Routing the Exciton Emissions of WS2 Monolayer with the High-Order Plasmon Modes of Ag Nanorods.

Locally routing the exciton emissions in two-dimensional (2D) transition-metal dichalcogenides along different directions at the nanophotonic interface is of great interest in exploiting the promising 2D excitonic systems for functional nano-optical components. However, such control has remained elusive. Herein we report on a facile plasmonic approach for electrically controlled spatial modulation of the exciton emissions in a WS2 monolayer. The emission routing is enabled by the resonance coupling between the WS2 excitons and the multipole plasmon modes in individual silver nanorods placed on a WS2 monolayer. Different from prior demonstrations, the routing effect can be modulated by the doping level of the WS2 monolayer, enabling electrical control. Our work takes advantage of the high-quality plasmon modes supported by simple rod-shaped metal nanocrystals for the angularly resolved manipulation of 2D exciton emissions. Active control is achieved, which offers great opportunities for the development of nanoscale light sources and nanophotonic devices.

Emergence and Disruption of Spin-Charge Separation in One-Dimensional Repulsive Fermions.

At low temperature, collective excitations of one-dimensional (1D) interacting fermions exhibit spin-charge separation, a unique feature predicted by the Tomonaga-Luttinger liquid (TLL) theory, but a rigorous understanding remains challenging. Using the thermodynamic Bethe ansatz (TBA) formalism, we analytically derive universal properties of a 1D repulsive spin-1/2 Fermi gas with arbitrary interaction strength. We show how spin-charge separation emerges from the exact TBA formalism, and how it is disrupted by the interplay between the two degrees of freedom that brings us beyond the TLL paradigm. Based on the exact low-lying excitation spectra, we further evaluate the spin and charge dynamical structure factors (DSFs). The peaks of the DSFs exhibit distinguishable propagating velocities of spin and charge as functions of interaction strength, which can be observed by Bragg spectroscopy with ultracold atoms.

Structures, electronic properties, and superconductivities of alkaline-earth metal-doped phenanthrene and charge transfer characteristics of metal-doped phenanthrene.

To find potential alkaline-earth metal-doped aromatic superconductors and clarify the origin of superconductivity in metal-doped phenanthrene (PHN) systems, we have systematically investigated the crystal and electronic structures of bivalent metal (Mg, Ca, Sr and Ba)-doped PHNs by first-principles calculations. The results show that only Ba1.5PHN can satisfy the conditions of both thermodynamic stability and metallization. We predicted that Ba1.5PHN is superconducting with the critical temperature of 5.3 K. Based on the metal atomic radius and electronegativity and combined with monovalent metal- and trivalent metal-doped PHNs, the relations among charge transfer, metallization, and superconductivity were analyzed. The results indicate that the electronegativity of the metal element rather than the atomic radius is predominant in the charge transfer and superconductivity of metal-doped phenanthrene.

Magnetic Plasmon-Enhanced Second-Harmonic Generation on Colloidal Gold Nanocups.

The magnetic plasmons of three-dimensional nanostructures have unique optical responses and special significance for optical nanoresonators and nanoantennas. In this study, we have successfully synthesized colloidal Au and AuAg nanocups with a well-controlled asymmetric geometry, tunable opening sizes, and normalized depths ( h/ b, where h is depth and b is the height of the templating PbS nanooctahedrons), variable magnetic plasmon resonance, and largely enhanced second-harmonic generation (SHG). The most-efficient SHG of the bare Au nanocups is experimentally observed when the normalized depth h/ b is adjusted to ∼0.78-0.79. We find that the average magnetic field enhancement is maximized at h/ b = ∼0.65 and reveal that the maximal SHG can be attributed to the joint action of the optimized magnetic plasmon resonance and the "lightning-rod effect" of the Au nanocups. Furthermore, we demonstrate for the first time that the AuAg heteronanocups prepared by overgrowth of Ag on the Au nanocups can synergize the magnetic and electric plasmon resonances for nonlinear enhancement. By the tailoring of the dual resonances at the fundamental excitation and second-harmonic wavelengths, the far-field SHG intensity of the AuAg nanocups is enhanced 21.8-fold compared to that of the bare Au nanocups. These findings provide a strategy for the design of nonlinear optical nanoantennas based on magnetic plasmon resonances and can lead to diverse applications ranging from nanophotonics to biological spectroscopy.

