Optical manipulation of the charge-density-wave state in RbV3Sb5.

Broken time-reversal symmetry in the absence of spin order indicates the presence of unusual phases such as orbital magnetism and loop currents1-4. The recently discovered kagome superconductors AV3Sb5 (where A is K, Rb or Cs)5,6 display an exotic charge-density-wave (CDW) state and have emerged as a strong candidate for materials hosting a loop current phase. The idea that the CDW breaks time-reversal symmetry7-14 is, however, being intensely debated due to conflicting experimental data15-17. Here we use laser-coupled scanning tunnelling microscopy to study RbV3Sb5. By applying linearly polarized light along high-symmetry directions, we show that the relative intensities of the CDW peaks can be reversibly switched, implying a substantial electro-striction response, indicative of strong nonlinear electron-phonon coupling. A similar CDW intensity switching is observed with perpendicular magnetic fields, which implies an unusual piezo-magnetic response that, in turn, requires time-reversal symmetry breaking. We show that the simplest CDW that satisfies these constraints is an out-of-phase combination of bond charge order and loop currents that we dub a congruent CDW flux phase. Our laser scanning tunnelling microscopy data open the door to the possibility of dynamic optical control of complex quantum phenomenon in correlated materials.

Dual quantum spin Hall insulator by density-tuned correlations in TaIrTe4.

The convergence of topology and correlations represents a highly coveted realm in the pursuit of new quantum states of matter1. Introducing electron correlations to a quantum spin Hall (QSH) insulator can lead to the emergence of a fractional topological insulator and other exotic time-reversal-symmetric topological order2-8, not possible in quantum Hall and Chern insulator systems. Here we report a new dual QSH insulator within the intrinsic monolayer crystal of TaIrTe4, arising from the interplay of its single-particle topology and density-tuned electron correlations. At charge neutrality, monolayer TaIrTe4 demonstrates the QSH insulator, manifesting enhanced nonlocal transport and quantized helical edge conductance. After introducing electrons from charge neutrality, TaIrTe4 shows metallic behaviour in only a small range of charge densities but quickly goes into a new insulating state, entirely unexpected on the basis of the single-particle band structure of TaIrTe4. This insulating state could arise from a strong electronic instability near the van Hove singularities, probably leading to a charge density wave (CDW). Remarkably, within this correlated insulating gap, we observe a resurgence of the QSH state. The observation of helical edge conduction in a CDW gap could bridge spin physics and charge orders. The discovery of a dual QSH insulator introduces a new method for creating topological flat minibands through CDW superlattices, which offer a promising platform for exploring time-reversal-symmetric fractional phases and electromagnetism2-4,9,10.

Pair density wave state in a monolayer high-Tc iron-based superconductor.

The pair density wave (PDW) is an extraordinary superconducting state in which Cooper pairs carry non-zero momentum1,2. Evidence for the existence of intrinsic PDW order in high-temperature (high-Tc) cuprate superconductors3,4 and kagome superconductors5 has emerged recently. However, the PDW order in iron-based high-Tc superconductors has not been observed experimentally. Here, using scanning tunnelling microscopy and spectroscopy, we report the discovery of the PDW state in monolayer iron-based high-Tc Fe(Te,Se) films grown on SrTiO3(001) substrates. The PDW state with a period of λ ≈ 3.6aFe (aFe is the distance between neighbouring Fe atoms) is observed at the domain walls by the spatial electronic modulations of the local density of states, the superconducting gap and the π-phase shift boundaries of the PDW around the vortices of the intertwined charge density wave order. The discovery of the PDW state in the monolayer Fe(Te,Se) film provides a low-dimensional platform to study the interplay between the correlated electronic states and unconventional Cooper pairing in high-Tc superconductors.

Ordered and tunable Majorana-zero-mode lattice in naturally strained LiFeAs.

Majorana zero modes (MZMs) obey non-Abelian statistics and are considered building blocks for constructing topological qubits1,2. Iron-based superconductors with topological bandstructures have emerged as promising hosting materials, because isolated candidate MZMs in the quantum limit have been observed inside the topological vortex cores3-9. However, these materials suffer from issues related to alloying induced disorder, uncontrolled vortex lattices10-13 and a low yield of topological vortices5-8. Here we report the formation of an ordered and tunable MZM lattice in naturally strained stoichiometric LiFeAs by scanning tunnelling microscopy/spectroscopy. We observe biaxial charge density wave (CDW) stripes along the Fe-Fe and As-As directions in the strained regions. The vortices are pinned on the CDW stripes in the As-As direction and form an ordered lattice. We detect that more than 90 per cent of the vortices are topological and possess the characteristics of isolated MZMs at the vortex centre, forming an ordered MZM lattice with the density and the geometry tunable by an external magnetic field. Notably, with decreasing the spacing of neighbouring vortices, the MZMs start to couple with each other. Our findings provide a pathway towards tunable and ordered MZM lattices as a platform for future topological quantum computation.

