Loeb Lectures in Physics: Steven Kivelson (Stanford), Feb 3-6, 2025
Steven Kivelson (Stanford University)
Monday, February 3 @4:30PM:
"Theory of superconductivity in the cuprate 'high temperature superconductors' − A progress report."
The study of the cuprate high temperature superconductors has been one of the central focusses of condensed matter research for much of the past four decades. It has stimulated the development of a plethora of new and increasingly sensitive experimental probes of the properties of correlated electron systems and has inspired remarkable advances in theory that have transformed our understanding of emergent phenomena in highly correlated quantum systems. In this talk I will present a unified perspective on the broadly accepted understanding of the nature of the superconducting state itself, the key features that determine the rough magnitude of the superconducting Tc, and the relation between the antiferromagnetism of the closely related insulating “parent” materials and the mechanism of pairing. While the superconducting states in the cuprates are not all that exotic, they differ from those in “conventional” superconductors not only in having “d-wave” symmetry, but also in important quantitative ways that have significant qualitative implications – not all of which are entirely understood. As a coda, I will discuss a theoretical proposal of a way to raise Tc, and some recent experiments on a particular family of cuprates that seem encouraging.
Lecture I: Wednesday, February 5 @4:30PM
"Intertwined Orders” and the complex phase diagrams of highly correlated electronic systems
One striking feature of the cuprate phase diagram is its unexpected complexity. In addition to superconductivity and Neel antiferromagnetism, direct and indirect experimental evidence suggests the presence of a number of other, distinct forms of spontaneously broken symmetries that occur in the same range of material parameters and with comparable onset temperatures. At the very least, this includes unidirectional charge and spin density waves (colloquially referred to as “stripes’’), and possibly other, more subtle orders including electron-nematic and pair-density-wave orders. Notably, this same failure of the physics to clearly favor a specific order appears also to be a feature of many “highly correlated materials’’ (i.e. not just the cuprates) as well as of the simple models of correlated electron systems that have been studied in this context. Indeed, this same issue is the reason that - despite heroic efforts by many serious scientists – there is still uncertainty concerning the ground-state phase diagram of the two-dimensional Hubbard model in the intermediate coupling regime. Here, I will summarize some of the evidence that support these assertions and highlight some aspects of these problems that have been understood – notwithstanding the advertised difficulties.
Lecture II: Thursday, February 6 @4:30PM
Machine learning for sampling high-dimensional probability distributions in lattice field theory
The superconducting phase in the cuprates spans a limited range of doping concentrations, x; it forms a superconducting “dome” in the x-T plane that terminates on the high doping side at a superconductor-to-metal quantum-critical point. Recent experiments have uncovered a number of interesting features of the states proximate to this transition that likely reflect some of the special features of the high temperature superconducting phase itself. Specifically, a combination of the short superconducting coherence length and the d-wave character of the pairing lead to an amplified electronic response to the mesoscale variations in local structure that inevitably arise in a doped system. Aspects of the resulting emergent granularity of the superconducting correlations will be discussed leading to the proposal that they hold the key to understanding some of the more dramatic observations.
Steven Kivelson, Prabhu Goel Family Professor at Stanford University, has been awarded the 2025 Oliver E. Buckley Condensed Matter Physics Prize from the American Physical Society for his broad theoretical contributions to the understanding of correlated quantum systems. The prize is the highest honor the APS awards in the field of condensed matter physics.
Prof. Kivelson also received the Guggenheim fellowship in 1995, and was elected to the American Academy of Arts and Sciences in 2001, and to the National Academy of Sciences in 2010. He received his PhD from Harvard University in 1979.
His research focuses on the search for theoretical characterization of qualitatively new behaviors of interacting electrons (i.e., new states of matter)as well as new regimes of parameters in which familiar states of matter behave in new and different ways. In particular, he seeks to explore; qualitatively... the relation between the microscopic interactions between electrons and the effective parameters that control the macroscopic behavior of solids.
Current Areas of Focus:
- theory of quantum liquid crystalline phases of highly correlated electronic fluids
- intertwined orders and the theory of high temperature superconductivity
- theory of spin liquids and other fractionalized quantum phases
- theory of the glass transition in super cool liquids
all lectures will be held in Jefferson Lab 250
and streamed live through zoom (please see the link below)
The lectures are sponsored by the Morris Loeb Lectureship Fund.