Cavity engineering of solid-state materials without external driving

Chemical heuristics have been fundamental to the advancement of chemistry and materials science. These heuristics are typically established by scientists using knowledge and creativity to extract patterns from limited datasets. Machine learning offers opportunities to perfect this approach using computers and larger datasets. Here, we discuss the relationships between traditional heuristics and machine learning approaches. We show how traditional rules can be challenged by large-scale statistical assessment and how traditional concepts commonly used as features are feeding the machine learning techniques. We stress the waste involved in relearning chemical rules and the challenges in terms of data size requirements for purely data-driven approaches. Our view is that heuristic and machine learning approaches are at their best when they work together.

Large reversible changes of the electronic transport properties of solid-state oxide materials induced by electrochemical fields have received much attention as a new research avenue in iontronics. In this research update, dramatic transport changes in vanadium dioxide (VO2) nanowires were demonstrated by electric field-induced hydrogenation at room temperature through the nanogaps separated by humid air in a field-effect transistor structure with planar-type gates. This unique structure allowed us to investigate hydrogen intercalation and diffusion behavior in VO2 channels with respect to both time and space. Our results will contribute to further strategic researches to examine fundamental chemical and physical properties of devices and develop iontronic applications, as well as offering new directions to explore emerging functions for sensing, energy, and neuromorphologic devices combining ionic and electronic behaviors in solid-state materials.

In situ measurement technologies on solid-state hydrogen storage materials: a review

Control over the optical properties of defects in solid-state materials is necessary for their application in quantum technologies. In this study, we demonstrate, from first principles, how to tune these properties via the formation of defect polaritons in an optical cavity. We show that the polaritonic splitting that shifts the absorption energy of the lower polariton is much higher than can be expected from a Jaynes-Cummings interaction. We also find that the absorption intensity of the lower polariton increases by several orders of magnitude, suggesting a possible route toward overcoming phonon-limited single-photon emission from defect centers. These findings are a result of an effective continuum of electronic transitions near the lowest-lying electronic transition that dramatically enhances the strength of the light-matter interaction. We expect our findings to spur experimental investigations of strong light-matter coupling between defect centers and cavity photons for applications in quantum technologies.

Investigating material properties is essential to assessing their application potential. While computational methods allow for a fast prediction of the material structure and properties, experimental validation is essential to determining the ultimate material potential. Herein, we report the synthesis and experimental magnetic properties of three previously reported Kagome compounds in the Li-Fe-Ge system. LiFe6Ge4, LiFe6Ge5, and LiFe6Ge6 were predicted to have ferromagnetic or antiferromagnetic ground states. The hydride route that replaces the ductile Li metal with salt-like LiH proved to be an excellent alternative for the facile synthesis of the Li-Fe-Ge powders with appreciable purity, permitting the investigation of their bulk magnetic properties. Magnetometry below room temperature and room-temperature 57Fe Mössbauer spectroscopy collectively indicate an antiferromagnetic ground state for the three compounds with ordering temperatures above 300 K, contrary to the prediction of ferromagnetic ground states. Moreover, Mössbauer spectroscopy reveals a magnetization of 1.1-1.3 μB/Fe atom for the Li-Fe-Ge compounds, while higher moments of 1.63-2.90 μB/Fe atom were theoretically predicted. Experimental (in)validation addresses the issue of inaccuracy in determining material properties in silico only and helps to improve the prediction power of the computational models. This work underlines that the contribution of experimentalists continues to be valuable for the accurate determination of structure-property relationships in solid-state materials.

