arXiv subjects

Yuki Takahashi

Publications and source records attributed to Yuki Takahashi.

At least 19 recordsLinked to original sources

arXiv2026

Telecom-band Chiral Light Detection through Hidden Giant Third-Order Nonlinear Circular Dichroism in Two-dimensional Halide Perovskite

Chiral nonlinear optical (NLO) responses enable efficient discrimination of circularly polarized light (CPL) and are attracting increasing interest for optical and optoelectronic technologies. However, studies on NLO properties in chiral materials have largely focused on second-order NLO processes, while the role of chirality in third-order NLO processes remains poorly explored. Here, we demonstrate telecom-band CPL detection by third harmonic generation circular dichroism (THG-CD) in the chiral two-dimensional perovskite (R/S-MBACl)2PbI4 and uncover a giant hidden THG-CD anisotropy that is accessible via polarization-resolved detection. Polarization-resolved THG measurements reveal that opposite chiral NLO responses emerge in orthogonal THG polarization channels. Therefore, these chiral anisotropic contributions largely cancel each other in the total-THG signal detection, leading to underestimation of the THG-CD dissymmetry in conventional evaluations based on total-THG intensity. By separating these hidden chiral contributions, we observe exceptionally large dissymmetry factors exceeding 1.9 and achieve selective extraction of chiral NLO responses with opposite handedness, without any structural chiral inversion. These findings highlight the importance of polarization-resolved analysis for evaluating more accurate chiral NLO responses inherent to the material and provide a promising platform for optical information processing, encryption, and anti-counterfeiting technologies at technologically relevant telecommunication wavelengths.

cond-mat.mtrl-sci↗

arXiv2026

Quantitative Transversal Theorems in the Plane

Hadwiger's theorem is a Helly-type theorem involving common transversals to families of convex sets instead of common intersections. Subsequently, Pollack and Wenger identified a necessary and sufficient condition, called a consistent $k$-ordering, for the existence of a hyperplane transversal for sets in $\mathbb{R}^d$. We obtain a quantitative generalization of Hadwiger's theorem in $\mathbb{R}^2$, showing that compact convex sets in $\mathbb{R}^2$ with a quantitative version of consistent ordering have a transversal satisfying quantitative requirements. Our proof generalizes the methods in Wenger's proof of Hadwiger's theorem in $\mathbb{R}^2$. We also prove colorful versions of our results.

math.CO↗

arXiv2026

Consequences of Dependent Dividing on Burden

If $T$ has dependent dividing, then the burden agrees with the dp-rank witnessed by NIP formulas. We use this observation to prove that if $T$ has dependent dividing, then the burden is sub-additive. We also state a connection between the burden and the dual VC density.

math.LO↗

arXiv2026

Intimate relationship between spin configuration in the triplet pair and superconductivity in UTe$_2$

Spin-triplet superconductivity is an intriguing quantum coherent state with both spin and orbital degrees of freedom, which holds significant potential for future applications in quantum technology. However, how the spin of the triplet pairs responds to an external magnetic field remains poorly understood. This is mainly due to the absence of suitable spin-triplet superconductors. Here, we report results of Knight-shift and ac-susceptibility measurements on UTe$_2$. We demonstrate that the spin susceptibility, which slightly decreases compared to the normal-state value below the superconducting (SC) transition temperature $T_{\rm c}$, is rapidly restored and nearly recovers to the normal-state values around 5 T, well below the SC upper critical field $H_{c2}$ when the magnetic field is applied along the $c$ axis ($H \parallel c$). In addition, we found that $H_{\rm c2}$ of superconductivity becomes larger when the SC spin aligns with the magnetic field. By considering the results on $H \parallel b$, our results suggest the presence of a close relationship between the spin configuration of the triplet pair and $H_{\rm c2}$, as well as the anisotropic pinning interaction acting on the triplet pairs. These phenomena, which have never been observed in spin-singlet superconductors, represent characteristic features unique to spin-triplet superconductors. We discuss the similarities between superconductivity in UTe$_2$ and superfluid $^3$He, focusing on their spin-triplet pairing states.

cond-mat.supr-con↗

arXiv2025

$b$-axis and $c$-axis Knight shift measurements in the superconducting state on ultraclean UTe$_2$ with $T_c$ = 2.1 K

