective Weyl model

Authors: Shen Zhang, Jinying Yang, Meng Lyu, Junyan Liu, Binbin Wang, Hongxiang Wei, Claudia Felser, Wenqing Zhang, Enke Liu, Baogen Shen

Abstract: Magnetic topological semimetals are increasingly fueling interests in exotic electronic-thermal physics including thermoelectrics and spintronics. To control the transports of topological carriers in such materials becomes a central issue. However, the topological bands in real materials are normally intricate, leaving obstacles to understand the transports in a physically clear way. Parallel to t… ▽ More Magnetic topological semimetals are increasingly fueling interests in exotic electronic-thermal physics including thermoelectrics and spintronics. To control the transports of topological carriers in such materials becomes a central issue. However, the topological bands in real materials are normally intricate, leaving obstacles to understand the transports in a physically clear way. Parallel to the renowned effective two-band model in magnetic field scale for semiconductors, here, an effective Weyl-band model in temperature scale was developed with pure Weyl state and a few meaningful parameters for topological semimetals. Based on the model, a universal scaling was established and subsequently verified by reported experimental transports. The essential sign regularity of anomalous Hall and Nernst transports was revealed with connection to chiralities of Weyl nodes and carrier types. Upon a double-Weyl model, a concept of Berry-curvature ferrimagnetic structure, as an analogy to the real-space magnetic structure, was further proposed and well described the emerging sign reversal of Nernst thermoelectric transports in temperature scale. Our study offers a convenient tool for scaling the Weyl-fermion-related transport physics, and promotes the modulations and applications of magnetic topological materials in future topological quantum devices. △ Less

Submitted 15 September, 2024; originally announced September 2024.

Comments: Five figs

Above room-temperature two-dimensional ferromagnetic half-metals in Mn-based Janus magnets

Authors: Xiang-Fan Huang, Kang-Jie Li, Zequan Wang, Shi-Bo Zhao, Bing Shen, Zu-Xin Chen, Yusheng Hou

Abstract: Two-dimensional (2D) ferromagnets and their heterostructures offer fertile grounds for designing fascinating functionalities in ultra-thin spintronic devices. Here, by first-principles calculations, we report the discovery of energetically and thermodynamically stable 2D ferromagnets with very strong inplane magnetic anisotropy in MnXY (X = S, and Se; Y = Cl, Br and I) monolayers. Remarkably, we f… ▽ More Two-dimensional (2D) ferromagnets and their heterostructures offer fertile grounds for designing fascinating functionalities in ultra-thin spintronic devices. Here, by first-principles calculations, we report the discovery of energetically and thermodynamically stable 2D ferromagnets with very strong inplane magnetic anisotropy in MnXY (X = S, and Se; Y = Cl, Br and I) monolayers. Remarkably, we find that the Curie temperatures of the ferromagnetic MnSBr, MnSI, MnSeCl, and MnSeI monolayers are as high as 271, 273, 231 and 418 K, respectively. In addition, we demonstrate that these ferromagnetic monolayers are intrinsic half-metals with large spin band gaps ranging from 2.5 eV to 3.2 eV. When spin-orbit coupling is considered in these ferromagnetic monolayers, the nature of their half-metal is almost unaffected. Finally, the strong inplane magnetic anisotropy of MnSY (Y = Br, I) and MnSeY (Y = Cl, I) monolayers originate mainly from halogen and chalcogen atoms, respectively. Our work shows 2D Janus Mn-based ferromagnetic half-metals may have appealing functionalities in high-performance spintronic applications. △ Less

Submitted 9 June, 2024; originally announced June 2024.

Comments: 16 pages, 4 figures, accepted by Applied Physics Letters

Journal ref: Appl. Phys. Lett. 124, 252402 (2024)

Strong enhancement of magnetic coercivity induced by uniaxial stress

Authors: Bin Shen, Franziska Breitner, Philipp Gegenwart, Anton Jesche

Abstract: The performance of permanent magnets is intricately tied to their magnetic hysteresis loop. In this study, we investigate the heavy-fermion ferromagnet CeAgSb$_2$ through magnetization measurements under uniaxial stress. We observe a 2400 % increase in magnetic coercivity with just a modest stress of approximately 1 kbar. This effect persists even after pressure release, attributable to stress-ind… ▽ More The performance of permanent magnets is intricately tied to their magnetic hysteresis loop. In this study, we investigate the heavy-fermion ferromagnet CeAgSb$_2$ through magnetization measurements under uniaxial stress. We observe a 2400 % increase in magnetic coercivity with just a modest stress of approximately 1 kbar. This effect persists even after pressure release, attributable to stress-induced defects that efficiently pin domain walls. Other magnetic properties such as ordering temperature and saturation moment exhibit only weak pressure dependencies and display full reversibility. Our findings offer a promising route for increasing coercive field strength and enhancing the energy product in ferromagnetic materials and are potentially applicable to a broad spectrum of commercial or emerging magnetic applications. △ Less

