In CePdAl, the $4f$ moments of cerium arrange to form a geometrically frustrated kagome lattice. Due to frustration, in addition to Kondo and Ruderman-Kittel-Kasuya-Yosida interactions, this metallic system shows a long-range magnetic order (LRO) with a $T_{\mathrm{N}}$ of only 2.7 K. Upon Ni doping at the Pd sites, $T_{\mathrm{N}}$ is further suppressed, to reach zero at a critical concentration $x_c\approx 0.15$. Here, by using muon-spin relaxation and rotation ($\text{µ}\mathrm{SR}$), we investigate ${\mathrm{CePd}}_{1-x}{\mathrm{Ni}}_x\mathrm{Al}$ at a local level for five different Ni concentrations, both above and below $x_c$. Like the parent CePdAl compound, for $x=0.05$, we observe an incommensurate LRO, which turns into a quasistatic magnetic order for $x=0.1$ and 0.14. More interestingly, away from $x_c$, for $x=0.16$ and 0.18, we still observe a non-Fermi-liquid (NFL) regime, evidenced by a power-law divergence of the longitudinal relaxation at low temperatures. In this case, longitudinal field measurements exhibit a time-field scaling, indicative of cooperative spin dynamics that persists for $x>x_c$. Furthermore, like the externally applied pressure, the chemical pressure induced by Ni doping suppresses the region below $T^{*}$, characterized by a spin-liquid-like dynamical behavior. Our results suggest that the magnetic properties of CePdAl are similarly affected by the hydrostatic and the chemical pressure. We also confirm that the unusual NFL regime (compared with conventional quantum critical systems) is due to the presence of frustration that persists up to the highest Ni concentrations.

We present proof-of-principle experiments of stroboscopic time-of-flight (TOF) neutron diffraction in long pulsed magnetic fields. By utilizing electric double-layer capacitors, we developed a long pulsed magnet for neutron diffraction measurements, which generates pulsed magnetic fields with the full widths at half maximum of >${10}^2$ ms. The field variation is slow enough to be approximated as a steady field within the time scale of a polychromatic neutron pulse passing through a sample placed in a distance of the order of ${10}^1$ m from the neutron source. This enables us to efficiently explore the reciprocal space using a wide range of neutron wavelength in high magnetic fields. We applied this technique to investigate field-induced magnetic phases in the triangular lattice antiferromagnets ${\mathrm{CuFe}}_{1-x}{\mathrm{Ga}}_x{\mathrm{O}}_2$ ($x=0,0.035$).

Hyperuniformity, the suppression of density fluctuations at large length scales, is observed across a wide variety of domains, from cosmology to condensed matter and biological systems. Although the standard definition of hyperuniformity only utilizes information at the largest scales, hyperuniform configurations have distinctive local characteristics. However, the influence of global hyperuniformity on local structure has remained largely unexplored; establishing this connection can help uncover long-range interaction mechanisms and detect hyperuniform traits in finite-size systems. Here, we study the topological properties of hyperuniform point clouds by characterizing their persistent homology and the statistics of local graph neighborhoods. We find that varying the structure factor results in configurations with systematically different topological properties. Moreover, these topological properties are conserved for subsets of hyperuniform point clouds, establishing a connection between finite-sized systems and idealized reference arrangements. Comparing distributions of local topological neighborhoods reveals that the hyperuniform arrangements lie along a primarily one-dimensional manifold reflecting an order-to-disorder transition via hyperuniform configurations. The results presented here complement existing characterizations of hyperuniform phases of matter, and they show how local topological features can be used to detect hyperuniformity in size-limited simulations and experiments.

Our studies of the cyclotron resonance (CR) photoresistance in GaAs-based two-dimensional electron systems (2DES) reveal an anomalously low sensitivity to the helicity of the incoming circularly polarized terahertz radiation. We find that this anomaly is strongly intensity dependent, and the ratio of the low-temperature photoresistance signals for the CR-active (CRA) and CR-inactive (CRI) polarities of magnetic field increases with lowering power, but, nevertheless, remains substantially lower than expected from conventional theory assuming interaction of the plane electromagnetic wave with the uniform 2DES. Our analysis shows that all data can be well described by the nonlinear CR-enhanced electron gas heating in both CRA and CRI regimes. This description, however, does not specify the source of anomalous CRI absorption that remains unclear.

