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Abstract Quasi-phase matching (QPM) is a technique extensively utilized in nonlinear optics for enhancing the efficiency and stability of frequency conversion processes. However, the conventional QPM relies on periodically poled ferroelectric crystals, which are limited in availability. The 3R phase of molybdenum disulfide (3R-MoS2), a transition metal dichalcogenide (TMDc) with the broken inversion symmetry, stands out as a promising candidate for QPM, enabling efficient nonlinear process. Here, we experimentally demonstrate the QPM at nanoscale, utilizing van der Waals stacking of 3R-MoS2 layers with specific orientation to realize second harmonic generation (SHG) enhancement beyond the non QPM limit. We have also demonstrated enhanced spontaneous parametric down-conversion (SPDC) via QPM of 3R-MoS2 homo-structure, enabling more efficient generation of entangled photon pairs. The tunable capacity of 3R-MoS2 van der Waals stacking provides a platform for tuning phase-matching condition. This technique opens interesting possibilities for potential applications in nonlinear process and quantum technology.

Reducing dimensionality can induce profound modifications to the physical properties of a system. In two-dimensional TaS2 and TaSe2, the charge-density wave phase accompanies a Mott transition, thus realizing the strongly correlated insulating state. However, this scenario deviates from TaTe2 due to p–d hybridization, resulting in a substantial contribution of Te 5p at the Fermi level. Here, we show that, differently from the Mott insulating phase of its sister compounds, bilayer TaTe2 hosts a power-law (V-shaped) gap at the Fermi level reminiscent of a Coulomb gap. It suggests the possible role of unscreened long-range Coulomb interactions emerging in lowered dimensions, potentially coupled with a disordered short-range charge-density wave. Our findings reveal the importance of long-range interactions sensitive to interlayer screening, providing another venue for the interplay of complex quantum phenomena in two-dimensional materials.

Abstract Colloidal quantum dots are sub-10 nm semiconductors treated with liquid processes, rendering them attractive candidates for single-electron transistors operating at high temperatures. However, there have been few reports on single-electron transistors using colloidal quantum dots due to the difficulty in fabrication. In this work, we fabricated single-electron transistors using single oleic acid-capped PbS quantum dot coupled to nanogap metal electrodes and measured single-electron tunneling. We observed dot size-dependent carrier transport, orbital-dependent electron charging energy and conductance, electric field modulation of the electron confinement potential, and the Kondo effect, which provide nanoscopic insights into carrier transport through single colloidal quantum dots. Moreover, the large charging energy in small quantum dots enables single-electron transistor operation even at room temperature. These findings, as well as the commercial availability and high stability, make PbS quantum dots promising for the development of quantum information and optoelectronic devices, particularly room-temperature single-electron transistors with excellent optical properties.

Abstract Van der Waals dielectrics are fundamental materials for condensed matter physics and advanced electronic applications. Most dielectrics host isotropic structures in crystalline or amorphous forms, and only a few studies have considered the role of anisotropic crystal symmetry in dielectrics as a delicate way to tune electronic properties of channel materials. Here, we demonstrate a layered anisotropic dielectric, SiP2, with non-symmorphic twofold-rotational C 2 symmetry as a gate medium which can break the original threefold-rotational C 3 symmetry of MoS2 to achieve unexpected linearly-polarized photoluminescence and anisotropic second harmonic generation at SiP2/MoS2 interfaces. In contrast to the isotropic behavior of pristine MoS2, a large conductance anisotropy with an anisotropy index up to 1000 can be achieved and modulated in SiP2-gated MoS2 transistors. Theoretical calculations reveal that the anisotropic moiré potential at such interfaces is responsible for the giant anisotropic conductance and optical response. Our results provide a strategy for generating exotic functionalities at dielectric/semiconductor interfaces via symmetry engineering.

