arXiv subjects

Maximilian Huber

Publications and source records attributed to Maximilian Huber.

8 recordsLinked to original sources

arXiv2026

A magnetic environment with reproducible spatio-temporal magnetic conditions at picotesla level

Walk-in, picotesla-scale environments are essential for measurements of biomagnetism and fundamental physics. However, conventional rooms require typical active dynamic compensation, which adds complexity and magnetic noise. Here, we present a solution that achieves an absolute residual field well below 100$\,$pT within its central measurement volume. Following magnetic equilibration, this environment achieves picotesla-scale reproducibility. Consequently, optically pumped magnetometers operate at their design noise and drift performance and remain operational during sensor motion without active feedback. A key technique is robotic mapping, which resolves the ultra-low residual field patterns and demagnetization stability. We demonstrate the platform's versatility through high-fidelity adult and fetal magnetocardiography, standing magnetoencephalography, and ultra-low field magnetic resonance with polarized noble gases in the limit of strongly coupled spins in a negligible holding field. The achieved passive reproducibility turns the ultra-low magnetic background into a predictable, correctable property, establishing a novel foundation for next-generation quantum sensing and precision physics.

physics.ins-det↗

arXiv2026

Spin-Valley Locking in 2H-TaS2 and Its Co-Intercalated Counterpart: Roles of Surface Domains and Co Intercalation

Tuning and probing spin-valley coupling is key to understanding correlated ground states in 2$\it{H}$-TaS$_2$. Its magnetically intercalated analogue, Co$_{1/3}$TaS$_2$, introduces additional degrees of freedom, including modified interlayer coupling and magnetism, to modulate spin-valley physics. Surface-sensitive probes like ARPES are essential for accessing surface spin texture, yet previous studies on 2$\it{H}$-TMDs have reported conflicting results regarding spin-polarized bands, leaving open whether these discrepancies are intrinsic or extrinsic. Here we performed spatially resolved spin-ARPES measurements on 2$\it{H}$-TaS$_2$ and Co$_{1/3}$TaS$_2$. Our results reveal robust spin-valley locking on both compounds. Importantly, Co intercalation enhances interlayer hybridization and introduces magnetism while preserving the TaS$_2$-derived spin texture. We further observe a spatial reversal of the out-of-plane spin polarization, which we attribute to different surface domains. This effect complicates quantifying spin textures and may underlie prior inconsistent observations. Our findings provide microscopic insight into how interlayer interactions and surface domains together govern spin-valley phenomena in layered TMDs.

cond-mat.mtrl-sci↗

arXiv2026

Discovery of Van Hove Singularities: Electronic Fingerprints of 3Q Magnetic Order in a van der Waals Quantum Magnet

Magnetically intercalated transition metal dichalcogenides are emerging as a rich platform for exploring exotic quantum states in van der Waals magnets. Among them, CoxTaS2 has attracted intense interest following the recent discovery of a distinctive 3Q magnetic ground state and a pronounced topological Hall effect below a critical doping of x=1/3, both intimately tied to cobalt concentration. To date, direct signatures of this enigmatic 3Q magnetic order in the electronic structure remain elusive. Here we report a comprehensive doping dependent angle resolved photoemission spectroscopy study that unveils these long-sought fingerprints. Our data reveal an unexpected "inverse Mexican hat" dispersion along the K-M-K direction, accompanied by two van Hove singularities. These features are consistent with theoretical predictions for a 3Q magnetic order near three-quarters band filling on a cobalt triangular lattice. These results provide evidence of 3Q magnetic order in the electronic structure, establishing TMD van der Waals magnets as tunable materials to explore the interplay between magnetism and topology.

cond-mat.mtrl-sci↗

arXiv2025

Scalar-Magnetometer Search for Ultralight Dark Photon Dark Matter with a Single-Site, Two-Sensor Array: A 6-Channel DTFT Likelihood Analysis with Scalar Optically Pumped Magnetometers

We report on a laboratory search for ultralight dark photon dark matter using a single-site, two-sensor scalar magnetometer array. The experiment employs two scalar optically pumped magnetometers (OPMs) operated in a differential configuration to suppress common-mode noise and enhance sensitivity to spatially coherent dark photon fields. We analyze 10.5 hours of continuous data with a six-channel complex data vector evaluated at the three physical frequencies of the expected dark photon signal triplet. Assuming Gaussian noise, we develop a likelihood framework to set robust, frequency-resolved upper limits on the kinetic-mixing parameter $\varepsilon$, which governs the coupling between Standard Model photons and dark photons. Within the mass range $4\times10^{-15}\,\mathrm{eV} \leq m_{A'} \leq 3\times10^{-14}\,\mathrm{eV}$, we obtain the most stringent direct laboratory limits to date on $\varepsilon$, complementing existing astrophysical bounds including those inferred from observations of the Leo-T dwarf galaxy.