Cascade of correlated electron states in the kagome superconductor CsV3Sb5.

The kagome lattice of transition metal atoms provides an exciting platform to study electronic correlations in the presence of geometric frustration and nontrivial band topology1-18, which continues to bear surprises. Here, using spectroscopic imaging scanning tunnelling microscopy, we discover a temperature-dependent cascade of different symmetry-broken electronic states in a new kagome superconductor, CsV3Sb5. We reveal, at a temperature far above the superconducting transition temperature Tc ~ 2.5 K, a tri-directional charge order with a 2a0 period that breaks the translation symmetry of the lattice. As the system is cooled down towards Tc, we observe a prominent V-shaped spectral gap opening at the Fermi level and an additional breaking of the six-fold rotational symmetry, which persists through the superconducting transition. This rotational symmetry breaking is observed as the emergence of an additional 4a0 unidirectional charge order and strongly anisotropic scattering in differential conductance maps. The latter can be directly attributed to the orbital-selective renormalization of the vanadium kagome bands. Our experiments reveal a complex landscape of electronic states that can coexist on a kagome lattice, and highlight intriguing parallels to high-Tc superconductors and twisted bilayer graphene.

Roton pair density wave in a strong-coupling kagome superconductor.

The transition metal kagome lattice materials host frustrated, correlated and topological quantum states of matter1-9. Recently, a new family of vanadium-based kagome metals, AV3Sb5 (A = K, Rb or Cs), with topological band structures has been discovered10,11. These layered compounds are nonmagnetic and undergo charge density wave transitions before developing superconductivity at low temperatures11-19. Here we report the observation of unconventional superconductivity and a pair density wave (PDW) in CsV3Sb5 using scanning tunnelling microscope/spectroscopy and Josephson scanning tunnelling spectroscopy. We find that CsV3Sb5 exhibits a V-shaped pairing gap Δ ~ 0.5 meV and is a strong-coupling superconductor (2Δ/kBTc ~ 5) that coexists with 4a0 unidirectional and 2a0 × 2a0 charge order. Remarkably, we discover a 3Q PDW accompanied by bidirectional 4a0/3 spatial modulations of the superconducting gap, coherence peak and gap depth in the tunnelling conductance. We term this novel quantum state a roton PDW associated with an underlying vortex-antivortex lattice that can account for the observed conductance modulations. Probing the electronic states in the vortex halo in an applied magnetic field, in strong field that suppresses superconductivity and in zero field above Tc, reveals that the PDW is a primary state responsible for an emergent pseudogap and intertwined electronic order. Our findings show striking analogies and distinctions to the phenomenology of high-Tc cuprate superconductors, and provide groundwork for understanding the microscopic origin of correlated electronic states and superconductivity in vanadium-based kagome metals.

Chiral superconductivity in heavy-fermion metal UTe2.

Spin-triplet superconductors are condensates of electron pairs with spin 1 and an odd-parity wavefunction1. An interesting manifestation of triplet pairing is the chiral p-wave state, which is topologically non-trivial and provides a natural platform for realizing Majorana edge modes2,3. However, triplet pairing is rare in solid-state systems and has not been unambiguously identified in any bulk compound so far. Given that pairing is usually mediated by ferromagnetic spin fluctuations, uranium-based heavy-fermion systems containing f-electron elements, which can harbour both strong correlations and magnetism, are considered ideal candidates for realizing spin-triplet superconductivity4. Here we present scanning tunnelling microscopy studies of the recently discovered heavy-fermion superconductor UTe2, which has a superconducting transition temperature of 1.6 kelvin5. We find signatures of coexisting Kondo effect and superconductivity that show competing spatial modulations within one unit cell. Scanning tunnelling spectroscopy at step edges reveals signatures of chiral in-gap states, which have been predicted to exist at the boundaries of topological superconductors. Combined with existing data that indicate triplet pairing in UTe2, the presence of chiral states suggests that UTe2 is a strong candidate for chiral-triplet topological superconductivity.

Li metal deposition and stripping in a solid-state battery via Coble creep.

