Coherent helicity-dependent spin-phonon oscillations in the ferromagnetic van der Waals crystal CrI3.

The discovery of two-dimensional systems hosting intrinsic magnetic order represents a seminal addition to the rich landscape of van der Waals materials. CrI3 is an archetypal example, where the interdependence of structure and magnetism, along with strong light-matter interactions, provides a new platform to explore the optical control of magnetic and vibrational degrees of freedom at the nanoscale. However, the nature of magneto-structural coupling on its intrinsic ultrafast timescale remains a crucial open question. Here, we probe magnetic and vibrational dynamics in bulk CrI3 using ultrafast optical spectroscopy, revealing spin-flip scattering-driven demagnetization and strong transient exchange-mediated interactions between lattice vibrations and spin oscillations. The latter yields a coherent spin-coupled phonon mode that is highly sensitive to the driving pulse's helicity in the magnetically ordered phase. Our results elucidate the nature of ultrafast spin-lattice coupling in CrI3 and highlight its potential for applications requiring high-speed control of magnetism at the nanoscale.

Direct Observation of Coherent Longitudinal and Shear Acoustic Phonons in TaAs Using Ultrafast X-Ray Diffraction.

Using femtosecond time-resolved x-ray diffraction, we investigated optically excited coherent acoustic phonons in the Weyl semimetal TaAs. The low symmetry of the (112) surface probed in our experiment enables the simultaneous excitation of longitudinal and shear acoustic modes, whose dispersion closely matches our simulations. We observed an asymmetry in the spectral line shape of the longitudinal mode that is notably absent from the shear mode, suggesting a time-dependent frequency chirp that is likely driven by photoinduced carrier diffusion. We argue on the basis of symmetry that these acoustic deformations can transiently alter the electronic structure near the Weyl points and support this with model calculations. Our study underscores the benefit of using off-axis crystal orientations when optically exciting acoustic deformations in topological semimetals, allowing one to transiently change their crystal and electronic structures.

Photocurrent-driven transient symmetry breaking in the Weyl semimetal TaAs.

Symmetry plays a central role in conventional and topological phases of matter, making the ability to optically drive symmetry changes a critical step in developing future technologies that rely on such control. Topological materials, like topological semimetals, are particularly sensitive to a breaking or restoring of time-reversal and crystalline symmetries, which affect both bulk and surface electronic states. While previous studies have focused on controlling symmetry via coupling to the crystal lattice, we demonstrate here an all-electronic mechanism based on photocurrent generation. Using second harmonic generation spectroscopy as a sensitive probe of symmetry changes, we observe an ultrafast breaking of time-reversal and spatial symmetries following femtosecond optical excitation in the prototypical type-I Weyl semimetal TaAs. Our results show that optically driven photocurrents can be tailored to explicitly break electronic symmetry in a generic fashion, opening up the possibility of driving phase transitions between symmetry-protected states on ultrafast timescales.

Erratum: Dynamic Multiferroicity of a Ferroelectric Quantum Critical Point [Phys. Rev. Lett. 122, 057208 (2019)].

This corrects the article DOI: 10.1103/PhysRevLett.122.057208.

Electronic and magnetic properties of stoichiometric CeAuBi2.

We report the electronic and magnetic properties of stoichiometric CeAuBi2 single crystals. At ambient pressure, CeAuBi2 orders antiferromagnetically below a Néel temperature (TN ) of 19 K. Neutron diffraction experiments revealed an antiferromagnetic propagation vector τ ^ = [ 0 , 0 , 1 ∕ 2 ] , which doubles the paramagnetic unit cell along the c axis. At low temperatures several metamagnetic transitions are induced by the application of fields parallel to the c axis, suggesting that the magnetic structure of CeAuBi2 changes as a function of field. At low temperatures, a linear positive magnetoresistance may indicate the presence of band crossings near the Fermi level. Finally, the application of external pressure favors the antiferromagnetic state, indicating that the 4f electrons become more localized.

Tracking Ultrafast Photocurrents in the Weyl Semimetal TaAs Using THz Emission Spectroscopy.

We investigate polarization-dependent ultrafast photocurrents in the Weyl semimetal TaAs using terahertz (THz) emission spectroscopy. Our results reveal that highly directional, transient photocurrents are generated along the noncentrosymmetric c axis regardless of incident light polarization, while helicity-dependent photocurrents are excited within the ab plane. This is consistent with earlier static photocurrent experiments, and demonstrates on the basis of both the physical constraints imposed by symmetry and the temporal dynamics intrinsic to current generation and decay that optically induced photocurrents in TaAs are inherent to the underlying crystal symmetry of the transition metal monopnictide family of Weyl semimetals.

