arXiv subjects

N. Li

Publications and source records attributed to N. Li.

At least 19 recordsLinked to original sources

arXiv2026

Frustrated Magnetism in FeGe$_3$O$_4$ with a Chiral Trillium Network

The discovery of new magnetic ground states in geometrically frustrated lattices remains a central challenge in materials science. Here, we report the synthesis, structural characterization, and frustrated magnetic properties of FeGe$_3$O$_4$, a newly identified compound that crystallizes in the noncentrosymmetric cubic space group $P2_13$. In this structure, Fe atoms form an intricate double-trillium lattice with nearest-neighbor Fe--Fe distances of $\sim$4.2~\AA{}, while Ge$^{2+}$ ions mediate magnetic interactions through Fe-Ge-Fe pathways. Field-dependent magnetization at 2~K shows a pronounced nonlinearity, reaching a maximum moment of 2.55(3)~$\mu_\mathrm{B}$/Fe$^{2+}$ at 70~kOe without evidence of saturation. Magnetic susceptibility, heat capacity, and neutron scattering collectively reveal the onset of short-range magnetic interactions near 5~K, with no long-range ordering detected down to 0.06~K. Specific heat measurements demonstrate strong frustration: only $\sim$34\% of the expected magnetic entropy is recovered at 2.4~K. Taken together, these results establish FeGe$_3$O$_4$ as a rare example of a geometrically frustrated trillium-lattice magnet, offering a promising platform for exploring exotic quantum magnetic phenomena.

cond-mat.str-el↗

arXiv2025

Novel bipartite entanglement in the quantum dimer magnet Yb$_2$Be$_2$SiO$_7$

The quantum dimer magnet, with antiferromagnetic intradimer and interdimer Heisenberg exchange between spin-1/2 moments, is known to host an up/down - down/up singlet ground state when the intradimer exchange is dominant. Rare-earth-based quantum dimer systems with strong spin-orbit coupling offer the opportunity for tuning their magnetic properties by using magnetic anisotropy as a control knob. Here, we present bulk characterization and neutron scattering measurements of the quantum dimer magnet Yb$_2$Be$_2$SiO$_7$. We find that the Yb$^{3+}$ ions can be described by an effective spin-1/2 model at low temperatures and the system does not show signs of magnetic order down to 50 mK. The magnetization, heat capacity, and neutron spectroscopy data can be well-described by an isolated dimer model with highly anisotropic exchange that stabilizes a singlet ground state with a wavefunction up/up - down/down or up/up + down/down. Our results show that strong spin-orbit coupling can induce novel entangled states of matter in quantum dimer magnets.

cond-mat.str-el↗

arXiv2025

Possible quantum spin liquid state of CeTa$_7$O$_{19}$

CeTa$_7$O$_{19}$ is a recently found two-dimensional triangular lattice antiferromagnet without showing magnetic order. We grew high-quality CeTa$_7$O$_{19}$ single crystals and studied the low-temperature magnetic susceptibility, specific heat and thermal conductivity. The dc magnetic susceptibility and magnetization reveal its nature of effective spin-1/2, easy axis anisotropy, and antiferromagnetic spin coupling. The ultralow-temperature ac susceptibility and specific heat data indicate the absence of any phase transition down to 20 mK. The ultralow-temperature thermal conductivity ($\kappa$) at zero magnetic field exhibits a non-zero residual term $\kappa_0/T =$ 0.0056 W/K$^2$m. Although the magnetic field dependence of $\kappa$ is rather weak, the 14 T thermal conductivity shows an essential zero residual term. All these results point to a possible ground state of quantum spin liquid.

cond-mat.str-el↗

arXiv2025

Characterization of Multiple Channels Room Temperature Readout Electronics for Large Transition-Edge Sensor Array