Knight shifts along the $b$ and $c$ axes ($K_b$ and $K_c$) at two crystallographically distinct Te sites were measured down to 70 mK using $^{125}$Te nuclear magnetic resonance (NMR) on an ultraclean UTe$_2$ single crystal with a superconducting (SC) transition temperature $T_{\mathrm{c}}$ = 2.1 K. This was carried out to determine the $\boldsymbol{d}$-vector components, which are the order parameter in the spin-triplet pairing. Although the decrease in $K_b$ and $K_c$ is comparable to the theoretical estimation of the SC diamagnetic shielding effect, it is confirmed, by taking the difference between two Knight shifts at the distinct Te sites, that the spin susceptibility along the $b$ and $c$ axes decreases in the SC state. Taking into account the large decrease in $K_a$ in the SC state, we conclude that the $\boldsymbol{d}$ vector has components along all three crystal axes.

cond-mat.supr-con↗

arXiv2025

Are Men Less Generous to a Smarter Woman? Evidence from a Dictator Game Experiment

Although evidence suggests men are more generous to women than to men, it may stem from paternalism and could reverse when women excel in important skills for one's career success, such as cognitive skills. Using a dictator game, this paper studies whether male dictators allocate less to female receivers than to male receivers when these receivers have higher IQs than dictators. By exogenously varying the receivers' IQ relative to the dictators', I do not find evidence consistent with this hypothesis; if anything, male dictators allocate slightly more to female receivers with higher IQs than to male receivers with equivalent IQs. The results hold both in mean and distribution and are robust to the so-called ``beauty premium.'' Also, female dictators' allocations are qualitatively similar to male dictators. These findings suggest that women who excel in cognitive skills may not receive less favorable treatment than equally intelligent men in the labor market.

econ.GN↗

arXiv2024

Clear Reduction in Spin Susceptibility and Superconducting Spin Rotation for $H \parallel a$ in the Early-Stage Sample of Spin-Triplet Superconductor UTe$_2$

We report the re-measurement of the $a$-axis spin susceptibility component in an early-stage sample of the spin-triplet superconductor UTe$_2$ with the transition temperature of $T_{\rm SC}$ = 1.6 K. Using Knight-shift measurements along the $b$ axis and at a 10-degree tilt from the $b$ axis towards the $a$ axis, we accurately determined the $a$-axis component without directly measuring the $a$-axis Knight shift. Our results reveal a decrease of approximately 3\% in the $a$-axis spin susceptibility in the superconducting state under $a$-axis magnetic field $μ_0 H_a \sim 0.1$ T, indicating that the spin susceptibility decreases similarly in both early-stage and ultraclean samples with $T_{\rm SC}$ = 2.1 K. The previously reported absence of the reduction in Knight shift is attributed to the missing of signal from the superconducting region and to the detection of residual signals from the non-superconducting region instead. We also found that the decrease in the $a$-axis spin susceptibility is immediately suppressed with increasing the $a$-axis magnetic field and is estimated to be completely suppressed at around 1.5 T due to superconducting spin rotation.

cond-mat.supr-con↗

arXiv2024

Unveiling the orbital-selective electronic band reconstruction through the structural phase transition in TaTe$_2$

Tantalum ditelluride TaTe$_2$ belongs to the family of layered transition metal dichalcogenides but exhibits a unique structural phase transition at around 170 K that accompanies the rearrangement of the Ta atomic network from a "ribbon chain" to a "butterfly-like" pattern. While multiple mechanisms including Fermi surface nesting and chemical bonding instabilities have been intensively discussed, the origin of this transition remains elusive. Here we investigate the electronic structure of single-crystalline TaTe$_2$ with a particular focus on its modifications through the phase transition, by employing core-level and angle-resolved photoemission spectroscopy combined with first-principles calculations. Temperature-dependent core-level spectroscopy demonstrates a splitting of the Ta $4f$ core-level spectra through the phase transition indicative of the Ta-dominated electronic state reconstruction. Low-energy electronic state measurements further reveal an unusual kink-like band reconstruction occurring at the Brillouin zone boundary, which cannot be explained by Fermi surface nesting or band folding effects. On the basis of the orbital-projected band calculations, this band reconstruction is mainly attributed to the modifications of specific Ta $5d$ states, namely the $d_{XY}$ orbitals (the ones elongating along the ribbon chains) at the center Ta sites of the ribbon chains. The present results highlight the strong orbital-dependent electronic state reconstruction through the phase transition in this system and provide fundamental insights towards understanding complex electron-lattice-bond coupled phenomena.

cond-mat.str-el↗

arXiv2021

Frobenius templates in certain $2 \times 2$ matrix rings

The classical Frobenius problem is to find the largest integer that cannot be written as a linear combination of a given set of positive, coprime integers using nonnegative integer coefficients. Prior work has generalized the classical Frobenius problem from integers to Frobenius problems in other rings. This paper explores Frobenius problems in various rings of (upper) triangular $2 \times 2$ matrices with constant diagonal.