Dynamic Multiferroicity of a Ferroelectric Quantum Critical Point.

Quantum matter hosts a large variety of phases, some coexisting, some competing; when two or more orders occur together, they are often entangled and cannot be separated. Dynamical multiferroicity, where fluctuations of electric dipoles lead to magnetization, is an example where the two orders are impossible to disentangle. Here we demonstrate an elevated magnetic response of a ferroelectric near the ferroelectric quantum critical point (FE QCP), since magnetic fluctuations are entangled with ferroelectric fluctuations. We thus suggest that any ferroelectric quantum critical point is an inherent multiferroic quantum critical point. We calculate the magnetic susceptibility near the FE QCP and find a region with enhanced magnetic signatures near the FE QCP and controlled by the tuning parameter of the ferroelectric phase. The effect is small but observable-we propose quantum paraelectric strontium titanate as a candidate material where the magnitude of the induced magnetic moments can be ∼5×10^{-7} µ_{B} per unit cell near the FE QCP.

Rasagiline, an inhibitor of MAO-B, decreases colonic motility through elevating colonic dopamine content.

BACKGROUND: Dopamine (DA) is a negative modulator of gut motility. Monoamine oxidase-B (MAO-B) is an important metabolic enzyme degrading DA. Rasagiline, an irreversible MAO-B inhibitor, is used to treat Parkinson's disease because of its neuroprotective effect and increasing central DA. However, it is unclear whether MAO-B exists in the colon and rasagiline increases colonic DA, thereby affecting colonic motility. METHODS: Immunohistochemistry, western blotting, enzyme activity assay, colonic motility recording, gut transit test, and high-performance liquid chromatography-electrochemical detection were employed in this study. KEY RESULTS: Monoamine oxidase-B was distributed in the colonic muscular layers including neurons and glias of rat and human. When oral treatment of rats with rasagiline for 4 weeks, in vitro colonic motility was significantly reduced, but it was greatly reversed by SCH-23390, an antagonist of DA D1 receptor. The rasagiline-treated rats also manifested decreased MAO-B activity and increased DA content in the colonic muscular layer, but no alterations were detected in the protein expressions of D1 and D2 receptors, and MAO-A and MAO-B, as well as in the content of 5-hydroxytryptamine and noradrenaline. Moreover, acute administration of rasagiline did not affect the colonic motility in vitro and the colonic DA level in rats, although MAO-B activity was significantly inhibited. CONCLUSIONS & INFERENCES: Monoamine oxidase-B is abundant in the colonic muscular layer including myenteric plexus of rat and human. Long-term administration of rasagiline can increase colonic DA thereby inhibiting colonic motility, suggesting that colonic MAO-B could be a potential drug target for colonic dysmotility.

Band Dependent Interlayer f-Electron Hybridization in CeRhIn_{5}.

A key issue in heavy fermion research is how subtle changes in the hybridization between the 4f (5f) and conduction electrons can result in fundamentally different ground states. CeRhIn_{5} stands out as a particularly notable example: when replacing Rh with either Co or Ir, antiferromagnetism gives way to superconductivity. In this photoemission study of CeRhIn_{5}, we demonstrate that the use of resonant angle-resolved photoemission spectroscopy with polarized light allows us to extract detailed information on the 4f crystal field states and details on the 4f and conduction electron hybridization, which together determine the ground state. We directly observe weakly dispersive Kondo resonances of f electrons and identify two of the three Ce 4f_{5/2}^{1} crystal-electric-field levels and band-dependent hybridization, which signals that the hybridization occurs primarily between the Ce 4f states in the CeIn_{3} layer and two more three-dimensional bands composed of the Rh 4d and In 5p orbitals in the RhIn_{2} layer. Our results allow us to connect the properties observed at elevated temperatures with the unusual low-temperature properties of this enigmatic heavy fermion compound.

Temperature-tunable Fano resonance induced by strong coupling between Weyl fermions and phonons in TaAs.

Strong coupling between discrete phonon and continuous electron-hole pair excitations can induce a pronounced asymmetry in the phonon line shape, known as the Fano resonance. This effect has been observed in various systems. Here we reveal explicit evidence for strong coupling between an infrared-active phonon and electronic transitions near the Weyl points through the observation of a Fano resonance in the Weyl semimetal TaAs. The resulting asymmetry in the phonon line shape, conspicuous at low temperatures, diminishes continuously with increasing temperature. This behaviour originates from the suppression of electronic transitions near the Weyl points due to the decreasing occupation of electronic states below the Fermi level (EF) with increasing temperature, as well as Pauli blocking caused by thermally excited electrons above EF. Our findings not only elucidate the mechanism governing the tunable Fano resonance but also open a route for exploring exotic physical phenomena through phonon properties in Weyl semimetals.

