arXiv subjects

Chia-Hsiu Hsu

Publications and source records attributed to Chia-Hsiu Hsu.

13 recordsLinked to original sources

arXiv2026

Anomalous vortex shape in a frustrated superconductor hosting chiral multicomponent order parameters

Multicomponent chiral superconductors can host spatially separated superconducting components within a single Abrikosov vortex, leading to unconventional, anisotropic vortex shapes forbidden in conventional single-component superconductors. Here, using spectroscopic scanning tunneling microscopy at 0.3 K, we investigate the mixed state of the spinel superconductor LiTi2O4 (Tc = 13 K). In the low-field regime, where vortex-vortex interactions are minimized and the intrinsic single-vortex shape is preserved, reasonably isolated triangular Abrikosov vortices are directly visualized with high statistical significance. Remarkably, the vortex orientation is locked to crystallographic domains rather than the magnetic-field direction, revealing a hidden chirality selectivity embedded in the zero-field electronic state.

cond-mat.supr-con↗

arXiv2026

Stabilizing Itinerant Electrons in a Corner-Sharing Kagomé Oxide Nd4Os3ZnO14

Kagome oxides provide a fertile platform for exploring exotic electronic states arising from geometrical frustration and characteristic band topology. Here, we report the synthesis of a 5d transition-metal kagome oxide, Nd4Os3ZnO14, obtained via high-temperature, high-pressure hydrothermal synthesis. Single-crystal X-ray diffraction reveals a two-dimensional kagome network formed by corner-sharing OsO6 octahedra, with a nominal osmium valence of +4.67. In-plane resistivity and hard X-ray photoelectron spectroscopy measurements indicate that the semimetallic electronic structure at room temperature evolves into a semiconducting ground state upon cooling, accompanied by a pronounced enhancement of hole mobility. Magnetic susceptibility measurements demonstrate localized Nd3+ moments without long-range magnetic order down to 2 K. The coexistence of a metallic kagome plane, strong spin-orbit coupling inherent to 5d electrons, and rare-earth magnetism establishes Nd4Os3ZnO14 as a promising platform for investigating correlated electron phenomena in kagome oxides within the itinerant regime.

cond-mat.str-el↗

arXiv2026

Observation of a structurally driven, reversible topological phase transition in a distorted square net material

Topological materials hold immense promise for exhibiting exotic quantum phenomena, yet achieving controllable topological phase transitions remains challenging. Here, we demonstrate a structurally driven, reversible topological phase transition in the distorted square net material GdPS, induced via in situ potassium dosing. Using angle-resolved photoemission spectroscopy and first principles calculations, we demonstrate a cascade of topological phases in the sub-surface P layer: from a large, topologically trivial band gap to a gapless Dirac cone state with a 2 eV dispersion, and finally to a two-dimensional topological insulator as inferred from theory. This evolution is driven by subtle structural distortions in the first P layer caused by potassium adsorption, which in turn contribute to the band gap closure and topological phase transition. Furthermore, the ability to manipulate the topology of a sub-surface layer in GdPS offers a unique route for exploring and controlling topological states in bulk materials.

cond-mat.mtrl-sci↗

arXiv2025

Defects Engineering of ZrTe5 for Stabilizing Ideal Topological States

ZrTe5 is a highly tunable, high-mobility topological material that hosts a rich variety of quantum phenomena, making it a promising platform for next-generation quantum technologies. Despite intensive research efforts, experimental studies have reported inconsistent and sometimes conflicting results for its electronic and topological states, largely due to variations in sample quality. Here, through systematic frst-principles investigations of all intrinsic point defects, we identify a practical route to achieving stable and ideal topological characteristics in ZrTe5. We show that the competition between two dominant charged defects, donor-like Zr interstitials and acceptor-like Te vacancies, governs the Fermi-level position. Furthermore, variations in defect density determine the topological phases of the samples. We theoretically propose and experimentally confrm that increasing the Te/Zr ratio during crystal growth effectively suppresses intrinsic defects and stabilizes ZrTe5 in a nearly ideal weak topological insulator state. These fndings provide clear guidance for defect control and sample optimization, paving the way toward robust and reproducible realization of topological quantum states in ZrTe5 for future quantum applications.