Abstract Semiconducting colloidal quantum dots and their assemblies exhibit superior optical properties owing to the quantum confinement effect. Thus, they are attracting tremendous interest from fundamental research to commercial applications. However, the electrical conducting properties remain detrimental predominantly due to the orientational disorder of quantum dots in the assembly. Here we report high conductivity and the consequent metallic behaviour of semiconducting colloidal quantum dots of lead sulphide. Precise facet orientation control to forming highly-ordered quasi-2-dimensional epitaxially-connected quantum dot superlattices is vital for high conductivity. The intrinsically high mobility over 10 cm2 V−1 s−1 and temperature-independent behaviour proved the high potential of semiconductor quantum dots for electrical conducting properties. Furthermore, the continuously tunable subband filling will enable quantum dot superlattices to be a future platform for emerging physical properties investigations, such as strongly correlated and topological states, as demonstrated in the moiré superlattices of twisted bilayer graphene.

The crossover between the limiting ground states of fermionic systems, the so called BCS-BEC crossover, is of interest to superconductor and ultracold atomic gases communities. The authors study the dynamics of superconducting vortices in the crossover regime via the Hall response in a 2D superconductor LixZrNCl.

Van der Waals heterostructures made of 2D materials offer a rich platform for the study of novel proximity effects. Here, by means of Hall effect measurements, the authors show a proximity-induced ferromagnetic/ferrovalley ground state with spontaneous spin-valley polarization in a V5Se8/NbSe2 heterostructure.

We studied the nonreciprocal transport of layered MoTe_{2}, which undergoes a structural transition from centrosymmetric to the noncentrosymetric polar phase. Careful inspections of the temperature-dependent resistance showed an occurrence of additional phase transition at around T^{*}=50 K inside the noncentrosymmetric polar phase. We found that the nonreciprocal signal emerges below T^{*}, associated with the filling of the hole pocket. The present result suggests that the mechanism of the nonreciprocal transport is significantly distinct from that in simple polar semiconductors but is highly sensitive to the small hole pocket buried in the major carriers in semimetals.

Even-order nonlinear transport is a powerful probe of quantum materials, but such studies in superconductors have been limited to those which break time-reversal symmetry. Here, the authors observe second-order nonlinear transport in time-reversal-symmetric PbTaSe2, where the nonlinearity is enhanced in the superconducting state.

In intercalated transition metal dichalcogenides (I-TMDCs), transition metal intercalation introduces magnetic phases which in some cases induce topological band crossing. However, evidence of the topological properties remains elusive in such materials. Here, we employ angle-resolved photoemission spectroscopy to reveal the band structure of epitaxially grown ferromagnetic Cr_{1/3}NbSe_{2}. Experimental evidence of the Weyl crossing shows Cr_{1/3}NbSe_{2} to be a topological ferromagnet. This Letter highlights I-TMDCs as a platform towards the interplay of magnetic and topological physics in low-dimensional systems.

In this manuscript, the authors grow very thin layers of FeAs in a matrix of InAs. The resulting superlattice displays ferromagnetism, with the Curie temperature varying depending on the layer thickness. These results further illustrate the wide array of intriguing ground states of materials with tetrahedral FeAs bonds

In an effort to optimize the performance of two-dimensional materials for thermoelectric generation, compounds with advantageous intrinsic properties must be identified. Here, the authors report large thermoelectric effect in ultrathin FeSe thin films with high Tc superconductivity.

Orbital-selective superconductivity is crucial for understanding the pairing mechanism for multiband superconductors. Atomic d orbitals with anisotropic spatial extension can directly determine the energy dispersion of subbands with two-dimensional (2D) or three-dimensional (3D) nature in band structure. Theoretically, owing to the coexistence of these 2D and 3D subbands, the orbital-selective superconductivity can exhibit band-dependent dimensionality in multiband superconductors. However, to experimentally confirm this orbital-selective 2D superconductivity remains challenging and elusive. Herein, based on angle-dependent upper critical magnetic field on 2H-NbS_{2} flakes, we observe a cusp peak associated with a 2D superconducting subband from the d_{xy} and d_{x^{2}−y^{2}} orbitals of Nb atoms, and a round peak related to a 3D subband, directly confirming the existence of intrinsic 2D superconductivity in 2H-NbS_{2} thick flake and its orbital-selective superconducting nature. The 2D superconductivity remains robust under large electric current or high pressure. Such observations shed light on the orbital-selective pairing mechanism and resulting band-dependent dimensionality for multiband superconductors.

