{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"f8c244715ba34232452684273e7ccb8e483d4c17824e2b2ac819023fb0893750","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["a6567dbaa2dcfb8b91065890ac46a5cc5c4cf8dc1cc8a616fb538366fd5c942b","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"453482746d22c9247bf2601f89e4f3d8d44f779d744c171f4e4d8b2d7b04d9b4","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"cm.magnetic-topological-insulators.quantized-magnetoelectric","kind":"well-posed","literature_status":"partially-resolved","n":"2","parents":[],"plain":"An axion insulator should become electrically polarized in a magnetic field by an amount fixed only by the fine-structure constant, and this static effect has never been measured directly.","posed_since":"2008","precise":"For an axion insulator with $\\theta = \\pi$ (magnetic topological insulator sandwich or even-layer $\\mathrm{MnBi_2Te_4}$), measure the static (dc) magnetoelectric response $P = (\\theta \\alpha / 4\\pi^2) B$ in Gaussian units with $\\alpha = e^2/(\\hbar c)$, i.e., $\\alpha/(4\\pi)$ per unit field at $\\theta = \\pi$, or the equivalent magnetization induced by an electric field. An answer is the measured coefficient in units of $\\alpha/(4\\pi)$ with accuracy better than 10%.","problem_ref":"a6567dbaa2dcfb8b91065890ac46a5cc5c4cf8dc1cc8a616fb538366fd5c942b","references":"","settled_by":"Capacitive or SQUID detection of field-induced polarization, or electric-field-induced magnetization, in an insulating sample free of dissipative edge or side-wall conduction.","status_note":"Quantized Faraday and Kerr rotations, a terahertz-frequency form of the effect in an applied field, were reported in topological insulator films in 2016-2017; a static (dc) measurement of $P = (\\alpha/4\\pi) B$ in an axion insulator is lacking as of 2026.","title":"Direct measurement of the quantized topological magnetoelectric