Dopamine enhances duodenal epithelial permeability via the dopamine D5 receptor in rodent.

AIM: The intestinal barrier is made up of epithelial cells and intercellular junctional complexes to regulate epithelial ion transport and permeability. Dopamine (DA) is able to promote duodenal epithelial ion transport through D1-like receptors, which includes subtypes of D1 (D1 R) and D5 (D5 R), but whether D1-like receptors influence the duodenal permeability is unclear. METHODS: FITC-dextran permeability, short-circuit current (ISC ), Western blot, immunohistochemistry and ELISA were used in human D5 R transgenic mice and hyperendogenous enteric DA (HEnD) rats in this study. RESULTS: Dopamine induced a downward deflection in ISC and an increase in FITC-dextran permeability of control rat duodenum, which were inhibited by the D1-like receptor antagonist, SCH-23390. However, DA decreased duodenal transepithelial resistance (TER), an effect also reversed by SCH-23390. A strong immunofluorescence signal for D5 R, but not D1 R, was observed in the duodenum of control rat. In human D5 R knock-in transgenic mice, duodenal mucosa displayed an increased basal ISC with high FITC-dextran permeability and decreased TER with a lowered expression of tight junction proteins, suggesting attenuated duodenal barrier function in these transgenic mice. D5 R knock-down transgenic mice manifested a decreased basal ISC with lowered FITC-dextran permeability. Moreover, an increased FITC-dextran permeability combined with decreased TER and tight junction protein expression in duodenal mucosa were also observed in HEnD rats. CONCLUSION: This study demonstrates, for the first time, that DA enhances duodenal permeability of control rat via D5 R, which provides new experimental and theoretical evidence for the influence of DA on duodenal epithelial barrier function.

Observation of universal strong orbital-dependent correlation effects in iron chalcogenides.

Establishing the appropriate theoretical framework for unconventional superconductivity in the iron-based materials requires correct understanding of both the electron correlation strength and the role of Fermi surfaces. This fundamental issue becomes especially relevant with the discovery of the iron chalcogenide superconductors. Here, we use angle-resolved photoemission spectroscopy to measure three representative iron chalcogenides, FeTe0.56Se0.44, monolayer FeSe grown on SrTiO3 and K0.76Fe1.72Se2. We show that these superconductors are all strongly correlated, with an orbital-selective strong renormalization in the dxy bands despite having drastically different Fermi surface topologies. Furthermore, raising temperature brings all three compounds from a metallic state to a phase where the dxy orbital loses all spectral weight while other orbitals remain itinerant. These observations establish that iron chalcogenides display universal orbital-selective strong correlations that are insensitive to the Fermi surface topology, and are close to an orbital-selective Mott phase, hence placing strong constraints for theoretical understanding of iron-based superconductors.

The role of the vagal pathway and gastric dopamine in the gastroparesis of rats after a 6-hydroxydopamine microinjection in the substantia nigra.

AIM: Gastroparesis is a common non-motor system symptom of Parkinson's disease (PD). However, the mechanism responsible for the gastric motor abnormality is not clear. We previously reported on the impaired gastric motility in 6-hydroxydopamine (6-OHDA) rats, which were treated with a bilateral microinjection of 6-OHDA in the substantia nigra (SN). We hypothesize that the enhanced dopamine system and reduced acetylcholine (Ach) in gastric tissues might contribute to the delayed gastric emptying observed in PD. METHODS: A strain gauge force transducer, digital X-ray imaging system, Western blot, immunofluorescence and Radio Immunoassay were used in this study. RESULTS: Dopaminergic neurones in the SN were greatly reduced following the bilateral microinjection of 6-OHDA. 6-OHDA rats exhibited impaired gastric motility and delayed gastric emptying, accompanied by increased dopamine content and the overexpression of D2 receptors in the stomach. The administration of the D2 receptor antagonist domperidone relieved gastric dysmotility in 6-OHDA rats, but the D1 receptor antagonist SCH23390 failed to do so. Subdiaphragmatic vagotomy prevented the increase in the gastric dopamine content and D2 receptor expression and improved gastric dysmotility in 6-OHDA rats. CONCLUSION: Dopaminergic deficiency in the SN results in impaired gastric motility, possibly as a result of the enhanced activity of dopamine system and reduced Ach in gastric tissue. The vagus nerve plays an important role in peripheral gastric motility disorder.