While gauge symmetry is a well-established requirement for representing topological orders in projected entangled-pair state (PEPS), its impact on the properties of low-lying excited states remains relatively unexplored. Here we perform PEPS simulations of low-energy dynamics in the Kitaev honeycomb model, which supports fractionalized gauge flux (vison) excitations. We identify gauge symmetry emerging upon optimizing an unbiased PEPS ground state. Using the PEPS adapted local mode approximation, we further classify the low-lying excited states by discerning different vison sectors. Our simulations of spin and spin-dimer dynamical correlations establish close connections with experimental observations. Notably, the selection rule imposed by the locally conserved visons results in nearly flat dispersions in momentum space for excited states belonging to the 2-vison or 4-vison sectors.

Silicon polymorphs with exotic electronic and optical properties have recently attracted significant attention due to their wide range of useful band gap characteristics. They are typically formed by static high-pressure techniques, which limits the crystal structures that can be made. This constitutes a major obstacle to study these polymorphs and their incorporation into existing technology. Approaches have attempted to address this shortcoming through using dynamic conditions and chemical precursor materials. Here, we report on an approach to create unusual crystal structures deep in the bulk of a silicon crystal by irradiating it with a laser pulse at ultrarelativistic intensity of up to $7.5\times {10}^{19}$ $\text{W/}\mathrm{c}{\mathrm{m}}^2$. Laser-generated electrons with MeV energy swiftly penetrate the target with speed close to the speed of light and deposit their energy into a large volume across the whole thickness of the sample. The relativistic electron current creates, via branching propagation and ionization, high-energy-density conditions for thermodynamically nonequilibrium phase transformation paths into new crystal polymorphs. X-ray microdiffraction and synchrotron x-ray diffraction analyses indicate, along with conventional dc-Si, the presence of exotic silicon structures in the bulk of the laser intact target volume. These structures are identified as body-centered bc8-Si, rhombohedral r8-Si, hexagonal-diamond hd-Si, and the tetragonal Si-VIII, all phases of Si that have previously been made through static techniques. Additionally, simple-tetragonal st12-Si and body-centered tetragonal bt8-Si were observed along with signatures of not yet identified diffraction spots. Both st12-Si and bt8-Si have only been observed in ultrafast laser microexplosion conditions at much lower laser intensity $\sim {10}^{14}$ $\text{W/}\mathrm{c}{\mathrm{m}}^2$ and within a micron-thin surface layer. The findings here are supported by direct observation of nanoparticles with high-resolution transmission electron microscopy and corresponding fast Fourier transform analysis of their interatomic distances. The presented analyses of absorbed laser energy, generation of the MeV electron current, and deposition of energy across the whole target thickness provide a solid basis for drawing the conclusion that the observed silicon polymorphs were produced because of laser-generated high-energy electrons fast-penetrating deeply into the bulk of silicon. In contrast to solid-solid transformations, the plasma-solid transitions offer a paradigm for the creation of exotic, high-energy density materials inside the bulk of the sample by using laser pulses at relativistic intensities.

We present a theory of weak localization (WL) in the presence of generic spin-dependent fields, including any type of spin-orbit coupling, Zeeman fields, and nonhomogeneous magnetic textures. We go beyond the usual diffusive approximation, considering systems with short-range disorder of arbitrary strength and obtain a compact expression for the weak localization (WL) correction to the conductivity in terms of the singlet-triplet polarization operator in momentum space. The latter can be directly related to the solution of the quasiclassical Eilenberger equation for superconducting systems. This formulation presents an intuitive framework to explore how the interplay of various spin-dependent fields drives weak (anti) localization. We apply our results to study in-plane magnetoconductivity in systems with spin-orbit coupling and in newly discovered altermagnets. Our results enable straightforward calculation of the WL conductivity at arbitrary disorder strength, which can be particularly useful for interpreting experiments on high-mobility samples.

