skip to main content


Title: Fundamental figure of merit for engineering dipole-dipole interactions
Over the last decade there has been a debate regarding the role of the photonic environment in enhancing, inhibiting and imparting coherence to dipole-dipole interactions. We develop a unified figure of merit to conclusively explain multiple recent experiments.  more » « less
Award ID(s):
1654676
NSF-PAR ID:
10165119
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
Conference on Lasers and Electro Optics (CLEO)
Page Range / eLocation ID:
FTu3D.3
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Dipole-dipole interactions ( V dd ) between closely spaced atoms and molecules are related to real photon and virtual photon exchange between them and decrease in the near field connected with the characteristic Coulombic dipole field law. The control and modification of this marked scaling with distance have become a long-standing theme in quantum engineering since dipole-dipole interactions govern Van der Waals forces, collective Lamb shifts, atom blockade effects, and Förster resonance energy transfer. We show that metamaterials can fundamentally modify these interactions despite large physical separation between interacting quantum emitters. We demonstrate a two orders of magnitude increase in the near-field resonant dipole-dipole interactions at intermediate field distances (10 times the near field) and observe the distance scaling law consistent with a super-Coulombic interaction theory curtailed only by absorption and finite size effects of the metamaterial constituents. We develop a first-principles numerical approach of many-body dipole-dipole interactions in metamaterials to confirm our theoretical predictions and experimental observations. In marked distinction to existing approaches of engineering radiative interactions, our work paves the way for controlling long-range dipole-dipole interactions using hyperbolic metamaterials and natural hyperbolic two-dimensional materials. 
    more » « less
  2. Scott J. Miller (Ed.)
    Ground state destabilization is a promising strategy to modulate rotational barriers in amphidynamic crystals. DFT studies of polar phenylenes installed as rotators in pillared-paddle wheel metal-organic frameworks were performed to investigate the effects of ground state destabilization on their rotational dynamics. We found that as the steric size of phenylene substituents increases the ground state destabilization effect is also increased. Specifically, a significant destabilization of the ground state energy occurred as the size of the substituents increased, with values ranging from 2 kcal/mol to 11.7 kcal/mol. An evalua-tion of the effects of substituents on dipole-dipole interaction energies and rotational barriers suggest that it should be possi-ble to engineer amphidynamic crystals where the dipole-dipole interaction energy becomes comparable to the rotational barri-ers. Notably, dipole-dipole interaction energies reached values ranging from 0.6 kcal/mol to 2.4 kcal/mol. We propose that careful selection of polar substituents with different size may help create temperature-responsive materials with switchable collective polarization. 
    more » « less
  3. We experimentally demonstrate that the dipole-dipole interaction in a potassium vapor at cold atom density can be observed using optical 2D coherent spectroscopy. This paves the way to implement 2D spectroscopy in cold atoms. 
    more » « less
  4. In previous work with thermally robust salts [Cassity et al., Phys. Chem. Chem. Phys. , 2017, 19 , 31560] it was noted that an increase in the dipole moment of the cation generally led to a decrease in the melting point. Molecular dynamics simulations of the liquid state revealed that an increased dipole moment reduces cation–cation repulsions through dipole–dipole alignment. This was believed to reduce the liquid phase enthalpy, which would tend to lower the melting point of the IL. In this work we further test this principle by replacing hydrogen atoms with fluorine atoms at selected positions within the cation. This allows us to alter the electrostatics of the cation without substantially affecting the sterics. Furthermore, the strength of the dipole moment can be controlled by choosing different positions within the cation for replacement. We studied variants of four different parent cations paired with bistriflimide and determined their melting points, and enthalpies and entropies of fusion through DSC experiments. The decreases in the melting point were determined to be enthalpically driven. We found that the dipole moment of the cation, as determined by quantum chemical calculations, is inversely correlated with the melting point of the given compound. Molecular dynamics simulations of the crystalline and solid states of two isomers showed differences in their enthalpies of fusion that closely matched those seen experimentally. Moreover, this reduction in the enthalpy of fusion was determined to be caused by an increase in the enthalpy of the crystalline state. We provide evidence that dipole–dipole interactions between cations leads to the formation of cationic domains in the crystalline state. These cationic associations partially block favourable cation–anion interactions, which are recovered upon melting. If, however, the dipole–dipole interactions between cations is too strong they have a tendency to form glasses. This study provides a design rule for lowering the melting point of structurally similar ILs by altering their dipole moment. 
    more » « less
  5. Abstract

    Magnetic nanoparticle chains offer the anisotropic magnetic properties that are often desirable for micro‐ and nanoscale systems; however, to date, large‐scale fabrication of these nanochains is limited by the need for an external magnetic field during the synthesis. In this work, the unique self‐assembly of nanoparticles into chains as a result of their intrinsic dipolar interactions only is examined. In particular, it is shown that in a high concentration reaction regime, the dipole–dipole coupling between two neighboring magnetic iron cobalt (FeCo) nanocubes, was significantly strengthened due to small separation between particles and their high magnetic moments. This dipole–dipole interaction enables the independent alignment and synthesis of magnetic FeCo nanochains without the assistance of any templates, surfactants, or even external magnetic field. Furthermore, the precursor concentration ([M] = 0.016, 0.021, 0.032, 0.048, 0.064, and 0.096m) that dictates the degree of dipole interaction is examined—a property dependent on particle size and inter‐particle distance. By varying the spinner speed, it is demonstrated that the balance between magnetic dipole coupling and fluid dynamics can be used to understand the self‐assembly process and control the final structural topology from that of dimers to linear chains (with aspect ratio >10:1) and even to branched networks. Simulations unveil the magnetic and fluid force landscapes that determine the individual nanoparticle interactions and provide a general insight into predicting the resulting nanochain morphology. This work uncovers the enormous potential of an intrinsic magnetic dipole‐induced assembly, which is expected to open new doors for efficient fabrication of 1D magnetic materials, and the potential for more complex assemblies with further studies.

     
    more » « less