Solid-state lithium metal batteries require accommodation of electrochemically generated mechanical stress inside the lithium: this stress can be1,2 up to 1 gigapascal for an overpotential of 135 millivolts. Maintaining the mechanical and electrochemical stability of the solid structure despite physical contact with moving corrosive lithium metal is a demanding requirement. Using in situ transmission electron microscopy, we investigated the deposition and stripping of metallic lithium or sodium held within a large number of parallel hollow tubules made of a mixed ionic-electronic conductor (MIEC). Here we show that these alkali metals-as single crystals-can grow out of and retract inside the tubules via mainly diffusional Coble creep along the MIEC/metal phase boundary. Unlike solid electrolytes, many MIECs are electrochemically stable in contact with lithium (that is, there is a direct tie-line to metallic lithium on the equilibrium phase diagram), so this Coble creep mechanism can effectively relieve stress, maintain electronic and ionic contacts, eliminate solid-electrolyte interphase debris, and allow the reversible deposition/stripping of lithium across a distance of 10 micrometres for 100 cycles. A centimetre-wide full cell-consisting of approximately 1010 MIEC cylinders/solid electrolyte/LiFePO4-shows a high capacity of about 164 milliampere hours per gram of LiFePO4, and almost no degradation for over 50 cycles, starting with a 1× excess of Li. Modelling shows that the design is insensitive to MIEC material choice with channels about 100 nanometres wide and 10-100 micrometres deep. The behaviour of lithium metal within the MIEC channels suggests that the chemical and mechanical stability issues with the metal-electrolyte interface in solid-state lithium metal batteries can be overcome using this architecture.

Quantum-limit Chern topological magnetism in TbMn6Sn6.

The quantum-level interplay between geometry, topology and correlation is at the forefront of fundamental physics1-15. Kagome magnets are predicted to support intrinsic Chern quantum phases owing to their unusual lattice geometry and breaking of time-reversal symmetry14,15. However, quantum materials hosting ideal spin-orbit-coupled kagome lattices with strong out-of-plane magnetization are lacking16-21. Here, using scanning tunnelling microscopy, we identify a new topological kagome magnet, TbMn6Sn6, that is close to satisfying these criteria. We visualize its effectively defect-free, purely manganese-based ferromagnetic kagome lattice with atomic resolution. Remarkably, its electronic state shows distinct Landau quantization on application of a magnetic field, and the quantized Landau fan structure features spin-polarized Dirac dispersion with a large Chern gap. We further demonstrate the bulk-boundary correspondence between the Chern gap and the topological edge state, as well as the Berry curvature field correspondence of Chern gapped Dirac fermions. Our results point to the realization of a quantum-limit Chern phase in TbMn6Sn6, and may enable the observation of topological quantum phenomena in the RMn6Sn6 (where R is a rare earth element) family with a variety of magnetic structures. Our visualization of the magnetic bulk-boundary-Berry correspondence covering real space and momentum space demonstrates a proof-of-principle method for revealing topological magnets.

Optical single-pixel volumetric imaging by three-dimensional light-field illumination.

Three-dimensional single-pixel imaging (3D SPI) has become an attractive imaging modality for both biomedical research and optical sensing. 3D-SPI techniques generally depend on time-of-flight or stereovision principle to extract depth information from backscattered light. However, existing implementations for these two optical schemes are limited to surface mapping of 3D objects at depth resolutions, at best, at the millimeter level. Here, we report 3D light-field illumination single-pixel microscopy (3D-LFI-SPM) that enables volumetric imaging of microscopic objects with a near-diffraction-limit 3D optical resolution. Aimed at 3D space reconstruction, 3D-LFI-SPM optically samples the 3D Fourier spectrum by combining 3D structured light-field illumination with single-element intensity detection. We build a 3D-LFI-SPM prototype that provides an imaging volume of ∼390 × 390 × 3,800 µm3 and achieves 2.7-µm lateral resolution and better than 37-µm axial resolution. Its capability of 3D visualization of label-free optical absorption contrast is demonstrated by imaging single algal cells in vivo. Our approach opens broad perspectives for 3D SPI with potential applications in various fields, such as biomedical functional imaging.

Lattice Strain and Charge Redistribution of Pt Cluster/Ir Metallene Heterostructure for Ethylene Glycol to Glycolic Acid Conversion Coupled with Hydrogen Production.