Submitted 29 October, 2024; v1 submitted 30 April, 2024; originally announced April 2024.

Comments: Main text: 7 pages, 3 figures. Supplemental material: 3 pages, 4 figures

Sign-reversal Anomalous Hall effect driven by a magnetic transition in Cr$_{7-δ}$Te$_8$

Authors: Bowen Chen, Xiaokai Wu, Zhiyu Liao, Zhendong Fu, Bing Xu, Meng Wang, Bing Shen

Abstract: The search for exotic spin configurations and related novel transport properties continues to be fueled by the promise of new electronic states and outstanding candidate components for spintronic applications. In layered Cr$_{7-δ}$Te$_8$, the applied field drives a before unreported magnetic transition revealed by the alternating current magnetic susceptibility measurements around room temperature… ▽ More The search for exotic spin configurations and related novel transport properties continues to be fueled by the promise of new electronic states and outstanding candidate components for spintronic applications. In layered Cr$_{7-δ}$Te$_8$, the applied field drives a before unreported magnetic transition revealed by the alternating current magnetic susceptibility measurements around room temperature. This observed magnetic transition results in a sign change for the anomalous Hall effect which exhibits non-monotonous temperature dependence. The prominent topological Hall effect (THE) with a large value of 1$μΩ\cdot cm$ has been observed without breaking the inversion symmetry for Cr$_{7-δ}$Te$_8$. This robust THE can persist up to room temperature attributed to the nonzero fluctuation-driven scalar spin chirality. The complicated interactions of long-range and short-range magnetic orders lead to rich exotic magnetic states with related novel transport properties in Cr$_{7-δ}$Te$_8$. △ Less

Submitted 31 March, 2024; originally announced April 2024.

Magnetic versus nonmagnetic polymorphs of RuBr$_3$ under pressure

Authors: Bin Shen, Victoria A. Ginga, Angel M. Arévalo-López, Gaston Garbarino, Ece Uykur, Marcos Goncalves-Faria, Prashanta K. Mukharjee, Philipp Gegenwart, Alexander A. Tsirlin

Abstract: Pressure evolution of the crystal structure and magnetism of the honeycomb $α$-RuBr$_3$ is studied using high-pressure x-ray diffraction, magnetometry, and density-functional band-structure calculations. Hydrostatic compression transforms antiferromagnetic $α$-RuBr$_3$ ($R\bar 3$) into paramagnetic $α'$-RuBr$_3$ ($P\bar 1$) where short Ru-Ru bonds cause magnetism collapse above 1.3 GPa at 0 K and… ▽ More Pressure evolution of the crystal structure and magnetism of the honeycomb $α$-RuBr$_3$ is studied using high-pressure x-ray diffraction, magnetometry, and density-functional band-structure calculations. Hydrostatic compression transforms antiferromagnetic $α$-RuBr$_3$ ($R\bar 3$) into paramagnetic $α'$-RuBr$_3$ ($P\bar 1$) where short Ru-Ru bonds cause magnetism collapse above 1.3 GPa at 0 K and 2.5 GPa at 295 K. Below this critical pressure, the Néel temperature of $α$-RuBr$_3$ increases with the slope of 1.8 K/GPa. Pressure tunes $α$-RuBr$_3$ away from the Kitaev limit, whereas increased third-neighbor in-plane coupling and interlayer coupling lead to a further stabilization of the collinear zigzag state. Both $α$- and $α'$-RuBr$_3$ are metastable at ambient pressure, but their transformation into the thermodynamically stable $β$-polymorph is kinetically hindered at room temperature. △ Less

Submitted 5 June, 2024; v1 submitted 25 March, 2024; originally announced March 2024.

