arXiv subjects

Z. Yue

Publications and source records attributed to Z. Yue.

16 recordsLinked to original sources

arXiv2026

Exploring $\alpha$- and $\beta$-decay-induced quenching of the $^{229}$Th nuclear-clock isomer in solid-state hosts

The radiative decay dynamics of an ensemble of $^{229\mathrm{m}}$Th nuclei embedded in CaF$_2$ and MgF$_2$ is investigated. The isomer is populated through $\beta$ decay of $^{229}$Ac following ion implantation, and its radiative decay is detected using vacuum-ultraviolet spectroscopy and measured as a function of time. This allows to identify and quantify the quenching of the radiative-decay signal induced by $\alpha$ or $\beta$ radiation. The quenching probability density is determined in different CaF$_2$ crystals and in a MgF$_2$ crystal, revealing differences up to two orders of magnitude between the investigated samples and a strong dependence on the host material and defect densities. The results support a microscopic mechanism mediated by charge carriers in which electronic excitations created by the decay radiation are captured near Th defects, thereby favoring non-radiative decay channels.

nucl-ex↗

arXiv2025

The 76Cu conundrum remains unsolved

Near the doubly-magic nucleus \nuc{Ni}{78} ($Z=28$, $N=50$), there has been a decades-long debate on the existence of a long-lived isomer in \nuc{Cu}{76}. A recent mass measurement claimed to have settled the debate, by measuring the energy of the isomer and shedding light on the structure of the nucleus. In this work, we present new, more accurate, and precise values of the half-lives of the isomeric and ground states in \nuc{Cu}{76}. Our findings suggest that both states have very similar half-lives, in the 600-700 ms range, in disagreement with the literature values, implying that they cannot be differentiated by their decay curves. These results raise more questions than they answer, reopening the debate and showing that the structures in \nuc{Cu}{76} are still not fully understood.

nucl-ex↗

arXiv2025

Antiferromagnetic Chiral Bobber Formation and Topological Proximity Effect in MnBi2Te4

With topological materials being billed as the key to a new generation of nanoelectronics via either functional real-space topological structures (domain walls, skyrmions etc.) or via momentum-space topology (topological insulators), tailored and controllable topological properties are of paramount significance, since they lead to topologically protected states with negligible dissipation, enabling stable and non-volatile information processing. Here, we report on the evolution of topological magnetic textures in the proximity of other topological defects, i.e., antiferromagnetic domain walls in the topological insulator MnBi2Te4. The transition from the antiferromagnetic ground state to a canted antiferromagnetic state at finite magnetic fields is accompanied by the formation of chiral bobbers - bulk-terminated topological defects adjacent to the domain walls in this system, leading to a topological proximity effect.

cond-mat.mes-hall↗

arXiv2024

Radiative Decay of the $^{229m}$Th Nuclear Clock Isomer in Different Host Materials

A comparative vacuum ultraviolet spectroscopy study conducted at ISOLDE-CERN of the radiative decay of the $^{229m}$Th nuclear clock isomer embedded in different host materials is reported. The ratio of the number of radiative decay photons and the number of $^{229m}$Th embedded are determined for single crystalline CaF$_2$, MgF$_2$, LiSrAlF$_6$, AlN, and amorphous SiO$_2$. For the latter two materials, no radiative decay signal was observed and an upper limit of the ratio is reported. The radiative decay wavelength was determined in LiSrAlF$_6$ and CaF$_2$, reducing its uncertainty by a factor of 2.5 relative to our previous measurement. This value is in agreement with the recently reported improved values from laser excitation.

nucl-ex↗

arXiv2023

Magneto-transport and electronic structures in MoSi$_2$ bulks and thin films with different orientations