Upgrading overall water splitting (OWS) system and developing high-performance electrocatalysts is an attractive way to the improve efficiency and reduce the consumption of hydrogen (H2 ) production from electrolyzed water. Here, a Pt cluster/Ir metallene heterojunction structure (Pt/Ir hetero-metallene) with a unique Pt/Ir interface is reported for the conversion of ethylene glycol (EG) to glycolic acid (GA) coupled with H2 production. With the assistance of ethylene glycol oxidation (EGOR), the Pt/Ir||Pt/Ir hetero-metallene two-electrode water electrolysis system exhibits a lower cell voltage of 0.36 V at 10 mA cm-2 . Furthermore, the Faradaic efficiency of EG to GA is as high as 87%. The excellent performance of this new heterostructure arise from the charge redistribution and strain effects induced by Pt-Ir interactions between the heterogeneous interfaces, as well as the larger specific surface area and more active sites due to the metallene structure.

Targeting CXCR4/CXCL12 axis via [177Lu]Lu-DOTAGA.(SA.FAPi)2 with CXCR4 antagonist in triple-negative breast cancer.

PURPOSE: Radiopharmaceutical therapies targeting fibroblast activation protein (FAP) have shown promising efficacy against many tumor types. But radiopharmaceuticals alone in most cases are insufficient to completely eradicate tumor cells, which can partially be attributed to the protective interplay between tumor cells and cancer-associated fibroblasts (CAFs). The C-X-C chemokine receptor type 4/C-X-C motif chemokine 12 (CXCR4/CXCL12) interaction plays an important role in orchestrating tumor cells and CAFs. We hereby investigated the feasibility and efficacy of [177Lu]Lu-DOTAGA.(SA.FAPi)2, a FAP-targeting radiopharmaceutical, in combination with AMD3100, a CXCR4 antagonist, in a preclinical murine model of triple-negative breast cancer (TNBC). METHODS: Public database was first interrogated to reveal the correlation between CAFs' scores and the prognosis of TNBC patients, as well as the expression levels of FAP and CXCR4 in normal tissues and tumors. In vitro therapeutic efficacy regarding cell proliferation, migration, and colony formation was assessed in BALB/3T3 fibroblasts and 4T1 murine breast cancer cells. In vivo therapeutic efficacy was longitudinally monitored using serial 18F-FDG, [18F]AlF-NOTA-FAPI-04, and [68Ga]Ga-DOTA-Pentixafor PET/CT scans and validated using tumor sections through immunohistochemical staining of Ki-67, α-SMA, CXCR4, and CXCL12. Intratumoral abundance of myeloid-derived suppressive cells (MDSCs) was analyzed using flow cytometry in accordance with the PET/CT schedules. Treatment toxicity was evaluated by examining major organs including heart, lung, liver, kidney, and spleen. RESULTS: CAFs' scores negatively correlated with the survival of TNBC patients (p < 0.05). The expression of CXCR4 and FAP was both significantly higher in tumors than in normal tissues. The combination of [177Lu]Lu-DOTAGA.(SA.FAPi)2 and AMD3100 significantly suppressed cell proliferation, migration, and colony formation in cell culture, and exhibited synergistic effects in 4T1 tumor models along with a decreased number of MDSCs. PET/CT imaging revealed lowest tumor accumulation of 18F-FDG and [18F]AlF-NOTA-FAPI-04 on day 13 and day 14 after treatment started, both of which gradually increased at later time points. A similar trend was observed in the IHC staining of Ki-67, α-SMA, and CXCL12. CONCLUSION: The combination of [177Lu]Lu-DOTAGA.(SA.FAPi)2 and AMD3100 is a feasible treatment against TNBC with minimal toxicity in main organs.

Comparison of laparoscopic lateral lymph node dissection for rectal cancer with and without routine resection of the visceral branches of internal iliac artery.

PURPOSE: This study aimed to explore the safety and feasibility of the modified lateral lymph node dissection (LLND) with routine resection of the visceral branches of internal iliac vessels (IIVs) for mid-low-lying rectal cancer. MATERIALS AND METHOD: Consecutive patients undergoing LLND for rectal cancer were divided into the routine visceral branches of the IIVs resection group (RVR group) and the NRVR group (without routine resection). The main outcomes were postoperative complications and the number of lateral lymph nodes harvested. RESULTS: From 2012 to 2021, a total of 75 and 57 patients were included in the RVR and NRVR group, respectively. The operative time was reduced in the RVR group (p = 0.020). No significant difference was observed between the two groups for the incidence of total, major, or minor postoperative complications. Pathologically confirmed LLNM were 24 (32%) patients in the RVR group and 12 (21.1%) in the NRVR group (p = 0.162). The number of lateral lymph nodes harvested had no significant difference between two groups (11 vs. 12, p = 0.329). CONCLUSION: LLND with routine resection of visceral branches of IIVs is safe and feasible, which brings no major complication or long-term urinary disorder.

