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Excitons in two-dimensional (2D) semiconductors have offered an attractive platform for optoelectronic and valleytronic devices. Further realizations of correlated phases of excitons promise device concepts not possible in the single particle picture. Here we report tunable exciton "spin" orders in WSe2/WS2 moiré superlattices. We find evidence of an in-plane (xy) order of exciton "spin"—here, valley pseudospin—around exciton filling vex = 1, which strongly suppresses the out-of-plane "spin" polarization. Upon increasing vex or applying a small magnetic field of ~10 mT, it transitions into an out-of-plane ferromagnetic (FM-z) spin order that spontaneously enhances the "spin" polarization, i.e., the circular helicity of emission light is higher than the excitation. The phase diagram is qualitatively captured by a spin-1/2 Bose–Hubbard model and is distinct from the fermion case. Our study paves the way for engineering exotic phases of matter from correlated spinor bosons, opening the door to a host of unconventional quantum devices. Control of correlated excitonic states is a key goal of modern optoelectronic physics. Here, the authors demonstrate filling- and field-tunable exciton valley-pseudospin orders in a moiré heterostructure. [ABSTRACT FROM AUTHOR]

Alkali metal-noble gas comagnetometers operated in the regime of spin-exchange relaxation-free (SERF) have been widely used in fundamental physics tests and rotation sensing as gyroscope. Spin-exchange relaxation is an important systematic bias of the comagnetometer, which could limit sensitivity significantly. However, the suppression effect of the spin-exchange relaxation has not been examined quantitatively so far. Herein, we systematically investigate the relaxation of the alkali metal atoms and find that the spin-exchange relaxation is not completely eliminated under the normal operating condition of the K-Rb-21Ne comagnetometer. In addition to the optical pumping rate, the spin-exchange relaxation still plays a dominant role in the broadening of electron Zeeman resonances due to the large electron magnetic field. This is the first demonstration that the alkali metal atoms are operated in the near-SERF regime in the alkali metal-noble gas comagnetometer with a large election magnetic field, which will shed light on the way to reduce the relaxation of the alkali metal atoms and enhance the sensitivity of the comagnetometer. [ABSTRACT FROM AUTHOR]

Materials with a large linear magnetoresistance (MR) are great candidates for magnetic sensors, but rarity boosts investigations for exploring this MR in material physics. 2D electron system (2DES) formed at the nonisostructural heterointerfaces between γ‐Al2O3 (GAO) and SrTiO3 (STO) provides plenty of intriguing or even superior emergent properties compared with the conventional isomorphic all‐perovskite counterparts. Herein, a large MR exceeding 2000% in magnitude at the magnetic GAO/STO heterointerfaces with a high carrier mobility of 30 000 cm2 V−1 s−1 at low temperature is demonstrated. In contrast to the quadratic dependence on the magnetic field of the conventional oxide 2DES, MR in GAO/STO is linear and nonsaturating at high fields, which is stemmed from the magnetic inhomogeneities‐induced inhomogeneous conductivities. In addition, weak antilocalization effect gives rise to an extra quantum correction to the MR in low‐field region. Furthermore, a general qualitative picture of MR proportional to the mobility is established. These findings reveal the nonisostructural GAO/STO heterointerface is of great promise in magnetic sensor‐based practical memory applications and transistor designs. [ABSTRACT FROM AUTHOR]