math.NT↗

arXiv2021

Graphs with prescribed radius, diameter, and center

Among other things, it is shown that for every pair of positive integers $r$, $d$, satisfying $1<r<d\leq 2r$, and every finite simple graph $H,$ there is a connected graph $G$ with diameter $d$, radius $r$, and center $H.$

math.CO↗

arXiv2021

Lifting methods in mass partition problems

Many results in mass partitions are proved by lifting $\mathbb{R}^d$ to a higher-dimensional space and dividing the higher-dimensional space into pieces. We extend such methods to use lifting arguments to polyhedral surfaces. Among other results, we prove the existence of equipartitions of $d+1$ measures in $\mathbb{R}^d$ by parallel hyperplanes and of $d+2$ measures in $\mathbb{R}^d$ by concentric spheres. For measures whose supports are sufficiently well separated, we prove results where one can cut a fixed (possibly different) fraction of each measure either by parallel hyperplanes, concentric spheres, convex polyhedral surfaces of few facets, or convex polytopes with few vertices.

math.CO↗

arXiv2021

Gender Differences in the Cost of Corrections in Group Work

Corrections among colleagues are an integral part of group work, but people may take corrections as personal criticism, especially corrections by women. I study whether people dislike collaborating with someone who corrects them and more so when that person is a woman. People, including those with high productivity, are less willing to collaborate with a person who has corrected them even if the correction improves group performance. Yet, people respond to corrections by women as negatively as by men. These findings suggest that although women do not face a higher hurdle, correcting colleagues is costly and reduces group efficiency.

econ.GN↗

arXiv2019

Diophantine property of matrices and attractors of projective iterated function systems in $\mathbb{RP}^1$

We prove that almost every finite collection of matrices in $GL_d(\mathbb{R})$ and $SL_d(\mathbb{R})$ with positive entries is Diophantine. Next we restrict ourselves to the case $d=2$. A finite set of $SL_2(\mathbb{R})$ matrices induces a (generalized) iterated function system on the projective line $\mathbb{RP}^1$. Assuming uniform hyperbolicity and the Diophantine property, we show that the dimension of the attractor equals the minimum of 1 and the critical exponent.

math.DS↗

arXiv2018

Sums of two self-similar Cantor sets

We show that for any pair of self-similar Cantor sets with sum of Hausdorff dimensions greater than 1, one can create an interval in the sumset by applying arbitrary small perturbations (without leaving the class of self-similar Cantor sets). In our setting the perturbations have more freedom than in the setting of the Palis conjecture, so our result can be viewed as an affirmative answer to a weaker form of the Palis conjecture.

math.DS↗

arXiv2018

On the interior of projections of planar self-similar sets

We consider projections of planar self-similar sets, and show that one can create nonempty interior in the projections by applying arbitrary small perturbations, if the self-similar set satisfies the open set condition and has Hausdorff dimension greater than 1.

math.DS↗

arXiv2018

Sums of two homogeneous Cantor sets

We show that for any two homogeneous Cantor sets with sum of Hausdorff dimensions that exceeds 1, one can create an interval in the sumset by applying arbitrary small perturbations (without leaving the class of homogeneous Cantor sets). In our setting the perturbations have more freedom than in the setting of the Palis' conjecture, so our result can be viewed as an affirmative answer to a weaker form of the Palis' conjecture. We also consider self-similar sets with overlaps on the real line (not necessarily homogeneous), and show that one can create an interval by applying arbitrary small perturbations, if the uniform self-similar measure has $L^2$-density.

math.DS↗

arXiv2017

Products of two Cantor sets

We consider products of two Cantor sets, and obtain the optimal estimates in terms of their thickness that guarantee that their product is an interval. This problem is motivated by the fact that the spectrum of the Labyrinth model, which is a two dimensional quasicrystal model, is given by a product of two Cantor sets. We also discuss the connection with the question on the structure of intersections of two Cantor sets, which was considered by many authors previously.

math.DS↗

arXiv2016

Quantum and Spectral Properties of the Labyrinth Model

We consider the Labyrinth model, which is a two-dimensional quasicrystal model. We show that the spectrum of this model, which is known to be a product of two Cantor sets, is an interval for small values of the coupling constant. We also consider the density of states measure of the Labyrinth model, and show that it is absolutely continuous with respect to Lebesgue measure for almost all values of coupling constants in small coupling regime.

math-ph↗