arXiv subjects

Uihyeon Seo

Publications and source records attributed to Uihyeon Seo.

3 recordsLinked to original sources

arXiv2025

Tunneling magnetoresistance in altermagnetic RuO$_2$-based magnetic tunnel junctions

Altermagnets exhibit characteristics akin to antiferromagnets, with spin-split anisotropic bands in momentum space. RuO$_2$ has been considered as a prototype altermagnet; however, recent reports have questioned altermagnetic ground state in this material. In this study, we provide direct experimental evidence of altermagnetic characteristics in RuO$_2$ films by demonstrating spin-dependent tunneling magnetoresistance (TMR) in RuO$_2$-based magnetic tunnel junctions. Our results show the spin-splitted anisotropic band structure of RuO$_2$, with the observed TMR determined by the direction of the Néel vector of RuO$_2$. These results reflect the altermagnetic nature of RuO$_2$ and highlight its potential for spintronic applications, leveraging the combined strengths of ferromagnetic and antiferromagnetic systems.

cond-mat.mtrl-sci↗

arXiv2024

Colossal optical anisotropy in wide-bandgap semiconductor CuAlO2

Colossal optical anisotropy in the entire visible spectrum is crucial for advanced photonic applications, enabling precise light manipulation without optical loss across a broad spectral range. Here, we demonstrate that CuAlO2 exhibits colossal optical anisotropy and transparency across the visible spectrum, enabled by its unique three-dimensional O-Cu-O dumbbell structure and two-dimensionally confined excitons. Using mm-sized single crystals, we independently measured ab-plane and c-axis optical properties, revealing maximum birefringence (= 3.67) and linear dichroism (= 5.21), the highest reported to date. CuAlO2 retains birefringence over 0.5 throughout the entire visible range and possesses a wide direct bandgap of 3.71 eV, surpassing the birefringence of commercial anisotropic crystals transparent in the visible spectrum. From the two-dimensional screened hydrogen model and first-principles calculations, we demonstrate that the colossal anisotropy arises from a unique excitonic Cu d-p transition confined to the atomic-thick layer. This colossal optical anisotropy and transparency across the entire visible spectrum makes CuAlO2 a promising candidate for future photonic technologies.

cond-mat.mtrl-sci↗

arXiv2023

Suppression of Antiferromagnetic Order by Strain in Honeycomb Cobaltate: Implication for Quantum Spin Liquid

Recently, layered honeycomb cobaltates have been predicted as a new promising system for realizing the Kitaev quantum spin liquid, a many-body quantum entangled ground state characterized by fractional excitations. However, these cobaltates, similar to other candidate materials, exhibit classical antiferromagnetic ordering at low temperatures, which impedes the formation of the expected quantum state. Here, we demonstrate that the control of the trigonal crystal field of Co ions is crucial to suppress classical antiferromagnetic ordering and to locate its ground state in closer vicinity to quantum spin liquid in layered honeycomb cobaltates. By utilizing heterostructure engineering on Cu3Co2SbO6 thin films, we adjust the trigonal distortion of CoO6 octahedra and the associated trigonal crystal field. The original Néel temperature of 16 K in bulk Cu3Co2SbO6 decreases (increases) to 7.8 K (22.7 K) in strained Cu3Co2SbO6 films by decreasing (increasing) the magnitude of the trigonal crystal fields. Our experimental finding substantiates the potential of layered honeycomb cobaltate heterostructures and strain engineering to accomplish the extremely elusive quantum phase of matter.

cond-mat.str-el↗