Valence transitions in strongly correlated electron systems are caused by orbital hybridization and Coulomb interactions between localized and delocalized electrons. The transition can be triggered by changes in the electronic structure and is sensitive to temperature variations, applications of magnetic fields, and physical or chemical pressure. Launching the transition by photoelectric fields can directly excite the electronic states and thus provides an ideal platform to study the correlation among electrons on ultrafast timescales. The $\mathrm{EuN}{\mathrm{i}}_2{\left({\mathrm{Si}}_{0.21}{\mathrm{Ge}}_{0.79}\right)}_2$ mixed-valence metal is an ideal material to investigate the valence transition of the Eu ions via the amplified orbital hybridization by the photoelectric field on subpicosecond timescales. A direct view on the $4f$ electron occupancy of the Eu ions is required to understand the microscopic origin of the transition. Here we probe the $4f$ electron states of $\mathrm{EuN}{\mathrm{i}}_2{\left({\mathrm{Si}}_{0.21}{\mathrm{Ge}}_{0.79}\right)}_2$ at the sub-ps timescale after photoexcitation by x-ray absorption spectroscopy across the Eu $M_5$-absorption edge. The observed spectral changes due to the excitation indicate a population change of total angular momentum multiplet states $J$ = 0, 1, 2, and 3 of $\mathrm{E}{\mathrm{u}}^{3+}$ and the $\mathrm{E}{\mathrm{u}}^{2+} J$ = 7/2 multiplet state caused by an increase in $4f$ electron temperature that results in a $4f$ localization process. This electronic temperature increases combined with fluence-dependent screening accounts for the strongly nonlinear effective valence change. The data allow us to extract a time-dependent determination of an effective temperature of the $4f$ shell, which is also of great relevance in the understanding of metallic systems' properties, such as the ultrafast demagnetization of ferromagnetic rare-earth intermetallic and their all-optical magnetization switching. In addition, our results elucidate the energetics of charge fluctuations in valence-mixed electronic systems, which provide enriched knowledge regarding the role of valence transitions and orbital hybridization for quantum critical phenomena.

The tunneling of Cooper pairs across a Josephson junction (JJ) allows for the nonlinear inductance necessary to construct superconducting qubits, amplifiers, and various other quantum circuits. An alternative approach using hybrid superconductor-semiconductor JJs can enable superconducting qubit architectures with all electric control. Here we present continuous-wave and time-domain characterization of gatemon qubits and coplanar waveguide resonators based on an InAs two-dimensional electron gas. We show that the qubit undergoes a vacuum Rabi splitting with a readout cavity, and we drive coherent Rabi oscillations between the qubit ground and first excited states. We measure qubit relaxation times to be $T_1=$ 100 ns over a 1.5 GHz tunable band. We detail the loss mechanisms present in these materials through a systematic study of the quality factors of coplanar waveguide resonators. While various loss mechanisms are present in III-V gatemon circuits, we detail future directions in enhancing the relaxation times of qubit devices on this platform.

As a rare topological phonon material, $\beta \text{−}{\mathrm{MoB}}_2$ exhibits superconductivity (SC) and undergoes structural transitions when subjected to pressure or doping. This unique property makes it an intriguing platform for investigating the interplay of diverse quantum order. However, the current understanding of phonons in this material remains limited. Therefore, in this study, we employ a combination of Raman scattering and first-principle calculations to investigate the phonon properties of $\beta \text{−}{\mathrm{MoB}}_2$. Several noteworthy observations were made during the study. (1) We identified five Raman-active modes ($3A_{1g}+2E_g$) and two abnormal modes in $\beta \text{−}{\mathrm{MoB}}_2$. The authenticity of the five Raman-active modes was further confirmed through angle-resolved polarized Raman spectra (ARPRS) measurements and theoretical calculations. (2) We found that all Raman spectra obtained at various temperatures exhibited symmetric Lorentzian profiles. This finding implies a weak electron-phonon coupling (EPC) strength in $\beta \text{−}{\mathrm{MoB}}_2$. We calculated the EPC strength $\lambda$ of bulk $\beta \text{−}{\mathrm{MoB}}_2$ to be 0.37, which is significantly lower than 1.71 of superconducting $\alpha \text{−}{\mathrm{MoB}}_2$. (3) Based on ARPRS measurements and the phonon dispersion, we attributed the origin of the two abnormal modes to structural distortions with regard to B atom layers of $\beta \text{−}{\mathrm{MoB}}_2$. This research provides a foundation for exploring the relationship between defect structures and various intriguing physical phenomena observed in $\beta \text{−}{\mathrm{MoB}}_2$.

The coherent energy transfer between two quantum devices (a quantum charger and a quantum battery) mediated by a photonic cavity is investigated, in presence of dissipative environments, with particular focus on the ultrastrong coupling regime. Here, very short transfer times and high charging power can be achieved in comparison with the usually addressed weak coupling case. Such phenomenology is further magnified by the presence of level crossings appearing in the energy spectrum and which reveal very robust against dissipative environmental effects. Moreover, by carefully controlling the physical parameters of the model, e.g., the matter-radiation coupling and the frequencies of the system, it is possible to tune these crossings making this device more flexible and experimentally feasible. Finally to broaden our analysis, we assume the possibility of choosing between a Fock and a coherent initial state of the cavity, with the latter showing better energetic performances.

