Topological surface states interacting with bulk excitations in the Kondo insulator SmB6 revealed via planar tunneling spectroscopy.

Samarium hexaboride (SmB6), a well-known Kondo insulator in which the insulating bulk arises from strong electron correlations, has recently attracted great attention owing to increasing evidence for its topological nature, thereby harboring protected surface states. However, corroborative spectroscopic evidence is still lacking, unlike in the weakly correlated counterparts, including Bi2Se3 Here, we report results from planar tunneling that unveil the detailed spectroscopic properties of SmB6 The tunneling conductance obtained on the (001) and (011) single crystal surfaces reveals linear density of states as expected for two and one Dirac cone(s), respectively. Quite remarkably, it is found that these topological states are not protected completely within the bulk hybridization gap. A phenomenological model of the tunneling process invoking interaction of the surface states with bulk excitations (spin excitons), as predicted by a recent theory, provides a consistent explanation for all of the observed features. Our spectroscopic study supports and explains the proposed picture of the incompletely protected surface states in this topological Kondo insulator SmB6.

Theory of point contact spectroscopy in correlated materials.

We developed a microscopic theory for the point-contact conductance between a metallic electrode and a strongly correlated material using the nonequilibrium Schwinger-Kadanoff-Baym-Keldysh formalism. We explicitly show that, in the classical limit, contact size shorter than the scattering length of the system, the microscopic model can be reduced to an effective model with transfer matrix elements that conserve in-plane momentum. We found that the conductance dI/dV is proportional to the effective density of states, that is, the integrated single-particle spectral function A(ω = eV) over the whole Brillouin zone. From this conclusion, we are able to establish the conditions under which a non-Fermi liquid metal exhibits a zero-bias peak in the conductance. This finding is discussed in the context of recent point-contact spectroscopy on the iron pnictides and chalcogenides, which has exhibited a zero-bias conductance peak.

Extracts from Schizandra chinensis fruit activate estrogen receptors: a possible clue to its effects on nitric oxide-mediated vasorelaxation.

Schizandra chinensis fruit has long been used for the treatment of cardiovascular symptoms associated especially with menopausal symptoms in Korea. To provide a scientific rationale for such uses, we have investigated the vasorelaxant effects of Schizandra chinensis fruit on the vasomotor tone of the rat thoracic aorta in an organ bath. The crude extracts of Schizandra chinensis fruit (SC-Ex) elicited a transient relaxing response in the endothelium-intact rat aorta contracted with norepinephrine. This relaxant effect was abolished by removal of the endothelium, and also by pretreatment with nitric oxide synthase inhibitor. We then examined whether this vasodilatory effect occurs through estrogen receptor by reporter assays. SC-Ex activated the estrogen-responsive luciferase gene in COS cells transiently transfected with estrogen receptor and reporter plasmids. The activation was maintained in the butanol-soluble fraction and further increased in the successively fractionated C(18) cartridge-adsorbed fraction (SC-ADF). Reporter gene activation by SC-ADF was inhibited by the specific estrogen receptor antagonist ICI 182,780, indicating that the effect is estrogen receptor dependent. However, SC-ADF failed to activate the androgen receptor in COS cells transfected with the corresponding receptor and reporter plasmids. These data show that extracts of Schizandra chinensis fruit act as a weak phytoestrogen.

Ginsenoside-Rb1 acts as a weak phytoestrogen in MCF-7 human breast cancer cells.

Ginseng has been recommended to alleviate the menopausal symptoms, which indicates that components of ginseng very likely contain estrogenic activity. We have examined the possibility that a component of Panax ginseng, ginsenoside-Rb1, acts by binding to estrogen receptor. We have investigated the estrogenic activity of ginsenoside-Rb1 in a transient transfection system using estrogen-responsive luciferase plasmids in MCF-7 cells. Ginsenoside-Rb1 activated the transcription of the estrogen-responsive luciferase reporter gene in MCF-7 breast cancer cells at a concentration of 50 microM. Activation was inhibited by the specific estrogen receptor antagonist ICI 182,780, indicating that the estrogenic effect of ginsenoside-Rb1 is estrogen receptor dependent. Next, we evaluated the ability of ginsenoside-Rb1 to induce the estrogen-responsive gene c-fos by semi-quantitative RT-PCR assays and Western analyses. Ginsenoside-Rb1 increased c-fos both at mRNA and protein levels. However, ginsenoside-Rb1 failed to activate the glucocorticoid receptor, the retinoic acid receptor, or the androgen receptor in CV-1 cells transiently transfected with the corresponding steroid hormone receptors and hormone responsive reporter plasmids. These data support our hypothesis that ginsenoside-Rb1 acts a weak phytoestrogen, presumably by binding and activating the estrogen receptor.