博士候選人公開演講
形變二維材料引發之量子現象/ Strain-induced quantum phenomena in 2D materials
應變電子學提供了一個顯著改變物質的電子結構和特性的平台，例如，在不破壞時間反轉對稱性的情況下誘發偽量子霍爾效應和非常規霍爾效應。 然而，在介觀系統中引入完全可控的應變場仍然具有挑戰性。 在這裡，我們透過光刻雕刻六方氮化硼 (hBN) 開發了一種新穎的基板工程技術，以精確地創建任意可控的應變並保持二維材料的高品質。 因此，我們成功地在室溫下設計了波紋二硫化鉬的材料特性，包括聲子、光致發光和層間激子的設計。 展示實現二維材料屬性修改的靈活方法。
輸運系統中應變引起的一維贗磁邊界在波紋石墨烯中產生了明顯的縱向電阻率各向異性。 這種各向異性將透過施加外部磁場而增強。 當磁場足夠大以產生量子霍爾效應時，橫向電阻率會出現與相應的量子霍爾平台相關的獨特狀態。 可能的機制可能來自於所涉及的蛇態或贗Landua能階，使得應變區出現過早的量子霍爾電流。 這項發現可能為進一步探索二維材料中其他應變引起的量子現像打開大門，這表明我們的應變工程可能與量子現象交叉。
此外，我們將波紋結構擴展到週期性六邊形排列的孔，類似於將一維應變邊界彎曲成閉合的二維圓形應變邊界。 將此週期性應變陣列應用於多層石墨烯可製成應變三角形超晶格裝置。 透過原子力顯微鏡在應變三角形超晶格中檢測到異常形貌，可能是由於俘獲電荷造成的。 這導致了低溫下的金屬-絕緣體轉變（MIT）以及隨後的幾何挫敗狀磁性，這種情況讓人想起強相關係統。 與載子濃度敏感系統不同，強相關性會被更大的驅動電流所屏蔽，這意味著背後的基本機制不同。 這些結果極大地促進了對二維繫統中應變效應的理解和操縱，可能為探索材料科學和量子研究中的強相關狀態提供富有想像的途徑。
我們透過對不同設計的結構和二維材料進行應變工程，實現了各種奇異現象。 這為研究應變電子學提供了多種途徑，並為未來探索應變引起的量子現象鋪平了道路。 在我們的研究中，應變工程的創新應用是加深我們對二維材料機械變形和量子行為之間關係的理解的基石。
Straintronics provides a platform to significantly change the electronic structure and properties of matter, for example, inducing the pseudo-quantum Hall effect and unconventional Hall effects without breaking time-reversal symmetry. However, introducing a fully-controllable strain field in a mesoscopic system is still challenging. Here, we developed a novel substrate-engineering technique via lithographically engraved hexagonal boron nitride (hBN) to create arbitrarily controllable strains precisely and preserve the high quality of 2D materials. As a result, we successfully engineered the material properties, including the design of phonon, photoluminescence, and interlayer exciton, in corrugated molybdenum disulfide at room temperature. Demonstrate a flexible approach to achieving property modification in 2D materials.
The strain-induced 1D pseudo-magnetic boundary in the transport system creates an obvious anisotropy in longitudinal resistivity in corrugated graphene. Such anisotropy will be enhanced by applying an external magnetic field. When the magnetic field is large enough to create a quantum Hall effect, the transverse resistivity emerges unique states related to corresponding quantized Hall plateaus. The possible mechanism may come from the snake state or pseudo-Landua levels involved and make the premature quantum Hall current in the strain region. This finding may open the gate to further exploration into other strain-induced quantum phenomena in two-dimensional materials, which suggests our strain engineering could intersect with quantum phenomena.
Furthermore, We have extended the corrugation structure to periodic hexagonally arranged holes, an analogy to bending 1D strain boundaries into closed, 2D circular strain boundaries. Employing such a periodic strain array to multilayer graphene makes a strain-triangular superlattice device. An anomalous topography, possibly due to trapped charge, is detected in the strain-triangular superlattice via atomic force microscopy. This led to the metal-insulator transition (MIT) at low temperatures and subsequent geometrically frustrated-like magnetism, a scenario reminiscent of strongly correlated systems. Unlike the carrier concentration-sensitive system, the strong correlation will be screened with a larger driven current, implying the different fundamental mechanisms behind it. These results significantly advance understanding and manipulating strain effects in 2D systems, potentially offering imaginative paths for exploring strongly correlated states in materials science and quantum research.