Charge transfer effect on Raman shifts of aromatic hydrocarbons with three phenyl rings from ab initio study.

To clarify the charge transfer effect on Raman spectra of aromatic hydrocarbons, we investigate the Raman shifts of phenanthrene, p-terphenyl, and anthracene and their negatively charged counterparts by using density functional theory. For the three molecules, upon charge increasing, the computed Raman peaks generally shift down with the exception of a few shifting up. The characteristic Raman modes in the 0-1000 cm-1 region persist up, while some high-frequency ones change dramatically with three charges transferred. The calculated Raman shifts for one- and two-electron transfer are in agreement with the measured Raman spectra, and in accordance to the stoichiometric ratios 1:1 and 2:1 of the metal atom and aromatic hydrocarbon molecule in recent experimental and theoretical studies. Our theoretical results provide the fundamental information to elucidate the Raman shifts and the stoichiometric ratios for alkali-metal-doped aromatic hydrocarbons.

Giant Magnetoresistance in Hubbard Chains.

We use numerically unbiased methods to show that the one-dimensional Hubbard model with periodically distributed on-site interactions already contains the minimal ingredients to display the phenomenon of magnetoresistance; i.e., by applying an external magnetic field, a dramatic enhancement on the charge transport is achieved. We reach this conclusion based on the computation of the Drude weight and of the single-particle density of states, applying twisted boundary condition averaging to reduce finite-size effects. The known picture that describes the giant magnetoresistance, by interpreting the scattering amplitudes of parallel or antiparallel polarized currents with local magnetizations, is obtained without having to resort to different entities; itinerant and localized charges are indistinguishable.

Superconductivity and phase stability of potassium-doped biphenyl.

Phenyl molecules are proposed as potential high-temperature superconductors due to exhibiting interesting properties. Here, we report the discovery of superconductivity with the critical temperature (Tc) of ∼7.2 Kelvin in potassium (K)-doped biphenyl (C12H10). The dc magnetic susceptibility measurements provide solid evidence for the presence of the Meissner effect in KxC12H10. The Raman spectra detected bipolaronic characteristics in this superconducting state, which are proposed to account for the electron pairing. Theoretical simulations provided the information of the crystal structure of KxC12H10. Combining XRD data with formation energy, we suggest that the superconducting phase corresponds to K2C12H10 or with a small charge fluctuation in a layered structure. The discovery of superconductivity in K-doped biphenyl vastly expands the potential applications in the superconducting field.

Universal Scaling and Critical Exponents of the Anisotropic Quantum Rabi Model.

We investigate the quantum phase transition of the anisotropic quantum Rabi model, in which the rotating and counterrotating terms are allowed to have different coupling strengths. The model interpolates between two known limits with distinct universal properties. Through a combination of analytic and numerical approaches, we extract the phase diagram, scaling functions, and critical exponents, which determine the universality class at finite anisotropy (identical to the isotropic limit). We also reveal other interesting features, including a superradiance-induced freezing of the effective mass and discontinuous scaling functions in the Jaynes-Cummings limit. Our findings are extended to the few-body quantum phase transitions with N>1 spins, where we expose the same effective parameters, scaling properties, and phase diagram. Thus, a stronger form of universality is established, valid from N=1 up to the thermodynamic limit.

Pressure-induced superconductivity in CaC2.