Transition-edge sensor (TES) is a highly sensitive device that is capable of detecting extremely low levels of energy. It is characterised by low noise performance and high energy resolution. A mature method for reading out TES signal is through time-division multiplexing (TDM) direct current superconducting quantum interference device (SQUID). In a TDM system, the signal readout chain represents a significant source of noise other than the TES intrinsic noise. The noise generated by TES is in the range of several tens to several hundreds of $pA/\sqrt{Hz}$. In order to ensure the high energy resolution of TES, it is necessary to ensure that the noise contribution from the room temperature readout electronics is less than $10$ $pA/\sqrt{Hz}$ above 100 $Hz$. In this work, we have designed a low-noise, high-resolution room temperature readout circuit for TDM. The equivalent current noise contribution of ADC is about $0.05$ $pA/\sqrt{Hz}$ above 100 $Hz$ and $0.46$ $pA\sqrt{Hz}$ under 30:1 multiplexing. The resolution of the analog to digital converter (ADC) is larger than 11.5 bits, which can reconstruct the TES signal without distortion. The readout board, which has eight channels, has JESD204B serial ports, which has greatly simplified the space of room temperature electronics. The readout chain is based on multi-threaded CPU processing and can transfer data at 2 $Gbps$ for each channel in real time. This readout board can be used in a TDM system with smaller size for large TES arrays.

physics.ins-det↗

arXiv2024

Thermodynamics and heat transport of quantum spin liquid candidates NaYbS$_2$ and NaYbSe$_2$

We study the ultralow-temperature thermodynamics and thermal conductivity ($\kappa$) of the single-crystal rare-earth chalcogenides NaYbS$_2$ and NaYbSe$_2$, which have an ideal triangular lattice of the Yb$^{3+}$ ions and have been proposed to be quantum spin liquid candidates. The magnetic specific heat divided by temperature $C_{\rm{mag}}/T$ is nearly constant at $T <$ 200 mK, which is indeed the indication of the gapless magnetic excitations with a constant density of states. However, we observe a vanishingly small residual term $\kappa_0/T$, which points to the absence of mobile fermionic excitations in these materials. Both the weak temperature dependence of $\kappa$ and the strong magnetic-field dependence of $\kappa$ suggest the significant scattering between the spinons and phonons, which actually supports the existence of gapless or tiny-gapped quantum spin liquid. Moreover, the $\kappa(B)/\kappa(0)$ isotherms show a series of field-induced magnetic transitions for $B \parallel a$, confirming the easy-plane anisotropy, which is consistent with the results of ac magnetic susceptibility. We expect our results to inspire further interests in the understanding of the spinon-phonon coupling in the spin liquid systems.

cond-mat.str-el↗

arXiv2024

Latency Minimization for IRS-enhanced Wideband MEC Networks with Practical Reflection Model

Intelligent reflecting surface (IRS) has been considered as an efficient way to boost the computation capability of mobile edge computing (MEC) system, especially when the communication links is blocked or the communication signal is weak. However, most existing works are restricted to narrow-band channel and ideal IRS reflection model, which is not practical and may lead to significant performance degradation in realistic systems. To further exploit the benefits of IRS in MEC system, we consider an IRS-enhanced wideband MEC system with practical IRS reflection model. With the aim of minimizing the weighted latency of all devices, the offloading data volume, edge computing resource, BS's receiving vector, and IRS passive beamforming are jointly optimized. Since the formulated problem is non-convex, we employ the block coordinate descent (BCD) technique to decouple it into two subproblems for alternatively optimizing computing and communication settings. The effectiveness and convergence of the proposed algorithm are validate via numerical analyses. In addition, simulation results demonstrate that the proposed algorithm can achieve lower latency compared to that based on the ideal IRS reflection model, which confirms the necessary of considering practical model when designing an IRS-enhanced wideband MEC system.

