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Spin-orbit coupling (SOC) is pivotal for various fundamental spin-dependent phenomena in solids and their technological applications. In semiconductors, these phenomena have been so far studied in relatively weak electron-electron interaction regimes, where the single electron picture holds. However, SOC can profoundly compete against Coulomb interaction, which could lead to the emergence of unconventional electronic phases. Since SOC depends on the electric field in the crystal including contributions of itinerant electrons, electron-electron interactions can modify this coupling. Here we demonstrate the emergence of SOC effect in a high-mobility two-dimensional electron system in a simple band structure MgZnO/ZnO semiconductor. This electron system features also strong electron-electron interaction effects. By changing the carrier density with Mg-content, we tune the SOC strength and achieve its interplay with electron-electron interaction. These systems pave a way to emergent spintronic phenomena in strong electron correlation regime and to the formation of novel quasiparticles with the electron spin strongly coupled to the density., Main Text (4 Figures), Supplementary notes (4 Figures)

The topological nature of the quantum anomalous Hall effect (QAHE) causes a dissipationless chiral edge current at the sample boundary1,2. Of fundamental interest is whether the chirality of the band structure manifests itself in charge transport properties. Here we report the observation of large non-reciprocal charge transport3 in a magnetic topological insulator, Cr-doped (Bi,Sb)2Te3. When the surface massive Dirac band is slightly carrier doped by a gate voltage, the edge state starts to dissipate and exhibits a current-direction-dependent resistance with a directional difference as large as 26%. The polarity of this diode effect depends on the magnetization direction as well as on the carrier type, electrons or holes. The correlation between the non-reciprocal resistance and the Hall resistance indicates that the non-reciprocity originates from the interplay between the chiral edge state and the Dirac surface state.

We have investigated the nonreciprocal electrical transport, that is a nonlinear resistance effect depending on the current direction, in multiferroic Rashba semiconductor (Ge,Mn)Te. Due to coexistence of ferromagnetic and ferroelectric orders, (Ge,Mn)Te provides a unique platform for exploring the nonreciprocal electrical transport in a bulk form. (Ge,Mn)Te thin films shows a large nonreciprocal resistance compared to GeTe, the nonmagnetic counterpart with the same crystal structure. The magnetic-field-angle dependence of the nonreciprocal resistance is maximized when magnetic field is orthogonal to both current and electric polarization, in accord with the symmetry argument. From the analysis of temperature and magnetic field dependence, we deduce that inelastic scatterings of electrons mediated by magnons dominantly contribute to the observed nonreciprocal response. Furthermore, the nonreciprocal resistance is significantly enhanced by lowering hole density. The Fermi level dependence is attributed to the deformation of the Rashba band in which the spin-momentum locked single Fermi surface appears by exchange field from the in-plane magnetization. The present study provides a key insight to the mechanisms of novel transport phenomena caused by the interplay of ferroelectric and ferromagnetic orders in a semiconductor.

We report experimental signatures of topological transitions among the Weyl semimetal states of pyrochlore Pr2Ir2O7, where the Kondo coupling between the Ir topological electrons and the spin-ice like orders of Pr moments plays a decisive role. The magnetic-field dependence of resistivity and the Hall conductivity exhibits a plateau and a sharp jump associated with a magnetic-field hysteresis, similar to a liquid-gas-like transition in dipolar spin ice system. Furthermore, the Kondo coupling is controlled by the hydrostatic pressure, revealing that the field-induced displacement of Weyl points in the momentum space strongly depends on the respective electronic state as well as on the Kondo coupling strength. These observations pave a route toward the engineering of band topology in hybrid quantum materials with relativistic conduction electrons and localized magnetic moments.

Electrons in conventional metals become less mobile under the influence of electron correlation. Contrary to this empirical knowledge, we report here that electrons with the highest mobility ever found in known bulk oxide semiconductors emerge in the strong-correlation regime of the Dirac semimetal of perovskite CaIrO3. The transport measurements reveal that the high mobility exceeding 60,000 cm2V−1s−1 originates from the proximity of the Fermi energy to the Dirac node (ΔE, Electron correlation normally makes electrons less mobile, but it is still not clear when correlation becomes very strong in Dirac semimetals. Here, Fujioka et al. report a very high electron mobility exceeding 60,000 cm2V−1s−1 in correlated Dirac semimetal of perovskite CaIrO3, due to the enhanced electron correlation nearby the Mott transition.