We report a comprehensive study of magneto-transport properties in MoSi$_2$ bulk and thin films. Textured MoSi$_2$ thin films of around 70 nm were deposited on silicon substrates with different orientations. Giant magnetoresistance of 1000% was observed in sintered bulk samples while MoSi$_2$ single crystals exhibit a magnetoresistance (MR) value of 800% at low temperatures. At the low temperatures, the MR of the textured thin films show weak anti-localization behaviour owing to the spin orbit coupling effects. Our first principle calculation show the presence of surface states in this material. The resistivity of all the MoSi$_2$ thin films is significantly low and nearly independent of the temperature, which is important for electronic devices.

cond-mat.mtrl-sci↗

arXiv2023

Observation of large intrinsic anomalous Hall conductivity in polycrystalline Mn$_3$Sn films

We report the observation of anomalous Hall effect in Mn$_3$Sn polycrystalline thin films deposited on Pt coated Al$_2$O$_3$ substrate with a large anomalous Hall conductivity of 65($Ω$cm)$^{-1}$ at 3K. The Hall and magnetic measurements show a very small hysteresis owing to a weak ferromagnetic moment in this material. The longitudinal resistivity decreases sufficiently for the thin films as compared to the polycrystalline bulk sample used as the target for the film deposition. The anomalous Hall resistivity and conductivity decreases almost linearly with the increase in the temperature. A negative magnetoresistance is observed for all the measured temperatures with the negative decrease in the magnitude with the increase in temperature.

cond-mat.mes-hall↗

arXiv2016

Signature of Hanle Precession in Trilayer MoS2: Theory and Experiment

Valley-spin coupling in transition-metal dichalcogenides (TMDs) can result in unusual spin transport behaviors under an external magnetic field. Nonlocal resistance measured from 2D materials such as TMDs via electrical Hanle experiments are predicted to exhibit nontrivial features, compared with results from conventional materials due to the presence of intervalley scattering as well as a strong internal spin-orbit field. Here, for the first time, we report the all-electrical injection and non-local detection of spin polarized carriers in trilayer MoS_2 films. We calculate the Hanle curves theoretically when the separation between spin injector and detector is much larger than spin diffusion length, \lamda_s. The experimentally observed curve matches the theoretically-predicted Hanle shape under the regime of slow intervalley scattering. The estimated spin life-time was found to be around 110 ps at 30 K.

cond-mat.mtrl-sci↗

arXiv2016

Smearing of the quantum anomalous Hall effect due to statistical fluctuations of magnetic dopants

Quantum anomalous Hall effect (QAH) is induced by substitution of a certain portion, x, of Bi atoms in a BiTe-based insulating parent compound by magnetic ions (Cr or V). We find the density of in-gap states, N(E), emerging as a result of statistic fluctuations of the composition, x, in the vicinity of the transition point, where the average gap, E_g, passes through zero. Local gap follows the fluctuations of x. Using the instanton approach, we show that, near the gap edges, the tails are exponential, ln N(E) \propto -(E_g-|E|), and the tail states are due to small gap reduction. Our main finding is that, even when the smearing magnitude exceeds the gap-width, there exists are semi-hard gap around zero energy, where ln N(E) \propto -E_g/|E| (ln E_g/|E|). The states responsible for N(E) originate from local gap reversals within narrow rings. The consequence of semi-hard gap is the Arrhenius, rather than variable-range hopping, temperature dependence of the diagonal conductivity at low temperatures.

cond-mat.dis-nn↗

arXiv2016

Effect of extended confinement on the structure of edge channels in the quantum anomalous Hall effect