cs.IT↗

arXiv2024

Ising-type quantum spin liquid state in PrMgAl$_{11}$O$_{19}$

We have grown single crystals of PrMgAl$_{11}$O$_{19}$, an ideal triangular-lattice antiferromagnet, and performed magnetic susceptibility, specific heat and thermal conductivity measurements at low temperatures. The main results are as follows: (i) The temperature-dependent susceptibility shows a negligible in-plane response and the isothermal magnetization curves confirm the easy axis along the $c$ axis. (ii) The specific heat measurements reveal the absence of long-range magnetic order down to 60 mK, and the power-law temperature dependence indicates the existence of the gapless magnetic excitations in system. (iii) The ultralow-temperature thermal conductivity exhibits negligibly small residual term ($\kappa_0/T$) and strong spin-phonon scattering effect, suggesting that the spin excitations are also involved. Our results further demonstrate that PrMgAl$_{11}$O$_{19}$ is a rare quantum spin liquid candidate with Ising-like anisotropy.

cond-mat.str-el↗

arXiv2024

Spinons in a new Shastry-Sutherland lattice magnet Pr$_2$Ga$_2$BeO$_7$

Identifying the elusive spinon excitations in quantum spin liquid (QSL) materials is what scientists have long sought for. Recently, thermal conductivity ($\kappa$) has emerged to be a decisive probe because the fermionic nature of spinons leads to a characteristic nonzero linear $\kappa_0/T$ term while approaching zero Kelvin. So far, only a few systems have been reported to exhibit such term. Here, we report a $\kappa_0/T \approx$ 0.01 WK$^{-2}$m$^{-1}$, the largest $\kappa_0/T$ value ever observed in magnetic oxide QSL candidates, in a new quantum magnet Pr$_2$Ga$_2$BeO$_7$ with a Shastry-Sutherland lattice (SSL). Its QSL nature is further supported by the power-law temperature dependence of the specific heat, a plateau of muon spin relaxation rate, and gapless inelastic neutron spectra. Our theoretical analysis reveals that the introduction of XY spin anisotropy is the key for Pr$_2$Ga$_2$BeO$_7$ to be the first QSL realized on the SSL, after more than four decades of extensive studies on this celebrated magnetically frustrated lattice.

cond-mat.str-el↗

arXiv2023

A Configurable Ultra-Low Noise Current Source for Transition-Edge Sensor Characterization

Transition-edge sensors (TESs) are sensitive devices for detecting photons from millimeter radiation to gamma rays. Their photon counting efficiency and collecting area benefit from large-array multiplexing scheme, and therefore the development of multiplexing readout system has been an important topic in this field. Among the many multiplex techniques, time-division multiplexing (TDM) superconducting quantum interference device (SQUID) has been used most widely for TES readout. In this work, we design a Configurable Ultra-Low Noise Current Source (CLCS) for TES characterization and as a part of a whole TDM-TES bias control system. The CLCS is based on the feedback structure of ultra-low noise instrumentation amplifiers and low-noise, high-resolution (20 bits) digital-to-analog converter (DAC). CLCS has an ultra-high resolution of 10 nA in the 0 to 5 mA current output range, and can perform current-voltage (IV) sweep and bias-step tests to measure key TES parameters on board. The feedback structure of the CLCS also avoids the issue of impedance mismatch.

astro-ph.IM↗

arXiv2023

Low-temperature specific heat and heat transport of Tb$_2$Ti$_{2-x}$Zr$_x$O$_7$ single crystals

We report a study on the specific heat and heat transport of Tb$_2$Ti$_{2-x}$Zr$_x$O$_7$ ($x =$ 0, 0.02, 0.1, 0.2, and 0.4) single crystals at low temperatures and in high magnetic fields. The magnetic specific heat can be described by the Schottky contribution from the crystal-electric-field (CEF) levels of Tb$^{3+}$, with introducing Gaussian distributions of the energy split of the ground-state doublet and the gap between the ground state and first excited level. These crystals has an extremely low phonon thermal conductivity in a broad temperature range that can be attributed to the scattering by the magnetic excitations, which are mainly associated with the CEF levels. There is strong magnetic field dependence of thermal conductivity, which is more likely related to the field-induced changes of phonon scattering by the CEF levels than magnetic transitions or spin excitations. For magnetic field along the [111] direction, there is large thermal Hall conductivity at low temperatures which displays a broad peak around 8 T. At high fields up to 14 T, the thermal Hall conductivity decreases to zero, which supports its origin from either the spinon transport or the phonon skew scattering by CEF levels. The thermal Hall effect is rather robust with Zr doping up to 0.2 but is strongly weakened in higher Zr-doped sample.

