Electronic transport measurements reveal the formation of swirling spin textures, skyrmions, at high-quality oxide interface.

Magnetotransport properties have been investigated for epitaxial thin films of B20-type MnSi grown on Si(111) substrates. Lorentz transmission electron microscopy images clearly point to the robust formation of Skyrmions over a wide temperature-magnetic field region. New features distinct from those reported previously for MnSi are observed for epitaxial films: a shorter (nearly half) period of the spin helix and Skyrmions, and a topological Hall effect anomaly consisting in ∼2.2 times enhancement of the amplitude and in the opposite sign with respect to bulk samples.

Changing the interactions between particles in an ensemble--by varying the temperature or pressure, for example--can lead to phase transitions whose critical behaviour depends on the collective nature of the many-body system. Despite the diversity of ingredients, which include atoms, molecules, electrons and their spins, the collective behaviour can be grouped into several families (called 'universality classes') represented by canonical spin models. One kind of transition, the Mott transition, occurs when the repulsive Coulomb interaction between electrons is increased, causing wave-like electrons to behave as particles. In two dimensions, the attractive behaviour responsible for the superconductivity in high-transition temperature copper oxide and organic compounds appears near the Mott transition, but the universality class to which two-dimensional, repulsive electronic systems belongs remains unknown. Here we present an observation of the critical phenomena at the pressure-induced Mott transition in a quasi-two-dimensional organic conductor using conductance measurements as a probe. We find that the Mott transition in two dimensions is not consistent with known universality classes, as the observed collective behaviour has previously not been seen. This peculiarity must be involved in any emergent behaviour near the Mott transition in two dimensions.

PACS numbers:2 Skyrmions, topologically-protected nanometric spin vortices, are being investigated 1-11 extensively in various magnets.Among them, many of structurally-chiral cubic magnets host the triangular-lattice skyrmion crystal (SkX) as the thermodynamic equilibrium state. However, this state exists only in a narrow temperature and magnetic-field region just below the magnetic transition temperature T c , while a helical or conical magnetic state prevails at lower temperatures. Here we describe that for a room-temperature skyrmion material 12 , β-Mn-type Co 8 Zn 8 Mn 4 , a field-cooling via the equilibrium SkX state can suppress the transition to the helical or conical state, instead realizing robust metastable SkX states that survive over a very wide temperature and magnetic-field region, including down to zero temperature and up to the critical magnetic field of the ferromagnetic transition. Furthermore, the lattice form of the metastable SkX is found to undergo reversible transitions between a conventional triangular lattice and a novel square lattice upon varying the temperature and magnetic field. These findings exemplify the topological robustness of the once-created skyrmions, and establish metastable skyrmion phases as a fertile ground for technological applications. Skyrmions are promising for spintronics applications firstly because they are stable due to their topological nature, and secondly because they can be manipulated by an ultra-low current density [17][18][19][20][21] . The recent discovery of skyrmion formation at and above room temperature in a new group of chiral magnets, β-Mn-type Co-Zn-Mn alloys, has provided a significant step toward applications 12 . These materials possess a chiral cubic crystal structure with space group P 4 1 32 as shown in Fig. 1 A square-lattice SkX state, characterized by double-q vectors orthogonal to each other and perpendicular to the magnetic field, also shows up as a 4 spot pattern in the H beam geometry. In the H ⊥ beam geometry, the helical multi-domain state shows 4 spots, the conical state 2 spots on the horizontal axis, and both the triangular and square-lattice SkX states each 2 spots on the vertical axis.Keeping the above relations in mind, we next consider the results (Fig. 3) of the FC process at 0.04 T, i.e. by way of the thermodynamical equilibrium triangular-lattice SkX region (green region in Fig. 1(b)). The SANS images in Fig. 3(b) show that the pattern obtained from the equilibrium triangular-lattice SkX generated at 295 K persists down to 200K. This is a direct demonstration of the realization of the metastable SkX state that exists outside of the equilibrium state for temperatures below 284 K. The lifetime of this metastable SkX is very long and becomes essentially time-independent below 260 K ( Supplementary Fig. S4). At 120 K, the triangular-lattice SkX pattern has partially transformed into 4 spots.At 40 K, the 4 spots become clearer and their |q|(≡ q) values become larger than they were 6 at higher temperatures. The 4 spot patter...

Ferroelectric polarization of 6.3  μC cm(-2) is induced by the neutral-to-ionic transition, upon which nonpolar molecules of electron donor tetrathiafulvalene (TTF) and acceptor p-chloranil (CA) are incompletely ionized to ±0.60e and dimerized along the molecular stacking chain. We find that the ferroelectric properties are governed by intermolecular charge transfer rather than simple displacement of static point charge on molecules. The observed polarization and poling effect on the absolute structural configuration can be interpreted in terms of electronic ferroelectricity, which not only exhibits antiparallel polarity to the ionic displacement but also enhances the polarization more than 20 times that of the point-charge model.