Acoustically Driven Magnon-Phonon Coupling in a Layered Antiferromagnet.

Harnessing the causal relationships between mechanical and magnetic properties of Van der Waals materials presents a wealth of untapped opportunity for scientific and technological advancement, from precision sensing to novel memories. This can, however, only be exploited if the means exist to efficiently interface with the magnetoelastic interaction. Here, we demonstrate acoustically driven spin-wave resonance in a crystalline antiferromagnet, chromium trichloride, via surface acoustic wave irradiation. The resulting magnon-phonon coupling is found to depend strongly on sample temperature and external magnetic field orientation, and displays a high sensitivity to extremely weak magnetic anisotropy fields in the few mT range. Our work demonstrates a natural pairing between power-efficient strain-wave technology and the excellent mechanical properties of Van der Waals materials, representing a foothold toward widespread future adoption of dynamic magnetoacoustics.

Gate-Defined Josephson Weak-Links in Monolayer WTe2.

Systems combining superconductors with topological insulators offer a platform for the study of Majorana bound states and a possible route to realize fault tolerant topological quantum computation. Among the systems being considered in this field, monolayers of tungsten ditelluride (WTe2 ) have a rare combination of properties. Notably, it has been demonstrated to be a quantum spin Hall insulator (QSHI) and can easily be gated into a superconducting state. Measurements on gate-defined Josephson weak-link devices fabricated using monolayer WTe2 are reported. It is found that consideration of the 2D superconducting leads are critical in the interpretation of magnetic interference in the resulting junctions. The reported fabrication procedures suggest a facile way to produce further devices from this technically challenging material and the results mark the first step toward realizing versatile all-in-one topological Josephson weak-links using monolayer WTe2 .

Probing hole spin transport of disorder quantum dots via Pauli spin-blockade in standard silicon transistors.

Single hole transport and spin detection is achievable in standard p-type silicon transistors owing to the strong orbital quantization of disorder based quantum dots. Through the use of the well acting as a pseudo-gate, we discover the formation of a double-quantum dot system exhibiting Pauli spin-blockade and investigate the magnetic field dependence of the leakage current. This enables attributes that are key to hole spin state control to be determined, where we calculate a tunnel couplingtcof 57µeV and a short spin-orbit lengthlSOof 250 nm. The demonstrated strong spin-orbit interaction at the interface when using disorder based quantum dots supports electric-field mediated control. These results provide further motivation that a readily scalable platform such as industry standard silicon technology can be used to investigate interactions which are useful for quantum information processing.

Fully in situ Nb/InAs-nanowire Josephson junctions by selective-area growth and shadow evaporation.

Josephson junctions based on InAs semiconducting nanowires and Nb superconducting electrodes are fabricated in situ by a special shadow evaporation scheme for the superconductor electrode. Compared to other metallic superconductors such as Al, Nb has the advantage of a larger superconducting gap which allows operation at higher temperatures and magnetic fields. Our junctions are fabricated by shadow evaporation of Nb on pairs of InAs nanowires grown selectively on two adjacent tilted Si (111) facets and crossing each other at a small distance. The upper wire relative to the deposition source acts as a shadow mask determining the gap of the superconducting electrodes on the lower nanowire. Electron microscopy measurements show that the fully in situ fabrication method gives a clean InAs/Nb interface. A clear Josephson supercurrent is observed in the current-voltage characteristics, which can be controlled by a bottom gate. The large excess current indicates a high junction transparency. Under microwave radiation, pronounced integer Shapiro steps are observed suggesting a sinusoidal current-phase relation. Owing to the large critical field of Nb, the Josephson supercurrent can be maintained to magnetic fields exceeding 1 T. Our results show that in situ prepared Nb/InAs nanowire contacts are very interesting candidates for superconducting quantum circuits requiring large magnetic fields.

Radiation effects on wild medaka around Fukushima Dai-ichi Nuclear Power Plant assessed by micronucleus assay.