cond-mat.mtrl-sci↗

arXiv2024

Insulator-to-Metal Transition and Isotropic Gigantic Magnetoresistance in Layered Magnetic Semiconductors

Magnetotransport, the response of electrical conduction to external magnetic field, acts as an important tool to reveal fundamental concepts behind exotic phenomena and plays a key role in enabling spintronic applications. Magnetotransport is generally sensitive to magnetic field orientations. In contrast, efficient and isotropic modulation of electronic transport, which is useful in technology applications such as omnidirectional sensing, is rarely seen, especially for pristine crystals. Here we propose a strategy to realize extremely strong modulation of electron conduction by magnetic field which is independent of field direction. GdPS, a layered antiferromagnetic semiconductor with resistivity anisotropies, supports a field-driven insulator-to-metal transition with a paradoxically isotropic gigantic negative magnetoresistance insensitive to magnetic field orientations. This isotropic magnetoresistance originates from the combined effects of a near-zero spin-orbit coupling of Gd3+-based half-filling f-electron system and the strong on-site f-d exchange coupling in Gd atoms. Our results not only provide a novel material system with extraordinary magnetotransport that offers a missing block for antiferromagnet-based ultrafast and efficient spintronic devices, but also demonstrate the key ingredients for designing magnetic materials with desired transport properties for advanced functionalities.

cond-mat.mtrl-sci↗

arXiv2023

Imaging emergent exotic quasiparticle state in a frustrated transition metal oxide

The existence of rich Fermiology in anomalous metal phase in exotic superconductors has attracted considerable interests, as exemplified in copper, iron-based, and intermetallic frustrated kagome-based compounds. A common feature in these cases is pseudo-gap opening or long-range lattice/electronic ordering above superconducting critical temperature Tc. As yet developed area is the potential existence of exotic Fermiology in superconducting transition metal oxides on a geometrically frustrated lattice. Here, we focus on the spinel oxide superconductor LiTi2O4, which can be viewed as the hole-doped side of the orbital ordered 3d1 Mott system on the Ti-derived pyrochlore frustrated network. By the in-situ combination of angle-resolved photoemission spectroscopy (ARPES) and epitaxial thin film growth, we discovered the abrupt flattening of near Fermi energy dispersion below the characteristic temperature T* ~ 150 K. While the emergent negative thermal expansion below T* strongly supports a distinct phase at low-temperature, absence of energy gap opening, splitting/folding of bands, nor long-range lattice distortion are seen across T*. We propose that the competition between growing instability towards orbital ordering and its inherent geometric frustration in the Ti-pyrochlore network results in a new quantum state of matter with robust high entropic nature below T*. Our findings collectively point to a unique Fermiology in frustrated three-dimensional transition metal oxides, and its connection to superconductivity below Tc is open as an interesting future challenge. Also, a potential guideline is unexpectedly provided for designing zero thermal expansion metal to develop future solid-state devices.

cond-mat.supr-con↗

arXiv2023

Intertwining of magnetism and charge ordering in kagome FeGe

Recent experiments report a charge density wave (CDW) in the antiferromagnet FeGe, but the nature of the charge ordering and the associated structural distortion remains elusive. We discuss the structural and electronic properties of FeGe. Our proposed ground state phase accurately captures atomic topographies acquired by scanning tunneling microscopy. We show that the 2$\times$2$\times$1 CDW likely results from the Fermi surface nesting of hexagonal-prism-shaped kagome states. FeGe is found to exhibit distortions in the positions of the Ge atoms instead of the Fe atoms in the kagome layers. Using in-depth first-principles calculations and analytical modeling, we demonstrate that this unconventional distortion is driven by the intertwining of magnetic exchange coupling and CDW interactions in this kagome material. Movement of Ge atoms from their pristine positions also enhances the magnetic moment of the Fe kagome layers. Our study indicates that magnetic kagome lattices provide a material candidate for exploring the effects of strong electronic correlations on the ground state and their implications for transport, magnetic, and optical responses in materials.

