### Abstract

The description of disorder-induced electron localization by Anderson over 60 years ago began a quest for novel phenomena emerging from electronic interactions in the presence of disorder. Even today, the interplay of interactions and disorder remains incompletely understood. This holds in particular for strongly disordered materials where charge transport depends on ‘hopping’ between localized sites. Here we report an unexpected spin sensitivity of the electrical conductivity at the transition from diffusive to hopping conduction in a material that combines strong spin-orbit coupling and weak inter-electronic interactions. In thin films of the disordered crystalline phase change material $$\mathrm{SnSb_2 Te_4}$$, a distinct change in electrical conductance with applied magnetic field is observed at low temperatures. This magnetoconductance changes sign and becomes anisotropic at the disorder-driven crossover from strongly localized (hopping) to weakly localized (diffusive) electron motion. The positive and isotropic magnetoconductance arises from disruption of spin correlations that inhibit hopping transport. This experimental observation of a recently hypothesized “spin memory” demonstrates the spin plays a previously overlooked role in the disorder-driven transition between weak and strong localization in materials with strong spin–orbit interactions.

### Abstract

We study the potential of the LHCb experiment to discover, for the first time, the true muonium bound state. We propose a search for the vector state, which kinetically mixes with the photon and dominantly decays to electron-positron pairs. We demonstrate that a search for true muonium produced in eta meson decays and decaying at a displaced vertex can exceed a significance of 5 standard deviations assuming statistical uncertainties. We present two possible searches: an inclusive search for the electron-positron vertex, and an exclusive search which requires an additional photon and a reconstruction of the eta mass.

### Abstract

Charge order is now accepted as an integral constituent of cuprate high-temperature superconductors, one that is intimately related to other electronic instabilities including anti-ferromagnetism and superconductivity. Unlike conventional Peierls density waves, the charge correlations in cuprates have been predicted to display a rich momentum space topology depending on the underlying fermiology. However, charge order has only been observed along the high-symmetry Cu–O bond directions. Here, using resonant soft X-ray scattering, we investigate the evolution of the full momentum space topology of charge correlations in $$T'-\mathrm{(Nd,Pr)_2 CuO_4}$$ as a function of electron doping. We report that, when the parent Mott insulator is doped, charge correlations first emerge with full rotational symmetry in momentum space, indicating glassy charge density modulation in real space possibly seeded by local defects. At higher doping levels, the orientation of charge correlations is locked to the Cu–O bond directions, restoring a more conventional long-ranged bidirectional charge order. Through charge susceptibility calculations, we reproduce the evolution in topology of charge correlations across the antiferromagnetic phase boundary and propose a revised phase diagram of $$T'-\mathrm{Ln_2 CuO_4}$$ with a superconducting region extending toward the Mott limit.

### Abstract

The discovery of quantum oscillations in hole- and electron-doped cuprate families has underscored the importance of the Fermi surface in cuprate superconductivity. While the observed quantum oscillations in both families have revealed the presence of reconstructed Fermi surfaces, there remains an important distinction between the two. In hole-doped cuprates the oscillations are thought to arise from the effects of a charge density wave, while in the electron-doped cuprates it is thought that these oscillations occur from an antiferromagnetically reconstructed Fermi surface, despite the fact that the oscillations are observed in overdoped compounds, far from the putative antiferromagnetic critical point. In this work we study thin films of $$\mathrm{Pr_Cu O_{4 \pm \delta}}$$, whose apparent doping can be finely tuned by annealing, allowing studies of quantum oscillations in samples straddling the critical point. We show that even though there is a mass enhancement of the quasiparticles, there are only small changes to the Fermi surface itself, suggesting that charge order is a more likely origin, with electronic correlations that are strongly dependent on the structural parameters.

### Abstract

We study the field of an electric point charge that is slowly lowered into an $$n + 1$$ dimensional Schwarzschild-Tangherlini black hole. We find that if $$n > 3$$, then countably infinite nonzero multipole moments manifest to observers outside the event horizon as the charge falls in. This suggests the final state of the black hole is not characterized by a Reissner-Nordström-Tangherlini geometry. Instead, for odd $$n$$, the final state either possesses a degenerate horizon, undergoes a discontinuous topological transformation during the infall of the charge, or both. For even $$n$$, the final state is not guaranteed to be asymptotically flat.