Since the Fukushima Dai-ichi Nuclear Power Plant (F1-NPP) accident in 2011, radiation effects on wildlife in the contaminated areas have been a major concern. The outskirts of the F1-NPP are mainly rural areas, where many rice fields, streams and reservoirs are located. We searched for wild medaka (small aquarium fish) around the F1-NPP and found two wild medaka habitats (S1 and S2). S1 is a stream located 4 km from the F1-NPP, where the ambient dose equivalent rate was 0.4-0.9 µSv/h (2013-14), and S2 is a reservoir located 7.5 km from the F1-NPP, where the ambient dose equivalent rate was 9.8-22 µSv/h (2013-14 and 2017-18). Dosimeters were placed for one day at the locations where the medaka were captured, and the absorbed dose rates were estimated. Radiation effects on wild medaka were examined using micronucleus assay between 2013 and 2018. No significant difference in frequency of micronucleated gill cells was observed among the wild medaka from S1, S2 and our cultivated medaka that were used as a control.

Gate Tunable Hole Charge Qubit Formed in a Ge/Si Nanowire Double Quantum Dot Coupled to Microwave Photons.

A controllable and coherent light-matter interface is an essential element for a scalable quantum information processor. Strong coupling to an on-chip cavity has been accomplished in various electron quantum dot systems, but rarely explored in the hole systems. Here we demonstrate a hybrid architecture comprising a microwave transmission line resonator controllably coupled to a hole charge qubit formed in a Ge/Si core/shell nanowire (NW), which is a natural one-dimensional hole gas with a strong spin-orbit interaction (SOI) and lack of nuclear spin scattering, potentially enabling fast spin manipulation by electric manners and long coherence times. The charge qubit is established in a double quantum dot defined by local electrical gates. Qubit transition energy can be independently tuned by the electrochemical potential difference and the tunnel coupling between the adjacent dots, opening transverse (σ x) and longitudinal (σ z) degrees of freedom for qubit operation and interaction. As the qubit energy is swept across the photon level, the coupling with resonator is thus switched on and off, as detected by resonator transmission spectroscopy. The observed resonance dynamics is replicated by a complete quantum numerical simulation considering an efficient charge dipole-photon coupling with a strength up to 2π × 55 MHz, yielding an estimation of the spin-resonator coupling rate through SOI to be about 10 MHz. The results inspire the future researches on the coherent hole-photon interaction in Ge/Si nanowires.

Helical Hole State in Multiple Conduction Modes in Ge/Si Core/Shell Nanowire.

Helical states, a prerequisite for the engineering of Majorana zero modes in solid-state systems, have recently been reported in the conduction band of III-V nanowires (NWs) subject to strong Rashba spin-orbit interaction. We report the observation of re-entrant conductance features consistent with the presence of helical hole states in multiple conduction modes of a Ge/Si core/shell NW. The Ge/Si system has several potential advantages over electron systems such as longer spin coherence time due to weaker coupling to nuclear spins and the possibility of isotope-purified materials for nuclear spin-free devices. We derive the Landé g factor of 3.6 from magneto-transport measurements, comparable to theoretical predictions and significantly larger when compared with that in strongly confined quantum dots. The spin-orbit energy is evaluated as ∼2.1 meV, on par with values in III-V NWs, showing good agreement with previous theoretical predictions and weak antilocalization measurements.

Surface-plasmon-induced ultra-broadband light absorber operating in the visible to infrared range.

We propose a novel broadband absorber that shows a strong absorption band much broader than that shown in previous work. In our proposed absorber, randomly arranged metal nanobumps are introduced in the incident-side metal layer of a metal/insulator / metal structure. The random structure converts broadband light into surface plasmons without any angular or polarization dependence. Using silver as the metal layer, we obtained an ultrawide region in which the absorption was higher than 50% in the wavelength region from 0.4 to 3.2 µm, which corresponds to a three-octave bandwidth.

Surface exciton polaritons supported by a J-aggregate-dye/air interface at room temperature.

