arXiv subjects

Markel Pardo-Almanza

Publications and source records attributed to Markel Pardo-Almanza.

6 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

Quantifying quasiparticle chirality in a chiral topological semimetal

Recently, the projection of the electron's spin on its crystal momentum has been proposed as a metric to quantify electronic chirality of Bloch states in crystals, which is expected to affect a wide range of physical properties, such as magnetoelectric and optical responses. However, a direct experimental quantification of this chirality metric over an entire iso-energy surface has remained elusive. Here, we have used spin- and angle-resolved photoemission spectroscopy to directly probe the electronic chirality by measuring the bulk spin texture of Kramers-Weyl and Weyl cones in RhSi, a chiral topological semimetal with strong spin-orbit coupling (SOC). After quantifying the SOC splitting of Weyl cones, we determine their spin direction along different azimuthal angles to extract energy dependent the deviations (up to ~40°) from perfect parallel spin-momentum locking. From these deviations we define an energy-dependent normalized electron chirality density (NECD), a directly accessible metric of bulk electronic chirality. In RhSi, the NECD decreases from 1 at the Kramers-Weyl point to ~0.8 at ~200 meV below it. Finally, we show that this experimentally grounded NECD provides predictive power for magneto-optical and transport responses of chiral materials, exemplified by the longitudinal Edelstein effect.

cond-mat.mes-hall↗

arXiv2025

Long-range magnetic perturbations at Bi2Te3/Cr2Te3 interfaces induced by chemical diffusion and proximity effects

The heterointerface between topological insulators and magnetic materials provides a crucial platform for investigating exotic electronic and magnetic phases, with implications for both fundamental studies and potential applications. A key challenge is determining the spatial extent of magnetic perturbation across the interface. In this study, we grew Bi2Te3 films with mixed thicknesses of 5 and 6 quintuple layers (QLs) on a thick ferromagnetic Cr2Te3 film. Chemical analysis indicates gradual Cr diffusion across the interface into Bi2Te3, reaching up to the 4th QL, while the 5th and 6th QL remain free of Cr. Despite the absence of direct Cr incorporation, quasiparticle interference imaging using spectroscopic scanning tunneling microscopy reveals strong backscattering on the 5th QL surface. This suggests an intrinsic magnetic proximity effect, which breaks time-reversal symmetry without magnetic doping, extending into the 5th QLs. Although variations may exist across different systems, the large magnetic perturbation length scale observed here is a valuable guiding principle for engineering exotic electronic and magnetic states at heterointerfaces between topological insulators and magnetic materials.

cond-mat.mtrl-sci↗

arXiv2024

Imaging Josephson Vortices on Curved Junctions

Understanding the nature of vortices in type-II superconductors is crucial for comprehending exotic superconductors and advancing the application of superconducting materials in future electronic devices. This study uses spectroscopic scanning tunneling microscopy to visualize Josephson vortices along crystalline domain boundaries in the superconducting spinel oxide LiTi2O4 (LTO). Our experimental results reveal that the local curvature of the Josephson junction dictates the positioning of Josephson vortices. Self-consistent solutions of the Bogoliubov-de Gennes and gap equations theoretically corroborate this observation. In addition to enhancing our understanding of the physics of Josephson vortex formation, this study offers potential guidelines for developing vortex-based superconducting devices.

cond-mat.supr-con↗

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↗

arXiv2022

Large antiferromagnetic fluctuation enhancement of the thermopower at a critical doping in magnetic semimetal Cr1+dTe2

Cr1+dTe2 is a self-intercalated transition metal dichalcogenide that hosts tunable electronic filling and magnetism in its semimetallic band structure. Recent angle-resolved photoemission spectroscopy (ARPES) studies have unveiled a systematic shift in this semimetallic band structure relative to the chemical potential with increased Cr doping. This report presents the temperature and magnetic field dependence of the longitudinal thermopower Sxx for different Cr1+dTe2 compositions. We show that as doping increases, the sign of Sxx changes from positive to negative at the critical doping level of d ~ 0.5. This observed doping-dependent trend in the thermopower is consistent with the evolution of the semimetallic band structure from ARPES. Importantly, an anomalous enhancement of the thermoelectric response is also observed around d~0.5. Combining information from magnetometry and ARPES measurements, existence of the critical nature of the doping level dc (~0.5) is unveiled in magnetic semimetal Cr1+dTe2, where antiferromagnetic fluctuation and near-Fermi-energy pseudogap formation play a potential vital role in enhancing thermoelectric energy conversion.

cond-mat.mtrl-sci↗