Measurement of two low-temperature energy gaps in the electronic structure of antiferromagnetic USb2 using ultrafast optical spectroscopy.

Ultrafast optical spectroscopy is used to study the antiferromagnetic f-electron system USb(2). We observe the opening of two charge gaps at low temperatures (

Electronic tuning and uniform superconductivity in CeCoIn5.

We report a globally reversible effect of electronic tuning on the magnetic phase diagram in CeCoIn(5) driven by electron (Pt and Sn) and hole (Cd, Hg) doping. Consequently, we are able to extract the superconducting pair breaking component for hole and electron dopants with pressure and codoping studies, respectively. We find that these nominally nonmagnetic dopants have a remarkably weak pair breaking effect for a d-wave superconductor. The pair breaking is weaker for hole dopants, which induce magnetic moments, than for electron dopants. Furthermore, both Pt and Sn doping have a similar effect on superconductivity despite being on different dopant sites, arguing against the notion that superconductivity lives predominantly in the CeIn(3) planes of these materials. In addition, we shed qualitative understanding on the doping dependence with density functional theory calculations.

Superconducting gap structure of the 115s revisited.

Density functional theory calculations of the electronic structure of Ce- and Pu-based heavy fermion superconductors in the so-called 115 family are performed. The gap equation is used to consider which superconducting order parameters are most favorable assuming a pairing interaction that is peaked at (π, π, qz)­the wavevector for the antiferromagnetic ordering found in close proximity. In addition to the commonly accepted dx2−y2 order parameter, there is evidence that an extended s-wave order parameter with nodes is also plausible. We discuss whether these results are consistent with current observations and possible measurements that could help distinguish between these scenarios.

Chemical lesioning and glutamate administration reveal a major role for the nucleus tractus solitarius in the cardiac-somatic reflex in rats.

Many patients suffer from secondary muscle hyperalgesia after experiencing angina pectoris. In this study, we examined the role of the nucleus tractus solitarius (NTS) and glutamate receptors in modulating cardiac-evoked muscle hyperalgesia induced by pericardial capsaicin, which was monitored by recording electromyogram (EMG) activity from the spinotrapezius muscle in the anesthetized rat. Unilateral chemical lesioning of the commissural NTS with the neurotoxin ibotenic acid significantly depressed the cardiac-somatic reflex; the EMG responses decreased to 56.4 ± 6.9% of that of the controls (5 of 5). Microinjection of the excitatory amino acid glutamate, at 10, 20, and 50 nmol, into the commissural NTS increased the EMG response, in a dose-dependent manner, to 116.9 ± 4.9%, 143.9 ± 10.2%, and 214.2 ± 15.8% (n=8), respectively, of that of the controls. In contrast, microinjection of the N-methyl-D-aspartate (NMDA) receptor antagonist (+)-5-methyl-10, 11-dihydro-5H-dibenzo [a, d]-cyclohepten-5,10-imine maleate (MK-801) at 4 and 6 nmol, decreased the EMG response to 45.2 ± 10.6% and 36.8 ± 14.3%, respectively, of that of the controls (n=8 for each dose). Similarly, the metabotropic glutamate receptor (mGluR) antagonist (RS)-a-methyl-4-carboxyphenylglycine (MCPG), at 2.5 and 5 nmol, decreased the EMG response to 65.2 ± 16.3% and 57.0 ± 4.2%, respectively, of that of the controls. When a combination of MK-801 and MCPG was administrated, the EMG response further decreased to 22.5 ± 13.2% (n=6) of that of the controls. However, administration of a non-NMDA receptor antagonist 6, 7-dinitroquinoxaline-2, 3-dione (DNQX), at 2 and 5 nmol, had no effect on the EMG response. These results suggest that the NTS is involved in the facilitation of the cardiac-somatic reflex, and that the NMDA receptor and mGluRs play an important role in mediating this effect.

Emodin induces chloride secretion in rat distal colon through activation of mast cells and enteric neurons.