Superconductor-insulator transitions predominantly occur in highly disordered thin films. Here, Saito et al. report that a quantum metallic state transforms via the quantum Griffiths state to a weakly localized metal at high magnetic fields in a crystalline two-dimensional superconductor.

Abstract Reducing the power consumption necessary for magnetization reversal is one of the most crucial issues facing spintronics devices. Electric field control of the magnetic anisotropy of ferromagnetic thin films is a promising method to solve this problem. However, the electric field is believed to be effective only within several nanometres of the surface in ferromagnetic metals because of its short Thomas-Fermi screening length, which prevents its practical application to devices. Herein, we successfully modulate the magnetic anisotropy of the entire region of the ferromagnetic layers in the elongated mesas of vertical spin field-effect transistors with widths as large as ~500 nm by applying an electric field to the side surface of the metallic GaMnAs-based mesas through an electric double layer. Our results will open up a new pathway for spintronics devices with ultra-low power consumption.

Dynamical behavior of vortices plays central roles in the quantum phenomena of two-dimensional (2D) superconductors. The quantum metallic state, for example, showing an anomalous temperature-independent resistive state down to low temperatures, has been a topical subject in recently developed 2D crystalline superconductors, whose microscopic origin is still under debate. Here, we unveil an interesting aspect of the vortex dynamics in a noncentrosymmetric 2D crystalline superconductor of gated MoS_{2} through the nonreciprocal transport measurement. The second-harmonic resistance R^{2ω} at low temperature with high current indicates the classical vortex flow accompanying the ratchet motion. Furthermore, we found that R^{2ω} is substantially suppressed in the quantum metallic state with the low current region, allowing identification of the quantum and classical ratchet motions of vortices by the magnitude of the second-harmonic resistance. Combining R^{2ω} with the linear resistance R^{ω} allowed us to establish a comprehensive vortex phase diagram for crystalline 2D superconductors with minimal disorder.

A pair-breaking mechanism of a superconductor under magnetic fields, namely, the origin of the upper critical field H_{c2}, can be categorized into the orbital effect and the paramagnetic effect, which have been separately discussed so far because the physical pictures are totally different. Here we propose a model that unifies these two origins into one formalism with a generalized physical picture. The obtained formula well describes the experimental results on the angle dependence of H_{c2} in a recently developed noncentrosymmetric superconductor, two-dimensional (2D) NbSe_{2}, providing essential information on the spin states of Cooper pairs in 2D NbSe_{2}. The proposed model is widely applicable to all superconductors, offering a powerful approach for comprehensive understanding of the origin of H_{c2}.

We report an ambipolar operation in field-effect transistors of C60 and metallofullerene Dy@C82 by modification of semiconductor/metal electrode interface with perfluoroalkylsilane (FAS) molecules. Kelvin probe experiments revealed that the work function of the gold surface modified with FAS molecules increased by 0.55 eV as compared to the untreated gold. Hole injection into fullerenes is qualitatively understood in terms of this work-function change induced by the FAS molecules. The present results indicate that the charge injection from electrodes to organic semiconductors can be controlled simply by modification of semiconductor/metal interface without changing materials themselves. [ABSTRACT FROM AUTHOR]

Recent progress in understanding the electronic band topology and emergent topological properties encourage us to reconsider the band structure of well-known materials including elemental substances. Controlling such a band topology by external field is of particular interest from both fundamental and technological viewpoints. Here we report possible signatures of the pressure-induced topological phase transition from a semiconductor to a Weyl semimetal in elemental tellurium probed by transport measurements. Pressure variation of the periods of Shubnikov-de Haas oscillations, as well as oscillation phases, shows an anomaly around the pressure theoretically predicted for topological phase transition. This behavior is consistent with the pressure-induced band deformation and resultant band-crossing effect. Moreover, effective cyclotron mass is reduced toward the critical pressure, potentially reflecting the emergence of massless linear dispersion. The present result paves the way for studying the electronic band topology in well-known compounds and topological phase transition by the external field. [ABSTRACT FROM AUTHOR]

Abstract An 88-year-old man had intermittent claudication of his right leg. Angiography revealed severely calcified plaque in the common femoral artery. Endovascular treatment was performed by contralateral approach. We attempted to penetrate the center of the calcified plaque and perform balloon dilatation. However, a 0.014-inch stiff guidewire could not enter the center of the lesion. Thus, we used an inner cylinder of 15-cm 20G long needle directly through the retrograde femoral sheath and successfully introduced the guidewire into the calcified plaque. Crosser and balloon dilatation resulted in 50 % stenosis. To cross the center of calcified plaque, it is important to obtain sufficient lumen gain at the non-stenting zone.

