Ziying Wang
Position: Grad Students
Affiliation: NUS Centre for Advanced 2D Materials
Research Type: Experiment
Office: MD1
Email: a0112448@u.nus.edu
CA2DM Publications:
2023 |
Liu, Chaofei; Zhang, Xiuying; Wang, Xinyun; Wang, Ziying; Abdelwahab, Ibrahim; Verzhbitskiy, Ivan; Shao, Yan; Eda, Goki; Sun, Wanxin; Shen, Lei; Loh, Kian Ping Ferroelectricity in Niobium Oxide Dihalides NbOX2 (X = Cl, I): A Macroscopic- to Microscopic-Scale Study Journal Article ACS NANO, 17 (8), pp. 7170-7179, 2023, ISSN: 1936-0851. @article{ISI:000969846300001, title = {Ferroelectricity in Niobium Oxide Dihalides NbOX2 (X = Cl, I): A Macroscopic- to Microscopic-Scale Study}, author = {Chaofei Liu and Xiuying Zhang and Xinyun Wang and Ziying Wang and Ibrahim Abdelwahab and Ivan Verzhbitskiy and Yan Shao and Goki Eda and Wanxin Sun and Lei Shen and Kian Ping Loh}, doi = {10.1021/acsnano.2c09267}, times_cited = {0}, issn = {1936-0851}, year = {2023}, date = {2023-04-10}, journal = {ACS NANO}, volume = {17}, number = {8}, pages = {7170-7179}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {2D materials with ferroelectric and piezoelectric properties are of interest for energy harvesting, memory storage and electromechanical systems. Here, we present a systematic study of the ferroelectric properties in NbOX2 (X = Cl, I) across different spatial scales. The in-plane ferroelectricity in NbOX2 was investigated using transport and piezoresponse force microscopy (PFM) measurements, where it was observed that NbOCl2 has a stronger ferroelectric order than NbOI2. A high local field, exerted by both PFM and scanning tunneling microscopy (STM) tips, was found to induce 1D collinear ferroelectric strips in NbOCl2. STM imaging reveals the unreconstructed atomic structures of NbOX2 surfaces, and scanning tunneling spectroscopy was used to probe the electronic states induced at defect (vacancy) sites.}, keywords = {}, pubstate = {published}, tppubtype = {article} } 2D materials with ferroelectric and piezoelectric properties are of interest for energy harvesting, memory storage and electromechanical systems. Here, we present a systematic study of the ferroelectric properties in NbOX2 (X = Cl, I) across different spatial scales. The in-plane ferroelectricity in NbOX2 was investigated using transport and piezoresponse force microscopy (PFM) measurements, where it was observed that NbOCl2 has a stronger ferroelectric order than NbOI2. A high local field, exerted by both PFM and scanning tunneling microscopy (STM) tips, was found to induce 1D collinear ferroelectric strips in NbOCl2. STM imaging reveals the unreconstructed atomic structures of NbOX2 surfaces, and scanning tunneling spectroscopy was used to probe the electronic states induced at defect (vacancy) sites. |
2022 |
Wang, Ziying; Wang, Zishen; Feng, Yuan Ping; Loh, Kian Ping Probing the Origin of Chiral Charge Density Waves in the Two-Dimensional Limits Journal Article NANO LETTERS, 2022, ISSN: 1530-6984. @article{ISI:000856557800001, title = {Probing the Origin of Chiral Charge Density Waves in the Two-Dimensional Limits}, author = {Ziying Wang and Zishen Wang and Yuan Ping Feng and Kian Ping Loh}, doi = {10.1021/acs.nanolett.2c02723}, times_cited = {0}, issn = {1530-6984}, year = {2022}, date = {2022-09-13}, journal = {NANO LETTERS}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Chirality generates spontaneous symmetry breaking and profoundly influences the topology, charge, and spin orders of materials. The chiral charge density wave (CDW) exhibits macroscopic chirality in the achiral crystal during the spontaneous electronic phase transitions. However, the mechanism of chiral CDW formation is shrouded in controversy. In this work, we report that two-dimensional H-phase TaS2 synthesized by molecular-beam epitaxy (MBE) shows a predominantly chiral CDW phase. Scanning tunneling microscopy (STM) imaging of the CDW reconstruction spots reveals a clockwise or anticlockwise intensity variation along the STM-imaged spots. First-principles calculations further show that the rotational symmetry of the momentum-dependent electronphonon coupling is broken, giving rise to chirality. Our work provides new insights into the physical origin of the chiral charge-ordered states, shedding light on a general ordering rule in chiral CDWs.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Chirality generates spontaneous symmetry breaking and profoundly influences the topology, charge, and spin orders of materials. The chiral charge density wave (CDW) exhibits macroscopic chirality in the achiral crystal during the spontaneous electronic phase transitions. However, the mechanism of chiral CDW formation is shrouded in controversy. In this work, we report that two-dimensional H-phase TaS2 synthesized by molecular-beam epitaxy (MBE) shows a predominantly chiral CDW phase. Scanning tunneling microscopy (STM) imaging of the CDW reconstruction spots reveals a clockwise or anticlockwise intensity variation along the STM-imaged spots. First-principles calculations further show that the rotational symmetry of the momentum-dependent electronphonon coupling is broken, giving rise to chirality. Our work provides new insights into the physical origin of the chiral charge-ordered states, shedding light on a general ordering rule in chiral CDWs. |
