9:25 PM - *NM01.06.02
Novel Physics Induced by Dimensional Reduction from 3D to 2D in Layered Materials
University of Science and Technology of China1
Two-dimensional (2D) materials have attracted plenty of interests due to the novel physical properties induced by the reduction of dimension compared to three-demensional (3D) system, and the practical and potential application of revolutionary current technologies as well. It is of great significance to extensively investigate the fundamental physics of the related materials in the two-dimensional limit. The success of 2D materials is based on the development of suitable synthesis methods, mainly including exfoliation, chemical vapour deposition and various solution-phase methods. New and more efficient methods are under developing. Recently, we have successfully intercalated organic ion cetyltrimethyl ammonium (CTA+) and tetrabutyl ammonium (TBA+) into several layered crystals via electrochemical intercalation method, realizing two-dimensionalization of the related functional layers and observing some intriguing new physical phenomena. We intercalated CTA+ and TBA+ into the FeSe single crystal by the electrochemical method, achieving high superconducting transition temperature (Tc) to be 45 and 50 K for (CTA)0.3FeSe and (TBA)0.3FeSe, respectively. By measuring Knight shift and nuclear spin-lattice relaxation rate, we unambiguously observed a pseudogap behavior below Tp ∼ 60 K in these two kinds of layered FeSe-based high-temperature superconductors, and revealed that the pseudogap behavior is related to strong superconducting fluctuations due to the quasi-2D nature induced by the organic-ion intercalations. With intercalating the same organic ions into an intrinsic semiconductor SnSe2, superconductivity with Tc to ~6.4 (TBA+) and 7.1 K (CTA+) was achieved. We also synthesized an organic-ion intercalated transition-metal dichalcogenides (TBA)0.3VSe2, where the metallic charge-density-wave (CDW) state with transition temperature (TCDW) of 110 K in the pristine system was changed to an insulating CDW state with TCDW of 165 K by the intercalation. With TBA+-intercalation, the insulating ferromagnetic van der Waals material Cr2Ge2Te6 with Curie temperature Tcurie of 67 K was altered to a metallic ferromagnet with Tcurie of 208 K, accompanied by the magnetic easy axis changing from <001> direction to the ab plane. Our work indicated that the 3D-to-2D crossover induced by intercalation of the large organic ion CTA+ and TBA+ between functional layers plays a key role in the dramatic changes of the physical properties in the several material systems, and demonstrated that the intercalation of organic ions with large size can serves as a convenient and efficient approach to explore and manipulate the versatile electronic and magnetic properties in the layered crystals.
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