Quantum anomalous Hall (QAH) effect in the films with nontrivial band structure accompanies the ferromagnetic transition in the system of magnetic dopants. Experimentally, the QAH transition manifests itself as a jump in the dependence of longitudinal resistivity on a weak external magnetic field. Microscopically, this jump originates from the emergence of a chiral edge mode on one side of the ferromagnetic transition. We study analytically the effect of an extended confinement on the structure of the edge modes. We employ the simplest model of the extended confinement in the form of potential step next to the hard wall. It is shown that, unlike the conventional quantum Hall effect, where all edge channels are chiral, in QAH effect, a complex structure of the boundary leads to nonchiral edge modes which are present on both sides of the ferromagnetic transition. Wave functions of nonchiral modes are different above and below the transition: on the "topological" side, where the chiral edge mode is supported, nonchiral modes are "repelled" from the boundary, i.e. they are much less localized than on the "trivial" side. Thus, the disorder-induced scattering into these modes will boost the extension of the chiral edge mode. The prime experimental manifestation of nonchiral modes is that, by contributing to longitudinal resistance, they smear the QAH transition.

cond-mat.mes-hall↗

arXiv2016

Spin transport in n-type single-layer transition metal dichalcogenides

Valley asymmetry of the electron spectrum in transition metal dichalcogenides (TMDs) originates from the spin-orbit coupling. Presence of spin-orbit fields of opposite signs for electrons in K and K' valleys in combination with possibility of intervalley scattering result in a nontrivial spin dynamics. This dynamics is reflected in the dependence of nonlocal resistance on external magnetic field (the Hanle curve). We calculate theoretically the Hanle shape in TMDs. It appears that, unlike conventional materials without valley asymmetry, the Hanle shape in TMDs is different for normal and parallel orientations of the external field. For normal orientation, it has two peaks for slow intervalley scattering, while, for fast intervalley scattering the shape is usual. For parallel orientation, the Hanle curve exhibits a cusp at zero field. This cusp is a signature of a slow-decaying valley-asymmetric mode of the spin dynamics.

cond-mat.mes-hall↗

arXiv2016

Spectral narrowing and spin echo for localized carriers with heavy-tailed Levy distribution of hopping times

We study analytically the free induction decay and the spin echo decay originating from the localized carriers moving between the sites which host random magnetic fields. Due to disorder in the site positions and energies, the on-site residence times, τ, are widely spread according to the Levy distribution. The power-law tail \propto τ^{-1-α} in the distribution of waiting times does not affect the conventional spectral narrowing for α>2, but leads to a dramatic acceleration of the free induction decay in the domain 2>α>1. The next abrupt acceleration of the decay takes place as the tail parameter, α, becomes smaller than 1. In the latter domain the decay does not follow a simple-exponent law. To capture the behavior of the average spin in this domain, we solve the evolution equation for the average spin using the approach different from the conventional approach based on the Laplace transform. Unlike the free induction decay, the tail in the distribution of the residence times leads to the slow decay of the spin echo. The echo is dominated by realizations of the carrier motion for which the number of sites, visited by the carrier, is minimal.

cond-mat.dis-nn↗

arXiv2015

Effective spin Hall properties of a mixture of materials with and without spin-orbit coupling: Tailoring the effective spin-diffusion length

We study theoretically the effective spin Hall properties of a composite consisting of two materials with and without spin-orbit (SO) coupling. In particular, we assume that SO material represents a system of grains in a matrix with no SO. We calculate the effective spin Hall angle and the effective spin diffusion length of the mixture. Our main qualitative finding is that, when the bare spin diffusion length is much smaller than the radius of the grain, the effective spin diffusion length is strongly enhanced, well beyond the "geometrical" factor. The physical origin of this additional enhancement is that, with small diffusion length, the spin current mostly flows around the grain without suffering much loss. We also demonstrate that the voltage, created by a spin current, is sensitive to a very weak magnetic field directed along the spin current, and even reverses sign in a certain domain of fields. The origin of this sensitivity is that the spin precession, caused by magnetic field, takes place outside the grains where SO is absent.

cond-mat.mes-hall↗

arXiv2015

Spin pumping from a ferromagnet into a hopping insulator: the role of resonant absorption of magnons

