We use microwaves to engineer repulsive long-range interactions between ultracold polar molecules. The resulting shielding suppresses various loss mechanisms and provides large elastic cross ...sections. Hyperfine interactions limit the shielding under realistic conditions, but a magnetic field allows suppression of the losses to below 10^{-14} cm^{3} s^{-1}. The mechanism and optimum conditions for shielding differ substantially from those proposed by Gorshkov et al. Phys. Rev. Lett. 101, 073201 (2008)PRLTAO0031-900710.1103/PhysRevLett.101.073201, and do not require cancellation of the long-range dipole-dipole interaction that is vital to many applications.
The crystal structure of a solid largely dictates its electronic, optical and mechanical properties. Indeed, much of the exploration of quantum materials in recent years including the discovery of ...new phases and phenomena in correlated, topological and two-dimensional materials—has been based on the ability to rationally control crystal structures through materials synthesis, strain engineering or heterostructuring of van der Waals bonded materials. These static approaches, while enormously powerful, are limited by thermodynamic and elastic constraints. An emerging avenue of study has focused on extending such structural control to the dynamical regime by using resonant laser pulses to drive vibrational modes in a crystal. This paradigm of ‘nonlinear phononics’ provides a basis for rationally designing the structure and symmetry of crystals with light, allowing for the manipulation of functional properties at high speed and, in many instances, beyond what may be possible in equilibrium. Here we provide an overview of the developments in this field, discussing the theory, applications and future prospects of optical crystal structure engineering.The interaction between light and the crystal lattice of a quantum material can modify its properties. Utilizing nonlinear interactions allows this to be done in a controlled way to design specific non-equilibrium functionalities.
Strain engineering is widely used to manipulate the electronic and magnetic properties of complex materials. For example, the piezomagnetic effect provides an attractive route to control magnetism ...with strain. In this effect, the staggered spin structure of an antiferromagnet is decompensated by breaking the crystal field symmetry, which induces a ferrimagnetic polarization. Piezomagnetism is especially appealing because, unlike magnetostriction, it couples strain and magnetization at linear order, and allows for bi-directional control suitable for memory and spintronics applications. However, its use in functional devices has so far been hindered by the slow speed and large uniaxial strains required. Here we show that the essential features of piezomagnetism can be reproduced with optical phonons alone, which can be driven by light to large amplitudes without changing the volume and hence beyond the elastic limits of the material. We exploit nonlinear, three-phonon mixing to induce the desired crystal field distortions in the antiferromagnet CoF2. Through this effect, we generate a ferrimagnetic moment of 0.2 μB per unit cell, nearly three orders of magnitude larger than achieved with mechanical strain.This paper shows how lattice distortions induced by a laser pulse can create a ferrimagnetic moment in an antiferromagnet. This mechanism gives a magnetic response that is orders of magnitude larger than using mechanical strain.
Rationally designed artificial materials enable mechanical properties that are inaccessible with ordinary materials. Pushing on an ordinary linearly elastic bar can cause it to be deformed in many ...ways. However, a twist, the counterpart of optical activity in the static case, is strictly zero. The unavailability of this degree of freedom hinders applications in terms of mode conversion and the realization of advanced mechanical designs using coordinate transformations. Here, we aim at realizing microstructured three-dimensional elastic chiral mechanical metamaterials that overcome this limitation. On overall millimeter-sized samples, we measure twists per axial strain exceeding 2°/%. Scaling up the number of unit cells for fixed sample dimensions, the twist is robust due to metamaterial stiffening, indicating a characteristic length scale and bringing the aforementioned applications into reach.