Prediction of symptomatic anastomotic leak after rectal cancer surgery: A machine learning approach.

INTRODUCTION: Anastomotic leakage (AL) remains the most dreaded and unpredictable major complication after low anterior resection for mid-low rectal cancer. The aim of this study is to identify patients with high risk for AL based on the machine learning method. METHODS: Patients with mid-low rectal cancer undergoing low anterior resection were enrolled from West China Hospital between January 2008 and October 2019 and were split by time into training cohort and validation cohort. The least absolute shrinkage and selection operator (LASSO) method and stepwise method were applied for variable selection and predictive model building in the training cohort. The area under the receiver operating characteristic curve (AUC) and calibration curves were used to evaluate the performance of the models. RESULTS: The rate of AL was 5.8% (38/652) and 7.2% (15/208) in the training cohort and validation cohort, respectively. The LASSO-logistic model selected almost the same variables (hypertension, operating time, cT4, tumor location, intraoperative blood loss) compared to the stepwise logistic model except for tumor size (the LASSO-logistic model) and American Society of Anesthesiologists score (the stepwise logistic model). The predictive performance of the LASSO-logistics model was better than the stepwise-logistics model (AUC: 0.790 vs. 0.759). Calibration curves showed mean absolute error of 0.006 and 0.013 for the LASSO-logistics model and stepwise-logistics model, respectively. CONCLUSION: Our study developed a feasible predictive model with a machine-learning algorithm to classify patients with a high risk of AL, which would assist surgical decision-making and reduce unnecessary stoma diversion. The involved machine learning algorithms provide clinicians with an innovative alternative to enhance clinical management.

Interstitial Boron-Modulated Porous Pd Nanotubes for Ammonia Electrosynthesis.

Electrochemical conversion of nitrogen into ammonia at ambient conditions as a sustainable approach has gained significant attention, but it is still extremely challenging to simultaneously obtain a high faradaic efficiency (FE) and NH3 yield. In this work, the interstitial boron-doped porous Pd nanotubes (B-Pd PNTs) are constructed by combining the self-template reduction method with boron doping. Benefiting from distinctive one-dimensional porous nanotube architectonics and the incorporation of the interstitial B atoms, the resulting B-Pd PNTs exhibit high NH3 yield (18.36 µg h-1 mgcat.-1) and FE (21.95%) in neutral conditions, outperforming the Pd/PdO PNTs (10.4 µg h-1 mgcat.-1 and 8.47%). The present study provides an attractive method to enhance the efficiency of the electroreduction of nitrogen into ammonia by incorporating interstitial boron into porous Pd-based catalysts.

Boron-intercalation-triggered crystalline transition of Pd nanosheet assemblies for an enhanced oxygen reduction reaction.

The development of effective and stable cathode electrocatalysts is highly desired for fuel cells. Controlling the composition and morphology of Pd-based materials can provide a great opportunity to improve their oxygen reduction reaction (ORR) performance. Here, we report the synthesis of hexagonal close-packed (hcp) Pd2B nanosheet assemblies (Pd2B NAs) via the boronation reaction between as-synthesized Pd NAs and N,N-dimethylformamide. The hcp Pd2B NAs with uniform pore distribution can provide sufficient active sites for ORRs. The insertion of B atoms can induce the phase transition from face-centered cubic structure to hcp structure, as the most thermodynamically stable phase in the Pd-B alloy, which is beneficial for enhancing the ORR stability and toxicity resistance. Therefore, the hcp Pd2B NAs exhibit superior mass activity, specific activity and excellent stability for ORR. The present strategy of boron-intercalation-triggered crystalline transition of Pd-based nanomaterials is valuable for the design of metal-nonmetal catalysts with enhanced performance.

Amorphous/crystalline RhFeP metallene for hydrazine-assisted water splitting.

Replacing the slow oxygen evolution reaction with favorable hydrazine oxidation reaction (HzOR) is a green and efficient way to produce hydrogen. In this work, we synthesize amorphous/crystalline RhFeP metallene via phase engineering and heteroatom doping. RhFeP metallene has good catalytic activity and stability for HER and HzOR, and only an ultralow voltage of 18 mV is required to achieve 10 mA cm-2in a two-electrode hydrazine-assisted water splitting system. The superior result is mainly ascribed to the co-doping of Fe and P and the formation of amorphous/crystalline RhFeP metallene with abundant phase boundaries, thereby adjusting electronic structure and increasing active sites.