Comments: 8 pages + Supplemental Material: published version

Journal ref: Phys. Rev. B 109, 224402 (2024)

Observation of in-gap states in a two-dimensional CrI2/NbSe2 heterostructure

Authors: Peigen Li, Jihai Zhang, Di Zhu, Cui-Qun Chen, Enkui Yi, Bing Shen, Yusheng Hou, Zhongbo Yan, Dao-Xin Yao, Donghui Guo, Dingyong Zhong

Abstract: Low-dimensional magnetic structures coupled with superconductors are promising platforms for realizing Majorana zero modes, which have potential applications in topological quantum computing. Here, we report a two-dimensional (2D) magnetic-superconducting heterostructure consisting of single-layer chromium diiodide (CrI2) on a niobium diselenide (NbSe2) superconductor. Single-layer CrI2 nanosheets… ▽ More Low-dimensional magnetic structures coupled with superconductors are promising platforms for realizing Majorana zero modes, which have potential applications in topological quantum computing. Here, we report a two-dimensional (2D) magnetic-superconducting heterostructure consisting of single-layer chromium diiodide (CrI2) on a niobium diselenide (NbSe2) superconductor. Single-layer CrI2 nanosheets, which hold antiferromagnetic (AFM) ground states by our first-principles calculations, were epitaxially grown on the layered NbSe2 substrate. Using scanning tunneling microscopy/spectroscopy, we observed robust in-gap states spatially located at the edge of the nanosheets and defect-induced zero-energy peaks inside the CrI2 nanosheets. Magnetic-flux vortices induced by an external field exhibit broken threefold rotational symmetry of pristine NbSe2 superconductor, implying the efficient modulation of the interfacial superconducting states by the epitaxial CrI2 layer. A phenomenological model suggests the existence of chiral edge states in a 2D AFM-superconducting hybrid system with an even Chern number, providing a qualitatively plausible understanding for our experimental observation. △ Less

Submitted 25 July, 2024; v1 submitted 10 March, 2024; originally announced March 2024.

Comments: 21 pages, 5 figures

Journal ref: Nano Letters 2024

Intermediate field-induced phase of the honeycomb magnet BaCo$_2$(AsO$_4$)$_2$

Authors: Prashanta K. Mukharjee, Bin Shen, Sebastian Erdmann, Anton Jesche, Julian Kaiser, Priya R. Baral, Oksana Zaharko, Philipp Gegenwart, Alexander A. Tsirlin

Abstract: We use magnetometry, calorimetry, and high-resolution capacitive dilatometry, as well as single-crystal neutron diffraction to explore temperature-field phase diagram of the anisotropic honeycomb magnet BaCo$_2$(AsO$_4)_2$. Our data reveal four distinct ordered states observed for in-plane magnetic fields. Of particular interest is the narrow region between 0.51 and 0.55 T that separates the up-up… ▽ More We use magnetometry, calorimetry, and high-resolution capacitive dilatometry, as well as single-crystal neutron diffraction to explore temperature-field phase diagram of the anisotropic honeycomb magnet BaCo$_2$(AsO$_4)_2$. Our data reveal four distinct ordered states observed for in-plane magnetic fields. Of particular interest is the narrow region between 0.51 and 0.55 T that separates the up-up-down order from the fully polarized state and coincides with the field range where signatures of the spin-liquid behavior have been reported. We show that magnetic Bragg peaks persist in this intermediate phase, thus ruling out its spin-liquid nature. However, the simultaneous nonmonotonic evolution of nuclear Bragg peaks suggests the involvement of the lattice, witnessed also in other regions of the phase diagram where large changes in the sample length are observed upon entering the magnetically ordered states. Our data highlight the importance of lattice effects in BaCo$_2$(AsO$_4)_2$. △ Less

Submitted 21 October, 2024; v1 submitted 7 March, 2024; originally announced March 2024.

Journal ref: Phys. Rev. B 110, L140407 (2024)

The de Haas-van Alphen quantum oscillations in the kagome metal RbTi3Bi5

Authors: Zixian Dong, Lei Shi, Bing Wang, Mengwu Huo, Xing Hua, Chaoxin Huang, Peiyue Ma, Yunwei Zhang, Bing Shen, Meng Wang