cond-mat.str-el↗

arXiv2022

Thermal Transport of Fractionalized Antiferromagnetic and Field Induced States in the Kitaev Material Na$_2$Co$_2$TeO$_6$

We report an in-plane thermal transport study of the honeycomb Kitaev material Na$_2$Co$_2$TeO$_6$ at subKelvin temperatures. In zero field, the $\kappa(T)$ displays a rather weak $T$-dependence but has a non-zero residual term $\kappa_0/T$, indicating strong phonon scattering by magnetic excitation and the possibility of itinerant spinon-like excitations coexisting with an antiferromagnetic order below 27 K. We propose the zero-field ground state is a novel fractionalized antiferromagnetic (AF*) state with both magnetic order and fractionalized excitations. With both the heat current and external field along the $a*$ (Co-Co bond) direction, the $\kappa_{a*}$ exhibits two sharp minima at 7.5 T and 10 T, and its value at 8.5 T is almost the same as the pure phononic transport for the high-field polarized state. This confirms the phase boundaries of the reported field-induced intermediate state and suggest its gapless continuum excitations possibly transport heat. No such intermediate phase was found in the $\kappa_a$ for the current and field along the $a$ (zigzag chain) direction. Finally, Na$_2$Co$_2$TeO$_6$ displays a strongly anisotropic magneto-thermal conductivity since the in-plane (out-of-plane) field strongly enhances (suppresses) the $\kappa_{a*}$ and $\kappa_a$.

cond-mat.str-el↗

arXiv2022

Low-temperature transport properties of intermetallic compound HoAgGe with kagome spin ice state

We study the magnetic susceptibility, magnetization, resistivity and thermal conductivity of intermetallic HoAgGe single crystals at low temperatures and in magnetic fields along the $a$ and $c$ axis, while the electric and heat currents are along the $c$ axis. The magnetization curves show a series of metamagnetic transitions and small hysteresis at low field for $B \parallel a$, and a weak metamagnetic transition for $B \parallel c$, respectively. Both the magnetic susceptibility and $\rho(T)$ curve show anomalies at the antiferromagnetic transition ($T\rm_N \sim$ 11.3 K) and spin reorientation transition ($\sim$ 7 K). In zero field and at very low temperatures, the electrons are found to be the main heat carriers. For $B \parallel a$, the $\rho(B)$ curves display large and positive transverse magnetoresistance (MR) with extraordinary field dependence between $B^2$ and $B$-linear, accompanied with anomalies at the metamagnetic transitions and low-field hysteresis; meanwhile, the $\kappa(B)$ mainly decrease with increasing field and display some anomalies at the metamagnetic transitions. For $B \parallel c$, there is weak and negative longitudinal MR while the $\kappa(B)$ show rather strong field dependence, indicating the role of phonon heat transport.

cond-mat.mtrl-sci↗

arXiv2022

Na$_5$Co$_{15.5}$Te$_6$O$_{36}$: an $S$ = 1/2 stacked Ising kagome antiferromagnet with a partially disordered ground state

