Experiments on the Self-Organized Critical State of 4He

Abstract

AcknowledgementsThere are a number of people I would like to thank for their contributions to this thesis. My advisor David Goodstein was insightful, encouraging, and patient throughout the many challenges of performing a low-temperature experiment. Our conversations were always helpful because David has an extraordinary ability to make complicated concepts seem simple and intuitive. I had two mentors in the lab, Peter Day and Richard Lee, who taught me everything I know about performing experiments in low-temperature physics. My first lab experience was working with Peter. He provided me with the cryostat I used throughout my graduate career, answered hundreds of questions, and patiently showed me the techniques I needed. Richard returned to Caltech as my thesis experiment was taking shape. He was also an excellent resource for the tricks and techniques of low-temperature physics. (Plus, he made B.O.B.2, the electrical filtering system on this cryostat). However, what helped me most was that he patiently asked hundreds of questions, which forced me to think through all the details of my experiment. It is with his help that I avoided many pitfalls.There are a number of other physicists who made significant contributions to this work. Particularly helpful were the members of the DYNAMX team from the University of New Mexico (Rob Duncan, Dimitri Sergatskov, Alex Babkin, and Steve Boyd). They provided material help with the cryo-valve system and the construction of the experimental cell. In addition, they provided a lot of expertise on performing experiments on the SOC state of 4 He. In particular, I would like to thank Rob Duncan, who served as a secondary thesis advisor during a critical time in the experiment as David Goodstein recovered from an injury. Also helpful were discussions with two theorists, Peter Weichman and Rudolf Haussmann, who helped give meaning to my results.I would like to thank my parents for many many years of encouragement and support, and not asking me too often when I was going to get my degree.I would also like to thank my wife Avital, who provided an enormous amount of support and, through an intricate dance of prodding and patience, helped guide me through this endeavor. Lastly, I thank my son Jacob, whose arrival helped destroy the illusion that maybe, just maybe, I could be a graduate student forever. We report the first results of the heat capacity of the SOC state, C ∇T , for heat fluxes 60nW/cm 2 < Q < 13 µW/cm 2 and corresponding temperatures 9 nK > T SOC − T λ > −1.1 µK. We find that C ∇T tracks the static (i.e., zero heat flux) unrounded (i.e., in zero gravity) heat capacity C 0 with two exceptions. The first is that within 250 nK of T λ , C ∇T is depressed relative to C 0 and the maximum in C ∇T is shifted to 50 nK below T λ . The second difference is that at high heat flux, C ∇T is again depressed relative to C 0 with the departure starting at about 650 nK below T λ .We present the most extensive measurements of the speed and attenuation of the SOC wave to date. We report wav...

Renormalization-group calculation of the superfluid/normal-fluid interface of liquid4He in gravity nearTλ

“…IV we present our numerical results for the superfluid/normalfluid interface in gravity where small heat currents are flowing upward or downward. We compare our results with the experiment of Chatto et al [17] and find good agreement for the local thermal resistivity. In Sec.…”

“…In a recent experiment Chatto et al [17] performed an experiment to measure the thermal conductivity/resistivity indirectly where the explicit measurement of the temperature is avoided. Instead they measured the velocity v of a propagating thermal mode as a function of the heat current Q in the interval 30 nW/cm 2 Q 15 µW/cm 2 .…”

Self-organization inH4enear the superfluid transition in heat flow and gravity

“…Analyzing the nonlinear diffusive equation (10), Weichman and Miller 26 also predicted a new thermal wave propagating only upward in self-organized normal states. This wave was observed both above and below the lambda line 20,21 .…”

“…On the other hand, if heated from above, they can compete to produce new nonequilibrium states. In fact, Moeur et al [19][20][21] realized selforganized superfluid in 4 He heated from above, where the temperature gradient and the gradient of T λ (p) were balanced as…”

Depression of the Superfluid Transition Temperature in 4 He by a Heat Flow

“…The read of the RIRT at 0.5 mA measurement current is also recorded to calculate the effect of self-heating. The formula of the self-heating effect of the RIRT is ∆𝑇 SH = (𝑇 0.5 − 𝑇 0.28 ) × 0.28 2 /(0.5 2 − 0.28 2 ), (5) where ∆𝑇 SH is the self-heating value of RIRT, 𝑇 0.5 is the temperature at 0.5 mA measurement current, 𝑇 0.28 is the temperature at 0.28 mA measurement current.…”