Abstract: Kagome system usually attracts great interest in condensed matter physics due to its unique structure hosting various exotic states such as superconductivity (SC), charge density wave (CDW), and nontrivial topological states. Topological semimetal RbTi3Bi5 consisting of the kagome layer of Ti shares a similar crystal structure to topological correlated materials AV3Sb5 (A = K, Rb, Cs) but with the… ▽ More Kagome system usually attracts great interest in condensed matter physics due to its unique structure hosting various exotic states such as superconductivity (SC), charge density wave (CDW), and nontrivial topological states. Topological semimetal RbTi3Bi5 consisting of the kagome layer of Ti shares a similar crystal structure to topological correlated materials AV3Sb5 (A = K, Rb, Cs) but with the absence of CDW and SC. Systematic de Haas-van Alphen (dHvA) oscillation measurements are performed on the single crystals of RbTi3Bi5 to pursue nontrivial topological physics and exotic states. Combining with theoretical calculations, detailed Fermi surface topology and band structure are investigated. A two-dimensional (2D) Fermi pocket \b{eta} is revealed with a light-effective mass in consistent with the semimetal predictions. Landau Fan of RbTi3Bi5 reveals a zero Berry phase for the \b{eta} oscillation in contrast to that of CsTi3Bi5. These results suggest the kagome RbTi3Bi5 is a good candidate to explore nontrivial topological exotic states and topological correlated physics. △ Less

Submitted 4 March, 2024; originally announced March 2024.

Journal ref: Chinese Physics B 33, 107102 (2024)

Observation of the fractional quantum spin Hall effect in moiré MoTe2

Authors: Kaifei Kang, Bowen Shen, Yichen Qiu, Kenji Watanabe, Takashi Taniguchi, Jie Shan, Kin Fai Mak

Abstract: Quantum spin Hall (QSH) insulators are two-dimensional electronic materials that have a bulk band gap like an ordinary insulator but have topologically protected pairs of edge modes of opposite chiralities. To date, experimental studies have found only integer QSH insulators with counter-propagating up-spins and down-spins at each edge leading to a quantized conductance G0=e^2/h. Here we report tr… ▽ More Quantum spin Hall (QSH) insulators are two-dimensional electronic materials that have a bulk band gap like an ordinary insulator but have topologically protected pairs of edge modes of opposite chiralities. To date, experimental studies have found only integer QSH insulators with counter-propagating up-spins and down-spins at each edge leading to a quantized conductance G0=e^2/h. Here we report transport evidence of a fractional QSH insulator in 2.1-degree-twisted bilayer MoTe2, which supports spin-Sz conservation and flat spin-contrasting Chern bands. At filling factor v = 3 of the moiré valence bands, each edge contributes a conductance 3/2 G0 with zero anomalous Hall conductivity. The state is likely a time-reversal pair of the even-denominator 3/2-fractional Chern insulators. Further, at v = 2, 4 and 6, we observe a single, double and triple QSH insulator with each edge contributing a conductance G0, 2G0 and 3G0, respectively. Our results open up the possibility of realizing time reversal symmetric non-abelian anyons and other unexpected topological phases in highly tunable moiré materials. △ Less

Submitted 11 February, 2024; v1 submitted 5 February, 2024; originally announced February 2024.

Neutron Scattering Studies on the High-$T_c$ Superconductor La$_3$Ni$_2$O$_{7-δ}$ at Ambient Pressure

Authors: Tao Xie, Mengwu Huo, Xiaosheng Ni, Feiran Shen, Xing Huang, Hualei Sun, Helen C. Walker, Devashibhai Adroja, Dehong Yu, Bing Shen, Lunhua He, Kun Cao, Meng Wang

Abstract: After several decades of studies of high-temperature superconductivity, there is no compelling theory for the mechanism yet; however, the spin fluctuations have been widely believed to play a crucial role in forming the superconducting Cooper pairs. The recent discovery of high-temperature superconductivity near 80 K in the bilayer nickelate La$_3$Ni$_2$O$_7$ under pressure provides a new platform… ▽ More After several decades of studies of high-temperature superconductivity, there is no compelling theory for the mechanism yet; however, the spin fluctuations have been widely believed to play a crucial role in forming the superconducting Cooper pairs. The recent discovery of high-temperature superconductivity near 80 K in the bilayer nickelate La$_3$Ni$_2$O$_7$ under pressure provides a new platform to elucidate the origins of high-temperature superconductivity. We perform elastic and inelastic neutron scattering studies on a polycrystalline sample of La$_3$Ni$_2$O$_{7-δ}$ at ambient pressure. No magnetic order can be identified down to 10 K. The absence of long-range magnetic order in neutron diffraction measurements may be ascribed to the smallness of the magnetic moment. However, we observe a weak flat spin-fluctuation signal at $\sim$ 45 meV in the inelastic scattering spectra. The observed spin excitations could be interpreted as a result of strong interlayer and weak intralayer magnetic couplings for stripe-type antiferromagnetic orders. Our results provide crucial information on the spin dynamics and are thus important for understanding the superconductivity in La$_3$Ni$_2$O$_7$. △ Less

Submitted 4 April, 2024; v1 submitted 23 January, 2024; originally announced January 2024.