$S$ = 1/2 Ising kagome antiferromagnets (KAFs) are rare in reality. In this work, we report the magnetic ground state and field-induced transitions of an $S$ = 1/2 Ising antiferromagnet with a stacked kagome geometry, Na$_5$Co$_{15.5}$Te$_6$O$_{36}$. Upon cooling, magnetic susceptibility measurement reveals three successive magnetic transitions at $T_1$ = 45.2 K, $T_2$ = 35.4 K, and $T_3 \sim$ 20 K. When the magnetic field is applied along the Ising $c$ axis, a strikingly anomalous initial magnetization lying outside the hysteresis loop is observed below $T_3$. Through the detailed characterizations, the magnetic field $vs$ temperature phase diagram is established. A partially disordered antiferromagnetic state is proposed below $T_1$, which becomes frozen below $T_3$. Na$_5$Co$_{15.5}$Te$_6$O$_{36}$ is therefore a promising candidate for $S$ = 1/2 Ising KAFs, and this unique composite structure may shed light on the exploratory path for $S$ = 1/2 Ising KAFs.

cond-mat.str-el↗

arXiv2022

Magnon-Polaron Driven Thermal Hall Effect in a Heisenberg-Kitaev Antiferromagnet

The thermal Hall effect, defined as a heat current response transversal to an applied temperature gradient, is a central experimental probe of exotic electrically insulating phases of matter. A key question is how the interplay between magnetic and structural degrees of freedom gives rise to a nonzero thermal Hall conductivity (THC). Here, we present evidence for an intrinsic thermal Hall effect in the Heisenberg-Kitaev antiferromagnet and spin-liquid candidate Na$_2$Co$_2$TeO$_6$ brought about by the quantum-geometric Berry curvature of so-called magnon polarons, resulting from magnon-phonon hybridization. At low temperatures, our field- and temperature-dependent measurements show a negative THC for magnetic fields below 10 T and a sign change to positive THC above. Theoretically, the sign and the order of magnitude of the THC cannot be solely explained with magnetic excitations. We demonstrate that, by incorporating spin-lattice coupling into our theoretical calculations, the Berry curvature of magnon polarons counteracts the purely magnonic contribution, reverses the overall sign of the THC, and increases its magnitude, which significantly improves agreement with experimental data. Our work highlights the crucial role of spin-lattice coupling in the thermal Hall effect.

cond-mat.str-el↗

arXiv2021

Solid solution and precipitation strengthening effects in basal slip, extension twinning and pyramidal slip in Mg-Zn alloys

A high-throughput methodology is proposed, based on the combination of diffusion couples and advanced nanomechanical testing methods, to directly measure alloying effects on the critical resolved shear stress (CRSS) of individual deformation modes in Mg alloys. The methodology is tested in Mg-Zn alloys by assessing the alloying effects, up to Zn contents of 2 at.%, on basal slip, extension twining and pyramidal slip in two metallurgical condition: as-quenched, for which the Zn solute atoms remain homogenously dispersed in solid solution; and peak-aged, for which the Zn atoms form rod-shape $MgZn_{2}$ precipitates. A combined approach including micromechanical testing, transmission Kikuchi diffraction, and high-resolution transmission electron microscopy was performed to reveal the corresponding deformation mechanisms. It was found that the CRSS enhancement for basal slip and extension twinning by $MgZn_{2}$ precipitates is considerably larger than the effect of Zn in solid solution, while the strengthening of pyramidal slip is similar in both cases. As a result, the anisotropy ratios remain high and similar to pure Mg in the solid solution strengthened Mg-Zn alloys. However, they are substantially reduced in precipitation strengthened Mg-Zn alloys.

cond-mat.mtrl-sci↗

arXiv2021

Survival of itinerant excitations and quantum spin state transitions in YbMgGaO$_4$ with chemical disorder

