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Tuning Lattice Dynamics and Electron...

Hu, Yajian.

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Tuning Lattice Dynamics and Electronic Structure in Superconducting Correlated Electron Systems.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Tuning Lattice Dynamics and Electronic Structure in Superconducting Correlated Electron Systems./
作者:	Hu, Yajian.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2019,
面頁冊數:	127 p.
附註:	Source: Dissertations Abstracts International, Volume: 81-09, Section: B.
Contained By:	Dissertations Abstracts International81-09B.
標題:	Electromagnetics. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=27783959
ISBN:	9781392427651

Tuning Lattice Dynamics and Electronic Structure in Superconducting Correlated Electron Systems.
Hu, Yajian.

Tuning Lattice Dynamics and Electronic Structure in Superconducting Correlated Electron Systems. - Ann Arbor : ProQuest Dissertations & Theses, 2019 - 127 p.

Source: Dissertations Abstracts International, Volume: 81-09, Section: B.

Thesis (Ph.D.)--The Chinese University of Hong Kong (Hong Kong), 2019.

Tuning a material towards the phase boundary has been a pivotal area in the modern research of quantum materials because the interaction between quasiparticles can be varied and novel physics arises. In this thesis, we focus on two systems, A3T4Sn13 and MoTe2, for the purpose of exploring different phases under pressure and their influence on the superconductivity.Certain members of A3T4Sn13 family (A = Ca,Sr, T = Rh, Ir, Co) are strong coupling superconductors, where electron-phonon interaction plays an important role. In T = Rh, Ir series, the suppression of a second-order structural transition and a superconducting dome were observed by applying chemical or physical pressure, featuring a structural quantum critical point (QCP). This competition between the structural order and superconductivity can be interpreted by the soft phonon scenario associated with the structural transition.In our work, a universal temperature-lattice constant phase diagram for A3T4Sn13 materials is constructed. We use a deconvolution method to obtain the spectral phonon density of states and the electron-phonon transport coupling function from the lattice specfic heat and resistivity. The comparison between Ca3Co4Sn13 which is far from the structural instability, and other compositions located near QCP demonstrates the phonon softening when the system is tuned towards the QCP. Furthermore, our analysis implies that the strong coupling with these low energy phonons is responsible for the enhancement of Tc in the vicinity of QCP. MoTe2 is predicted to be a type-II Weyl semimetal in Td phase, which host topologically non-trivial band structure. It undergoes a superconducting transition at ambient pressure, which is rarely seen among topological semimetals and makes MoTe2 a strong candidate to realize bulk topological superconductivity. At high temperature around 250 K, MoTe2 undergoes a structural transition from Td to 1T' phase. With an increasing pressure, the structural transition temperature can be drastically suppressed and the superconducting transition temperature can be rapidly enhanced. Intense research effort have been invested to probe the electronic structure of MoTe2. However, the quantum oscillation experiments have never detected the frequencies from the hole pockets, which were well-resolved by spectroscopic studies and DFT calculations. The absence of hole pockets raises uncertainty regarding the electron-hole carrier compensation picture and more importantly, the existence of type-II Weyl points in MoTe2.In this thesis, we use hydrostatic pressure to tune the system and study the magnetotransport properties in both Td and 1T0 phase of MoTe2. By applying pressure, the extremely large magnetoresistance are suppressed. Upper critical eld at 15 kbar (1T' phase) is studied, showing two-dimensional superconductivity in MoTe2 at high pressure. Furthermore, we investigate the electronic structure of MoTe2 via Shubnikov-de Haas (SdH) oscillations. The high frequencies associated with the hole pockets are successfully detected. The pressure evolution of the SdH oscillations were measured. Under pressure, Fermi surfaces in MoTe2 expand, becoming more two-dimensional. Our data, together with calculations, solve the long-standing discrepancy between DFT calculations and quantum oscillation data. The importance of electron correlation energy is highlighted. Moreover, our results serve to re-establish the type-II Weyl physics in MoTe2.

ISBN: 9781392427651Subjects--Topical Terms:

3173223
Electromagnetics.
Subjects--Index Terms:

Phase boundary

Tuning Lattice Dynamics and Electronic Structure in Superconducting Correlated Electron Systems.
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520 $a Tuning a material towards the phase boundary has been a pivotal area in the modern research of quantum materials because the interaction between quasiparticles can be varied and novel physics arises. In this thesis, we focus on two systems, A3T4Sn13 and MoTe2, for the purpose of exploring different phases under pressure and their influence on the superconductivity.Certain members of A3T4Sn13 family (A = Ca,Sr, T = Rh, Ir, Co) are strong coupling superconductors, where electron-phonon interaction plays an important role. In T = Rh, Ir series, the suppression of a second-order structural transition and a superconducting dome were observed by applying chemical or physical pressure, featuring a structural quantum critical point (QCP). This competition between the structural order and superconductivity can be interpreted by the soft phonon scenario associated with the structural transition.In our work, a universal temperature-lattice constant phase diagram for A3T4Sn13 materials is constructed. We use a deconvolution method to obtain the spectral phonon density of states and the electron-phonon transport coupling function from the lattice specfic heat and resistivity. The comparison between Ca3Co4Sn13 which is far from the structural instability, and other compositions located near QCP demonstrates the phonon softening when the system is tuned towards the QCP. Furthermore, our analysis implies that the strong coupling with these low energy phonons is responsible for the enhancement of Tc in the vicinity of QCP. MoTe2 is predicted to be a type-II Weyl semimetal in Td phase, which host topologically non-trivial band structure. It undergoes a superconducting transition at ambient pressure, which is rarely seen among topological semimetals and makes MoTe2 a strong candidate to realize bulk topological superconductivity. At high temperature around 250 K, MoTe2 undergoes a structural transition from Td to 1T' phase. With an increasing pressure, the structural transition temperature can be drastically suppressed and the superconducting transition temperature can be rapidly enhanced. Intense research effort have been invested to probe the electronic structure of MoTe2. However, the quantum oscillation experiments have never detected the frequencies from the hole pockets, which were well-resolved by spectroscopic studies and DFT calculations. The absence of hole pockets raises uncertainty regarding the electron-hole carrier compensation picture and more importantly, the existence of type-II Weyl points in MoTe2.In this thesis, we use hydrostatic pressure to tune the system and study the magnetotransport properties in both Td and 1T0 phase of MoTe2. By applying pressure, the extremely large magnetoresistance are suppressed. Upper critical eld at 15 kbar (1T' phase) is studied, showing two-dimensional superconductivity in MoTe2 at high pressure. Furthermore, we investigate the electronic structure of MoTe2 via Shubnikov-de Haas (SdH) oscillations. The high frequencies associated with the hole pockets are successfully detected. The pressure evolution of the SdH oscillations were measured. Under pressure, Fermi surfaces in MoTe2 expand, becoming more two-dimensional. Our data, together with calculations, solve the long-standing discrepancy between DFT calculations and quantum oscillation data. The importance of electron correlation energy is highlighted. Moreover, our results serve to re-establish the type-II Weyl physics in MoTe2.
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