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Engineering Correlation and Topologi...

Redell, Matthew D.

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Engineering Correlation and Topological Effects in Transition Metal Oxides.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Engineering Correlation and Topological Effects in Transition Metal Oxides./
作者:	Redell, Matthew D.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2020,
面頁冊數:	149 p.
附註:	Source: Dissertations Abstracts International, Volume: 82-04, Section: B.
Contained By:	Dissertations Abstracts International82-04B.
標題:	Condensed matter physics. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28086012
ISBN:	9798678160683

Engineering Correlation and Topological Effects in Transition Metal Oxides.
Redell, Matthew D.

Engineering Correlation and Topological Effects in Transition Metal Oxides. - Ann Arbor : ProQuest Dissertations & Theses, 2020 - 149 p.

Source: Dissertations Abstracts International, Volume: 82-04, Section: B.

Thesis (Ph.D.)--State University of New York at Binghamton, 2020.

This item must not be sold to any third party vendors.

One of the most diverse classes of materials studied in condensed matter physics is the transition metal oxides. These materials are a playground for researchers to modulate properties like magnetism, superconductivity, charge ordering and topology. One material, SrTiO3 (STO), plays an important role as a substrate for other materials to host novel effects. The surface of STO is notorious for hosting oxygen vacancies which often cause the surface to become reconstructed and promotes correlation effects for Ti sites near the vacancy. When monolayer FeSe is deposited on the surface-reconstructed STO (SR-STO), the superconducting Tc is enhanced by nearly an order of magnitude. We collaborated with Dr. Wei-Li Lee's experimental group at Academia Sinica in Taiwan to explore whether this effect was general for all superconductors. To do this, they grew thin-film Nb on top of c(4 x 2) and √5 times √5R26.6° SR-STO. They observed the onset of a peak in the resistivity near the superconducting transition, and a decrease in the superconductivity for increasing in-plane applied magnetic fields. Using first-principles, we determined that the SR-STO has a strong tendency toward ferromagnetic ordering because of the spin density wave pattern that forms at the surface and confirmed the decrease in Andreev reflection due to surface ferromagnetism using the Landauer formula.Furthermore, ferromagnetic SrRuO3 (SRO) grown on STO has been proposed as a topological Weyl semimetal. The Weyl semimetal is a particularly interesting subset of topological materials because of the chiral bulk bands and Fermi arc surface states. We investigate the axionic charge density wave (CDW) state of the Weyl semimetal and find that in the normal state, an undamped collective mode that forms in the presence of an attractive interaction that is not seen in other materials and can be attributed to the chirality of the Weyl nodes. Furthermore, in the CDW state the plasmon excitations couple to the phonon mode of the CDW which results in a resonant plasmon-axion mode which may be detectable by momentum-resolved electron energy loss spectroscopy.We finally investigate the Weyl/superconductor (W/S) heterostructures. Using a slab geometry, we observe the presence of Fermi arc surface states in the Bi2Se3 model with broken time-reversal symmetry. By coupling this system to a superconductor, we compute the conductance using the Landauer formula to study the Andreev reflection and find that for W/S systems, the proximity effect gaps the surface Fermi arc that is coupled to the superconductor, leading to a suppression of the tunneling conductance from a chirality blockade in the bulk. However, in superconductor/Weyl/superconductor (S/W/S) systems, both surface Fermi arcs become equally gapped, which results in a nearly zero-bias sub-gap peak in the conductance. Thus, by including all effects in the Hamiltonian, we propose a new way for studying these systems, which may have more interesting effects in proximity to unconventional p-wave superconductors.

ISBN: 9798678160683Subjects--Topical Terms:

3173567
Condensed matter physics.
Subjects--Index Terms:

Andreev reflection

Engineering Correlation and Topological Effects in Transition Metal Oxides.
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500 $a Source: Dissertations Abstracts International, Volume: 82-04, Section: B.
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506 $a This item must not be sold to any third party vendors.
520 $a One of the most diverse classes of materials studied in condensed matter physics is the transition metal oxides. These materials are a playground for researchers to modulate properties like magnetism, superconductivity, charge ordering and topology. One material, SrTiO3 (STO), plays an important role as a substrate for other materials to host novel effects. The surface of STO is notorious for hosting oxygen vacancies which often cause the surface to become reconstructed and promotes correlation effects for Ti sites near the vacancy. When monolayer FeSe is deposited on the surface-reconstructed STO (SR-STO), the superconducting Tc is enhanced by nearly an order of magnitude. We collaborated with Dr. Wei-Li Lee's experimental group at Academia Sinica in Taiwan to explore whether this effect was general for all superconductors. To do this, they grew thin-film Nb on top of c(4 x 2) and √5 times √5R26.6° SR-STO. They observed the onset of a peak in the resistivity near the superconducting transition, and a decrease in the superconductivity for increasing in-plane applied magnetic fields. Using first-principles, we determined that the SR-STO has a strong tendency toward ferromagnetic ordering because of the spin density wave pattern that forms at the surface and confirmed the decrease in Andreev reflection due to surface ferromagnetism using the Landauer formula.Furthermore, ferromagnetic SrRuO3 (SRO) grown on STO has been proposed as a topological Weyl semimetal. The Weyl semimetal is a particularly interesting subset of topological materials because of the chiral bulk bands and Fermi arc surface states. We investigate the axionic charge density wave (CDW) state of the Weyl semimetal and find that in the normal state, an undamped collective mode that forms in the presence of an attractive interaction that is not seen in other materials and can be attributed to the chirality of the Weyl nodes. Furthermore, in the CDW state the plasmon excitations couple to the phonon mode of the CDW which results in a resonant plasmon-axion mode which may be detectable by momentum-resolved electron energy loss spectroscopy.We finally investigate the Weyl/superconductor (W/S) heterostructures. Using a slab geometry, we observe the presence of Fermi arc surface states in the Bi2Se3 model with broken time-reversal symmetry. By coupling this system to a superconductor, we compute the conductance using the Landauer formula to study the Andreev reflection and find that for W/S systems, the proximity effect gaps the surface Fermi arc that is coupled to the superconductor, leading to a suppression of the tunneling conductance from a chirality blockade in the bulk. However, in superconductor/Weyl/superconductor (S/W/S) systems, both surface Fermi arcs become equally gapped, which results in a nearly zero-bias sub-gap peak in the conductance. Thus, by including all effects in the Hamiltonian, we propose a new way for studying these systems, which may have more interesting effects in proximity to unconventional p-wave superconductors.
590 $a School code: 0792.
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650 4 $a Theoretical physics. $3 2144760
650 4 $a Materials science. $3 543314
653 $a Andreev reflection
653 $a CDW
653 $a Proximity effect
653 $a Strontium titanate
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710 2 $a State University of New York at Binghamton. $b Physics, Applied Physics, and Astronomy. $3 1266322
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