Recently, emulation of topological states based on electrical circuits draws much attention in view of future quantum computing. We have demonstrated a topological phase transition by switching a step-variable-resettable SOI-MEMS capacitor for the first time. The circuit shows significantly different responses for the topological and trivial phases of the Su-Schrieffer-Heeger (SSH) model by switching the capacitance. We have fabricated a mechanical latching structure integrated with comb capacitors to realize such a MEMS variable capacitance. Our device will open a new field called “topological MEMS (TopoMEMS) circuit”.

Epitaxial thin films of ${({\mathrm{Sn}}_{x}{\mathrm{Pb}}_{1\ensuremath{-}x})}_{1\ensuremath{-}y}{\mathrm{In}}_{y}\mathrm{Te}$ were successfully grown by molecular-beam epitaxy in a broad range of compositions ($0\ensuremath{\le}x\ensuremath{\le}1$, $0\ensuremath{\le}y\ensuremath{\le}0.23$). We investigated electronic phases of the films by the measurements of electrical transport and optical second-harmonic generation. In this system, one can control the inversion of the band gap, the electric polarization that breaks the inversion symmetry, and the Fermi-level position by tuning the Pb/Sn ratio and In composition. A plethora of topological electronic phases is expected to emerge, such as the topological crystalline insulator, the topological semimetal, and superconductivity. For the samples with large Sn compositions $(xg0.5)$, hole density increases with In composition $(y)$, which results in the appearance of superconductivity. On the other hand, for those with small Sn compositions $(xl0.5)$, an increase in In composition reduces the hole density and changes the carrier type from $p$ type to $n$ type. In a narrow region centered at $(x,y)=(0.16,0.07)$ where the $n$-type carriers are slightly doped, charge transport with high mobility exceeding $5000\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\text{--}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\text{--}1}$ shows up, representing the possible semimetal states. In those samples, the optical second-harmonic generation measurement showing the breaking of inversion symmetry along the out-of-plane [111] direction, which is a necessary condition for the emergence of the polar semimetal state. The thin films of ${({\mathrm{Sn}}_{x}{\mathrm{Pb}}_{1\ensuremath{-}x})}_{1\ensuremath{-}y}{\mathrm{In}}_{y}\mathrm{Te}$ material systems with a variety of electronic states would become a promising materials platform for the exploration of novel quantum phenomena.

We report a systematic study on the growth conditions of ${\mathrm{Sn}}_{1\text{\ensuremath{-}}x}{\mathrm{In}}_{x}\mathrm{Te}$ thin films by molecular beam epitaxy for maximization of superconducting transition temperature ${T}_{\mathrm{c}}$. Careful tuning of the flux ratios of Sn, In, and Te enables us to find an optimum condition for substituting rich In content $(x=0.66)$ into the Sn site in a single phase of ${\mathrm{Sn}}_{1\text{\ensuremath{-}}x}{\mathrm{In}}_{x}\mathrm{Te}$ beyond the bulk solubility limit at ambient pressure $(x=0.5)$. ${T}_{\mathrm{c}}$ shows a dome-shaped dependence on In content $x$ with the highest ${T}_{\mathrm{c}}=4.20\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at $x=0.55$, being consistent to that reported for bulk crystals. The well-regulated ${\mathrm{Sn}}_{1\text{\ensuremath{-}}x}{\mathrm{In}}_{x}\mathrm{Te}$ films can be a useful platform to study possible topological superconductivity by integrating them into the state-of-the-art junctions and/or proximity-coupled devices.

