Colloquium, Seminar and General Audience Talks: Robert B. Hallock

Available Colloquium and Other Talks:


Introduction:

Below are listed some colloquium and seminar talks which are generally available for delivery. Following the listing of the talks, some biographical information is given. The organization is as follows:


Title: Wetting Phenomena - A New Story for Helium

Abstract:

Until relatively recently it was believed that helium was "the universal wetting agent". This was based on the fact that the helium-helium interaction is very weak and helium was observed to wet any surface with which it was brought into contact. In 1991 the startling prediction was made that this might not be the case for 4He in the presence of alkali metal substrates. Following an introduction of the ideas of wetting phenomena, we will review the early discovery experimeents and some of the recent experimental evidence for the novel wetting behavior of 4He on cesium and other alkali metal substrates, the presence of pre-wetting and the ability of 3He to act as a "detergent" for 4He.

Suitable for a Colloquim or a Seminar.


Title: The World of 3He in Two or Nearly Two Dimensions

abstract:

When placed atop a thin film of superfluid 4He, atoms of 3He reside in a nearly two dimensional world. Following a brief review of the properties of the thin helium film system, experiments will be described which probe the properties of the 3He atoms as a function of the 3He coverage, 4He coverage and the temperature. A remarkable world of two dimensional behavior of the 3He is revealed including well-defined quantum states, a staircase of magnetization and interesting structure of the lateral mobility as a function of the underlying 4He film thickness. Some of the observations can be readily understood by appeal to picturesque models and physical intuition; others present a challenge to emerging theory.

Suitable for a Colloquim or a Seminar.


Title: Capillary Condensation: Superfluidity Tests Nature's Memory, and Finds Glitches.

abstract:

Hysteresis is a widespread phenomena, encountered in a broad range of physical systems including magnetic materials, microfracturing of rock, fluid invasion of porous beds and adsorption of gases. In an effort to further understand hysteretic behavior and capillary condensation, experiments which involve the capillary condensation of superfluid 4He in the porous materials Nuclepore and Anopore are currently underway and some of these will be described. The experiments reveal a hierarchy of memory effects, and near-congruence of closed loops. Interactions among the pores of the material lead to dramatic avalanche events as the behavior of one pore influences neighboring pores. The avalanches are shown to be non-local events, and the question of the origin of pore-to-pore communication is explored. Connection to a theoretical model originally devised to understand magnetic phenomena and the relevance of the experiments to more recent theoretical developments will be made.

Suitable for a Colloquim or a Seminar.


Title: The Magic of Superfluid Helium

Abstract:

Helium, the inert element which provides the "lift" for the Goodyear blimp, and the balloon you buy at the circus, remains a gas at any temperature above -451.8 degrees Fahrenheit. At this unimaginably cold temperature, Helium condenses into a liquid and remains a liquid as the temperature is lowered toward the absolute zero of temperature, -459.4 degrees Fahrenheit. A remarkable transition to a spectacular new liquid state takes place as one cools the liquid below -455.4 degrees Fahrenheit. For lower temperatures Helium becomes what is known as a superfluid, and displays totally unexpected and magical properties. We will discuss some of these properties, including persistent frictionless flow, and the remarkable phenomena of film flow, in which films of helium only a few atoms in thickness can move freely and support waves similar in some ways to tidal waves on the ocean.

Suitable for a General Physics Audience, including non-science faculty and students.


Title: Superfluid Helium: Testing Your Intuition and Nature’s Memory

abstract:

Helium, the inert element which provides the "lift" for the Goodyear blimp, remains a gas at any temperature above -451.8 degrees Fahrenheit. Below this unimaginably cold temperature, Helium condenses into a liquid and remains a liquid as the temperature is lowered toward absolute zero. At -455.4 degrees Fahrenheit the liquid makes a transition to a spectacular new liquid state. Below this temperature Helium becomes what is known as a superfluid, and displays totally unexpected and magical properties. We will discuss some of these properties, including the remarkable phenomena of film flow, in which films of helium only a few atoms in thickness can move freely and support waves similar in some ways to tidal waves on the ocean, and persistent frictionless flow, and unexpected behavior seen in the capillary condensation and draining of microporous materials.

Can be created for a Colloquim, a Seminar, or a more general audience.


Title: A Trip Toward Absolute Zero

abstract:

The world in the vicinity of the absolute zero of temperature is a remarkable place, with phenomena which are totally foreign to our everyday experience. We will take a tour of some of the these phenomena, beginning with a review of temperature scales and a description of what happens to common things when they are cooled much more than is ordinarily the case. The tour will include aspects of superfluidity and superconductivity, phenomena which have no counterpart in ordinary life. Some of the phenomena to be described, such as persistent superfluid flow, will tease your intuition.

Suitable for a General Physics Audience, including non-science faculty and students.



Title: Can a Solid have Superfluid-like Behavior

abstract:

About 40 years ago it was predicted that it might be possible for solid helium to display some of the properties of a superfluid, thus there might be a supersolid. Experiments in the mid to late 1970's were negative and the prediction languished. Then in 2004 an experiment was done that was interpreted as positive evidence for the presence of a supersolid in solid helium. But, the interpretation has been controversial and other evidence complicated the picture. An experiment underway in our laboratory is conceptually different from all the others and is regarded by many as providing the most direct evidence to date for superfluid behavior in solid helium. Some of the predictions for superfluid behavior due to theorists at UMass and their colleagues, which differ substantially from the original theory of 40 years ago, are regarded as the most consistent with the observations. The subject will be reviewed with an emphasis on the locally-done experimental work.

Suitable for a General Physics Colloquium or a Seminar, including faculty and students.


Biographical Information:

Biographical information which may be useful to the person who will have the task of introducting Bob Hallock as a speaker is available. Some, all or none of this can be used at the option of the person who will do the introduction. In the past people have sometimes asked for information like this and have found it convenient, so this is provided in case it might be useful. A complete vitae is also available.