Eric Sembrat's Test Bonanza

Superfluidity is a fascinating emergent phenomenon not only because matters are transported without energy dissipation but fundamentally it is a macroscopic manifestation of the quantum state of microscopic particles. Superfluidity was discovered in quantum liquids like liquid helium and most recently in ultra cold atomic gas Bose condensate. However the experimental evidence of the existence of superfluid state in the crystalline solid (“supersolid”) has been elusive in spite of a theoretical prediction more than 40 years ago [1]. The discovery of Non Classical Rotational Inertial (NCRI) in the solid ⁴He with torsional oscillator (TO) technique [2] ignited renewed interest in solid helium. Further studies indicate multiple possible origins of NCRI. In this presentation, I will give a concise introduction about the progress in the search for “supersolid”. I will also discuss our NMR experiments on dilute solid solution of ³He in ⁴He. We observed isotopic phase separation in all the samples we studied. We detected a significant change in the spin lattice relaxation time (T₁) in the regime where NCRI was reported, which suggests an abnormal dynamics of ³He atoms near the Larmor frequency. A phenomenological model of thermally activated relaxation is proposed to describe this anomaly.

[1] A. F. Andreev and I. M. Lifshits, JEPT 29, 1107 (1969)

[2] E. Kim and M. H. W. Chan, Nature 427, 225 (2004); Science 305, 1941 (2004)

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When sufficiently charged, the interface between a conducting liquid and an insulator (vacuum, gas, liquid) becomes unstable and forms sharp conical tips (Taylor cones) which inject liquid into the insulator. This injection most often takes the form of a micro-jet issuing from the tip of the Taylor cone. The physics of this cone-jet is approximately understood. In particular, the larger the electrical conductivity K of the liquid and the smaller its flow rate Q pushed through the cone-jet, the smaller the jet radius R. However, the process of jet shrinking with increasing K does not go forever. When K reaches values in the range of 1 S/m, R may become as small as 5 nm. This leads to electric fields strong enough for ions dissolved in the liquid conductor to be field-evaporated through the interface, resulting in a mixed regime with simultaneous ejection of ions and drops. An extreme behavior when only ions and no drops are formed has been known for decades in the case of positively charged liquid metals exposed to vacuum. The subject of our enquiry is whether a transition takes place between the convex drop-emitting cone-jet and the presumably concave tip emitting ions alone. We have studied this presumed transition under a variety of circumstances It is better probed with electrolytes than with liquid metals, as the latter have conductivities many orders of magnitude higher than the transitional range K~1 S/m. It is not readily studied when either a liquid metal or an electrolyte is surrounded by a gas because the evaporated ions produce electrical breakdown turning the insulating gas into a conductor. One line of research therefore involves the study (by time of flight mass spectrometry) of highly conducting electrolytes (including molten salts or ionic liquids) in a vacuum. In another approach we substitute the gas by a dielectric liquid, and explore whether or not ions or nanodrops are injected into an insulating liquid.  Although the dielectric liquid alters drastically the situation through space charge effects limiting the current, we observe the production of nanodrops in the 5-10 nm size range, as well as ion injection. The purely ionic regime has been encountered with ionic liquids in vacuum, but not yet in insulating liquids.

We present a Hamiltonian derivation of a class of reduced models in plasma physics obtained by imposing dynamical constraints on a parent Hamiltonian model. We will consider MHD equations and Maxwell-Vlasov equations as parent models. It is shown that the Poisson bracket associated with these reduced models is the Dirac bracket obtained from the Poisson bracket of the parent model.

Topological states of matter have quantum entangled ground states characterized by topological quantum numbers rather than symmetry
breaking. Inspired by the discovery of topological insulators, I describe recent progress in finding a variety of new classes of topological materials
in semiconductors and superconductors. Potential applications in electronics and quantum computation will be briefly discussed.

The development of the technology for trapping atoms in the vacuum and cooling them to ultralow temperatures has opened up the exciting new field of cold atom physics.  This field provides a new domain of applications for local quantum field theory, an approach whose previous applications have been primarily in high energy particle physics and have involved energy scales that are more than 20 orders of magnitude higher.  I will describe a systematic approximation method for quantum field theory called Effective Field Theory that has proved to be a powerful framework for addressing many important problems in ultracold atoms.