Superconductivity in the doped topological crystalline insulator ${\mathrm{Sn}}_{1\ensuremath{-}x}{\mathrm{In}}_{x}\mathrm{Te}$ is studied by first-principles calculation based on superconducting density functional theory (SCDFT) and tunneling spectroscopy. By considering the spin-orbit coupling and frequency dependence of the screened Coulomb interaction in SCDFT, we succeed in reproducing the critical temperature of ${\mathrm{Sn}}_{1\ensuremath{-}x}{\mathrm{In}}_{x}\mathrm{Te}$ quantitatively, in which the spin-orbit coupling is found to play an essential role. The leading gap function is a conventional $s$ wave with moderate anisotropy in $\mathbit{k}$ space, and we find that the subdominant odd-parity instability is significantly weaker than the $s$-wave instability. We perform tunneling spectroscopy measurement and confirm that the spectrum is consistent with the calculated gap function.

We have studied the fundamental properties of weak-link ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}/{\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ Josephson junctions fabricated by making a narrow constriction on superconducting ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ films through laser micropatterning. The junctions show a typical overdamped behavior with much higher critical current density compared with those previously reported for bulk ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}/s$-wave-superconductor junctions. Observed magnetic-field and temperature dependencies of the Josephson critical current suggest that the chiral $p$ wave is unlikely for the superconducting symmetry, encouraging further theoretical calculations of the ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}/{\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$-type junctions.

We report a current scaling study of a quantum phase transition between a quantum anomalous Hall insulator and a trivial insulator on the surface of a heterostructure film of magnetic topological insulators. The transition was observed by tilting the magnetization while measuring the Hall conductivity $\sigma_{xy}$. The transition curves of $\sigma_{xy}$ taken under various excitation currents cross each other at a single point, exemplifying a quantum critical behavior of the transition. The slopes of the transition curves follow a power law dependence of the excitation current, giving a scaling exponent. Combining with the result of the previous temperature scaling study, critical exponents $\nu$ for the localization length and $p$ for the coherence length are separately evaluated as $\nu$ = 2.8 $\pm$ 0.3 and $p$ = 3.3 $\pm$ 0.3., Comment: 6 pages, 4 figures

Aims Neurotropin® (NTP), an analgesic for chronic pain, has antihyperalgesic effects in specific alternation of rhythm in temperature (SART)-stressed rats. Previous studies have shown that SART stress induces hyperalgesia, as well as post-translational modification of proteins (including substrates for calpain, a calcium-dependent cysteine protease) in the mesencephalon of rats. To better understand the mechanism of action of NTP, we investigated whether SART stress activates calpain in the mesencephalon of rats and whether NTP inhibits this activation. Main methods Wistar rats were exposed to SART stress for 5 days. NTP (200 NU/kg/day) was administered intraperitoneally every day from the onset of SART stress. The mechanical pain threshold was measured using the Randall-Selitto test on the 6th day. Thereafter, the rat mesencephalon was immediately collected and calpain activity was examined using western blot analysis with a calpain cleavage site-specific antibody. Key findings SART stress induced hyperalgesia and increased the calpain activity in the mesencephalon of rats. In contrast, NTP treatment attenuated the hyperalgesia and prevented the increase in calpain activity in the mesencephalon of SART-stressed rats. Interestingly, a negative correlation was identified between calpain activity and mechanical pain threshold in SART-stressed rats treated with or without NTP. Furthermore, NTP inhibited calpain activity on mammalian uncoordinated-18 in rat mesencephalon homogenate and Ac-LLY-AFC as substrates in an in vitro cell-free system. Significance Our data demonstrate that NTP treatment prevents SART stress-induced calpain activation in the mesencephalon of rats and suggests that NTP-mediated antihyperalgesia is associated with an inhibition of calpain activity in the mesencephalon.

The impact of electron correlation on the Dirac semimetal state is investigated for perovskite ${\text{CaIrO}}_{3}$ in terms of the magnetotransport properties under varying pressures. The reduction of electron correlation with a pressure of 1 GPa enhances the Fermi velocity as much as 40%, but it reduces the mobility by an order of magnitude by detuning the Dirac node from the Fermi energy. Moreover, the giant magnetoresistance at the quantum limit due to the one-dimensional confinement of Dirac electrons is critically suppressed under pressure. These results indicate that the electron correlation is a crucial knob for controlling the transport of a correlated Dirac semimetal.