cond-mat.mtrl-sci↗

arXiv2021

Proximity-Effect-Induced Anisotropic Superconductivity in Monolayer Ni-Pb Binary Alloy

Proximity effect facilitates the penetration of Cooper pairs that permits superconductivity in normal metal, offerring a promising approach to turn heterogeneous materials into superconducting and develop exceptional quantum phenomena. Here, we have systematically investigated proximity-induced anisotropic superconductivity in monolayer Ni-Pb binary alloy by combining scanning tunneling microscopy/ spectroscopy(STM/STS) with theoretical calculations. By means of high temperature growth, the(3root3by3root3)R30o Ni-Pb surface alloy has been fabricated on the Pb(111), where the appearance of domain boundary as well as lattice transformation are further corroborated by the STM simulations. Given the high spatial and energy resolution, tunnelling conductance (dI/dU) spectra have resolved a reduced but anisotropic superconducting gap NiPb about 1.0 meV, in stark contrast to the isotropic Pb about 1.3 meV on the conventional Pb(111). In addition, the higher density of states at Fermi energy (D(EF)) of Ni-Pb surface alloy results in an enhancement of coherence peak height. According to the same Tc about 7.1 K with Pb(111) from the temperature dependent NiPb and a short decay length Ld about 3.55 nm from the spatially monotonic decrease of NiPb, both results are supportive for the proximity-induced superconductivity. Despite a lack of bulk counterpart, the atomic-thick Ni-Pb bimetallic compound opens a new pathway to engineer superconducting properties down to the low-dimensional limit, giving rise to the emergence of anisotropic superconductivity via proximity effect.

cond-mat.supr-con↗

arXiv2021

Observation of near EF Fermi-arc van Hove singularity with prominent coupling to phonon in a van der Waals coupled Weyl semimetal

A van der Waals coupled Weyl semimetal material NbIrTe4 is investigated by combining scanning tunneling microscopy/spectroscopy and first principles calculations. We observe a sharp peak in the tunneling conductance near the zero bias energy, and its origin is ascribed to a van Hove singularity associated with a Lifshitz transition of the topologically none trivial Fermi arc states. Furthermore, tunneling spectroscopy measurements show a surprisingly large signature of electron boson coupling, which presumably represents anomalously enhanced electron phonon coupling through the enhanced charge susceptibility. Our finding in van der Waals coupled material is particularly invaluable due to applicable exfoliation technology for searching exotic topological states by further manipulating near Fermi energy van Hove singularity in nanometer scale flakes and their devices.

cond-mat.mes-hall↗

arXiv2021

Co-existence of Topological Non-trivial and Spin Gapless Semiconducting Behavior in MnPO$_4$: A Composite Quantum Compound

Composite quantum compounds (CQC) are classic example of quantum materials which host more than one apparently distinct quantum phenomenon in physics. Magnetism, topological superconductivity, Rashba physics etc. are few such quantum phenomenon which are ubiquitously observed in several functional materials and can co-exist in CQCs. In this letter, we use {\it ab-initio} calculations to predict the co-existence of two incompatible phenomena, namely topologically non-trivial Weyl semimetal and spin gapless semiconducting (SGS) behavior, in a single crystalline system. SGS belong to a special class of spintronics material which exhibit a unique band structure involving a semiconducting state for one spin channel and a gapless state for the other. We report such a SGS behavior in conjunction with the topologically non-trivial multi-Weyl Fermions in MnPO$_4$. Interestingly, these Weyl nodes are located very close to the Fermi level with the minimal trivial band density. A drumhead like surface state originating from a nodal loop around Y-point in the Brillouin zone is observed. A large value of the simulated anomalous Hall conductivity (1265 $Ω^{-1} cm^{-1}$) indirectly reflects the topological non-trivial behavior of this compound. Such co-existent quantum phenomena are not common in condensed matter systems and hence it opens up a fertile ground to explore and achieve newer functional materials.