Molecular dynamics simulations are carried out to investigate the deformation response during shock compression of nanocrystalline Al microstructures at the atomic scales. The shock response is ...investigated for various grain sizes (18 nm–100 nm) and impact velocities (700 m/s to 1500 m/s). The simulations suggest an increase in shock front width and a decay in the velocity and the amplitude of the elastic precursor wave (Hugoniot elastic limit) as the wave travels through the microstructure. For a limited sample depth of 500 nm of polycrystalline Al, the Hugoniot elastic limit (HEL) values are higher for larger grain sizes due to a lower density of grain boundaries and higher for higher piston velocities/shock pressures. Quasi-coarse-grained dynamics (QCGD) simulations are carried out to extend this investigation of the shock response of polycrystalline microstructures to the mesoscales. The capability of QCGD simulations to reproduce the atomic scale evolution of dislocation density fractions and shock wave structures is first demonstrated for a 100 nm grain-sized Al system. The evolution of shock front width, HEL, and dislocation densities are investigated for microstructures with grain sizes ranging from 100 nm to 800 nm and system lengths ranging from 600 nm to 9.6 μm. The MD and QCGD simulations indicate that the decay behavior is attributed to the capability of the shock wave to generate Shockley partial dislocations in the compressed microstructure. The simulations indicate that grain size and impact velocities affect the rates of generation of Shockley partials and hence affect the decay of the HEL. The MD and QCGD predicted values for HEL reported here show excellent agreement with the experimentally observed sample thickness dependence for Al. An empirical model is developed to predict the HEL of Al microstructures with grain size, shock pressure and sample depth as variables.
•MD simulations of shock compression behavior of nanocrystalline Al system demonstrated that the decay of elastic precursor is related to the rate of generation of densities of Shockley partials within the plastic zone of the propagating shock wave.•For all the microstructures considered, a gradual decrease in the rate of generation of Shockley partials and dissociation of Perfect dislocations is observed as the shock wave travels through the metal that results in the decay in the dynamic yield point.•QCGD simulations are able to predict the MD-predicted shock compression behavior and decay of elastic precursor and expand the investigation of role of microstructure and grain size (up to 1 μm and system lengths up to 10 μm).•MD and QCGD simulations suggest that an increase in the grain size results in reduced rates of the generation of Shockley partials and dissociation of Perfect dislocations.•A microstructure-informed empirical evolution law is developed to predict the decay of elastic precursor in Al microstructures with grain size, shock pressure and sample depth as variables.
Due to superior mechanical and optical properties, yttrium–aluminum–garnet (YAG) is emerging as a potential transparent armor material. Its dynamic behavior, however, remains largely unexplored. In ...this work, both impact experiments and mesoscopic simulations have been performed to better understand the dynamic response of YAG polycrystalline and single‐crystal transparent ceramics. Experimental results demonstrate that the two samples have remarkably different dynamic behaviors with the increasing shock pressure, in which the Hugoniot elastic limit basically keeps unchanged (∼14 GPa) in YAG polycrystalline ceramic, whereas it varies from 11 to 31 GPa in YAG single crystals. Moreover, elastic precursor decay is visible only in single‐crystal samples. Mesoscopic simulations with a lattice‐spring model reveal that the difference arises from the distinct fracture mode in the two samples. Less damage and coarser fragmentations in YAG single crystal also suggest a probability of better ballistic resistance as transparent armor materials.
We report the best limit on coherent elastic scattering of electron antineutrinos emitted from a nuclear reactor off germanium nuclei. The measurement was performed with the CONUS detectors ...positioned at 17.1 m from the 3.9 GW_{th} reactor core of the nuclear power plant in Brokdorf, Germany. The antineutrino energies of less than 10 MeV assure interactions in the fully coherent regime. The analyzed dataset includes 248.7 kg d with the reactor turned on and background data of 58.8 kg d with the reactor off. With a quenching parameter of k=0.18 for germanium, we determined an upper limit on the number of neutrino events of 85 in the region of interest at 90% confidence level. This new CONUS dataset disfavors quenching parameters above k=0.27, under the assumption of standard-model-like coherent scattering of the reactor antineutrinos.
We investigate the emergence of a time crystal (TC) in a driven dissipative many-body spin array. In this system the interplay between incoherent spin pumping and collective emission stabilizes a ...synchronized non-equilibrium steady state which in the thermodynamic limit features a self-generated time-periodic pattern imposed by collective elastic interactions. In contrast to prior realizations where the time symmetry is already broken by an external drive, here it is only spontaneously broken by the elastic exchange interactions and manifest in the two-time correlation spectrum. Employing a combination of exact numerical calculations and a second-order cumulant expansion, we investigate the impact of many-body correlations on the TC formation and establish a connection between the regime where it is stable and where the system features a slow growth rate of the mutual information. This observation allows us to conclude that the TC studied here is an emergent semi-classical out-of-equilibrium state of matter. We also confirm the rigidity of the TC to single-particle dephasing. Finally, we discuss an experimental implementation using long lived dipoles in an optical cavity.
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