Quantum-relativistic materials often host electronic phenomena with exotic spatial distributions. In particular, quantum anomalous Hall (QAH) insulators feature topological boundary currents whose chirality is determined by the magnetization orientation. However, understanding the microscopic nature of edge vs. bulk currents has remained a challenge due to the emergence of multidomain states at the phase transitions. Here we use microwave impedance microscopy (MIM) to directly image chiral edge currents and phase transitions in a magnetic topological insulator. Our images reveal a dramatic change in the edge state structure and an unexpected microwave response at the topological phase transition between the Chern number [Formula: see text] and [Formula: see text] states, consistent with the emergence of an insulating [Formula: see text] state. The magnetic transition width is independent of film thickness, but the transition pattern is distinct in differently initiated field sweeps. This behavior suggests that the [Formula: see text] state has 2 surface states with Hall conductivities of [Formula: see text] but with opposite signs.

We report a proximity-driven large anomalous Hall effect in all-telluride heterostructures consisting of ferromagnetic insulator Cr2Ge2Te6 and topological insulator (Bi,Sb)2Te3. Despite small magnetization in the (Bi,Sb)2Te3 layer, the anomalous Hall conductivity reaches a large value of 0.2e2/h in accord with a ferromagnetic response of the Cr2Ge2Te6. The results show that the exchange coupling between the surface state of the topological insulator and the proximitized Cr2Ge2Te6 layer is effective and strong enough to open the sizable exchange gap in the surface state., 33 pages, 12 figures including supplemental material, accepted by PRL

We report large enhancement of upper critical field ${H}_{\mathrm{c}2}$ observed in superconducting ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ thin films. Through dimensional crossover approaching two dimensions, ${H}_{\mathrm{c}2}$ except the in-plane field direction is dramatically enhanced compared to bulks, following a definite relation distinct from bulk one between ${H}_{\mathrm{c}2}$ and the transition temperature. The anomalous enhancement of ${H}_{\mathrm{c}2}$ is highly suggestive of important changes of the superconducting properties, possibly accompanied with rotation of the triplet $d$ vector. Our findings will become a crucial step to further explore exotic properties by employing ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ thin films.

The accuracy of Hall resistance in the quantum anomalous Hall effect has been studied at zero magnetic field using Crx(Bi,Sb) 2 − x Te3-based magnetic heterostructure films of topological insulators. The measured deviation of the Hall resistance from its theoretical value h / e 2 was less than 2 ppm when the source drain current was 30 nA. This result has verified that the quantization of the Hall resistance is very accurate in the magnetic heterostructure films and in the previously reported uniformly doped films.

We theoretically investigate the dynamical nuclear spin polarization in a quantum point contact (QPC) at finite magnetic field. We find that when the QPC is tuned to be spin selective, at the conductance of e^2/h, a finite bias induces a dipole-like (spatially anti-symmetric) nuclear polarization: at the QPC center the polarization is zero, while, for GaAs parameters, the nuclear spins down (up) are induced on the source (drain) side. We predict that the dipole-like polarization pattern can be distinguished from a uniform polarization due to a qualitatively different response of the QPC conductance to the NMR field., Comment: 17 pages, 8 figures; referees' comments incorporated, some typos corrected, footnotes' format changed

Objective Although the daily urinary sodium excretion (UNaV) is considered to provide the most reliable estimate of the daily sodium intake, it may be affected by salt loss due to sweating in summer. However, the seasonal variation in the daily UNaV associated with a normal lifestyle is unknown. Methods This study was performed in 348 outpatients from the Morioka region during three seasons: summer (summer 1), winter, and the following summer (summer 2). The daily UNaV (g salt/day) was estimated by the second morning urine method three times during each season. Seasonal variation was defined as a significant trend across the three seasons together with a significant difference between winter and both summers. Results In women, the daily UNaV was higher in winter (11.8±3.0 g salt/day) than in summer 1 (11.2±2.9 g salt/day) or summer 2 (11.0±2.9 g salt/day). In contrast, there was no marked seasonal variation in men. An analysis stratified by age (4 quartiles) identified seasonal variation in the older 2 quartiles of women (aged ≥68 years). In these women, the mean seasonal difference in the daily UNaV was 0.9 g of salt/day for both winter vs. summer 1 and winter vs. summer 2, while it was 0.1-0.8 g of salt/day in the other groups. Conclusion Seasonal variation in the daily UNaV only occurred in older female patients and was relatively small. This is evidence for restricting salt intake throughout the year and should reassure patients who are anxious about salt loss due to sweating in summer.