Surface exciton polaritons (SEPs) are very important for the realization of novel sensors and next-generation optical devices. Here we propose for the first time, to the best of our knowledge, a Kretschmann-Raether device that is able to induce SEPs propagating along the interface between a J-aggregate cyanine dye and air at room temperature. This configuration has the advantages of being straightforward to realize and easy to study because the Kretschmann-Raether approach is the most simple and fundamental from the theoretical point of view. Here a J-aggregate cyanine dye produces strong binding energy due to Frenkel excitons, and this enables the observation of SEPs easily at room temperature. One of the advantages of the use of the J-aggregate cyanine dye is the simple device preparation. This is because the J-aggregate cyanine dye can be easily deposited on any arbitrary substrates with a spincoating or dip-coating technique from its aqueous solution in ambient condition. We observed SEPs at room temperature, and the deepest resonant peak was obtained for a 94 nm thick 5,6-dichloro-2-[[5,6-dichloro-1-ethyl-3-(4-sulfobutyl)-benzimidazol-2-ylidene]-propenyl]-1-ethyl-3-(4-sulfobutyl)-benzimidazolium hydroxide film at 532 nm wavelength. Our results may pave the way for the realization of novel SEP biosensors in a simple and straightforward way at room temperature.

Gapless Andreev bound states in the quantum spin Hall insulator HgTe.

In recent years, Majorana physics has attracted considerable attention because of exotic new phenomena and its prospects for fault-tolerant topological quantum computation. To this end, one needs to engineer the interplay between superconductivity and electronic properties in a topological insulator, but experimental work remains scarce and ambiguous. Here, we report experimental evidence for topological superconductivity induced in a HgTe quantum well, a 2D topological insulator that exhibits the quantum spin Hall (QSH) effect. The a.c. Josephson effect demonstrates that the supercurrent has a 4π periodicity in the superconducting phase difference, as indicated by a doubling of the voltage step for multiple Shapiro steps. In addition, this response like that of a superconducting quantum interference device to a perpendicular magnetic field shows that the 4π-periodic supercurrent originates from states located on the edges of the junction. Both features appear strongest towards the QSH regime, and thus provide evidence for induced topological superconductivity in the QSH edge states.

Scanning gate imaging of two coupled quantum dots in single-walled carbon nanotubes.

Two coupled single wall carbon nanotube quantum dots in a multiple quantum dot system were characterized by using a low temperature scanning gate microscopy (SGM) technique, at a temperature of 170 mK. The locations of single wall carbon nanotube quantum dots were identified by taking the conductance images of a single wall carbon nanotube contacted by two metallic electrodes. The single electron transport through single wall carbon nanotube multiple quantum dots has been observed by varying either the position or voltage bias of a conductive atomic force microscopy tip. Clear hexagonal patterns were observed in the region of the conductance images where only two sets of overlapping conductance rings are visible. The values of coupling capacitance over the total capacitance of the two dots, C(m)/C(1(2)) have been extracted to be 0.21 ∼ 0.27 and 0.23 ∼ 0.28, respectively. In addition, the interdot coupling (conductance peak splitting) has also been confirmed in both conductance image measurement and current-voltage curves. The results show that a SGM technique enables spectroscopic investigation of coupled quantum dots even in the presence of unexpected multiple quantum dots.

GR-FET application for high-frequency detection device.

A small forbidden gap matched to low-energy photons (meV) and a quasi-Dirac electron system are both definitive characteristics of bilayer graphene (GR) that has gained it considerable interest in realizing a broadly tunable sensor for application in the microwave region around gigahertz (GHz) and terahertz (THz) regimes. In this work, a systematic study is presented which explores the GHz/THz detection limit of both bilayer and single-layer graphene field-effect transistor (GR-FET) devices. Several major improvements to the wiring setup, insulation architecture, graphite source, and bolometric heating of the GR-FET sensor were made in order to extend microwave photoresponse past previous reports of 40 GHz and to further improve THz detection.

In vitro selection of peptide aptamers with affinity to single-wall carbon nanotubes using a ribosome display.

A ribosome display from a diverse random library was applied for selecting peptide aptamers with high binding affinity to single-wall carbon nanotubes (SWCNTs). The selected peptide aptamer bound to and solubilized SWCNTs more strongly than did the peptide aptamer selected by a phage display method reported previously, and more strongly than other commonly used organic surfactants. The fluorescence spectrum of this aptamer showed a red shift upon interaction with SWCNTs but circular dichroism spectroscopy did not show any significant difference between the presence or absence of SWCNT binding.