effect","topic_ref":null},"content_withheld":"false","files":[],"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"3b7441227b8f5eac1049d0413941f96936ce27e9558fe2636db2f0e2c7d677e0","schema":"pubphys.attested/1"},"id_token":null,"id_token_withheld":"false","envelope":{"attested_hash":"7e8eef6baa387a7ad8bcdf28f49d0ffbb805b4e0f1c7e20526f7ed2621473aaf","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"zrY2pQyIQ-ASE_JLfdG7zBvjSGYi-k8r9sJlerVeE5rrSz2JQJisVtQNbIBqBOXGDcYfRhYTNCVGQO1usKPGCQ"},"schema":"pubphys.envelope/1"},"ots":{"attested":["AE9wZW5UaW1lc3RhbXBzAABQcm9vZgC_ieLohOiSlAEIfo7va6o4enrYvN8o9J0P-7gFtODxx-IFJvftJiFHOq_xIH52xJmaxT2Pgb8BOpLXRM9ytOoerrUEs-PjUq4-sIVcCPEg_FLSLa4dlTGNraBPAVE8aDY-vuWXA6gY40wL6vkn6OMI8SCWVa604vk7BTdtpBZ4Tr_yJTGI33ggLuw-gIqL267TXgjxIO11eKLE1wwXTV5mZM3KrNrFG5jAjipk7yjaveanYlr3CPAglwDEkyjScBXTfV1uUZ1cyBkJXUvTHM2KrTucYJHwnr4I8CAGNtz83AQ9v5-gxKZQwTuf04yoihPFlPqicB12zVGvsgjwINcabnKDjMkLxRvsoaPCbX0K9J56jcSSW0dTiX8obtbECPEgC07znjc0bVDgPzONkw3aBXeRFcSLeM3BhuNQIWI6mKkI8CCCFfNrg2ZeB51PNa84j-z6Sin0AxT6aP9r7HupgUKbMwjxICknnLxa8xs8qmAdhtb0NnANbtwYyrlRTgqcMVLLl8ogCPEgHd9u6OIGCvUV12A1B1xdiOprSJ-4w0cqwfe7CzVX5HsI8CDQo_sIWZiWXaTGRSQBLmU-lHJKskYKqsjO1r02DhB8LAj_8Ajn9YmozHwo9QjwEJ46aM9ZDv3TdtqV3ZbRsNgI8SBOF8pILGf1kodr5MKmQs6Cd93joraGn3g6UPt_-kewPwjwIOG-gmM7bd_eR4AiDMNfluS3xvr7vicLR-sCBr5qtG2cCPAgrVNFrCoeQcCxhlmnE0BzHgR8HQpZAlfqzDDFzfWb8GUI8QRq0WWT8AjZJ2cF_c7k8ACD3-MNLvkMjiwraHR0cHM6Ly9ib2IuYnRjLmNhbGVuZGFyLm9wZW50aW1lc3RhbXBzLm9yZ_AI9ZMS1zxd7IEI8BDd00WgJZ0RncsC1Fyai_4aCPEgvxMFrnu7F05IW5INiraQ3OVEYMjNx6JfBxw1Q4jPLi4I8QRq0WWS8Ag2zxPAtI5JsP8Ag9_jDS75DI4uLWh0dHBzOi8vYWxpY2UuYnRjLmNhbGVuZGFyLm9wZW50aW1lc3RhbXBzLm9yZwjxIHAnv4KFFf4uiYEFJvLxiMxSyz8VowJP4roTfDD9h7bICPAgj5tgvbNF7mxSP4jGGE66ezUFRLnI4g1VTkvuV4VtCPAI8CCxlc1HuKORuHgn7DYIYcDhc4oo99OkTWBEvddBypoa7AjwIFcjjaF8kDNDYCZGaNISlRjvX-I7in-QNwsr4JYQbFJvCPAgnl0k4gs7LuY5i1umiHO-J7My3uBThLJUWQoY9LdVSrQI8SA6-Ft11_K_GqMNWYhkVsVqCFvXSYbp4S8JoLsLBnUzvgjxIBC8_mAE7JBP35SNxDBcG7joLJwURpMxdV2vSO64_jEOCPEge04Coj1xSi7CE8UwqiBGNhPyZ5QdD_YZwn-heSdObU4I8SBgdDSgr3VUx1j8m_pK7-OzMwwFgXeLy43ujffCv-hf5AjwIMl-PnAt4xjoBEVU4-nkyN0NKRa9AvX4kEMfllFyIJS9CPFZAQAAAAHz4rV-uwQFg02bVnEMUFgpIdGKjM4tWuID1kTVnrjisAAAAAAA_v___wJURAIAAAAAABYAFBFys2oc0-U-bYrC3VulGLzND5fbAAAAAAAAAAAiaiDwBHLTDgAICPEgMJIBYi46xOIuFDwzJ9nOx14ngW5HbglUf65ORpkoIYcICPAgHgGWEGCDHWgscwT92NOoJ7s-ezbPkyiWr2RnYZDC_dwICPAgtffMyyLu-MscJsDc0dzwGspwSrrmvVAnMNgsgWhHClgICPAgMUl1OfBDUwhp5VZjHwVA0nuz1F5HZTUJCHAnM1L1F3MICPAgStK7UWpnrUueV5EaE7uE0y6BLMp6EANmrbhrTqEBZu8ICPAg5LVW7IHtUL5mNOvPx1hOTfLMmqlQ7t9EFW-KDtrISIQICPAgABgXZ6upFU8qiDQKFtQFpqkjKwl0PsxM4JUjVLlDKbkICPAgEwb96FiOhjlbwI8GFZQ4a5GXwxs4bUdqVOMKrtBWV30ICPEgqBg-wp0c8CAPV9k6J7wIa9_GtQfpWmhpE1zqFZyi2pQICPAg2pZLTVPGJbriiz0UhMytYDVYAXOgQnWDcrMOewK9O8cICPEgxm3QwzbvT4siJzubQGnST67bWv-exYwSPP1KDi7CaUwICPEgm6udUudfjUaM0gUFTylKGDMypj7ptMTG0zmxd_T5yTcICPAgMpOInkjFCVp1pOZhfZnyPAl8hdWGmHzQcrGLgLwSKLgICAAFiJYNc9cZAQPzpjs"],"envelope":["AE9wZW5UaW1lc3RhbXBzAABQcm9vZgC_ieLohOiSlAEIuetqZh14NMhhS_qj3truWhv-Pmci9bwps3k2n3kZiE7xILnZxBzyXHSD0cMPOKL3LgtGdkrhi4pwh9p8eLcd2DCJCPEgOgT_AFtrBfmZ57BoxIQ_N_ztBKYHM0LtiCRQ4w_jLWAI8CA582xz0WbbcsHHcRo6rbzSxtMzrE2nNg5Q7f-RM_VzSAjxINtgXF7F584fOy_mDXnNwiqv0k1RvGEshb8-5h3Q2J1gCPAga3QIXt4f5YeSS9sXxZv-eC_duRuxnBuA9pV6A2iWlM4I8CA4nJ8ltAzLfcK2q2BIZKAS5JW2dkOGfc10zbAD3n0c-AjwIIg82Jvk6sG9d_qFEsDPR33QWZO6pmDRJWIBF6p7sCc5CPEgraRI2npokG3tsYuZYconfMt0ARYLxAQQuCOiQUqeUM8I8SDArwsGYVuomKH_DJiJGziPwECn7skqn20TGM58Ezco0wjwIIgwugvlgSNOmTWMhquqetKjeLf0x7d1a1MH4KU52JbFCPAg3mczMYDKOd7Nhf3ojA9ZvuTsN66Y1NnyYTp9j8GKQNwI8SCvAiiN-Hrv7IEejd8wdUihoozu5KOvpoBFJ0vg3UnGAQj_8Ajn9YmozHwo9QjwEJ46aM9ZDv3TdtqV3ZbRsNgI8SBOF8pILGf1kodr5MKmQs6Cd93joraGn3g6UPt_-kewPwjwIOG-gmM7bd_eR4AiDMNfluS3xvr7vicLR-sCBr5qtG2cCPAgrVNFrCoeQcCxhlmnE0BzHgR8HQpZAlfqzDDFzfWb8GUI8QRq0WWT8AjZJ2cF_c7k8ACD3-MNLvkMjiwraHR0cHM6Ly9ib2IuYnRjLmNhbGVuZGFyLm9wZW50aW1lc3RhbXBzLm9yZ_AI9ZMS1zxd7IEI8BDd00WgJZ0RncsC1Fyai_4aCPEgvxMFrnu7F05IW5INiraQ3OVEYMjNx6JfBxw1Q4jPLi4I8QRq0WWS8Ag2zxPAtI5JsP8Ag9_jDS75DI4uLWh0dHBzOi8vYWxpY2UuYnRjLmNhbGVuZGFyLm9wZW50aW1lc3RhbXBzLm9yZwjxIHAnv4KFFf4uiYEFJvLxiMxSyz8VowJP4roTfDD9h7bICPAgj5tgvbNF7mxSP4jGGE66ezUFRLnI4g1VTkvuV4VtCPAI8CCxlc1HuKORuHgn7DYIYcDhc4oo99OkTWBEvddBypoa7AjwIFcjjaF8kDNDYCZGaNISlRjvX-I7in-QNwsr4JYQbFJvCPAgnl0k4gs7LuY5i1umiHO-J7My3uBThLJUWQoY9LdVSrQI8SA6-Ft11_K_GqMNWYhkVsVqCFvXSYbp4S8JoLsLBnUzvgjxIBC8_mAE7JBP35SNxDBcG7joLJwURpMxdV2vSO64_jEOCPEge04Coj1xSi7CE8UwqiBGNhPyZ5QdD_YZwn-heSdObU4I8SBgdDSgr3VUx1j8m_pK7-OzMwwFgXeLy43ujffCv-hf5AjwIMl-PnAt4xjoBEVU4-nkyN0NKRa9AvX4kEMfllFyIJS9CPFZAQAAAAHz4rV-uwQFg