Instability of quantum anomalous Hall (QAH) effect has been studied as function of electric current and temperature in ferromagnetic topological insulator thin films. We find that a characteristic current for the breakdown of the QAH effect is roughly proportional to the Hall-bar width, indicating that Hall electric field is relevant to the breakdown. We also find that electron transport is dominated by variable range hopping (VRH) at low temperatures. Combining the current and temperature dependences of the conductivity in the VRH regime, the localization length of the QAH state is evaluated to be about 5 $\mu$m. The long localization length suggests a marginally insulating nature of the QAH state due to a large number of in-gap states., Comment: 5 pages, 4 figures, accepted for publication in PRL

Gigantic magnetoresistance is shown in a Cr- and V-doped topological insulator multilayer, assuring robust axion insulator., Exploration of novel electromagnetic phenomena is a subject of great interest in topological quantum materials. One of the unprecedented effects to be experimentally verified is the topological magnetoelectric (TME) effect originating from an unusual coupling of electric and magnetic fields in materials. A magnetic heterostructure of topological insulator (TI) hosts such exotic magnetoelectric coupling and can be expected to realize the TME effect as an axion insulator. We designed a magnetic TI with a tricolor structure where a nonmagnetic layer of (Bi, Sb)2Te3 is sandwiched by a soft ferromagnetic Cr-doped (Bi, Sb)2Te3 and a hard ferromagnetic V-doped (Bi, Sb)2Te3. Accompanied by the quantum anomalous Hall (QAH) effect, we observe zero Hall conductivity plateaus, which are a hallmark of the axion insulator state, in a wide range of magnetic fields between the coercive fields of Cr- and V-doped layers. The resistance of the axion insulator state reaches as high as 109 ohms, leading to a gigantic magnetoresistance ratio exceeding 10,000,000% upon the transition from the QAH state. The tricolor structure of the TI may not only be an ideal arena for the topologically distinct phenomena but can also provide magnetoresistive applications for advancing dissipation-less topological electronics.

The quantum anomalous Hall effect (QAHE) is an exotic quantum phenomenon originating from dissipation-less chiral channels at the sample edge. While the QAHE has been observed in magnetically doped topological insulators (TIs), exploiting magnetic proximity effect on the TI surface from adjacent ferromagnet layers may provide an alternative approach to the QAHE by opening an exchange gap with less disorder than that in the doped system. Nevertheless, the engineering of a favorable heterointerface that realizes the QAHE based on the magnetic proximity effect remains to be achieved. Here, we report on the observation of the QAHE in a proximity coupled system of non-magnetic TI and ferromagnetic insulator (FMI). We have designed sandwich heterostructures of (Zn,Cr)Te/(Bi,Sb)2Te3/(Zn,Cr)Te that fulfills two prerequisites for the emergence of the QAHE; the formation of a sizable exchange gap at the TI surface state and the tuning of the Fermi energy into the exchange gap. The efficient proximity coupling in the all-telluride based heterostructure as demonstrated here will enable a realistic design of versatile tailor-made topological materials coupled with ferromagnetism, ferroelectricity, superconductivity, and so on., 18 pages, 4 figures

The axion insulator which may exhibit an exotic quantized magnetoelectric effect is one of the most interesting quantum phases predicted for the three-dimensional topological insulator (TI). The axion insulator state is expected to show up in magnetically doped TIs with magnetizations pointing inwards and outwards from the respective surfaces. Towards the realization of the axion insulator, we here engineered a TI heterostructure in which magnetic ions (Cr) are modulation-doped only in the vicinity of the top and bottom surfaces of the TI ((Bi,Sb)

