Significant thermal rectification has the potential to revolutionize approaches to controlled heat flow and enable breakthrough technologies such as phononic computing. We demonstrate a framework based on phonon population confinement and filtering that has potential to reach rectifications that are an order of magnitude larger than previous literature. With the use of a straightforward modification of the phonon gas model, we illustrate theoretical thermal rectification in a thin film of diamond (1–10 nm) graded to dimensions $>1\mu \mathrm{m}$ of between 25% and 250%. Utilizing this mechanism for thermal rectification sets the stage for significant development in thermal devices.

We report the anomalous bulk transformation of vapor deposited stable glasses into the liquid state. The transformation proceeds through two competing parallel processes: partial rejuvenation of the stable glass and nucleation and growth of liquid patches within the glass. The kinetics of the transformation extracted from heat capacity curves after isothermal runs is dominated by the heterogeneous nucleation and growth process that initiates at preexisting seeds and propagates radially at a velocity proportional to the alpha relaxation time. Remarkably, the distance between the activation seeds is independent of temperature within experimental uncertainty and amounts to several micrometers, a value in close agreement with the crossover length for TPD glasses. We speculate the initiation sites for the transformation of the glass into the supercooled liquid are localized regions of lower stability (or density).

Exploration of the novel relationship between magnetic order and topological semimetals has received enormous interest in a wide range of both fundamental and applied research. Here we predict that “soft” ferromagnetic material ${\mathrm{EuB}}_6$ can achieve multiple topological semimetal phases by simply tuning the direction of the magnetic moment. Explicitly, ${\mathrm{EuB}}_6$ is a topological nodal-line semimetal when the moment is aligned along the [001] direction, and it evolves into a Weyl semimetal with three pairs of Weyl points by rotating the moment to the [111] direction. Interestingly, we identify a composite semimetal phase featuring the coexistence of a nodal line and Weyl points with the moment in the [110] direction. Topological surface states and anomalous Hall conductivity, which are sensitive to the magnetic order, have been computed and are expected to be experimentally observable. Large-Chern-number quantum anomalous Hall effect can be realized in its [111]-oriented quantum-well structures.

The zone-center $E_{2g}$ modes play a crucial role in ${\mathrm{MgB}}_2$, controlling the scattering mechanisms in the normal state as well the superconducting pairing. Here, we demonstrate via first-principles quantum-field theory calculations that, due to the anisotropic electron-phonon interaction, a hot-phonon regime where the $E_{2g}$ phonons can achieve significantly larger effective populations than other modes, is triggered in ${\mathrm{MgB}}_2$ by the interaction with an ultrashort laser pulse. Spectral signatures of this scenario in ultrafast pump-probe Raman spectroscopy are discussed in detail, revealing also a fundamental role of nonadiabatic processes in the optical features of the $E_{2g}$ mode.

In this work we combine theory and experiment to study transient magnetic circular dichroism (TRMCD) in the extreme ultraviolet spectral range in bulk Co and CoPt. We use the ab initio method of real-time time-dependent density functional theory to simulate the magnetization dynamics in the presence of short laser pulses. From this we demonstrate how TRMCD may be calculated using an approximation to the excited-state linear response. We apply this approximation to Co and CoPt and show computationally that element-specific dynamics of the local spin moments can be extracted from the TRMCD in the extreme ultraviolet energy range, as is commonly assumed. We then compare our theoretical prediction for the TRMCD for CoPt with experimental measurement and find excellent agreement at many different frequencies including the $M_{23}$ edge of Co and $N_{67}$ and $O_{23}$ edges of Pt.

We investigate the spin relaxation of Ho single atom magnets on $\mathrm{MgO}/\mathrm{Ag}(100)$ as a function of temperature and magnetic field. We find that the spin relaxation is thermally activated at low field, while it remains larger than 1000 s up to 30 K and 8 T. This behavior contrasts with that of single molecule magnets and bulk paramagnetic impurities, which relax faster at high field. Combining our results with density functional theory, we rationalize this unconventional behavior by showing that local vibrations activate a two-phonon Raman process with a relaxation rate that peaks near zero field and is suppressed at high field. Our work shows the importance of these excitations in the relaxation of axially coordinated magnetic atoms.