Comments: 10 pages, 9 figures with supplementary information

Journal ref: Science Bulletin 69, 3221-3227 (2024)

Extended Kohler's Rule of Magnetoresistance in TaCo$_2$Te$_2$

Authors: Samuel Pate, Bowen Chen, Bing Shen, Kezhen Li, Xiuquan Zhou, Duck Young Chung, Ralu Divan, Mercouri G. Kanatzidis, Ulrich Welp, Wai-Kwong Kwok, Zhi-Li Xiao

Abstract: TaCo$_2$Te$_2$ is recently reported to be an air-stable, high mobility Van der Waals material with probable magnetic order. Here we investigate the scaling behavior of its magnetoresistance. We measured both the longitudinal ($ρ_{xx}$) and Hall ($ρ_{xy}$) magnetoresistivities of TaCo$_2$Te$_2$ crystals in magnetic fields parallel to the c-axis and found that the magnetoresistance violates the Kohl… ▽ More TaCo$_2$Te$_2$ is recently reported to be an air-stable, high mobility Van der Waals material with probable magnetic order. Here we investigate the scaling behavior of its magnetoresistance. We measured both the longitudinal ($ρ_{xx}$) and Hall ($ρ_{xy}$) magnetoresistivities of TaCo$_2$Te$_2$ crystals in magnetic fields parallel to the c-axis and found that the magnetoresistance violates the Kohler's rule $MR \sim f[H/ρ_0]$ while obeying the extended Kohler's rule $MR \sim f[H/(n_Tρ_0)]$, where $MR \sim [ρ_{xx}(H)-ρ_0]/ρ_0$, $H$ is the magnetic field, $n_T$ is a thermal factor, $ρ_{xx}(H)$ and $ρ_0$ are the resistivities at $H$ and zero field, respectively. While deviating from those of the densities of electrons ($n_e$) and holes ($n_h$) obtained from the two-band model analysis of the magnetoconductivities, the temperature dependence of $n_T$ is close to that of the Hall carrier densities $n_H$ calculated from the slopes of $ρ_{xy}(H)$ curves at low magnetic fields, providing a new way to obtain the thermal factor in the extended Kohler's rule. △ Less

Submitted 9 December, 2023; originally announced December 2023.

Journal ref: Phys. Rev. B 109, 035129 (2024)

Structural transition, electric transport, and electronic structures in the compressed trilayer nickelate La4Ni3O10

Authors: Jingyuan Li, Cui-Qun Chen, Chaoxin Huang, Yifeng Han, Mengwu Huo, Xing Huang, Peiyue Ma, Zhengyang Qiu, Junfeng Chen, Xunwu Hu, Lan Chen, Tao Xie, Bing Shen, Hualei Sun, Dao-Xin Yao, Meng Wang

Abstract: Atomic structure and electronic band structure are fundamental properties for understanding the mechanism of superconductivity. Motivated by the discovery of pressure-induced high-temperature superconductivity at 80 K in the bilayer Ruddlesden-Popper nickelate La3Ni2O7, the atomic structure and electronic band structure of the trilayer nickelate La4Ni3O10 under pressure up to 44.3 GPa are investig… ▽ More Atomic structure and electronic band structure are fundamental properties for understanding the mechanism of superconductivity. Motivated by the discovery of pressure-induced high-temperature superconductivity at 80 K in the bilayer Ruddlesden-Popper nickelate La3Ni2O7, the atomic structure and electronic band structure of the trilayer nickelate La4Ni3O10 under pressure up to 44.3 GPa are investigated. A structural transition from the monoclinic P21/a space group to the tetragonal I4/mmm around 12.6-13.4 GPa is identified, accompanying with a drop of resistance below 7 K. Density functional theory calculations suggest that the bonding state of Ni 3dz2 orbital rises and crosses the Fermi level at high pressures, which may give rise to possible superconductivity observed in resistance under pressure in La4Ni3O10. The trilayer nickelate La4Ni3O10 shows some similarities with the bilayer La3Ni2O7 and has unique properties, providing a new platform to investigate the underlying mechanism of superconductivity in nickelates. △ Less

Submitted 30 March, 2024; v1 submitted 28 November, 2023; originally announced November 2023.