Transition metal dichalcogenide monolayers have attracted much attention due to their strong light absorption and excellent electronic properties. These advantages make this type of twodimensional crystal a promising one for optoelectronic device applications. In the case of photoelectric conversion devices such as photodetectors and photovoltaic cells, p-n junctions are one of the most important devices. Here, we demonstrate photodetection with WSe2 monolayer films. We prepare the electrolyte-gated ambipolar transistors and electrostatic p-n junctions are formed by the electrolyte-gating technique at 270 K. These p-n junctions are cooled down to fix the ion motion (and p-n junctions) and we observed the reasonable photocurrent spectra without the external bias, indicating the formation of p-n junctions. Very interestingly, two-terminal devices exhibit higher photoresponsivity than that of three-terminal ones, suggesting the formation of highly balanced anion and cation layers. The maximum photoresponsivity reaches 5mA/W in resonance with the first excitonic peak. Our technique provides important evidence for optoelectronics in atomically thin crystals. [ABSTRACT FROM AUTHOR]

Control of dimensionality has proven to be an effective way to manipulate the electronic properties of materials, thereby enabling exotic quantum phenomena, such as superconductivity, quantum Hall effects, and valleytronic effects. Another example is thermoelectricity, which has been theoretically proposed to be favorably controllable by reducing the dimensionality. Here, we verify this proposal by performing a systematic study on a gate-tuned 2D electron gas (2DEG) system formed at the surface of ZnO. Combining state-of-the-art electric-double-layer transistor experiments and realistic tight-binding calculations, we show that, for a wide range of carrier densities, the 2DEG channel comprises a single subband, and its effective thickness can be reduced to ~1 nm at sufficiently high gate biases. We also demonstrate that the thermoelectric performance of the 2DEG region is significantly higher than that of bulk ZnO. Our approach opens up a route to exploit the peculiar behavior of 2DEG electronic states and realize thermoelectric devices with advanced functionalities. [ABSTRACT FROM AUTHOR]

We report modulation of the superconducting critical temperature (Tc) of ultrathin niobium diselenide (NbSe2) single crystals by gating an electric double-layer transistor. We realized reversible and irreversible changes of the Tc by adjusting the operating range of the voltage. The reversible and irreversible responses correspond to the electrostatic carrier doping and the electrochemical etching of the crystal, respectively. The results suggest that electric double-layer gating provides opportunities to control and functionalize collective electronic phenomena in two-dimensional crystals. [ABSTRACT FROM AUTHOR]

The coupling between the valley degree of freedom and the optical helicity is one of the unique phenomena in transition metal dichalcogenides. The significant valley polarization evaluated from circularly polarized photoluminescence (PL) has been reported in many transition metal dichalcogenides, except in MoSe2. This compound is an anomalous material showing ultra-fast relaxation of the valley polarized states, which causes negligible polarization in the PL. Meanwhile, circularly polarized electroluminescence (EL) has been recently reported in a WSe2 light-emitting transistor, providing another method for using the valley degree of freedom. Here, we report the EL properties of MoSe2, demonstrating electrical switching of the optical helicity. Importantly, we observed high circular polarization reaching 66%. The results imply that the dominant mechanism of circularly polarized EL is robust against intervalley scattering, in marked contrast to the PL. [ABSTRACT FROM AUTHOR]