Carbon can exist as isolated dumbbell, 1D chain, 2D plane, and 3D network in carbon solids or carbon-based compounds, which attributes to its rich chemical binding way, including sp-, sp(2)-, and sp(3)-hybridized bonds. sp(2)-hybridizing carbon always captures special attention due to its unique physical and chemical property. Here, using an evolutionary algorithm in conjunction with ab initio method, we found that, under compression, dumbbell carbon in CaC2 can be polymerized first into 1D chain and then into ribbon and further into 2D graphite sheet at higher pressure. The C2/m structure transforms into an orthorhombic Cmcm phase at 0.5 GPa, followed by another orthorhombic Immm phase, which is stabilized in a wide pressure range of 15.2-105.8 GPa and then forced into MgB2-type phase with wide range stability up to at least 1 TPa. Strong electron-phonon coupling λ in compressed CaC2 is found, in particular for Immm phase, which has the highest λ value (0.562-0.564) among them, leading to its high superconducting critical temperature Tc (7.9∼9.8 K), which is comparable with the 11.5 K value of CaC6. Our results show that calcium not only can stabilize carbon sp(2) hybridization at a larger range of pressure but also can contribute in superconducting behavior, which would further ignite experimental and theoretical interest in alkaline-earth metal carbides to uncover their peculiar physical properties under extreme conditions.

[Preventive Effect of Different Compatibilities of Ramulus Cinnamomi and Radix Paeomlae alba in Guizhi Decoction on Cardiac Sympathetic Denervation Induced by 6-OHDA].

OBJECTIVE: To observe the preventive effect of different compatibilities of Ramulus Cinnamomi (RC) and Radix Paeomiae alba (RPA) in Guizhi Decoction (GZD) on neurotransmitters and their rate-limiting enzymes, and neurotrophic factors of cardiac sympathetic denervation model rats induced by 6-hydroxydopamine (6-OHDA). METHODS: Totally 54 male Wistar rats were randomly divided into 6 groups, i.e., the blank control group, the model group, the methycobal group, the 2:1 (RC/RPA) Guishao group, the 1:2 Guishao group, and the 1:1 Guishao group, 9 in each group. Sympathetic denervation was induced by intraperitoneal injection of 6-OHDA for three successive days. Rats in the methycobal group and GZD groups were administered with corresponding decoction by gastrogavage 1 week before modeling (methycobal at the daily dose 0.15 mg/kg; GZD at the daily dose of 4.0, 5.5, 5.5 g crude drugs/kg for GZD 1:1, 1:2, and 2:1 groups). All medication lasted for 10 successive days. Levels of norepinephrine (NE), tyrosine hydroxylase (TH), choline acetyl-transferase (ChAT), nerve growth factor (NGF), growth associated protein43 (GAP-43) and ciliary neurotrophic factor (CNTF) in myocar- dial homogenates of right atrium and ventricular septum were detected by ELISA. RESULTS: Compared with the blank control group, levels of NE, TH, TH/ChAT ratio, and GAP-43 in myocardial homogenates of right atrium and ventricular septum decreased in the model group, and level of NGF increased (P < 0.01, P < 0.05). Compared with the model group, levels of NE and GAP-43 increased in the right atrium and interventricular septum; NGF level of the ventricular septum decreased in the methycobal group and each GZD groups. TH and TH/ChAT ratio in the right atrium increased in the 2:1 Guishao group and the 1:2 Guishao group (P < 0.01, P < 0.05); NGF levels in the right atrium and interventricular septum decreased only in the 1:1 Guishao group (P < 0.01, P< 0.05). Compared with the methycobal group, levels of NE, TH, and GAP-43 in the right atrium and interventricular septum increased, and NGF levels in the right atrium and interventricular septum decreased in the 1:1 Guishao group (P < 0.05). Compared with the methycobal group, levels of NE and GAP-43 in interventricular septum increased in the 2:1 Guishao group (P < 0.05). CONCLUSION: GZD (with the proportion between RC and RPA 2:1 and 1:1) could improve contents of neurotransmitters and their rate-limiting enzymes, as well as neurotrophic factors in cardiac sympathetic denervation model rats induced by 6-OHDA, alleviate cardiac sympathetic denervation induced by 6-OHDA, and maintain the balance of sympathetic-vagal nerve system.