### Abstract

We investigate Palatini $$f( \mathcal{R}, \mathcal{L}_m, \mathcal{R}_{\mu\nu}T^{\mu\nu})$$ modified theories of gravity. As such, the metric and affine connection are treated as independent dynamical fields, and the gravitational Lagrangian is made a function of the Ricci scalar $$\mathcal{R}$$, the matter Lagrangian density $$\mathcal{L}_{m}$$, and a “matter-curvature scalar” $$\mathcal{R}_{\mu\nu}T^{\mu\nu}$$. The field equations and the equations of motion for massive test particles are derived, and we find that the independent connection can be expressed as the Levi-Civita connection of an auxiliary, energy momentum–dependent metric that is related to the physical metric by a matrix transformation. Similar to metric $$f(\mathcal{R}, T, \mathcal{R}_{\mu\nu}T^{\mu\nu})$$ gravity, the field equations impose the nonconservation of the energy- momentum tensor, leading to the appearance of an extra force on massive test particles. We obtain the explicit form of the field equations for massive test particles in the case of a perfect fluid and an expression for the extra force. The nontrivial modifications to scalar fields and both linear and nonlinear electrodynamics are also considered. Finally, we detail the conditions under which the present theory is equivalent to the Eddington-inspired Born-Infeld theory of gravity.

### Abstract

Photons from distant astronomical sources can be used as a classical source of randomness to improve fundamental tests of quantum nonlocality, wave-particle duality, and local realism through Bell’s inequality and delayed-choice quantum eraser tests inspired by Wheeler’s cosmic-scale Mach-Zehnder interferometer gedanken experiment. Such sources of random numbers may also be useful for information-theoretic applications such as key distribution for quantum cryptography. Building on the design of an astronomical random number generator developed for the recent cosmic Bell experiment [Handsteiner et al. Phys. Rev. Lett. 118, 060401 (2017)], in this paper we report on the design and characterization of a device that, with 20-nanosecond latency, outputs a bit based on whether the wavelength of an incoming photon is greater than or less than ≈700 nm. Using the one-meter telescope at the Jet Propulsion Laboratory Table Mountain Observatory, we generated random bits from astronomical photons in both color channels from 50 stars of varying color and magnitude, and from 12 quasars with redshifts up to $$z = 3.9$$. With stars, we achieved bit rates of $$\sim1 \times 10^6\,\mathrm{Hz/m^2}$$, limited by saturation of our single-photon detectors, and with quasars of magnitudes between 12.9 and 16, we achieved rates between $$\sim 10^2$$ and $$2 \times 10^3 \,\mathrm{Hz/m^2}$$. For bright quasars, the resulting bitstreams exhibit sufficiently low amounts of statistical predictability as quantified by the mutual information. In addition, a sufficiently high fraction of bits generated are of true astronomical origin in order to address both the locality and freedom-of-choice loopholes when used to set the measurement settings in a test of the Bell-CHSH inequality.

### Abstract

We demonstrate that rare decays of the Standard Model $$Z$$ boson can be used to discover and characterize the nature of new hidden-sector particles. We propose new searches for these particles in soft, high-multiplicity leptonic final states at the Large Hadron Collider. The proposed searches are sensitive to low-mass particles produced in $$Z$$ decays, and we argue that these striking signatures can shed light on the hidden-sector couplings and mechanism for mass generation.

### Abstract

The size dependence of the dielectric constants of barium titanate or other ferroelectric particles can be explored by embedding particles into an epoxy matrix whose dielectric constant can be measured directly. However, to extract the particle dielectric constant requires a model of the composite medium. We compare a finite-element model for various volume fractions and particle arrangements to several effective-medium approximations, which do not consider particle arrangement explicitly. For a fixed number of particles, the composite dielectric constant increases with the degree of agglomeration, and we relate this increase to the number of regions of enhanced electric field along the applied field between particles in an agglomerate. Additionally, even for dispersed particles, we find that the composite method of assessing the particle dielectric constant may not be effective if the particle dielectric constant is too high compared to the background medium dielectric constant.

