Discovery and Manipulation of van der Waals Polarons in Sb2O3 Ultrathin Molecular Crystal.

Manipulating single electrons at the atomic scale is vital for mastering complex surface processes governed by the transfer of individual electrons. Polarons, composed of electrons stabilized by electron-phonon coupling, offer a pivotal medium for such manipulation. Here, using scanning tunneling microscopy and spectroscopy (STM/STS) and density functional theory (DFT) calculations, we report the identification and manipulation of a new type of polaron, dubbed van der Waals (vdW) polaron, within mono- to trilayer ultrathin films composed of Sb2O3 molecules that are bonded via vdW attractions. The Sb2O3 films were grown on a graphene-covered SiC(0001) substrate via molecular beam epitaxy. Unlike prior molecular polarons, STM imaging observed polarons at the interstitial sites of the molecular film, presenting unique electronic states and localized band bending. DFT calculations revealed the lowest conduction band as an intermolecular bonding state, capable of ensnaring an extra electron through locally diminished intermolecular distances, thereby forming an intermolecular vdW polaron. We also demonstrated the ability to generate, move, and erase such vdW polarons using an STM tip. Our work uncovers a new type of polaron stabilized by coupling with intermolecular vibrations where vdW interactions dominate, paving the way for designing atomic-scale electron transfer processes and enabling precise tailoring of electron-related properties and functionalities.

Charge-density wave mediated quasi-one-dimensional Kondo lattice in stripe-phase monolayer 1T-NbSe2.

The heavy fermion physics is dictated by subtle competing exchange interactions, posing a challenge to their understanding. One-dimensional (1D) Kondo lattice model has attracted special attention in theory, because of its exact solvability and expected unusual quantum criticality. However, such experimental material systems are extremely rare. Here, we demonstrate the realization of quasi-1D Kondo lattice behavior in a monolayer van der Waals crystal NbSe2, that is driven into a stripe phase via Se-deficient line defects. Spectroscopic imaging scanning tunneling microscopy measurements and first-principles calculations indicate that the stripe-phase NbSe2 undergoes a novel charge-density wave transition, creating a matrix of local magnetic moments. The Kondo lattice behavior is manifested as a Fano resonance at the Fermi energy that prevails the entire film with a high Kondo temperature. Importantly, coherent Kondo screening occurs only in the direction of the stripes. Upon approaching defects, the Fano resonance exhibits prominent spatial 1D oscillations along the stripe direction, reminiscent of Kondo holes in a quasi-1D Kondo lattice. Our findings provide a platform for exploring anisotropic Kondo lattice behavior in the monolayer limit.

Manipulating single excess electrons in monolayer transition metal dihalide.

Polarons are entities of excess electrons dressed with local response of lattices, whose atomic-scale characterization is essential for understanding the many body physics arising from the electron-lattice entanglement, yet difficult to achieve. Here, using scanning tunneling microscopy and spectroscopy (STM/STS), we show the visualization and manipulation of single polarons in monolayer CoCl2, that are grown on HOPG substrate via molecular beam epitaxy. Two types of polarons are identified, both inducing upward local band bending, but exhibiting distinct appearances, lattice occupations and polaronic states. First principles calculations unveil origin of polarons that are stabilized by cooperative electron-electron and electron-phonon interactions. Both types of polarons can be created, moved, erased, and moreover interconverted individually by the STM tip, as driven by tip electric field and inelastic electron tunneling effect. This finding identifies the rich category of polarons in CoCl2 and their feasibility of precise control unprecedently, which can be generalized to other transition metal halides.

Identification of autotoxic compounds in fibrous roots of Rehmannia (Rehmannia glutinosa Libosch.).

Rehmannia is a medicinal plant in China. Autotoxicity has been reported to be one of the major problems hindering the consecutive monoculture of Rehmannia. However, potential autotoxins produced by the fibrous roots are less known. In this study, the autotoxicity of these fibrous roots was investigated. Four groups of autotoxic compounds from the aqueous extracts of the fibrous roots were isolated and characterized. The ethyl acetate extracts of these water-soluble compounds were further analyzed and separated into five fractions. Among them, the most autotoxic fraction (Fr 3) was subjected to GC/MS analysis, resulting in 32 identified compounds. Based on literature, nine compounds were selected for testing their autotoxic effects on radicle growth. Seven out of the nine compounds were phenolic, which significantly reduced radicle growth in a concentration-dependent manner. The other two were aliphatic compounds that showed a moderate inhibition effect at three concentrations. Concentration of these compounds in soil samples was determined by HPLC. Furthermore, the autotoxic compounds were also found in the top soil of the commercially cultivated Rehmannia fields. It appears that a close link exists between the autotoxic effects on the seedlings and the compounds extracted from fibrous roots of Rehmannia.