Anionic chemistry of noble gases: formation of Mg-NG (NG = Xe, Kr, Ar) compounds under pressure.

While often considered to be chemically inert, the reactivity of noble gas elements at elevated pressures is an important aspect of fundamental chemistry. The discovery of Xe oxidation transformed the doctrinal boundary of chemistry by showing that a complete electron shell is not inert to reaction. However, the reductive propensity, i.e., gaining electrons and forming anions, has not been proposed or examined for noble gas elements. In this work, we demonstrate, using first-principles electronic structure calculations coupled to an efficient structure prediction method, that Xe, Kr, and Ar can form thermodynamically stable compounds with Mg at high pressure (≥125, ≥250, and ≥250 GPa, respectively). The resulting compounds are metallic and the noble gas atoms are negatively charged, suggesting that chemical species with a completely filled shell can gain electrons, filling their outermost shell(s). Moreover, this work indicates that Mg2NG (NG = Xe, Kr, Ar) are high-pressure electrides with some of the electrons localized at interstitial sites enclosed by the surrounding atoms. Previous predictions showed that such electrides only form in Mg and its compounds at very high pressures (>500 GPa). These calculations also demonstrate strong chemical interactions between the Xe 5d orbitals and the quantized interstitial quasiatom (ISQ) orbitals, including the strong chemical bonding and electron transfer, revealing the chemical nature of the ISQ.

Comparison of the plasmonic performances between lithographically fabricated and chemically grown gold nanorods.

Noble metal nanostructures, especially gold nanocrystals, have attracted intensive interest due to their rich plasmonic properties and enormous potential technological applications. The preparation process of gold nanocrystals can strongly affect their plasmonic properties and therefore their performances in various applications. Chemically synthesized colloidal gold nanocrystals are usually employed in biomedical fields, while lithographically fabricated ones are highly preferred for constructing optical meta-structures. A detailed careful comparison of the plasmonic performances between lithographical and chemical metal nanostructures is strongly desired for using them for different applications. Herein, we experimentally measured and quantitatively compared the plasmonic properties, including longitudinal localized surface plasmon wavelengths (LLSPWs) and plasmon peak widths, scattering intensities, and local electric field enhancements, of lithographically fabricated and chemically grown gold nanorods. The lithographical nanorods exhibit much weaker scattering, largely broadened spectral widths, and considerably reduced electric field enhancements. Electrodynamic simulations suggest that the reduction in the plasmonic performance of the lithographical nanorods is caused mainly by the use of an adhesive metal layer and slightly by their polycrystalline nature. Our quantitative comparison results will be very helpful in guiding the selection of proper types of metal nanostructures for targeted technological applications.

[Effects of Different Compatibilities of Ramulus Cinnamomi and Peony in Guizhi Decoction on Diabetic Cardiac Autonomic Neuropathy].