Supercurrent through InAs nanowires with highly transparent superconducting contacts.

One-dimensional superconducting transistors have been fabricated with individual InAs nanowires (NWs) using radio-frequency sputter cleaning followed by in situ metal deposition. Because of the highly transparent contacts formed in between the InAs NWs and the metals, supercurrent, multiple Andreev reflections and Shapiro steps under microwave radiation have been observed. Near pinch-off gate regions, Fabry-Perot interference and a normal conductance quantization with resonant features have been observed, which were found to be correlated with a supercurrent flow.

Evaluating the performance of quantum point contacts as nanoscale terahertz sensors.

Quantum point contacts (QPCs) are nanoscale constrictions that are realized in a high-mobility two-dimensional electron gas by applying negative bias to split Schottky gates on top of a semiconductor. Here, we explore the suitability of these nanodevices to THz detection, by making use of their ability to rectify THz signals via the strong nonlinearities that exist in their conductance. In addition to demonstrating the configuration of these devices that provides optimal THz sensitivity, we also determine their noise equivalent power and responsivity. Our studies suggest that, with further optimization, QPCs can provide a viable approach to broadband THz sensing in the range above 1 THz.

Time-dependent inhibitory effects of (1R,9S,12S,13R,14S,17R,18E,21S,23S,24R,25S,27R)-1,14-dihydroxy-12-(E)-2-[(1R,3R,4R)-4-hydroxy-3-methoxycyclohexyl]-1-methylvinyl-23,25-dimethoxy-13,19,21,27-tetramethyl-17-(2-oxopropyl)-11,28-dioxa-4-azatricyclo[22.3.1.0(4.9)]octacos-18-ene-2,3,10,16-tetrone (FK1706), a novel nonimmunosuppressive immunophilin ligand, on CYP3A4/5 activity in humans in vivo and in vitro.

We investigated the inhibitory effects of (1R,9S,12S,13R,14S,17R,18E,21S,23S,24R,25S,27R)-1, 14-dihydroxy-12-(E)-2-[(1R,3R,4R)-4-hydroxy-3-methoxycyclohexyl]-1-methylvinyl-23,25-dimethoxy-13,19,21,27-tetramethyl-17-(2-oxopropyl)-11,28-dioxa-4-azatricyclo [22.3.1.0(4.9)]octacos-18-ene-2,3,10,16-tetrone (FK1706), a novel nonimmunosuppressive immunophilin ligand, on CYP3A4/5 in in vitro and in vivo settings. First, the inhibitory effects of FK1706 (preincubation dependence, inactivation rate estimation, and reversibility) were tested using human liver microsomes. Second, the effect of repeated oral doses of FK1706 (60 mg q.d. for 14 days) on the pharmacokinetics of midazolam (single oral 2-mg dose) was tested in healthy volunteers. Finally, pharmacokinetic modeling and simulation were performed. In vitro experiments showed that FK1706 inhibited CYP3A4/5 in a time-dependent and irreversible manner. The in vitro maximum inactivation rate constant (k(inact)) and concentration of inhibitor that gave half-maximal k(inact) (K(I)) were estimated to be 10.1 h(-1) and 2050 ng/ml, respectively. In the clinical study, FK1706 produced a 2-fold increase in the area under the time-concentration curve (AUC) of midazolam. A pharmacokinetic model developed for this study, which described the time course of concentrations of both FK1706 and midazolam and incorporated CYP3A4/5 inactivation in the liver and intestine, successfully predicted the change in the pharmacokinetics of midazolam using in vitro k(inact) and K(I) values (1.66- to 2.81-fold increases in AUC predicted) and estimated the in vivo inactivation rate to be 0.00404 to 0.0318 h(-1) x ml/ng. In conclusion, FK1706 weakly or moderately inhibited the activity of CYP3A4/5 in vitro and vivo at the tested dose. The model developed here would be helpful in predicting drug-drug interactions and in the design of dose regimens that avoid drug-drug interactions.