X-ray science is undergoing one of its greatest revolutions to date with the construction of intense x-ray free electron lasers in Stanford, USA (LCLS), Hamburg, Germany (XFEL), and Harima Science Garden City, Japan (SCSS). These are vast, several-hundred-million dollar machines that will provide x-ray pulses that are many million times brighter than current sources. Similarly groundbreaking are the emerging attosecond light sources based on intense, pulsed lasers; they are relatively inexpensive laboratory-size instruments. These two emerging radiation sources will enable radically new research and have unnumbered potential applications in materials science, chemistry, biology, AMO, condensed-matter, and plasma physics. My work contributes to a theoretical understanding of atoms and molecules in gas phase which are exposed to x rays and optical lasers. Specifically, I discuss in my talk: * Electromagnetically induced transparency (EIT) for x rays and ultrafast x-ray pulse shaping * Attosecond Ramsey scheme for Auger decay * Double core holes in laser-aligned molecules

Superconducting circuitry can now be fabricated at the nanoscale by depositing suitable materials on to single molecules, such as DNA or carbon nanotubes. I shall discuss various themes that arise when superconductivity is explored in this new regime, including the thermal passage over and quantum tunneling through barriers by the superconducting condensate, as well as the hormetic impact that magnetism can have on nanosuperconductivity. I shall also describe circuits that realize nanoscale superconducting quantum interference devices, exploring their sensitivity to magnetic fields and spatial patterns of supercurrent. These features hint at possible uses of nanoscale superconducting circuitry, such as in mapping out the quantum phase of superconducting order and testing for superconducting correlations in novel materials and settings. If time permits, I shall also mention some emerging themes: the interplay between graphene and superconductivity, and what nanoprobes might be revealing about exotic superconductors.

The massive black holes found at the centers of most nearby galaxies, including our
own, are believed to be the ashes of the fuel that powered quasars early in the history of the universe. I will review the observational evidence for these objects and describe some of the exotic dynamical phenomena that originate in their vicinity, including hypervelocity stars, resonant relaxation, phase transitions, and lopsided stellar disks.

Neutron stars were discovered accidentally in 1967 although their existence was predicted 65 years earlier.  These exotic objects are the remnants from the deaths of massive stars, a death marked by one of the most spectacular pyrotechnic events in the cosmos, a supernovae explosion. Neutron stars have a solid crust overlying a sea of neutrons that can flow without friction (superfluidity). Their unique, yet not fully understood, internal structure, together with their immense gravitational field, makes them the perfect laboratory where the physics of the macro-cosmos meets microphysics phenomena. Explosive thermonuclear processes on neutron stars and their colossal magnetic field makes them observable across the electromagnetic spectrum, in radio, x, gamma rays and even in optical wavelengths. As members of binary systems, they are the best candidates for detection of gravitational waves. I will review our current understanding of neutron stars and the challenges in their theoretical and computational modeling.

The normal modes and the density of states (DOS) of any material provide a basis for understanding its thermal and mechanical transport properties. In perfect crystals, normal modes take the form of planewaves, but they can be complex in disordered systems. I will show our recent experimental measurement of the normal modes, the DOS and dynamical structure factor (DSF) in disordered colloidal solids: disordered colloidal crystals composed of thermally sensitive micron‐sized hydrogel particles at several different particle volume fractions, φ. Particle positions are tracked over long times using optical microscopy and particle tracking algorithms in a single two dimensional (2D) [111] plane of a 3D face‐centered‐cubic single crystal. The dynamical fluctuations are spatially heterogeneous while the lattice itself is highly ordered. At all φ, the DOS exhibits an excess of low frequency modes, a so‐called boson peak (BP), and the DSF exhibits a cross‐over from propagating to n‐propagating behavior, a socalled Ioffe‐Regel (IR) crossover, at a frequency somewhat below the BP for both longitudinal and transverse modes. As we tune φ from 0.64 to 0.56, the Lindemann parameter grows from ~3% to ~8%, however, the shape of the DOS and DSF remain largely unchanged when rescaled by the Debye level. This invariance indicates that the effective degree of disorder remains essentially constant even in the vicinity of melting.