OBJECTIVE: To observe the preventive effect different compatibilities of Ramulus Cinnamomi (RC) and peony in Guizhi Decoction (GD) on diabetic cardiac autonomic neuropathy (DCAN). METHODS: Totally 60 male rats were randomly divided into 5 groups, i.e., the blank control DM group, the model group, the methycobal group, the 1:1 (RC/peony) Guishao group, the 2:1 Guishao group, and the 1:2 Guishao group, 10 in each group. Rats were pretreated with corresponding drugs for 1 week, and then induced diabetes by intraperitoneal injection of STZ. Drugs were administrated by gastrogavage for 4 more weeks after STZ-injection. Enzyme-linked immunosorbent assay (ELISA) was employed to detect levels of tyrosine hydroxylase (TH), choline acetyltransferase (CHAT), nerve growth factor. (NGF), and ciliary neurotrophic factor (CNTF) in myocardial homogenates. RESULTS: After 4-week modeling, body weight (BW) was obviously lower, but blood glucose (BG) was higher in STZ rats than in rats of the blank control DM group. There was no statistical difference in BW or BG among the 5 groups (P >0.05). Compared with the blank control group, TH, TH/CHAT, and NGF in left ventricle and ventricular septum increased, CHAT and CNTF increased in the model group (P < 0.05, P < 0.01). Compared with the model group, TH and TH/CHAT in left ventricle decreased (P < 0.05, P < 0.01), CNTF in left ventricle increased (P < 0.05), CHAT in left ventricle and ventricular septum increased (P < 0.05, P < 0.01) in the methycobal group. TH and TH/CHAT in left ventricle and ventricular septum decreased, CNTF in left ventricle and ventricular septum increased (P < 0.05, P < 0.01), CHAT in left ventricle and ventricular septum increased (P < 0.01), NGF in ventricular septum decreased (P < 0.01) in the 1:1 Guishao group. TH/CHAT in left ventricle decreased (P < 0.01), CHAT and CNTF in left ventricle and ventricular septum increased (P < 0.05, P < 0.01) in the 1:2 Guishao group. Compared with the methycobal group, CHAT in left ventricle decreased, TH and TH/CHAT in left ventricle increased in the 2:1 Guishao group (P < 0.05, P < 0.01). TH and TH/CHAT in ventricular septum decreased (P < 0.05), CHAT and CNTF in left ventricle and ventricular septum increased (P < 0.05, P < 0.01) in the 1:1 Guishao group. Compared with the 1:2 Guishao group and the 2:1 Guishao group, CHAT in left ventricle increased, TH/CHAT in left ventricle decreased, TH and TH/CHAT in ventricular septum decreased, CHAT in ventricular septum increased, CNTF in left ventricle and ventricular septum also increased in the 1:1 Guishao group (all P < 0.01). CONCLUSIONS: STZ model rats had autonomic neural injury, manifested as lowered vagal nerve activity and hyperactive sympathetic nerves. GD could effectively suppress hyperactive cardiac sympathetic nerves and protect the vagus. Besides, GD (1:1) showed the optimal effect in regulating the balance of cardiac autonomic nerves and could be used in early prevention of DCAN.

Ba2phenanthrene is the main component in the Ba-doped phenanthrene superconductor.

We have systematically investigated the crystal structure of Ba-doped phenanthrene with various Ba doping levels by the first-principles calculations combined with the X-ray diffraction (XRD) spectra simulations. Although the experimental stoichiometry ratio of Ba atom and phenanthrene molecule is 1.5:1, the simulated XRD spectra, space group symmetry and optimized lattice parameters of Ba1.5phenanthrene are not consistent with the experimental ones, while the results for Ba2phenanthrene are in good agreement with the measurements. The strength difference of a few XRD peaks can be explained by the existence of pristine phenanthrene. Our findings suggest that instead of uniform Ba1.5phenanthrene, there coexist Ba2phenanthrene and undoped phenanthrene in the superconducting sample. The electronic calculations indicate that Ba2phenanthrene is a semiconductor with a small energy gap less than 0.05 eV.

High-pressure study of isoviolanthrone by Raman spectroscopy.

Vibrational properties of isoviolanthrone are investigated by Raman scattering at pressures up to 30.5 GPa and room temperature. A complete characterization of phonon spectra under pressure is given for this material. The onset of a phase transition at 11.0 GPa and the formation of a new phase above 13.8 GPa are identified from both the frequency shifts and the changes in the full width half maxima of the intra- and internal modes. The transition is proposed to result from the changes of intra- and intermolecular bonding. The tendencies of the intensity ratios with pressure are in good agreement with the pressure dependence of the resistance at room temperature, indicating that the phase transition may be an electronic origin. The absence of the changes in the lattice modes indicates that the observed phase transition is probably a result of the structural distortions or reorganizations. The reversible character of the transition upon compression and decompression is determined in the entire pressure region studied.

Constraint on the potassium content for the superconductivity of potassium-intercalated phenanthrene.