### Abstract

The physical properties of glassy polymer films change as they become confined. These changes are often attributed to increased average molecular mobility and reduction in entanglement density. Both are known to alter mechanical behavior, including the formation of strain localizations, e.g., crazing and shear deformation zones. Here, we determine how the entanglement density and surface mobility change the mechanical behavior of a glassy polymer film when it becomes confined. We utilize a custom-built uniaxial tensile tester for ultrathin films and dark-field optical microscopy to characterize the complete stress strain response and the associated strain localizations for ultrathin polystyrene films of varying thickness (h(F) = 20-360 nm). These experiments provide direct measurement of the stress in a craze as well as the stresses involved through the transition from crazing to shear deformation zones. Most significantly, we observe a transition in strain localization from crazing to shear deformation zones as film thickness changes from 30 to 20 nm, providing new insights into how the surfaces alter the mechanical behavior in confined polymer films.

# Recent Publications

Student authorFaculty author

1. Johannes Reindl, Hanno Volker, Nicholas P. Breznay, and Matthias Wuttig Persistence of Spin Memory in a Crystalline, Insulating Phase-Change Material Npj Quantum Materials 4 (2019) 1–7. Xabier Cid Vidal, Philip Ilten, Jonathan Plews, Brian Shuve, and Yotam Soreq Discovering True Muonium At LHCb Physical Review D 100 (2019) 053003. Mingu Kang, Jonathan Pelliciari, Alex Frano, Nicholas P. Breznay, Enrico Schierle, Eugen Weschke, Ronny Sutarto, Yuwei He, Padraic Shafer, Elke Arenholz, Mo Chen, Keto Zhang, Alejandro Ruiz, Zeyu Hao, Sylvia Lewin, James Analytis, Yoshiharu Krockenberger, Hideki Yamamoto, Kausik Das, and Riccardo Comin Evolution of Charge Order Topology Across a Magnetic Phase Transition in Cuprate Superconductors Nature Physics 15 (2019) 335–340. Nicholas P. Breznay, Corey Hayes, Nityan L Nair, Toni Helm, James G Analytis, Ross D McDonald, Zengwei Zhu, Yoshiharu Krockenberger, Hiroshi Irie, Hideki Yamamoto, K A Modic, Alex Frano, Padraic Shafer, and Elke Arenholz Interplay of Structure and Charge Order Revealed by Quantum Oscillations in Thin Films of $$\mathrm{Pr_2 Cu O_{4 \pm\delta}}$$ Physical Review B 100 (2019) 235111. Matthew Stephen Fox Multipole Hair of Schwarzschild-Tangherlini Black Holes Journal of Mathematical Physics 60 (2019) 102502. Matthew Stephen Fox Palatini $$f(\mathcal{R}, \mathcal{L}_m, \mathcal{R}_{\mu\nu} T^{\mu\nu})$$ gravity and its Born-Infeld semblance Physical Review D 99 (2019) 124027. Calvin Leung, Amy Frances Brown, Hien Nguyen, Andrew S. Friedman, David I. Kaiser, and Jason Gallicchio Astronomical Random Numbers for Quantum Foundations Experiments Physical Review A 97 (2018) 042120. Nikita Blinov, Eder Izaguirre, and Brian Shuve Rare Z Boson Decays to a Hidden Sector Physical Review D 97 (2018) 015009. Jonas Leif Kaufman, Scott H. Tan, Kirklann Lau, Ashka Shailesh Shah, Robert G. Gambee, Christopher P. Gage, Lupe Maria MacIntosh, Albert Dato, Peter N. Saeta, Richard C. Haskell, and Todd C. Monson Permittivity effects of particle agglomeration in ferroelectric ceramic-epoxy composites using finite element modeling AIP Advances 8 (2018) 125020. R. Konane Bay, Shinichiro Shimomura, Yujie Liu, Mark Ilton, and Alfred J. Crosby Confinement Effect on Strain Localizations in Glassy Polymer Films Macromolecules 51 (2018) 3647-3653.