Thermodynamical fluctuations in temperature and position exist in every physical system, and show up as a fundamental noise limit whenever we choose to measure some quantity in a laboratory environment. Thermodynamical fluctuations in the position of the atoms in the dielectric coatings on the mirrors for optical cavities at the forefront of precision metrology (e.g., LIGO, the cavities which probe atomic transitions to define the second) are a current limiting noise source for these experiments, and anything which involves locking a laser to an optical cavity. These thermodynamic noise sources scale physical geometry of experiment, material properties (such as mechanical loss in our dielectric coatings), and temperature. The temperature scaling provides a natural motivation to move to lower temperatures, with a potential huge benefit for redesigning a room temperature experiment which is limited by thermal noise for cryogenic operation. We design, build, and characterize a pair of linear Fabry-Perot cavities to explore limitations to ultra low noise laser stabilization experiments at cryogenic temperatures. We use silicon as the primary material for the cavity and mirrors, due to a zero crossing in its linear coefficient of thermal expansion (CTE) at 123 K, and other desirable material properties. We use silica tantala coatings, which are currently the best for making high finesse low noise cavities at room temperature. The material properties of these coating materials (which set the thermal noise levels) are relatively unknown at cryogenic temperatures, which motivates us to study them at these temperatures. We were not able to measure any thermal noise source with our experiment due to excess noise. In this work we analyze the design and performance of the cavities, and recommend a design shift from mid length cavities to short cavities in order to facilitate a direct measurement of cryogenic coating noise. In addition, we measure the cavities (frequency dependent) photo-thermal response. This can help characterize thermooptic noise in the coatings, which is poorly understood at cryogenic temperatures. We also explore the feasibility of using the cavity to do macroscopic quantum optomechanics such as ground state cooling.

Toward an Atomistic Understanding of Solid-State Electrochemical Interfaces for Energy Storage

Simultaneous control of the magnetic and electric properties of materials is crucial for their application in next-generation memory and sensor devices. Herein, we report a single-crystal Co(II) co...

This proposal emphasizes investigations of the thermal and electrical transport properties of new and novel solid-state materials, with the specific goal of achieving higher efficiency solid-state thermoelectric materials. This program will continue to build a very strong collaborative research effort between researchers at Oak Ridge National Laboratory (ONRL) and Clemson University. We propose three new faculty hires and major equipment purchases in order to further enhance our level of national recognition. We will be positioned for competition for major non-EPSCoR DOE and DOD funding (i.e. NSF-Materials Research Center) and able to address many other areas of DOE and national importance. Graduate and undergraduate students will be extensively involved in this project, spending significant time at ORNL, thus gaining important training and educational opportunities. We will also include an outreach program to bring in outside students and faculty. An External Advisory Board of distinguished scientists will provide oversight to the program.

A broad repertoire of potential solid-state electrolytes (SSEs) is a prerequisite for the development and optimization of high-energy-density all-solid-state batteries (ASSBs). In this context, the key challenge in solid state chemistry and material science is to get access to new materials with improved properties which allow for detailed investigation of structure-property relationships.[1]Recently, a new class of promising lithium ion conductors has been studied intensively. The so-called lithium phosphidotetrelates consisting of lithium phosphidosilicates, phosphidogermanates, and phosphidostannates as well as the closely related lithium phosphidoaluminates are suitable candidates for the systematic investigation of structure-property-relationships of next generation lithium ion conductors.[1-5] As the name implies, the materials are structurally related to (oxo-)silicates, thiosilicates and thiophosphates. In contrast to the latter, which are well-known for some of the most prominent sulfide-based lithium super ionic conductors, lithium phosphidotetrelates are basically built up by tetrahedrally coordinated [SiP4]8−, [GeP4]8−, and [SnP4]8− units. The substitution of sulfur by phosphorus allows for much higher charge carrier concentration within the structure and thus higher ionic conductivities (Figure 1: a) Structure of Li14SiP6. b) Arrhenius and Nyquist plot (inset) of Li14SiP6.).[4] Hence, lithium phosphidotetrelates and phosphidoaluminates offer a large structural variety combined with low activation energies and fast lithium ion conductivity up to 3 mS cm−1 at room temperature.[5]Here, the preparation and characterization of new lithium-rich phosphidotetrelates is reported. Characterization of the materials applying X-ray diffraction (powder and single crystal) and solid-state MAS NMR measurements as well as elastic coherent neutron scattering experiments enabled the thorough investigation of the structural and thermal behavior of the compounds. Activation energies, ionic and electronic conductivities have been determined using solid-state 7Li NMR measurements and electrochemical impedance spectroscopy. Furthermore, diffusion pathways were analyzed by temperature-dependent powder neutron diffraction measurements in combination with MEM and DFT calculations to extend the knowledge about the material properties. Finally, the structural differences and the consequential material properties are analyzed with respect to the resulting structure-property-relationship which is crucial for further development of high-performance lithium ion conductors.