Raman-scattering measurements were performed on K(x)phenanthrene (0 ⩽ x ⩽ 6.0) at room temperature. Three phases (x = 3.0, 3.5, and 4.0) are identified based on the obtained Raman spectra. Only the K3phenanthrene phase is found to exhibit the superconducting transition at 5 K. The C-C stretching modes are observed to broaden and become disordered in K(x)phenanthrene with x = 2.0, 2.5, 6.0, indicating some molecular disorder in the metal intercalation process. This disorder is expected to influence the nonmetallic nature of these materials. The absence of metallic character in these nonsuperconducting phases is found from the calculated electronic structures based on the local density approximation.

Synthesis and superconductivity in yttrium-cerium hydrides at high pressures.

Further increasing the critical temperature and/or decreasing the stabilized pressure are the general hopes for the hydride superconductors. Inspired by the low stabilized pressure associated with Ce 4f electrons in superconducting cerium superhydride and the high critical temperature in yttrium superhydride, we carry out seven independent runs to synthesize yttrium-cerium alloy hydrides. The synthetic process is examined by the Raman scattering and X-ray diffraction measurements. The superconductivity is obtained from the observed zero-resistance state with the detected onset critical temperatures in the range of 97-141 K. The upper critical field towards 0 K at pressure of 124 GPa is determined to be between 56 and 78 T by extrapolation of the results of the electrical transport measurements at applied magnetic fields. The analysis of the structural data and theoretical calculations suggest that the phase of Y0.5Ce0.5H9 in hexagonal structure with the space group of P63/mmc is stable in the studied pressure range. These results indicate that alloying superhydrides indeed can maintain relatively high critical temperature at relatively modest pressures accessible by laboratory conditions.

Quantum Monte Carlo study of a dominant s-wave pairing symmetry in iron-based superconductors.

We perform a systematic quantum Monte Carlo study of the pairing correlation in the S(4) symmetric microscopic model for iron-based superconductors. It is found that the pairing with an extensive s-wave symmetry robustly dominates over other pairings at low temperature in a reasonable parameter region regardless of the change of Fermi surface topologies. The pairing susceptibility, the effective pairing interaction, and the (π, 0) antiferromagnetic correlation strongly increase as the on-site Coulomb interaction increases, indicating the importance of the effect of electron-electron correlation. Our nonbiased numerical results provide a unified understanding of the superconducting mechanism in iron pnictides and iron chalcogenides and demonstrate that the superconductivity is driven by strong electron-electron correlation effects.

Van der Waals density functional study of the structural and electronic properties of La-doped phenanthrene.

By the first principle calculations based on the van der Waals density functional theory, we study the crystal structures and electronic properties of La-doped phenanthrene. Two stable atomic geometries of La1phenanthrene are obtained by relaxation of atomic positions from various initial structures. The structure-I is a metal with two energy bands crossing the Fermi level, while the structure-II displays a semiconducting state with an energy gap of 0.15 eV, which has an energy gain of 0.42 eV per unit cell compared to the structure-I. The most striking feature of La1phenanthrene is that La 5d electrons make a significant contribution to the total density of state around the Fermi level, which is distinct from potassium doped phenanthrene and picene. Our findings provide an important foundation for the understanding of superconductivity in La-doped phenanthrene.

Vibrational and structural properties of tetramethyltin under pressure.

The vibrational and structural properties of a hydrogen-rich group IVa hydride, Sn(CH(3))(4), have been investigated by combining Raman spectroscopy and synchrotron x-ray diffraction measurements at room temperature and at pressures up to 49.9 GPa. Both techniques allow the obtaining of complementary information on the high-pressure behaviors and yield consistent phase transitions at 0.9 GPa for the liquid to solid and 2.8, 10.4, 20.4, and 32.6 GPa for the solid to solid. The foregoing solid phases are identified to have the orthorhombic, tetragonal, monoclinic crystal structures with space groups of Pmmm for phase I, P4/mmm for phase II, P2/m for phase III, respectively. The phases IV and V coexist with phase III, resulting in complex analysis on the possible structures. These transitions suggest the variation in the inter- and intra-molecular bonding of this compound.