[Clinical phenotype genotype correlation in children with hemoglobin H disease in Zhuhai area of China].

OBJECTIVE: Alpha-thalassemia is one of the most common monogene disorders in the world. Most frequently, it is caused by deletions of alpha-globin gene (-alpha or --), and less commonly resulted from the non-deletional mutation (alpha(T)alpha). Hemoglobin H (HbH) disease is the most severe type among survivors of alpha-thalassemia. The clinical presentation of children with the disease was highly heterogeneous. The aim of this study was to investigate the effect of alpha-globin genotypes in the children with HbH disease on predicting the phenotypic severity and to define the factors involved in the disease progress. METHODS: Forty-three children with the disease in Zhuhai area of Guangdong, China were examined by using established techniques to detect genotypes of alpha-globin and to determine all hematological parameters. All detailed clinical data of the cases were recorded. Then clinical and hematological findings, and the correlation with genotypes were evaluated. RESULTS: Six alpha-thalassemia mutations were detected and interacted to produce 5 HbH disease genotypes. Of these genotypes, -alpha(3.7)/--(SEA)(60%), -alpha(4.2)/--(SEA) (19%) and alpha(CS)alpha/--(SEA) (12%) HbH diseases were prevalent in the area. Compared with -alpha(3.7)/--(SEA) HbH disease, significantly lower red blood cell (RBC) count, hemoglobin (Hb), mean corpuscular hemoglobin (MCHC) and HbA(2) (P < 0.05, 0.01, 0.01 and 0.01, respectively), and significantly higher mean corpuscular hemoglobin volume (MCV) and HbH levels (both P < 0.01), and more severe clinical phenotypes were found in the HbH disease with alpha(T)alpha/--(SEA) genotype. While the differences were much more significant when compared with -alpha(3.7)/--(SEA) then compared with -alpha(4.2)/--(SEA) not only in the hematological parameters, but also in the severity of clinical phenotypes. In addition, HbH levels showed anegatively correlation with the RBC count (r = -0.39, P < 0.01). CONCLUSION: The phenotypes of HbH disease may be mainly related to the underlying genotypes. The children with alpha(T)alpha/--(SEA) genotype presented with more severe hematological and clinical phenotypes followed by the -alpha(4.2)/--(SEA) and then -alpha(3.7)/--(SEA) genotypes. But phenotypic severity was not simply related to the degree of alpha-globin deficiency. HbH levels were found to exacerbate anemia. These data might provide comprehensive and very valuable and basic information for the management of HbH disease, genetic counseling and prenatal diagnosis.

Evaluation of clinical application of gap-PCR as a routine method for alpha-thalassemia carrier detection.

OBJECTIVE: To evaluate the feasibility of using gap-PCR for routine screening of alpha-thalassemia in clinical laboratory. METHODS: A total of 382 clinical blood samples randomly collected from the population of Zhuhai city were screened for alpha-thalassemia determinants with hematological and gap-PCR method respectively in a double-blind manner. Parallel analysis with Southern blotting was performed to verify the genotyping results by PCR. RESULTS: Of the 382 samples tested, 3 common alpha-thalassemia genes with genotypes of --(SEA)/alpha alpha, -alpha(3.7)/alpha alpha and -alpha(4.2)/alpha alpha were detected in 21 (5.50%), 7 (1.83%) and 3 (0.79%) cases respectively by gap-PCR, including 7 cases with normal phenotype and 3 case of iron-deficiency anemia. The overall incidence of alpha-thalassemia was 8.12% in the population of Zhuhai city, as determined by gap-PCR, in total agreement with the results by Southern blotting. Only 21 of the 31 alpha-thalassemia cases were identified by hematological analysis (besides 2 cases with alpha-thalassemia phenotype undetermined), which had a false-negative rate of 32.3%. Seven silent alpha-thalassemia and 3 mild alpha-thalassemia cases failed to be detected by hematological analysis, resulting in a rate of 2.62% for failure of detection. CONCLUSION: Gap-PCR method is specific and feasible as a better alternative for alpha-thalassemia screening, especially advantageous in detecting silent carriers in comparison with hematological method.