{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,4]],"date-time":"2026-09-04T06:14:55Z","timestamp":1788502495061,"version":"build-2803163510"},"reference-count":53,"publisher":"IOP Publishing","issue":"35","license":[{"start":{"date-parts":[[2026,9,4]],"date-time":"2026-09-04T00:00:00Z","timestamp":1788480000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/publishingsupport.iopscience.iop.org\/iop-standard\/v1"},{"start":{"date-parts":[[2026,9,4]],"date-time":"2026-09-04T00:00:00Z","timestamp":1788480000000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/iopscience.iop.org\/info\/page\/text-and-data-mining"}],"funder":[{"DOI":"10.13039\/100018335","name":"Tribhuvan University","doi-asserted-by":"crossref","id":[{"id":"10.13039\/100018335","id-type":"DOI","asserted-by":"crossref"}]},{"DOI":"10.13039\/100005156","name":"Alexander von Humboldt-Stiftung","doi-asserted-by":"crossref","id":[{"id":"10.13039\/100005156","id-type":"DOI","asserted-by":"crossref"}]}],"content-domain":{"domain":["iopscience.iop.org"],"crossmark-restriction":false},"short-container-title":["J. Phys.: Condens. Matter"],"published-print":{"date-parts":[[2026,9,4]]},"abstract":"Abstract<\/jats:title>\n \n The discovery of topological insulators has revolutionized condensed matter physics by introducing materials with insulating bulk states yet symmetry-protected metallic boundary states. Among these, the ternary compound\n \n \n \n <\/jats:tex-math>\n \n \n \n Bi<\/mml:mtext>\n \n 14<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n \n Rh<\/mml:mtext>\n \n 3<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n \n I<\/mml:mtext>\n \n 9<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n <\/mml:mrow>\n <\/mml:math>\n <\/jats:inline-formula>\n stands out as the first realized weak three-dimensional topological insulator constructed from stacked two-dimensional quantum spin Hall layers. This review comprehensively examines the advances in\n \n \n \n <\/jats:tex-math>\n \n \n \n Bi<\/mml:mtext>\n \n 14<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n \n Rh<\/mml:mtext>\n \n 3<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n \n I<\/mml:mtext>\n \n 9<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n <\/mml:mrow>\n <\/mml:math>\n <\/jats:inline-formula>\n and its derivatives, tracing the journey from theoretical prediction to experimental validation. We discuss the material\u2019s unique crystal structure comprising graphene-analogue intermetallic\n \n \n \n <\/jats:tex-math>\n \n \n [<\/mml:mo>\n (<\/mml:mo>\n \n Bi<\/mml:mtext>\n \n 4<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n Rh<\/mml:mtext>\n \n )<\/mml:mo>\n \n 3<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n I<\/mml:mtext>\n \n ]<\/mml:mo>\n \n 2<\/mml:mn>\n +<\/mml:mo>\n <\/mml:mrow>\n <\/mml:msup>\n <\/mml:mrow>\n <\/mml:math>\n <\/jats:inline-formula>\n layers alternating with insulating\n \n \n \n <\/jats:tex-math>\n \n \n [<\/mml:mo>\n \n Bi<\/mml:mtext>\n \n 2<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n \n I<\/mml:mtext>\n \n 8<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n \n ]<\/mml:mo>\n \n 2<\/mml:mn>\n \u2212<\/mml:mo>\n <\/mml:mrow>\n <\/mml:msup>\n <\/mml:mrow>\n <\/mml:math>\n <\/jats:inline-formula>\n spacer layers and its electronic structure characterized by a robust\n \n \n \n <\/jats:tex-math>\n \n \n \u223c<\/mml:mo>\n <\/mml:mrow>\n <\/mml:math>\n <\/jats:inline-formula>\n 210 meV topological gap opened via strong spin\u2013orbit coupling. Critical aspects of crystal growth, intrinsic defects, and real-structure effects are analyzed, alongside experimental confirmations through angle-resolved photoemission spectroscopy and scanning tunneling microscopy, revealing one-dimensional helical edge channels. Furthermore, we explore strategies for Fermi-level tuning via chemical gating and isoelectronic substitution, as well as the correlation between chemical bonding and topological character in related topological materials. This review highlights\n \n \n \n <\/jats:tex-math>\n \n \n \n Bi<\/mml:mtext>\n \n 14<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n \n Rh<\/mml:mtext>\n \n 3<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n \n I<\/mml:mtext>\n \n 9<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n <\/mml:mrow>\n <\/mml:math>\n <\/jats:inline-formula>\n as a model system for understanding weak topology, while critically identifying the key open challenges, including the absence of direct transport evidence for edge-channel conduction, Fermi-level misalignment at the cleaved surfaces, real-structure defects, and limited chemical design rules for the weak topological insulator class that must be addressed to fully realize the proposed functionalities of this material family.\n <\/jats:p>","DOI":"10.1088\/1361-648x\/ae98d0","type":"journal-article","created":{"date-parts":[[2026,8,12]],"date-time":"2026-08-12T22:54:28Z","timestamp":1786575268000},"page":"353001","update-policy":"https:\/\/doi.org\/10.1088\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["\n \n \n Bi<\/mml:mtext>\n \n 14<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n \n \n Rh<\/mml:mi>\n <\/mml:mrow>\n \n 3<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n \n \n I<\/mml:mi>\n <\/mml:mrow>\n \n 9<\/mml:mn>\n <\/mml:mrow>\n <\/mml:msub>\n <\/mml:mrow>\n <\/mml:math>\n : weak topology, crystal chemistry, and emerging functionalities"],"prefix":"10.1088","volume":"38","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2783-4008","authenticated-orcid":true,"given":"Madhav","family":"Prasad Ghimire","sequence":"first","affiliation":[{"name":"Tribhuvan University"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pradip","family":"Basnet","sequence":"additional","affiliation":[{"name":"Tribhuvan University"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8844-8077","authenticated-orcid":true,"given":"Bishnu","family":"Prasad Belbase","sequence":"additional","affiliation":[{"name":"Tribhuvan University"},{"name":"Purdue University"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"266","published-online":{"date-parts":[[2026,9,4]]},"reference":[{"key":"cmae98d0bib1","author":"Ashcroft","year":"1976","type":"book"},{"key":"cmae98d0bib2","doi-asserted-by":"publisher","first-page":"3045","DOI":"10.1103\/RevModPhys.82.3045","type":"journal-article","volume":"82","author":"Hasan","year":"2010","journal-title":"Rev. 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All rights, including for text and data mining, AI training, and similar technologies, are reserved.","name":"copyright_information","label":"Copyright Information"},{"value":"2026-05-08","name":"date_received","label":"Date Received","group":{"name":"publication_dates","label":"Publication dates"}},{"value":"2026-08-12","name":"date_accepted","label":"Date Accepted","group":{"name":"publication_dates","label":"Publication dates"}},{"value":"2026-09-04","name":"date_epub","label":"Online publication date","group":{"name":"publication_dates","label":"Publication dates"}}]}}