Motivated by recent experiments on spin pumping from a ferromagnet into organic materials in which the charge transport is due to hopping, we study theoretically the generation and propagation of spin current in a hopping insulator. Unlike metals, the spin polarization at the boundary with ferromagnet is created as a result of magnon absorption within pairs of localized states and it spreads following the current-currying resistor network (although the charge current is absent). We consider a classic resonant mechanism of the ac absorption in insulators and adapt it to the absorption of magnons. A strong enhancement of pumping efficiency is predicted when the Zeeman splitting of the localized states in external magnetic field is equal to the frequency of ferromagnetic resonance. Under this condition the absorption of a magnon takes place within individual sites.

cond-mat.mes-hall↗

arXiv2015

Strain-induced magnetic phase transition in SrCoO$_{3-δ}$ thin films

It has been well established that both in bulk at ambient pressure and for films under modest strains, cubic SrCoO$_{3-δ}$ ($δ< 0.2$) is a ferromagnetic metal. Recent theoretical work, however, indicates that a magnetic phase transition to an antiferromagnetic structure could occur under large strain accompanied by a metal-insulator transition. We have observed a strain-induced ferromagnetic to antiferromagnetic phase transition in SrCoO$_{3-δ}$ films grown on DyScO$_3$ substrates, which provide a large tensile epitaxial strain, as compared to ferromagnetic films under lower tensile strain on SrTiO$_3$ substrates. Magnetometry results demonstrate the existence of antiferromagnetic spin correlations and neutron diffraction experiments provide a direct evidence for a G-type antiferromagnetic structure with Neél temperatures between $T_N \sim 135\,\pm\,10\,K$ and $\sim 325\,\pm\,10\,K$ depending on the oxygen content of the samples. Therefore, our data experimentally confirm the predicted strain-induced magnetic phase transition to an antiferromagnetic state for SrCoO$_{3-δ}$ thin films under large epitaxial strain.

cond-mat.mtrl-sci↗

arXiv2015

Resonant magneto-tunneling between normal and ferromagnetic electrodes in relation to the three-terminal spin transport

The recently suggested mechanism [Y. Song and H. Dery, Phys. Rev. Lett. 113, 047205 (2014)] of the three-terminal spin transport is based on the resonant tunneling of electrons between ferromagnetic and normal electrodes via an impurity. The sensitivity of current to a weak external magnetic field stems from a spin blockade, which, in turn, is enabled by strong on-site repulsion. We demonstrate that this sensitivity exists even in the absence of repulsion when a single-particle description applies. Within this description, we calculate exactly the resonant-tunneling current between the electrodes. The mechanism of magnetoresistance, completely different from the spin blocking, has its origin in the interference of virtual tunneling amplitudes. Spin imbalance in ferromagnetic electrode is responsible for this interference and the resulting coupling of the Zeeman levels. This coupling also affects the current in the correlated regime.

cond-mat.mes-hall↗

arXiv2015

Evolution of the inhomogeneously-broadened spin noise spectrum with ac drive

In the presence of random hyperfine fields, the noise spectrum, δs_ω^2, of a spin ensemble represents a narrow peak centered at ω=0 and a broad "wing" reflecting the distribution of the hyperfine fields. In the presence of an ac drive, the dynamics of a single spin acquires additional harmonics at frequencies determined by both, the drive frequency and the local field. These harmonics are reflected as additional peaks in the noise spectrum. We study how the ensemble-averaged δs_ω^2 evolves with the drive amplitude, ω_dr (in the frequency units). Our main finding is that additional peaks in the spectrum, caused by the drive, remain sharp even when ω_dr is much smaller than the typical hyperfine field. The reason is that the drive affects only the spins for which the local Larmour frequency is close to the drive frequency. The shape of the low-frequency "Rabi"-peak in δs_ω^2 is universal with both, the position and the width, being of the order of ω_dr. When the drive amplitude exceeds the width of the hyperfine field distribution, the noise spectrum transforms into a set of sharp peaks centered at harmonics of the drive frequency.

cond-mat.mes-hall↗