Wang, Ziying; Wang, Zishen; Zhou, Xin; Fu, Wei; Li, Haohan; Liu, Chaofei; Qiao, Jingsi; Quek, Su Ying; Su, Chenliang; Feng, Yuanping; Loh, Kian Ping Giant g-factor in Self-Intercalated 2D TaS2 Journal Article SMALL, 18 (38), 2022, ISSN: 1613-6810. @article{ISI:000842350300001, title = {Giant \textit{g}-factor in Self-Intercalated 2D TaS_{2}}, author = {Ziying Wang and Zishen Wang and Xin Zhou and Wei Fu and Haohan Li and Chaofei Liu and Jingsi Qiao and Su Ying Quek and Chenliang Su and Yuanping Feng and Kian Ping Loh}, doi = {10.1002/smll.202201975}, times_cited = {0}, issn = {1613-6810}, year = {2022}, date = {2022-08-21}, journal = {SMALL}, volume = {18}, number = {38}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {Central to the application of spintronic devices is the ability to manipulate spins by electric and magnetic fields, which relies on a large Lande g-factor. The self-intercalation of layered transitional metal dichalcogenides with native metal atoms can serve as a new strategy to enhance the g-factor by inducing ferromagnetic instability in the system via interlayer charge transfer. Here, scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) are performed to extract the g-factor and characterize the electronic structure of the self-intercalated phase of 2H-TaS2. In Ta7S12, a sharp density of states (DOS) peak due to the Ta intercalant appears at the Fermi level, which satisfies the Stoner criteria for spontaneous ferromagnetism, leading to spin split states. The DOS peak shows sensitivity to magnetic field up to 1.85 mV T-1, equivalent to an effective g-factor of approximate to 77. This work establishes self-intercalation as an approach for tuning the g-factor.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Central to the application of spintronic devices is the ability to manipulate spins by electric and magnetic fields, which relies on a large Lande g-factor. The self-intercalation of layered transitional metal dichalcogenides with native metal atoms can serve as a new strategy to enhance the g-factor by inducing ferromagnetic instability in the system via interlayer charge transfer. Here, scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) are performed to extract the g-factor and characterize the electronic structure of the self-intercalated phase of 2H-TaS2. In Ta7S12, a sharp density of states (DOS) peak due to the Ta intercalant appears at the Fermi level, which satisfies the Stoner criteria for spontaneous ferromagnetism, leading to spin split states. The DOS peak shows sensitivity to magnetic field up to 1.85 mV T-1, equivalent to an effective g-factor of approximate to 77. This work establishes self-intercalation as an approach for tuning the g-factor. |
2019 |
Wang, Ziying; Chu, Leiqiang; Li, Linjun; Yang, Ming; Wang, Junyong; Eda, Goki; Loh, Kian Ping Modulating Charge Density Wave Order in a 1T-TaS2/Black Phosphorus Heterostructure Journal Article NANO LETTERS, 19 (5), pp. 2840-2849, 2019, ISSN: 1530-6984. @article{ISI:000467781900012, title = {Modulating Charge Density Wave Order in a 1T-TaS_{2}/Black Phosphorus Heterostructure}, author = {Ziying Wang and Leiqiang Chu and Linjun Li and Ming Yang and Junyong Wang and Goki Eda and Kian Ping Loh}, doi = {10.1021/acs.nanolett.8b04805}, times_cited = {0}, issn = {1530-6984}, year = {2019}, date = {2019-05-01}, journal = {NANO LETTERS}, volume = {19}, number = {5}, pages = {2840-2849}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Controllability of collective electron states has been a long-sought scientific and technological goal and promises development of new devices. Herein, we investigate the tuning of charge density wave (CDW) in 1T-TaS2 via a two-dimensional (2D) van der Waals heterostructure of 1T-TaS2/BP. Unusual gate-dependent conductance oscillations were observed in 1T-TaS2 nanoflake supported on BP in transport measurements. Scanning tunneling microscopy study shows that the nearly commensurate (NC) CDW phase survived to 4.5 K in this system, which is substantially lower than the NC to commensurate CDW phase transition temperature of 180 K. A Coulomb blockade model was invoked to explain the conductance oscillations, where the domain walls and domains in NC phase serve as series of quantum dot arrays and tunnelling barriers, respectively. Density functional theory calculations show that a range of interfacial interactions, including strain and charge transfer, influences the CDW stabilities. Our work sheds light on tuning CDW orders via 2D heterostructure stacking and provides new insights on the CDW phase transition and sliding mechanism.