Graphical Abstract
![](https://wqketang.oss-cn-beijing.aliyuncs.com/zip-unzip/zip-8cd3e3cc-9ee7-45fe-9b94-6ddac8bb3299/nr-11-12-6252/files/nr-11-12-6252-FE1.jpg?Expires=1725758027&OSSAccessKeyId=STS.NSssK71aLjDMY9SbRgGRGskMT&Signature=mbhZ1Yzj2ssh8JEL1mu1G0rYhlw%3D&security-token=CAISywJ1q6Ft5B2yfSjIr5DGOPGD3L5t3YamWx%2FihlIyS91rnK7mtjz2IHtKenhsBOsbtfk1mG5W5%2FgZlqJ9SptIAEfJa9d99Myjb%2F9FltCT1fau5Jko1beHewHKeTOZsebWZ%2BLmNqC%2FHt6md1HDkAJq3LL%2Bbk%2FMdle5MJqP%2B%2FUFB5ZtKWveVzddA8pMLQZPsdITMWCrVcygKRn3mGHdfiEK00he8TouufTinpHMskGA1Aell7Mvyt6vcsT%2BXa5FJ4xiVtq55utye5fa3TRYgxowr%2Fwo0v0YpGya5YzHXwcPskvdKZbo78UqLQlla6w%2BGqFJqvPxr%2Fp8t%2Fx5fWJKAezhVgs8cVM8JOjIqKOscIsixo262SmqFV55c8Fdm%2BgUooJVgIMhTnduUfAPJAGOxzJitP%2BUVGGphr60TEnBL4rB5MUctfzRpwT64j3UTzDnGoABhFRSspTLrn9GrEN9pQYzC6eepGdfWDQh3fr5hA1VnwVUJMCz%2BNQEDWKceF%2FnEjWVMtfbvqYxuyhSCmIMMyh5bEREEKEiD%2BFVv4ZfsqnV7hQy5w6HhIkN8kZzP6L0zPvPgkBLOtdMDeDxhf8dVPrCSG4etXHjxcwUaRVb3ZR7Yu8gAA%3D%3D)
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Possessing a valley degree of freedom and potential in information processing by manipulating valley features (such as valley splitting), group-VI monolayer transition metal dichalcogenides have attracted enormous interest. This valley splitting can be measured based on the difference between the peak energies of σ+ and σ- polarized emissions for excitons or trions in direct band gap monolayer transition metal dichalcogenides under perpendicular magnetic fields. In this work, a well-prepared heterostructure is formed by transferring exfoliated WSe2 onto a EuS substrate. Circular-polarization-resolved photoluminescence spectroscopy, one of the most facile and intuitive methods, is used to probe the difference of the gap energy in two valleys under an applied out-of-plane external magnetic field. Our results indicate that valley splitting can be enhanced when using a EuS substrate, as compared to a SiO2/Si substrate. The enhanced valley splitting of the WSe2/EuS heterostructure can be understood as a result of an interfacial magnetic exchange field originating from the magnetic proximity effect. The value of this magnetic exchange field, based on our estimation, is approximately 9 T. Our findings will stimulate further studies on the magnetic exchange field at the interface of similar heterostructures.
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