Two-dimensional crystals, especially graphene and transition metal dichalcogenides (TMDs), are attracting growing interests because they provide an ideal platform for novel and unconventional electronic band structures derived by thinning. The thinning may also affect collective phenomena of electrons in interacting electron systems and can lead to exotic states beyond the simple band picture. Here, we report the systematic control of charge-density-wave (CDW) transitions by changing thickness, cooling rate and gate voltage in nano-thick crystals of 1T-type tantalum disulfide (1T-TaS2). Particularly the clear cooling rate dependence, which has never been observed in bulk crystals, revealed the nearly-commensurate CDW state in nano-thick crystals is a super-cooled state. The present results demonstrate that, in the two-dimensional crystals with nanometer thickness, the first-order phase transitions are susceptible to various perturbations, suggestive of potential functions of electronic phase control. [ABSTRACT FROM AUTHOR]

The electric field effect on ferromagnetism offers a new dimension in the recent advancement of spintronics. We report on the gate control of transport properties in thin films of oxide-based ferromagnetic metal, SrRuO3. An electric double layer transistor configuration was utilized with an ionic liquid dielectric to apply a strong electric field on a SrRuO3 thin film of 5 monolayers in thickness. The application of gate voltage induced a clear electroresistance effect, despite a considerably-large initial carrier density of the order of 1022cm-3. Furthermore, we found that the gate modulation of the anomalous Hall conductivity rx y, which was as large as ~±40% at low temperatures, was about three times larger than that of the longitudinal conductivity σxx. The variation of σxy is characterized by the power-law scaling relation with σx x, which is widely observed in a bad metal regime of the charge transport. [ABSTRACT FROM AUTHOR]

Electric field tuning of superconductivity has been a long-standing issue in solid state physics since the invention of the field-effect transistor (FET) in 1960. Owing to limited available carrier density in conventional FET devices, electric-field-induced superconductivity was believed to be possible in principle but impossible in practice. However, in the past several years, this limitation has been overcome by the introduction of an electrochemical concept, and electric-field-induced superconductivity has been realized. In the electric double layer (EDL) formed at the electrochemical interfaces, an extremely high electric field is generated and hence high-density charge carriers sufficient to induce superconductivity exist and are collectively used as a charge accumulation device known as an EDL capacitor. Field-induced superconductivity has been used to establish the relationship between Tc and carrier density and can now be used to search for new superconductors. Here, we review electric-field-induced superconductivity using an FET device, with a particular focus on the latest advances in EDL transistors. [ABSTRACT FROM AUTHOR]

The study of strongly correlated electron systems is at the forefront of contemporary condensed matter research because such materials, which include transition metal oxides (colossal magnetoresistive manganites, high- T c cuprates) and intermetallic heavy fermion systems, display remarkable electronic properties that challenge existing theory for satisfactory explanations. The interplay between charge, lattice, orbital and magnetic degrees of freedom in all these systems can be tuned sensitively both physically (varying an external parameter like pressure or magnetic field) and chemically (changing the chemical composition). A prominent branch of strongly correlated electron systems is the family of metal-intercalated fullerides, which display superconductivity at temperatures as high as 40 K. In this chapter, we discuss the structures and electronic and magnetic properties of selected fullerene-based architectures focusing on ammonia co-intercalated metal fullerides which are located at the boundaries of metal-insulator transitions, on alkaline-earth fullerides which deviate strongly from rigid band behaviour and on rare-earth fullerides which present unique opportunities based on the coupling between the lanthanide and fulleride electronic structures. [ABSTRACT FROM AUTHOR]

In noncentrosymmetric superconductors, superconducting and normal conductions can interchange on the basis of the current flow direction. This effect is termed a superconducting diode effect (SDE), which is a focal point of recent research. The broken inversion and time-reversal symmetry is believed to be the requirements of SDE, but their intrinsic role has remained elusive. Here, we report strain-controlled SDEs in a layered trigonal superconductor, PbTaSe2. The SDE was found exclusively in a strained device with its absence in an unstrained device despite that it is allowed in unstrained trigonal structure. Moreover, the zero-field or magnetic field-even (magnetic field-odd) SDE is observed when the strain and current are along armchair (zigzag) direction The results unambiguously demonstrate the intrinsic SDE under time-reversal symmetry and the critical role of strain-induced electric polarization. [ABSTRACT FROM AUTHOR]