Fabrication of quantum-dot devices in graphene.

We describe our recent experimental results on the fabrication of quantum-dot devices in a graphene-based two-dimensional system. Graphene samples were prepared by micromechanical cleavage of graphite crystals on a SiO2/Si substrate. We performed micro-Raman spectroscopy measurements to determine the number of layers of graphene flakes during the device fabrication process. By applying a nanofabrication process to the identified graphene flakes, we prepared a double-quantum-dot device structure comprising two lateral quantum dots coupled in series. Measurements of low-temperature electrical transport show the device to be a series-coupled double-dot system with varied interdot tunnel coupling, the strength of which changes continuously and non-monotonically as a function of gate voltage.

Coupled quantum dots in a graphene-based two-dimensional semimetal.

We present an experimental demonstration of a graphene-based double quantum dot system, which exhibits single-electron transport of two lateral quantum dots coupled in series. Low-temperature transport measurements revealed honeycomb charge stability diagrams with a varied (from weak to strong) interdot tunnel-coupling regime, and we have extracted the relevant parameters associated with the double quantum dot system. These results are important for the realization of integrated quantum circuits in graphene-based electronics.

Direct observation of the deformation and the band gap change from an individual single-walled carbon nanotube under uniaxial strain.

We have fabricated a new device for applying uniaxial strain to an individual suspended SWNT, and the form and the photoluminescence (PL) of an individual suspended SWNT under stretching are investigated. The processes of deformation and break of a SWNT under stretching are directly observed by scanning electron microscopy (SEM). From the PL measurements, the emission energy shifts due to the band gap change are measured under the elastic strain. The behaviors of the emission shifts can be related to the deformation processes observed by SEM. Moreover, the emission intensity reduction due to the elastic strain of a SWNT is also observed just before breaking.

Anxiolytic activity of a novel potent serotonin 5-HT2C receptor antagonist FR260010: a comparison with diazepam and buspirone.

Hyperfunction of brain 5-hydroxytryptamine(2C) (5-HT(2C)) receptor is suggested to be involved in anxiety as evidenced by the fact that a putative 5-HT(2C) receptor agonist 1-(m-chlorophenyl)-piperazine (m-CPP) causes anxiety in humans. We have recently identified FR260010 (N-[3-(4-methyl-1H-imidazol-1-yl)phenyl]-5,6-dihydrobenzo[h]quinazolin-4-amine dimethanesulfonate) as novel 5-HT(2C) receptor antagonist from diaryl amine derivatives, and here characterized in vitro and in vivo profiles of the compound. FR260010 showed high affinity for human 5-HT(2C) receptor (K(i): 1.10 nM) and high selectivity over 5-hydroxytryptamine(2A) (5-HT(2A)) receptor (K(i): 386 nM) and many other transmitter receptors. FR260010 showed antagonist activity at human 5-HT(2C) receptor in an intracellular calcium assay and showed no detectable intrinsic activity. The compound dose-dependently inhibited the hypolocomotion (ID(50): 1.89 mg/kg, p.o.) and hypophagia (ID(50): 2.84 mg/kg, p.o.) in rats induced by m-CPP, putative indices of brain 5-HT(2C) receptor antagonist activity. We then compared the effects of FR260010 with those of two other anxiolytics belonging to different classes, diazepam and buspirone, in anxiety models in rats and mice and adverse effect tests in mice. FR260010 (0.1-3.2 mg/kg, p.o.) and diazepam (1-10 mg/kg, p.o.) decreased behavioral indices of anxiety in all models, whereas buspirone (0.32-10 mg/kg, p.o.) did not significantly affect them in any models. In adverse effect tests, FR260010 and buspirone showed modest effects, whereas diazepam showed significant effects in all tests. These results suggest that FR260010 is a novel, potent, orally active and brain penetrable antagonist of 5-HT(2C) receptor, and may have therapeutic potential for treatment of anxiety, with more desirable profiles than benzodiazepines or 5-hydroxytryptamine(1A) (5-HT(1A)) receptor agonists.