cond-mat.mtrl-sci↗

arXiv2020

Quantum Well Electronic States in Spatially Decoupled 2D Pb Nanoislands on Nb-doped SrTiO3(001)

Two-dimensional (2D) Pb nanoisland has established an ideal platform for studying the quantum size effects on growth mechanism, electronic structures as well as high-temperature superconductivity. Here, we investigate the growth and quantum well electronic states of the 2D Pb nanoisland on Nb-doped SrTiO3(001) by scanning tunneling microscopy and spectroscopy. In contrast to Pb/Si(111), Pb/Cu(111) and Pb/Ag(111), there is no wetting layer of Pb formed on Nb-doped SrTiO3(001) surface, resulting in isolated Pb nanoislands with an apparent height of 4 atomic layers as the building blocks for the island growth. According to the thickness-dependent quantum well states resolved in both occupied and unoccupied energy regions, the constant group velocity vg = 1.804+-0.106 m/s and Fermi wavevector kF = 1.575 Å-1, have been extracted from a linear fit of the Pb(111) band dipersion along the Γ-L direction. In addition, the energy-dependent scattering phase shift ϕ(E) obtained by means of phase accumulation model shows a metallic-like scattering interface analogous to Pb/Ag(111). These spatially decoupled 2D Pb nanoislands thus realize an opportunity to explore the intrinic quantum confinement phenomena in nanoscale superconductors on the doped titanium-oxide-type substrate.

cond-mat.mtrl-sci↗

arXiv2017

Topological surface electronic states in candidate nodal-line semimetal CaAgAs

We investigate systematically the bulk and surface electronic structure of the candidate nodal-line semimetal CaAgAs by angle resolved photoemission spectroscopy and density functional calculations. We observed a metallic, linear, non-$k_z$-dispersive surface band that coincides with the high-binding-energy part of the theoretical topological surface state, proving the topological nontriviality of the system. An overall downshift of the experimental Fermi level points to a rigid-band-like $p$-doping of the samples, due possibly to Ag vacancies in the as-grown crystals.

cond-mat.mtrl-sci↗

arXiv2015

Direct Evidence of Interaction-Induced Dirac Cones in Monolayer Silicene/Ag(111) System

Silicene, analogous to graphene, is a one-atom-thick two-dimensional crystal of silicon which is expected to share many of the remarkable properties of graphene. The buckled honeycomb structure of silicene, along with its enhanced spin-orbit coupling, endows silicene with considerable advantages over graphene in that the spin-split states in silicene are tunable with external fields. Although the low-energy Dirac cone states lie at the heart of all novel quantum phenomena in a pristine sheet of silicene, the question of whether or not these key states can survive when silicene is grown or supported on a substrate remains hotly debated. Here we report our direct observation of Dirac cones in monolayer silicene grown on a Ag(111) substrate. By performing angle-resolved photoemission measurements on silicene(3x3)/Ag(111), we reveal the presence of six pairs of Dirac cones on the edges of the first Brillouin zone of Ag(111), other than expected six Dirac cones at the K points of the primary silicene(1x1) Brillouin zone. Our result shows clearly that the unusual Dirac cone structure originates not from the pristine silicene alone but from the combined effect of silicene(3x3) and the Ag(111) substrate. This study identifies the first case of a new type of Dirac Fermion generated through the interaction of two different constituents. Our observation of Dirac cones in silicene/Ag(111) opens a new materials platform for investigating unusual quantum phenomena and novel applications based on two-dimensional silicon systems.

cond-mat.mtrl-sci↗