We have achieved various exotic phenomena through our strain engineering on differently designed structures and 2D materials. This offers diverse avenues for studying straintronics and paves the way for future explorations into strain-induced quantum phenomena. The innovative use of strain engineering in our studies is a cornerstone for advancing our understanding of the relationship between mechanical deformation and quantum behaviors in 2D materials.
輸運系統中應變引起的一維贗磁邊界在波紋石墨烯中產生了明顯的縱向電阻率各向異性。 這種各向異性將透過施加外部磁場而增強。 當磁場足夠大以產生量子霍爾效應時，橫向電阻率會出現與相應的量子霍爾平台相關的獨特狀態。 可能的機制可能來自於所涉及的蛇態或贗Landua能階，使得應變區出現過早的量子霍爾電流。 這項發現可能為進一步探索二維材料中其他應變引起的量子現像打開大門，這表明我們的應變工程可能與量子現象交叉。
此外，我們將波紋結構擴展到週期性六邊形排列的孔，類似於將一維應變邊界彎曲成閉合的二維圓形應變邊界。 將此週期性應變陣列應用於多層石墨烯可製成應變三角形超晶格裝置。 透過原子力顯微鏡在應變三角形超晶格中檢測到異常形貌，可能是由於俘獲電荷造成的。 這導致了低溫下的金屬-絕緣體轉變（MIT）以及隨後的幾何挫敗狀磁性，這種情況讓人想起強相關係統。 與載子濃度敏感系統不同，強相關性會被更大的驅動電流所屏蔽，這意味著背後的基本機制不同。 這些結果極大地促進了對二維繫統中應變效應的理解和操縱，可能為探索材料科學和量子研究中的強相關狀態提供富有想像的途徑。
我們透過對不同設計的結構和二維材料進行應變工程，實現了各種奇異現象。 這為研究應變電子學提供了多種途徑，並為未來探索應變引起的量子現象鋪平了道路。 在我們的研究中，應變工程的創新應用是加深我們對二維材料機械變形和量子行為之間關係的理解的基石。
Straintronics provides a platform to significantly change the electronic structure and properties of matter, for example, inducing the pseudo-quantum Hall effect and unconventional Hall effects without breaking time-reversal symmetry. However, introducing a fully-controllable strain field in a mesoscopic system is still challenging. Here, we developed a novel substrate-engineering technique via lithographically engraved hexagonal boron nitride (hBN) to create arbitrarily controllable strains precisely and preserve the high quality of 2D materials. As a result, we successfully engineered the material properties, including the design of phonon, photoluminescence, and interlayer exciton, in corrugated molybdenum disulfide at room temperature. Demonstrate a flexible approach to achieving property modification in 2D materials.
The strain-induced 1D pseudo-magnetic boundary in the transport system creates an obvious anisotropy in longitudinal resistivity in corrugated graphene. Such anisotropy will be enhanced by applying an external magnetic field. When the magnetic field is large enough to create a quantum Hall effect, the transverse resistivity emerges unique states related to corresponding quantized Hall plateaus. The possible mechanism may come from the snake state or pseudo-Landua levels involved and make the premature quantum Hall current in the strain region. This finding may open the gate to further exploration into other strain-induced quantum phenomena in two-dimensional materials, which suggests our strain engineering could intersect with quantum phenomena.
Furthermore, We have extended the corrugation structure to periodic hexagonally arranged holes, an analogy to bending 1D strain boundaries into closed, 2D circular strain boundaries. Employing such a periodic strain array to multilayer graphene makes a strain-triangular superlattice device. An anomalous topography, possibly due to trapped charge, is detected in the strain-triangular superlattice via atomic force microscopy. This led to the metal-insulator transition (MIT) at low temperatures and subsequent geometrically frustrated-like magnetism, a scenario reminiscent of strongly correlated systems. Unlike the carrier concentration-sensitive system, the strong correlation will be screened with a larger driven current, implying the different fundamental mechanisms behind it. These results significantly advance understanding and manipulating strain effects in 2D systems, potentially offering imaginative paths for exploring strongly correlated states in materials science and quantum research.
We have achieved various exotic phenomena through our strain engineering on differently designed structures and 2D materials. This offers diverse avenues for studying straintronics and paves the way for future explorations into strain-induced quantum phenomena. The innovative use of strain engineering in our studies is a cornerstone for advancing our understanding of the relationship between mechanical deformation and quantum behaviors in 2D materials.