02bVnEMUFgpIdGKjM4tWuID1kTVnrjisAAAAAAA_v___wJURAIAAAAAABYAFBFys2oc0-U-bYrC3VulGLzND5fbAAAAAAAAAAAiaiDwBHLTDgAICPEgMJIBYi46xOIuFDwzJ9nOx14ngW5HbglUf65ORpkoIYcICPAgHgGWEGCDHWgscwT92NOoJ7s-ezbPkyiWr2RnYZDC_dwICPAgtffMyyLu-MscJsDc0dzwGspwSrrmvVAnMNgsgWhHClgICPAgMUl1OfBDUwhp5VZjHwVA0nuz1F5HZTUJCHAnM1L1F3MICPAgStK7UWpnrUueV5EaE7uE0y6BLMp6EANmrbhrTqEBZu8ICPAg5LVW7IHtUL5mNOvPx1hOTfLMmqlQ7t9EFW-KDtrISIQICPAgABgXZ6upFU8qiDQKFtQFpqkjKwl0PsxM4JUjVLlDKbkICPAgEwb96FiOhjlbwI8GFZQ4a5GXwxs4bUdqVOMKrtBWV30ICPEgqBg-wp0c8CAPV9k6J7wIa9_GtQfpWmhpE1zqFZyi2pQICPAg2pZLTVPGJbriiz0UhMytYDVYAXOgQnWDcrMOewK9O8cICPEgxm3QwzbvT4siJzubQGnST67bWv-exYwSPP1KDi7CaUwICPEgm6udUudfjUaM0gUFTylKGDMypj7ptMTG0zmxd_T5yTcICPAgMpOInkjFCVp1pOZhfZnyPAl8hdWGmHzQcrGLgLwSKLgICAAFiJYNc9cZAQPzpjs"]},"log":{"leaf_index":"2924","tree_size":"3804","proof":["65e5d7d00906c03362c537bbdc9654daedcd0af5dee2f55b3709d4c7dd523ea3","7b622fb60d0870391ed0d06d7424594be12bf2e4726d49506239a35ede155ec5","c0901a73abad2712692433d840c2a8dfa3ed6a729147ae269a4ef2db78eb43be","8a8281d092c29a8cb0068c6969061faa185a08656af54bba2528c43b7fcaf788","32f3512ee624da4a3cfa8df2546c7d1e67b63e8f0e7d47aae6d0331dc03902d7","ffc6235d5386a6bc70e205de278dcaae55c42327844472103c384400165f692c","6984ff284df9cd05f5fc874363b51edd45630415b9fc04bbb281f18b0be18a5a","35943d50e127dd46c0e87af4e164fc8e3c68cc080e1e586a454baa6a53014e7a","56960156727d0f461a1b3857ab83f18526eaef848c820c927094afc1f989d56c","b0b232078d071c92816af6274529aef23a2ea1f41246694fec32d768cfa09dc8","325287f5a43e4f3ad4072ec4bd53d43c50c1393021a056122e9cb0fad83b868f","3c578dccc15502c5f3efe228cadc99fee76ab536ed01f66b14d316fdcc157429"],"checkpoint":"pubphys.com/log/v1\n3804\nAK6t4qgu96+M9wScTrIlsJ10d/zhKVEtYguyM3aeJvo=\n\n— pubphys.com/log/v1 JFPwIPP8EtoxgcsQg7V7CwIdL4UKPqJtpv+eB8sFNJjyQHIdyA1VabmBsPyLqq2bLxJPn57rA6fQi8y0QDDjRXHvlQg=\n","promise":"pubphys.com/log/v1 promise\nc6a9909f26fad344331e509f6e2561952f7e7663047b2a89a7f4dcadc217c929\n2924\n2026-10-15T23:43:57Z\n2026-10-16T01:43:57Z\n\n— pubphys.com/log/v1 JFPwIOdshhyzbFx2z4KSJ2Nqk64rErZ7OaTMWfhqJocnP92K8s6bLU4APitpy4KsPPkQRrzN3DpKHIoG8jL2aVbq4A4=\n"},"orcid_key_evidence":[],"attesting":null}