We report on emergence of two-dimensional conduction and ferromagnetism at the interface of MnTe thin films and InP substrates. The MnTe/InP heterostructures grown by molecular-beam epitaxy show thickness-independent sheet conductivity above a critical thickness of about 20 nm, indicating the formation of a conducting layer at the interface. Furthermore, the ferromagnetic behavior is confirmed by both magnetization and anomalous Hall effect measurements below a critical temperature of 270 K. The critical temperature is also independent of the thickness. By the investigation of the atomic structure with transmission electron microscopy, we observe a structural anomaly near the interface which consists of an antiprism-type Mn network unlike a prism-type Mn network of conventional MnTe. The band structure calculation shows that the antiprism-type MnTe can host metallic conduction and ferromagnetism, which is consistent with the present experimental results. The interface engineering based on the chalcogenide compound will develop a new arena for designing the emergent low dimensional conduction and magnetism.

The helical Dirac fermions on the surface of topological insulators host novel relativistic quantum phenomena in solids. Manipulating spins of topological surface state (TSS) represents an essential step towards exploring the theoretically predicted exotic states related to time reversal symmetry (TRS) breaking via magnetism or magnetic field. Understanding Zeeman effect of TSS and determining its g-factor are pivotal for such manipulations in the latter form of TRS breaking. Here, we report those direct experimental observations in Bi2Se3 and Sb2Te2Se by spectroscopic imaging scanning tunneling microscopy. The Zeeman shifting of zero mode Landau level is identified unambiguously by judiciously excluding the extrinsic influences associated with the non-linearity in the TSS band dispersion and the spatially varying potential. The g-factors of TSS in Bi2Se3 and Sb2Te2Se are determined to be 18 and -6, respectively. This remarkable material dependence opens a new route to control the spins in the TSS., main text: 17 pages, 4 figures; supplementary: 15 pages, 7 figures

We report an electronic magnetization measurement of a quantum point contact (QPC) based on nuclear magnetic resonance (NMR) spectroscopy. We find that NMR signals can be detected by measuring the QPC conductance under in-plane magnetic fields. This makes it possible to measure, from Knight shifts of the NMR spectra, the electronic magnetization of a QPC containing only a few electron spins. The magnetization changes smoothly with the QPC potential barrier height and peaks at the conductance plateau of 0.5 $\times$ $2e^2/h$. The observed features are well captured by a model calculation assuming a smooth potential barrier, supporting a no bound state origin of the 0.7 structure., 5 pages main text + 6 pages supplementary material. Accepted for publication in Phys. Rev. Lett

Aims Although the clinical use of Neurotropin ® as an analgesic for chronic pain has been firmly established, its analgesic mechanism is still unclear. In this study, we investigate the direct effects of Neurotropin using an electrophysiological method. Main methods Blind patch-clamp recordings were made from rat locus coeruleus (LC) and periaqueductal gray (PAG) neurons in brainstem slices of normal rats. The effects of intracerebroventricular (icv) injection of Neurotropin on nociceptive transmission were recorded from spinal substantia gelatinosa (SG) neurons in fifth lumbar spinal nerve-ligated (L5-SNL) rats using an in vivo patch-clamp method. Key findings Neurotropin (0.2–1.0 NU/mL) dose-dependently increased the firing rate in noradrenergic LC neurons of normal rats. Under the voltage-clamp condition, Neurotropin induced an inward current in 90% of LC neurons that was not affected by tetrodotoxin or an injection of GDP-β-S (G protein inhibitor) through recording pipettes. In contrast, Neurotropin had no effects on all PAG neurons tested. Using in vivo patch-clamp recordings, the icv injection of Neurotropin inhibited both frequency and amplitude of pinch-evoked excitatory postsynaptic currents of SG neurons in L5-SNL rats. These results suggest that Neurotropin directly excites the descending noradrenergic LC neurons and inhibits nociceptive transmission in the spinal dorsal horn. Significance This study is the first direct demonstration that Neurotropin activates the noradrenergic descending pain inhibitory systems, and this would reinforce the usefulness of Neurotropin in the treatment of human neuropathic pain.