A recent focus of quantum spin liquid (QSL) studies is how disorder/randomness in a QSL candidate affects its true magnetic ground state. The ultimate question is whether the QSL survives disorder or the disorder leads to a "spin-liquid-like" state, such as the proposed random-singlet (RS) state. Since disorder is a standard feature of most QSL candidates, this question represents a major challenge for QSL candidates. YbMgGaO$_4$, a triangular lattice antiferromagnet with effective spin-1/2 Yb$^{3+}$ ions, is an ideal system to address this question, since it shows no long-range magnetic ordering with Mg/Ga site disorder. Despite the intensive study, it remains unresolved as to whether YbMgGaO$_4$ is a QSL or in the RS state. Here, through ultralow-temperature thermal conductivity and magnetic torque measurements, plus specific heat and DC magnetization data, we observed a residual $\kappa_0/T$ term and series of quantum spin state transitions in the zero temperature limit for YbMgGaO$_4$. These observations strongly suggest that a QSL state with itinerant excitations and quantum spin fluctuations survives disorder in YbMgGaO$_4$.

cond-mat.str-el↗

arXiv2021

Quantum spin state transitions in spin-1 equilateral triangular lattice antiferromagnet Na$_2$BaNi(PO$_4$)$_2$

We have grown single crystals of Na$_2$BaNi(PO$_4$)$_2$, a new spin-1 equilateral triangular lattice antiferromagnet (ETLAF), and performed magnetic susceptibility, specific heat and thermal conductivity measurements at ultralow temperatures. The main results are (i) at zero magnetic field, Na$_2$BaNi(PO$_4$)$_2$ exhibits a magnetic ordering at 430 mK with a weak ferromagnetic moment along the $c$ axis. This suggests a canted 120$^\circ$ spin structure, which is in a plane including the crystallographic $c$ axis due to the existence of an easy-axis anisotropy and ferromagnetically stacked along the $c$ axis; (ii) with increasing field along the $c$ axis, a 1/3 magnetization plateau is observed which means the canted 120$^\circ$ spin structure is transformed to a up up down (UUD) spin structure. With even higher fields, the UUD phase further evolves to possible V and V' phases; (iii) with increasing field along the $a$ axis, the canted 120$^\circ$ spin structure is possibly transformed to a umbrella phase and a V phase. Therefore, Na$_2$BaNi(PO$_4$)$_2$ is a rare example of spin-1 ETLAF with single crystalline form to exhibit easy-axis spin anisotropy and series of quantum spin state transitions.

cond-mat.mtrl-sci↗

arXiv2021

Core Mass Estimates in Strong Lensing Galaxy Clusters: a Comparison Between Masses Obtained from Detailed Lens Models, Single-Halo Lens Models, and Einstein Radii

The core mass of galaxy clusters is both an important anchor of the radial mass distribution profile and probe of structure formation. With thousands of strong lensing galaxy clusters being discovered by current and upcoming surveys, timely, efficient, and accurate core mass estimates are needed. We assess the results of two efficient methods to estimate the core mass of strong lensing clusters: the mass enclosed by the Einstein radius ($M_{corr}(<\theta_E)$ where $\theta_{\rm E}$ is approximated from arc positions; Remolina Gonz\'{a}lez et al. 2020), and single-halo lens model ($M_{\rm{SHM}}(<\rm{e}\theta_{\rm{E}})$; Remolina Gonz\'{a}lez et al. 2021), against measurements from publicly available detailed lens models ($M_{\rm{DLM}}$) of the same clusters. We use data from the Sloan Giant Arc Survey, the Reionization Lensing Cluster Survey, the \Hubble\ Frontier Fields, and the Cluster Lensing and Supernova Survey with \Hubble. We find a scatter of $18.3\%$ ($8.4\%$) with a bias of $-7.5\%$ ($0.4\%$) between $M_{corr}(<\theta_E)$ ($M_{\rm{SHM}}(<\rm{e}\theta_{\rm{E}})$) and $M_{\rm{DLM}}$. Last, we compare the statistical uncertainties measured in this work to those from simulations. This work demonstrates the successful application of these methods to observational data. As the effort to efficiently model the mass distribution of strong lensing galaxy clusters continues, we need fast, reliable methods to advance the field.

astro-ph.CO↗