The Journal of Physics: Condensed Matter special issue is dedicated to the memory of David C Langreth and his contribution to research in the field of Van der Waals (vdW) interactions in advanced materials. David C Langreth was an outstanding condensed matter theorist and a scholar who significantly influenced researchers through his particle-physics based insights into density functional theory (DFT), surface science, and related areas. His seminal works ranged from conserving formulations of interacting nonequilibrium transport and formal-scattering theory to an explicit formulation the exact DFT exchange-correlation energy in the adiabatic connection formula (ACF). David C Langreth's another significant contribution was in the area of vdW interactions in materials, as he played a key role in developing and formulating the vdW density functional (vdW-DF) method.

The group velocity at which light pulses propagate through a dispersive material system is very different from the vacuum speed of light c, One refers to light as being “slow” for vg c or vg <0 (Stenner et al, 2003 ). For vg <0, the pulse envelope appears to travel backward in the material (Gehring et al, 2006), and hence it is sometimes referred to as “backward light.” The subject of slow light has caused keen interest in the past decade or more, and it is possible to control the group velocity of light pulses in the dispersive materials. Interest in slow and fast light dates back to the early days of the 20th century. Sommerfeld and Brillouin (Sommerfeld & Brillouin, 1960) were intrigued by the fact that theory predicts that vg can exceed c, which leads to apparent inconsistencies with Einstein’s special theory of relativity. Experimental investigations of extreme propagation velocities were performed soon after the invention of the laser (Faxvog and et al, 1970). In 1999, Harris’s group research work greatly stimulated researchers’ interests, which showed that light could be slowed down to 17m/s. The result was obtained in ultra cold atom clouds with the use of electromagnetically induced transparency (EIT), which induces transparency in a material while allowing it to retain strong linear and nonlinear optical properties (Hau et al, 1999). Slow light can also be obtained through the use of the optical response of hot atomic vapors (Philips et al, 2001). These early research works require hard conditions and the slow light cannot operate in room temperature. Recently, researchers found ways to realize slow light operating in room temperature and solid-state materials, which are more suited for many practical applications, namely slow light via stimulated Brillouin scattering(SBS), slow light via coherent population oscillations (CPO), tunable time delays based on group velocity dispersion or conversion/ dispersion(C/D), slow light in fiber Bragg gratings and so on. In this chapter, we describe some of the physical mechanisms that can be used to induce slow and fast light effects in room-temperature solids (Bigelow et al, 2003) and some of the exotic propagation effects that can thereby be observed. We also survey some applications of slow and fast light within the fields of quantum electronics and photonics.

The strength of the light–matter interaction depends on the number of dipoles that can couple with the photon trapped in an optical cavity. The coupling strength can thus be maximized by filling the entire cavity volume with an ensemble of interacting dipoles. In this work this is achieved by inserting a highly doped semiconductor layer in a subwavelength plasmonic resonator. In our system the ultra-strong light–matter coupling occurs between a collective electronic excitation and the cavity photon. The measured coupling strength is 73% of the matter excitation energy, the highest ever reported for a light–matter coupled system at room temperature. We experimentally and theoretically demonstrate that such an ultra-strong interaction modifies the optical properties on a very wide spectral range (20–250 meV), and results in the appearance of a photonic gap of 38 meV, independently of the light polarization and angle of incidence. Light–matter ultra-strong coupling can thus be exploited to conceive metasurfaces with an engineered reflectivity band.

Functional Scaffolds from AIE Building Blocks

Multidisciplinary Science at the Molecular Foundry