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Controllability of collective electron states has been a long-sought scientific and technological goal and promises development of new devices. Herein, we investigate the tuning of charge density wave (CDW) in 1T-TaS2 via a two-dimensional (2D) van der Waals heterostructure of 1T-TaS2/BP. Unusual gate-dependent conductance oscillations were observed in 1T-TaS2 nanoflake supported on BP in transport measurements. Scanning tunneling microscopy study shows that the nearly commensurate (NC) CDW phase survived to 4.5 K in this system, which is substantially lower than the NC to commensurate CDW phase transition temperature of 180 K. A Coulomb blockade model was invoked to explain the conductance oscillations, where the domain walls and domains in NC phase serve as series of quantum dot arrays and tunnelling barriers, respectively. Density functional theory calculations show that a range of interfacial interactions, including strain and charge transfer, influences the CDW stabilities. Our work sheds light on tuning CDW orders via 2D heterostructure stacking and provides new insights on the CDW phase transition and sliding mechanism. |
2018 |
Wang, Ziying; Sun, Yi-Yang; Abdelwahab, Ibrahim; Cao, Liang; Yu, Wei; Ju, Huanxin; Zhu, Junfa; Fu, Wei; Chu, Leiqiang; Xu, Hai; Loh, Kian Ping Surface-Limited Superconducting Phase Transition on 1T-TaS2 Journal Article ACS NANO, 12 (12), pp. 12619-12628, 2018, ISSN: 1936-0851. @article{ISI:000454567500085, title = {Surface-Limited Superconducting Phase Transition on 1\textit{T}-TaS_{2}}, author = {Ziying Wang and Yi-Yang Sun and Ibrahim Abdelwahab and Liang Cao and Wei Yu and Huanxin Ju and Junfa Zhu and Wei Fu and Leiqiang Chu and Hai Xu and Kian Ping Loh}, doi = {10.1021/acsnano.8b07379}, times_cited = {0}, issn = {1936-0851}, year = {2018}, date = {2018-12-01}, journal = {ACS NANO}, volume = {12}, number = {12}, pages = {12619-12628}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Controlling superconducting phase transition on a two-dimensional (2D) material is of great fundamental and technological interest from the viewpoint of making 2D resistance-free electronic circuits. Here, we demonstrate that a 1T-to-2H phase transition can be induced on the topmost monolayer of bulk (<100 nm thick) 1T-TaS2 by thermal annealing. The monolayer 2H-TaS2 on bulk 1T-TaS2 exhibits a superconducting transition temperature (T-c) of 2.1 K, which is significantly enhanced compared to that of bulk 2H-TaS2. Scanning tunneling microscopy measurements reveal a 3 X 3 charge density wave (CDW) in the phase-switched monolayer at 4.5 K. The enhanced Tc is explained by the suppressed 3 X 3 CDW and a charge-transfer doping from the IT substrate. We further show that the monolayer 2H-TaS2 could be switched back to 1T phase by applying a voltage pulse. The observed surface-limited superconducting phase transition offers a convenient way to prepare robust 2D superconductivity on bulk 1T-TaS2 crystal, thereby bypassing the need to exfoliate monolayer samples.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Controlling superconducting phase transition on a two-dimensional (2D) material is of great fundamental and technological interest from the viewpoint of making 2D resistance-free electronic circuits. Here, we demonstrate that a 1T-to-2H phase transition can be induced on the topmost monolayer of bulk (<100 nm thick) 1T-TaS2 by thermal annealing. The monolayer 2H-TaS2 on bulk 1T-TaS2 exhibits a superconducting transition temperature (T-c) of 2.1 K, which is significantly enhanced compared to that of bulk 2H-TaS2. Scanning tunneling microscopy measurements reveal a 3 X 3 charge density wave (CDW) in the phase-switched monolayer at 4.5 K. The enhanced Tc is explained by the suppressed 3 X 3 CDW and a charge-transfer doping from the IT substrate. We further show that the monolayer 2H-TaS2 could be switched back to 1T phase by applying a voltage pulse. The observed surface-limited superconducting phase transition offers a convenient way to prepare robust 2D superconductivity on bulk 1T-TaS2 crystal, thereby bypassing the need to exfoliate monolayer samples. |