Comments: 19 pages, 4 figures

Journal ref: SCIENCE CHINA Physics, Mechanics & Astronomy 67.11(2024):117403

Emergence of ferromagnetism at the onset of moiré Kondo breakdown

Authors: Wenjin Zhao, Bowen Shen, Zui Tao, Sunghoon Kim, Patrick Knüppel, Zhongdong Han, Yichi Zhang, Kenji Watanabe, Takashi Taniguchi, Debanjan Chowdhury, Jie Shan, Kin Fai Mak

Abstract: The interaction of a lattice of localized magnetic moments with a sea of conduction electrons in Kondo lattice models induces rich quantum phases of matter, such as Fermi liquids with heavily renormalized electronic quasiparticles, quantum critical non-Fermi liquid metals and unconventional superconductors, among others. The recent demonstration of moiré Kondo lattices has opened the door to inves… ▽ More The interaction of a lattice of localized magnetic moments with a sea of conduction electrons in Kondo lattice models induces rich quantum phases of matter, such as Fermi liquids with heavily renormalized electronic quasiparticles, quantum critical non-Fermi liquid metals and unconventional superconductors, among others. The recent demonstration of moiré Kondo lattices has opened the door to investigate the Kondo problem with continuously tunable parameters. Although a heavy Fermi liquid phase has been identified in moiré Kondo lattices, the magnetic phases and Kondo breakdown transitions remain unexplored. Here we report a density-tuned Kondo destruction in AB-stacked MoTe2/WSe2 moiré bilayers by combining magneto transport and optical studies. As the itinerant carrier density decreases, the Kondo temperature decreases. At a critical density, we observe a heavy Fermi liquid to insulator transition, and a nearly concomitant emergence of ferromagnetic order. The observation is consistent with the scenario of a ferromagnetic Anderson insulator and suppression of the Kondo screening effect. Our results pave the path for inducing other exotic quantum phase transitions in moiré Kondo lattices. △ Less

Submitted 9 October, 2023; originally announced October 2023.

Field Orientation Dependent Magnetic Phases In Weyl Semimetal Co3Sn2S2

Authors: Samuel E. Pate, Bin Wang, Bing Shen, J. Samuel Jiang, Ulrich Welp, Wai-Kwong Kwok, Jing Xu, Kezhen Li, Ralu Divan, Zhi-Li Xiao

Abstract: Magnetism plays a key role in the emergence of topological phenomena in the Weyl semimetal Co3Sn2S2, which exhibits a ferromagnetic (FM) interactions along the c-axis of the crystal and an antiferromagnetic (AFM) interactions within the ab plane. Extensive studies on the temperature dependence of the magnetism with the magnetic field along the c-axis have uncovered a number of magnetic phases. Cur… ▽ More Magnetism plays a key role in the emergence of topological phenomena in the Weyl semimetal Co3Sn2S2, which exhibits a ferromagnetic (FM) interactions along the c-axis of the crystal and an antiferromagnetic (AFM) interactions within the ab plane. Extensive studies on the temperature dependence of the magnetism with the magnetic field along the c-axis have uncovered a number of magnetic phases. Currently, the nature and origins of the reported magnetic phases are under debate. Here we report on magnetic field orientation effects on the magnetism in Co3Sn2S2. The shape of the hysteresis loop of the Hall resistance at a fixed temperature is found to change from rectangular to bow-tie-like as the magnetic field is tilted from the c-axis towards the ab plane, resembling that reported for magnetic fields along the c-axis as the temperature approaches the Curie temperature from below. Unlike their temperature-dependent counterparts, the newly observed bow-tie-like hysteresis loops show exchange bias. Our results showcase the contribution of the in-plane AFM interactions to the magnetism in Co3Sn2S2 and demonstrate a new way to tune its magnetic phases. They also shed light on the temperature-dependent magnetic phases occurring in the magnetic field along the c-axis of the crystal. △ Less

Submitted 18 September, 2023; originally announced September 2023.

Journal ref: Phys. Rev. B 108, L100408 (2023)