BACKGROUND AND PURPOSE: Emodin (1,3,8-trihydroxy-6-methylanthraquinone) is an active component of many herb-based laxatives. However, its mechanism of action is unclear. The aim of the present study was to investigate the role of mast cells and enteric neurons in emodin-induced ion secretion in the rat colon. EXPERIMENTAL APPROACH: Short-circuit current (I(SC)) recording was used to measure epithelial ion transport. A scanning ion-selective electrode technique was used to directly measure Cl(-) flux (J(Cl)-) across the epithelium. RIA was used to measure emodin-induced histamine release. KEY RESULTS: Basolateral addition of emodin induced a concentration-dependent increase in I(SC) in colonic mucosa/submucosa preparations, EC(50) 75 µM. The effect of emodin was blocked by apically applied glibenclamide, a Cl(-) channel blocker, and by basolateral application of bumetanide, an inhibitor of the Na(+) -K(+) -2Cl(-) cotransporter. Emodin-evoked J(Cl)- in mucosa/submucosa preparations was measured by scanning ion-selective electrode technique, which correlated to the increase in I(SC) and was significantly suppressed by glibenclamide and bumetanide. Pretreatment with tetrodotoxin and the muscarinic receptor antagonist atropine had no effect on emodin-induced ΔI(SC) in mucosa-only preparations, but significantly reduced emodin-induced ΔI(SC) and J(Cl)- in mucosa/submucosa preparations. The COX inhibitor indomethacin, the mast cell stabilizer ketotifen and H(1) receptor antagonist pyrilamine significantly reduced emodin-induced ΔI(SC) in mucosa and mucosa/submucosa preparations. The H(2) receptor antagonist cimetidine inhibited emodin-induced ΔI(SC) and J(Cl)- only in the mucosa/submucosa preparations. Furthermore, emodin increased histamine release from the colonic mucosa/submucosa tissues. CONCLUSIONS AND IMPLICATIONS: The results suggest that emodin-induced colonic Cl(-) secretion involves mast cell degranulation and activation of cholinergic and non-cholinergic submucosal neurons.

Rostroventral medulla-mediated biphasic modulation of the rat cardiosomatic motor reflex.

The purpose of the present study was to examine whether the rostroventral portion of the medulla oblongata (RVM) exerts descending modulation on the cardiosomatic motor reflex (CMR) in rats. Capsaicin (1 µg/ml, 0.2 ml) was injected into the pericardial sac as an algesic substance to induce the CMR, which was monitored via electromyogram (EMG) responses of dorsal spinotrapezius muscle to the noxious cardiac stimulus. Descending modulation of the CMR was observed by electrical or chemical stimulation of RVM. Specifically, electrical stimulation of RVM produced facilitatory, inhibitory or biphasic effects on the CMR evoked by noxious cardiac stimulation, depending on stimulation intensity. In addition, glutamate receptor activation in RVM replicated the effects of electrical stimulation. Lidocaine interruption of the ventrolateral funiculus/ventral funiculus (VLF/VF) or transection of the dorsolateral funiculus (DLF) revealed that the descending facilitatory and inhibitory influences from RVM were conveyed via the VLF/VF and DLF, respectively. Furthermore, intrathecal administration of naloxone or yohimbine partly reversed the inhibitory effect of RVM electrical stimulation, suggesting that opioid and noradrenergic systems are involved in descending RVM modulation of the CMR.

Entacapone promotes cAMP-dependent colonic Cl(-) secretion in rats.

BACKGROUND: Entacapone is a promising drug used widely for the treatment of Parkinson's disease (PD) as a catechol-O-methyl transferase (COMT) inhibitor. However, entacapone has gastrointestinal side effects. The aim of this study was to investigate the effects of entacapone on the epithelial ion transport in rat distal colon, and explore the underlying mechanism. METHODS: The study was performed on freshly isolated colonic mucosa-only, submucosa-only and mucosa-submucosa preparations in rat. The short circuit current (I(SC) ) was measured to determine electrogenic ion transport, and a scanning ion-selective electrode technique (SIET) was used to directly measure Cl(-) flux across the epithelium. The content of intracellular cAMP was measured with radioimmunoassay (RIA). KEY RESULTS: Entacapone increased mucosal I(SC) in the rat distal colon. I(SC) was inhibited significantly by apical addition of diphenylamine-2,2'-dicarboxylic acid (DPC), a blocker of the Cl(-) channel, basolateral application of bumetanide, an inhibitor of Na(+) -K(+) -2Cl(-) co-transporter (NKCC), removal of Cl(-) from the bathing solution, and pretreatment with MDL 12330A, an inhibitor of adenylate cyclase. Inhibiting endogenous prostaglandin (PG) synthesis with indomethacin, and eliminating submucosal enteric neural activity with tetrodotoxin (TTX)-inhibited entacapone-evoked I(SC) increases. Similar results were also obtained when Cl(-) flux was measured with SIET. Entacapone significantly increased intracellular cAMP content, which was greatly inhibited by either indomethacin or TTX in the tissues containing submucosal plexus, and by only indomethacin in the mucosa-only preparations. CONCLUSIONS & INFERENCES: Entacapone stimulates cAMP-dependent Cl(-) secretion in the rat colon, and this process is regulated by endogenous PG and the submucosal enteric nervous system.