The discovery of magnetic Weyl semimetal (magnetic WSM) in ${\mathrm{Co}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$ has triggered great interest for abundant fascinating phenomena induced by band topology conspiring with the magnetism. Understanding how the magnetization affects the band structure can give us a deeper comprehension of the magnetic WSMs and guide us for the innovation in applications. Here, we systematically study the temperature-dependent optical spectra of ferromagnetic WSM ${\mathrm{Co}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$ experimentally and simulated by first-principles calculations. Our results indicate that the many-body correlation effect due to Co $3d$ electrons leads to the renormalization of electronic kinetic energy by a factor about 0.43, which is moderate, and the description within density functional theory is suitable. As the temperature drops down, the magnetic phase transition happens, and the magnetization drives the band shift through exchange splitting. The optical spectra can well detect these changes, including the transitions sensitive and insensitive to the magnetization, and those from the bands around the Weyl nodes. The results support that, in magnetic WSM ${\mathrm{Co}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$, the bands that contain Weyl nodes can be tuned by magnetization with temperature change.

We report the experimental observation of tunable, nonreciprocal quantum transport of a Bose-Einstein condensate in a momentum lattice. By implementing a dissipative Aharonov-Bohm (AB) ring in momentum space and sending atoms through it, we demonstrate a directional atom flow by measuring the momentum distribution of the condensate at different times. While the dissipative AB ring is characterized by the synthetic magnetic flux through the ring and the laser-induced loss on it, both the propagation direction and transport rate of the atom flow sensitively depend on these highly tunable parameters. We demonstrate that the nonreciprocity originates from the interplay of the synthetic magnetic flux and the laser-induced loss, which simultaneously breaks the inversion and the time-reversal symmetries. Our results open up the avenue for investigating nonreciprocal dynamics in cold atoms, and highlight the dissipative AB ring as a flexible building element for applications in quantum simulation and quantum information.

Quantum measurement is essential to both the foundations and practical applications of quantum information science. Among many possible models of quantum measurement, feedback measurements that dynamically update their physical structure are highly interesting due to their flexibility, which enables a wide range of measurements that might otherwise be hard to implement. Here we investigate by detector tomography a measurement consisting of a displacement operation combined with photon detection followed by a real time feedback operation. We design the measurement in order to discriminate the superposition of vacuum and single photon states—the single-rail qubit—and find that it can discriminate the superposition states with a certainty of 96%. Such a feedback-controlled photon counter will facilitate the realization of quantum information protocols with single-rail qubits as well as the nonlocality test of certain entangled states.

We report a stable and efficient complex Langevin sampling scheme for performing approximation-free numerical simulations directly on the path-integral coherent-states field theory for an assembly of interacting bosons. We apply the method to generate the $\lambda$ line of critical phase transitions associated with Bose-Einstein condensation in a model ${\varphi }^4$ scalar field theory. The new approach enjoys near-linear scaling in the resolved ($d+1$) spatial and imaginary-time dimensions and should be particularly efficient for the study of dense systems at low temperature.

We present a search for nine lepton-number-violating and three lepton-flavor-violating neutral charm decays of the type $D^0\to h^{\prime -}{h}^{-}{\ell }^{\prime +}{\ell }^{+}$ and $D^0\to h^{\prime -}{h}^{+}{\ell }^{\prime \pm }{\ell }^{\mp }$, where $h$ and $h^{\prime }$ represent a $K$ or $\pi$ meson and $\ell$ and ${\ell }^{\prime }$ an electron or muon. The analysis is based on $468{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ annihilation data collected at or close to the $\mathrm{\Upsilon }(4S)$ resonance with the BABAR detector at the SLAC National Accelerator Laboratory. No significant signal is observed for any of the twelve modes, and we establish 90% confidence level upper limits on the branching fractions in the range $(1.0–30.6)\times {10}^{-7}$. The limits are between 1 and 3 orders of magnitude more stringent than previous measurements.

Three hidden-charm pentaquark $P_c$ states, $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$ were revealed in the ${\mathrm{\Lambda }}_b^0\to J/\psi p{K}^{-}$ process measured by LHCb using both run I and run II data. Their nature is under lively discussion, and their quantum numbers have not been determined. We analyze the $J/\psi p$ invariant mass distributions under the assumption that the crossed-channel effects provide a smooth background. For the first time, such an analysis is performed employing a coupled-channel formalism with the scattering potential involving both one-pion exchange as well as short-range operators constrained by heavy quark spin symmetry. We find that the data can be well described in the hadronic molecular picture, which predicts seven ${\mathrm{\Sigma }}_c^{(*)}{\overline{D}}^{(*)}$ molecular states in two spin multiplets, such that the $P_c(4312)$ is mainly a ${\mathrm{\Sigma }}_c\overline{D}$ bound state with $J^P=1/2^{-}$, while $P_c(4440)$ and $P_c(4457)$ are ${\mathrm{\Sigma }}_c{\overline{D}}^{*}$ bound states with quantum numbers $3/2^{-}$ and $1/2^{-}$, respectively. We also show that there is evidence for a narrow ${\mathrm{\Sigma }}_c^{*}\overline{D}$ bound state in the data which we call $P_c(4380)$, different from the broad one reported by LHCb in 2015. With this state included, all predicted ${\mathrm{\Sigma }}_c\overline{D}$, ${\mathrm{\Sigma }}_c^{*}\overline{D}$, and ${\mathrm{\Sigma }}_c{\overline{D}}^{*}$ hadronic molecules are seen in the data, while the missing three ${\mathrm{\Sigma }}_c^{*}{\overline{D}}^{*}$ states are expected to be found in future runs of the LHC or in photoproduction experiments.

Previous lattice QCD calculations of axial vector and pseudoscalar form factors show significant deviation from the partially conserved axial current (PCAC) relation between them. Since the original correlation functions satisfy PCAC, the observed deviations from the operator identity cast doubt on whether all of the systematics in the extraction of form factors from the correlation functions are under control. We identify the problematic systematic as a missed excited state, whose energy as a function of the momentum transfer squared $Q^2$ is determined from the analysis of the three-point functions themselves. Its energy is much smaller than those of the excited states previously considered, and including it impacts the extraction of all of the ground state matrix elements. The form factors extracted using these mass and energy gaps satisfy PCAC and another consistency condition, and they validate the pion-pole dominance hypothesis. We also show that the extraction of the axial charge $g_A$ is very sensitive to the value of the mass gaps of the excited states used, and current lattice data do not provide an unambiguous determination of these, unlike the $Q^2\ne 0$ case. To highlight the differences and improvement between the conventional vs the new analysis strategy, we present a comparison of results obtained on a physical pion mass ensemble at $a\approx 0.0871\mathrm{fm}$. With the new strategy, we find $g_A=1.30(6)$ and axial charge radius $r_A=0.74(6)\mathrm{fm}$, both extracted using the $z$ expansion to parametrize the $Q^2$ behavior of $G_A(Q^2)$, and $g_P^{*}=8.06(44)$, obtained using the pion-pole dominance ansatz to fit the $Q^2$ behavior of the induced pseudoscalar form factor ${\tilde{G}}_P(Q^2)$. These results are consistent with current phenomenological values.

We analyze the physics of self-bound droplets in a doubly dipolar Bose-Einstein condensate composed by particles with both electric and magnetic dipole moments. Using the particularly relevant case of dysprosium, we show that the anisotropy of the doubly dipolar interaction potential is highly versatile and nontrivial, depending critically on the relative orientation and strength between the two dipole moments. This opens novel possibilities for exploring intriguing quantum many-body physics. Interestingly, by varying the angle between the two dipoles we find a dimensional crossover from quasi-one-dimensional to quasi-two-dimensional self-bound droplets. This opens a so far unique scenario in condensate physics, in which a dimensional crossover is solely driven by interactions in the absence of any confinement.

Dominant multiparticle interactions can give rise to exotic physical phases with anyonic excitations and phase transitions without local order parameters. In spin systems with a global $\mathrm{SU}(N)$ symmetry, cyclic ring-exchange couplings constitute the first higher-order interaction in this class. In this Letter, we propose a protocol showing how $\mathrm{SU}(N)$-invariant multibody interactions can be implemented in optical tweezer arrays. We utilize the flexibility to rearrange the tweezer configuration on short timescales compared to the typical lifetimes, in combination with strong nonlocal Rydberg interactions. As a specific example, we demonstrate how a chiral cyclic ring-exchange Hamiltonian can be implemented in a two-leg ladder geometry. We study its phase diagram using density-matrix renormalization group simulations and identify phases with dominant vector chirality, a ferromagnet, and an emergent spin-1 Haldane phase. We also discuss how the proposed protocol can be utilized to implement the strongly frustrated $J–Q$ model, a candidate for hosting a deconfined quantum critical point.