Realizing spin MOSFETs is essential for non-volatile high-speed electronics; however, obtaining practically large magnetoresistance (MR) is challenging because of the difficulties of growing high-quality single-crystalline ferromagnet/semiconductor heterostructures and of obtaining efficient gate modulation. In this study, for realizing a vertical spin MOSFET, we demonstrate side-gate-induced current modulation in a magnetic tunnel junction composed of Fe electrodes and an oxide semiconductor GaOx barrier at RT. We show gate modulation of the current up to ∼10% and a MR ratio up to 40%, which is larger than that obtained at RT in previous spin-valve devices targeted for spin MOSFETs (∼0.1%). [ABSTRACT FROM AUTHOR]

A spin metal–oxide–semiconductor field-effect transistor (MOSFET) is a promising spintronics device for future low-power electronics. In this paper, we demonstrate the successful improvement of the performance of a spin-MOSFET-type device, a ferromagnetic-semiconductor GaMnAs-based vertical spin electric double-layer transistor (EDLT); the magnetoresistance ratio reaches 37%, which is 7 times larger than those obtained in previous studies. Furthermore, we find that the magnetic anisotropy of our device is modulated by changing the gate voltage. Our results open up the possibility of realizing novel functional devices, in which both current and magnetic anisotropy can be controlled by the gate electric field. [ABSTRACT FROM AUTHOR]

Magnetic semimetals form an attractive class of materials because of the nontrivial contributions of itinerant electrons to magnetism. Because of their relatively low-carrier-density nature, a doping level of those materials could be largely tuned by a gating technique. Here, we demonstrate gate-tunable ferromagnetism in an emergent van der Waals magnetic semimetal Cr3Te4 based on an ion-gating technique. Upon doping electrons into the system, the Curie temperature (TC) sharply increases, approaching near to room temperature, and then decreases to some extent. This non-monotonous variation of TC accompanies the switching of the magnetic anisotropy, synchronously followed by the sign changes of the ordinary and anomalous Hall effects. Those results clearly elucidate that the magnetism in Cr3Te4 should be governed by its semimetallic band nature. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) crystals are attracting growing interest in condensed matter physics, since these systems exhibit not only rich electronic and photonic properties but also exotic electronic phase transitions including superconductivity and charge density wave. Moreover, owing to the recent development of transfer methods after exfoliation and electric-double-layer transistors, superconducting 2D atomic crystals, the thicknesses of which are below 1–2 nm, have been successfully obtained. Here, we present a topical review on the recent discoveries of 2D crystalline superconductors by ionic-liquid gating and a series of their novel properties. In particular, we highlight two topics; quantum metallic states (or possible metallic ground states) and superconductivity robust against in-plane magnetic fields. These phenomena can be discussed with the effects of weakened disorder and/or broken spacial inversion symmetry leading to valley-dependent spin-momentum locking (spin-valley locking). These examples suggest the superconducting 2D crystals are new platforms for investigating the intrinsic quantum phases as well as exotic nature in 2D superconductors. [ABSTRACT FROM AUTHOR]

We report a molecular adsorption effect on the first-order metal–insulator transition of vanadium dioxide (VO2) thin films. The phase transition temperature is shifted higher by the adsorption of particular polar and rigid tripodal molecules on the film surfaces. The shift becomes larger with increasing dipole moment magnitude, which ranges from 0 to 20 D. The orientation of polar molecules aligned on the surface is most likely responsible for the higher shift of the transition temperature. Coating the surfaces with polar molecules, as demonstrated in this work, might provide a unique way of controlling the phase transition of materials. [ABSTRACT FROM AUTHOR]

Due to the requirements for large-area, uniform films, currently transition metal dichalcogenides (TMDC) cannot be used in flexible transistor industrial applications. In this study, we first transferred chemically grown large-area WSe2 monolayer films from the as-grown sapphire substrates to the flexible plastic substrates. We also fabricated electric double layer transistors using the WSe2 films on the plastic substrates. These transistors exhibited ambipolar operation and an ON/OFF current ratio of ∼104, demonstrating chemically grown WSe2 transistors on plastic substrates for the first time. This achievement can be an important first step for the next-generation TMDC based flexible devices. [ABSTRACT FROM AUTHOR]

The article discusses research on the symmetry engineering of a Van der Waals (vdW) interface which led to the production of a spontaneous photovoltaic effect (SPE). Topics explored include the physical properties and functionalities of vdW heterointerfaces, the selection of tungsten selenide and black phosphorus as building blocks of the interface, and the photovoltaic response observed in vdW crystals.