Total neoadjuvant therapy for locally advanced rectal cancer: a three-group propensity score matched study.

PURPOSE: Total neoadjuvant therapy (TNT) has emerged as a therapeutic approach for locally advanced rectal cancer (LARC). However, the optimal chemotherapy cycles within TNT remain uncertain. This study aimed to evaluate and compare the prognostic efficacy of varying cycles of chemotherapy during TNT for LARC. METHODS: Patients diagnosed with LARC (T3-4N0M0/T1-4N1-2M0), who underwent TNT or chemoradiotherapy followed by total mesorectal excision (TME) between 2015 and 2020, were retrospective included. Patients were categorized into three groups based on their neoadjuvant strategy: CRT (long-course chemoradiotherapy), STNT (long-course CRT with one to three cycles of chemotherapy), and LTNT (long-course CRT with four or more cycles of chemotherapy). Propensity score matching (PSM) based on gender, age, body mass index, tumor distance from the anal verge, clinical T stage, clinical N stage, and mesorectal fascia status was employed to reduce confounding bias. Primary endpoints were disease-free survival (DFS) and metastasis-free survival (MFS). RESULTS: The study comprised 372 patients, with 73 patients in each group after PSM. Compared with CRT, both STNT and LTNT demonstrated improved DFS (5-year rate: 59.7% vs. 77.8% vs. 76.5%, p = 0.027) and MFS (5-year rate: 65.1% vs. 81.3% vs. 81.4%, p = 0.030). There was no difference in DFS or MFS between STNT and LTNT. These favorable outcomes were consistent among subgroups defined by tumor distance from the anal verge ≥ 5 cm, clinical T3 stage, clinical N positive status, or involved mesorectal fascia. CONCLUSION: Compared to CRT, both STNT and LTNT demonstrated improved DFS and MFS outcomes. Notably, survival outcomes were similar between STNT and LTNT, suggesting that chemotherapy cycles in TNT may not significantly impact survival.

Giant and anisotropic many-body spin-orbit tunability in a strongly correlated kagome magnet.

Owing to the unusual geometry of kagome lattices-lattices made of corner-sharing triangles-their electrons are useful for studying the physics of frustrated, correlated and topological quantum electronic states1-9. In the presence of strong spin-orbit coupling, the magnetic and electronic structures of kagome lattices are further entangled, which can lead to hitherto unknown spin-orbit phenomena. Here we use a combination of vector-magnetic-field capability and scanning tunnelling microscopy to elucidate the spin-orbit nature of the kagome ferromagnet Fe3Sn2 and explore the associated exotic correlated phenomena. We discover that a many-body electronic state from the kagome lattice couples strongly to the vector field with three-dimensional anisotropy, exhibiting a magnetization-driven giant nematic (two-fold-symmetric) energy shift. Probing the fermionic quasi-particle interference reveals consistent spontaneous nematicity-a clear indication of electron correlation-and vector magnetization is capable of altering this state, thus controlling the many-body electronic symmetry. These spin-driven giant electronic responses go well beyond Zeeman physics and point to the realization of an underlying correlated magnetic topological phase. The tunability of this kagome magnet reveals a strong interplay between an externally applied field, electronic excitations and nematicity, providing new ways of controlling spin-orbit properties and exploring emergent phenomena in topological or quantum materials10-12.

Tuning Multiple Landau Quantization in Transition-Metal Dichalcogenide with Strain.

Landau quantization associated with the quantized cyclotron motion of electrons under magnetic field provides the effective way to investigate topologically protected quantum states with entangled degrees of freedom and multiple quantum numbers. Here we report the cascade of Landau quantization in a strained type-II Dirac semimetal NiTe2 with spectroscopic-imaging scanning tunneling microscopy. The uniform-height surfaces exhibit single-sequence Landau levels (LLs) at a magnetic field originating from the quantization of topological surface state (TSS) across the Fermi level. Strikingly, we reveal the multiple sequence of LLs in the strained surface regions where the rotation symmetry is broken. First-principles calculations demonstrate that the multiple LLs attest to the remarkable lifting of the valley degeneracy of TSS by the in-plane uniaxial or shear strains. Our findings pave a pathway to tune multiple degrees of freedom and quantum numbers of TMDs via strain engineering for practical applications such as high-frequency rectifiers, Josephson diode and valleytronics.