hep-ph↗

arXiv2024

Ultrafast creation of a light induced semimetallic state in strongly excited 1T-TiSe$_2$

Screening, a ubiquitous phenomenon associated with the shielding of electric fields by surrounding charges, has been widely adopted as a means to modify a material's properties. While so far most studies have relied on static changes of screening through doping or gating, here we demonstrate that screening can also drive the onset of distinct quantum states on the ultrafast timescale. By using time and angle-resolved photoemission spectroscopy we show that intense optical excitation can drive 1T-TiSe$_2$, a prototypical charge density wave material, almost instantly from a gapped into a semimetallic state. By systematically comparing changes in bandstructure over time and excitation strength with theoretical calculations we find that the appearance of this state is likely caused by a dramatic reduction of the screening length. In summary, this work showcases how optical excitation enables the screening driven design of a non-equilibrium semimetallic phase in TiSe$_2$, possibly providing a general pathway into highly screened phases in other strongly correlated materials.

cond-mat.mes-hall↗

arXiv2024

GreedLlama: Performance of Financial Value-Aligned Large Language Models in Moral Reasoning

This paper investigates the ethical implications of aligning Large Language Models (LLMs) with financial optimization, through the case study of GreedLlama, a model fine-tuned to prioritize economically beneficial outcomes. By comparing GreedLlama's performance in moral reasoning tasks to a base Llama2 model, our results highlight a concerning trend: GreedLlama demonstrates a marked preference for profit over ethical considerations, making morally appropriate decisions at significantly lower rates than the base model in scenarios of both low and high moral ambiguity. In low ambiguity situations, GreedLlama's ethical decisions decreased to 54.4%, compared to the base model's 86.9%, while in high ambiguity contexts, the rate was 47.4% against the base model's 65.1%. These findings emphasize the risks of single-dimensional value alignment in LLMs, underscoring the need for integrating broader ethical values into AI development to ensure decisions are not solely driven by financial incentives. The study calls for a balanced approach to LLM deployment, advocating for the incorporation of ethical considerations in models intended for business applications, particularly in light of the absence of regulatory oversight.

cs.CL↗

arXiv2022

Revealing the order parameter dynamics of 1T-TiSe$_2$ following optical excitation

The formation of a charge density wave state is characterized by an order parameter. The way it is established provides unique information on both the role that correlation plays in driving the charge density wave formation and the mechanism behind its formation. Here we use time and angle resolved photoelectron spectroscopy to optically perturb the charge-density phase in 1T-TiSe$_2$ and follow the recovery of its order parameter as a function of energy, momentum and excitation density. Our results reveal that two distinct orders contribute to the gap formation, a CDW order and pseudogap-like order, manifested by an overall robustness to optical excitation. A detailed analysis of the magnitude of the the gap as a function of excitation density and delay time reveals the excitonic long-range nature of the CDW gap and the short-range Jahn-Teller character of the pseudogap order. In contrast to the gap, the intensity of the folded Se$_{4p}$* band can only give access to the excitonic order. These results provide new information into the the long standing debate on the origin of the gap in TiSe$_2$ and place it in the same context of other quantum materials where a pseudogap phase appears to be a precursor of long-range order.

cond-mat.str-el↗

arXiv2022

Mapping the dispersion of the occupied and unoccupied band structure in photoexcited 1T-TiSe$_2$

Charge density waves (CDW) are states of broken symmetry with a periodic modulation of charge and lattice typically leading to the opening of a gap in the band structure. In the model CDW system 1T-TiSe$_2$ such a gap opens up between its Se$_{4p}$ valence and Ti$_{3d}$ conduction band, accompanied by a change of dispersion. These changes are crucial in understanding the CDW phase, as they provide a measure of the Se$_{4p}$-Ti$_{3d}$ hybridization strength and characteristic mechanistic features. Using time- and angle-resolved photoelectron spectroscopy (trARPES), the unoccupied band structure is populated with near-infrared (NIR) pump pulses which allows to to directly visualize the parabolically-shaped Ti$_{3d}$ conduction band. Furthermore, we observe a transient change of effective mass in the Se$_{4p}$ valence band following photoexcitation. This occurs alongside an overall reduction due to weakening of the CDW phase and is accompanied by an oscillating component with the frequency of the characteristic A$_{1g}$ phonon. These observations, enabled by trAPRES, highlight the importance of the lattice contributions in establishing the CDW order in 1T-TiSe$_2$.

cond-mat.str-el↗