The coupling between the valley degree of freedom and the optical helicity is one of the unique phenomena in transition metal dichalcogenides. The significant valley polarization evaluated from circularly polarized photoluminescence (PL) has been reported in many transition metal dichalcogenides, except in MoSe2. This compound is an anomalous material showing ultra-fast relaxation of the valley polarized states, which causes negligible polarization in the PL. Meanwhile, circularly polarized electroluminescence (EL) has been recently reported in a WSe2 light-emitting transistor, providing another method for using the valley degree of freedom. Here, we report the EL properties of MoSe2, demonstrating electrical switching of the optical helicity. Importantly, we observed high circular polarization reaching 66%. The results imply that the dominant mechanism of circularly polarized EL is robust against intervalley scattering, in marked contrast to the PL. [ABSTRACT FROM AUTHOR]

Recently emerging two-dimensional (2D) superconductors in atomically thin layers and at heterogeneous interfaces are attracting growing interest in condensed matter physics. Here, we report that an ion-gated zirconium nitride chloride surface, exhibiting a dome-shaped phase diagram with a maximum critical temperature of 14.8 kelvin, behaves as a superconductor persisting to the 2D limit. The superconducting thickness estimated from the upper critical fields is ≅ 1.8 nanometers, which is thinner than one unit-cell. The majority of the vortex phase diagram down to 2 kelvin is occupied by a metallic state with a finite resistance, owing to the quantum creep of vortices caused by extremely weak pinning and disorder. Our findings highlight the potential of electric-field-induced superconductivity, establishing a new platform for accessing quantum phases in clean 2D superconductors. [ABSTRACT FROM AUTHOR]

Two-dimensional crystals, especially graphene and transition metal dichalcogenides (TMDs), are attracting growing interests because they provide an ideal platform for novel and unconventional electronic band structures derived by thinning. The thinning may also affect collective phenomena of electrons in interacting electron systems and can lead to exotic states beyond the simple band picture. Here, we report the systematic control of charge-density-wave (CDW) transitions by changing thickness, cooling rate and gate voltage in nano-thick crystals of 1T-type tantalum disulfide (1T-TaS2). Particularly the clear cooling rate dependence, which has never been observed in bulk crystals, revealed the nearly-commensurate CDW state in nano-thick crystals is a super-cooled state. The present results demonstrate that, in the two-dimensional crystals with nanometer thickness, the first-order phase transitions are susceptible to various perturbations, suggestive of potential functions of electronic phase control. [ABSTRACT FROM AUTHOR]

The electric field effect on ferromagnetism offers a new dimension in the recent advancement of spintronics. We report on the gate control of transport properties in thin films of oxide-based ferromagnetic metal, SrRuO3. An electric double layer transistor configuration was utilized with an ionic liquid dielectric to apply a strong electric field on a SrRuO3 thin film of 5 monolayers in thickness. The application of gate voltage induced a clear electroresistance effect, despite a considerably-large initial carrier density of the order of 1022cm-3. Furthermore, we found that the gate modulation of the anomalous Hall conductivity rx y, which was as large as ~±40% at low temperatures, was about three times larger than that of the longitudinal conductivity σxx. The variation of σxy is characterized by the power-law scaling relation with σx x, which is widely observed in a bad metal regime of the charge transport. [ABSTRACT FROM AUTHOR]

We present NMR measurements of the layered nitride superconductor LixZrNCl. The nuclear spin-lattice relaxation rate 1/T1 shows that the coherence peak is strongly suppressed in LixZrNCl in contrast to conventional BCS superconductors. In the lightly doped region close to the insulating state, the system shows a gaplike behavior, i.e., pseudogap, that is characterized by a reduction in the magnitude of the Knight shift and 1/T1T . A higher superconducting (SC) transition temperature Tc is achieved by coexisting with the pseudogap state. These unusual behaviors, which deviate from the ordinary BCS framework, are the key ingredients to understanding the SC mechanism of Lix ZrNCl. [ABSTRACT FROM AUTHOR]