We consider a system of classical hard rods or billiard balls in one dimension, initially prepared in a Bragg-pulse state at a given temperature and subjected to external periodic fields. We show that at late times the system thermalizes in the thermodynamic limit via a three-stages process characterized by: an early phase where the dynamics is well described by Euler hydrodynamics, a subsequent phase where a (weak) turbulent phase is observed and where hydrodynamic gradient expansion can be broken, and a final one where the gas thermalizes according to viscous hydrodynamics. As the hard rod gas shares the same large-scale hydrodynamics as other quantum and classical integrable systems, we expect these features to universally characterize all many-body integrable systems in generic external potentials.

We determine the ground states and excitation spectra of the paradigmatic four-flavor Heisenberg model with nearest- and next-nearest-neighbor exchange couplings on the triangular lattice in a field controlling the population imbalance of flavor pairs. Such a system arises in the strongly correlated limit of moiré bilayers of transition metal dichalcogenides in an electric displacement field or in-plane magnetic field, and can be simulated via ultracold alkaline-earth atoms. We argue that the field tunes between effective SU(4) and SU(2) symmetries in the balanced and fully polarized limits and employ a combination of mean-field calculations, flavor-wave theory, and exact diagonalization to analyze the intermediate, imbalanced regime. We find different symmetry-broken phases with simultaneous spin and excitonic order depending on the field and next-nearest-neighbor coupling. Furthermore, we demonstrate that there is a strongly fluctuating regime without long-range order that connects candidate spin liquids of the SU(2) and SU(4) limit. The strong fluctuations are facilitated by an extensive classical degeneracy of the model, and we argue that they are also responsible for a strong polarizability at 1/3 polarization that survives from the mean-field level to the exact spectrum.

The competition between unitary time evolution and quantum measurements could induce phase transitions in the entanglement characteristics of quantum many-body dynamics. In this work, we reveal such entanglement transitions in the context of non-Hermitian Floquet systems. Focusing on noninteracting fermions in a representative bipartite lattice with balanced gain/loss and under time-periodic quenches, we uncover rich patterns of entanglement transitions due to the interplay between driving and non-Hermitian effects. Specially, we find that the monotonic increase of quenched hopping amplitude could flip the system between volume-law and area-law entangled Floquet phases, yielding alternated entanglement transitions. Meanwhile, the increase of gain/loss strength could trigger area-law to volume-law reentrant transitions in the scaling behavior of steady-state entanglement entropy, which are abnormal and highly unexpected in nondriven systems. Connections between entanglement transitions and parity-time-reversal (PT) transitions in Floquet spectra are further established. Our findings not only build a foundation for exploring entanglement phase transitions in Floquet non-Hermitian setups, but also provide efficient means to engineer and control such transitions by driving fields.

Temperature-dependent nitrogen-vacancy (NV)-center relaxometry is an established tool to characterize paramagnetic molecules near a sensing diamond, gaining momentum in different fields of science. However, recent results indicate that conversion between NV-center charge states impedes these measurements and influences the results for the $T_1$ time. While the temperature dependence of NV centers' $T_1$ time is well studied, additional contributions from temperature-dependent charge conversion during the dark time may further affect the measurement results. We combine temperature-dependent relaxometry and fluorescence spectroscopy at varying laser powers to unravel the temperature dependence of charge conversion in nanodiamond for biologically relevant temperatures. While we observe a decrease of the $T_1$ time with increasing temperatures, charge conversion remains unaffected by the temperature change. These results allow the temperature-dependent performance of $T_1$ relaxometry without further consideration of temperature dependence of charge conversion.

Strontium titanate (${\mathrm{SrTiO}}_3$) two-dimensional electron gases (2DEGs) have broken spatial inversion symmetry and possess a finite Rashba spin-orbit coupling. This enables the interconversion of charge and spin currents through the direct and inverse Edelstein effects, with record efficiencies at low temperature but more modest effects at room temperature. Here, we show that making these 2DEGs ferromagnetic enhances the conversion efficiency by nearly one order of magnitude. Starting from the experimental band structure of nonmagnetic ${\mathrm{SrTiO}}_3$ 2DEGs, we mimic magnetic exchange coupling by introducing an out-of-plane Zeeman term in a tight-binding model. We then calculate the band structure and spin textures for increasing internal magnetic fields and compute the Edelstein effect using a semiclassical Boltzmann approach. We find that the conversion efficiency first increases strongly with increasing magnetic field, then shows a maximum, and finally decreases. This field dependence is caused by the competition of the exchange coupling with the effective Rashba interaction. While the magnetic field enhances the splitting of band pairs (both in momentum and in spin expectation value), it also weakens the in-plane Rashba-type spin texture. The former mechanism increases the Edelstein effect, and the latter reduces it.