A diagram showing different states of matter as a function of temperature, T, and the interaction force, U (normalized to amplitude, t, of electrons jumping between sites). Strange metals emerge in a regime that separates a rotating metal glass and a Fermi liquid. Credit: P. Cha et al. / Procedures of the National Academy of Sciences 2020
Even by the standards of quantum physicists, foreign metals are simply foreign. The materials are related to high-temperature superconductors and have surprising connections to the properties of black holes. Electrons in foreign metals dissipate energy as fast as they are allowed under the laws of quantum mechanics, and the electrical resistivity of a foreign metal, unlike ordinary metals, is proportional to temperature.
Generating a theoretical understanding of foreign metals is one of the biggest challenges in condensed matter physics. Now, using cutting-edge computational techniques, researchers from the Flatiron Institute in New York City and Cornell University have solved the first robust theoretical model of foreign metals. The work reveals that foreign metals are a new state of matter, researchers report July 22 in the procedures of the National Academy of Sciences.
“The fact that we call them foreign metals should tell you how well we understand them,” says study co-author Olivier Parcollet, senior research scientist at the Flatiron Institute Center for Computational Quantum Physics (CCQ). “Foreign metals share remarkable properties with black holes, opening exciting new directions for theoretical physics.”
In addition to Parcollet, the research team consisted of Cornell doctoral student Peter Cha, CCQ associate data scientist Nils Wentzell, CCQ director Antoine Georges, and Cornell professor of physics Eun-Ah Kim.
In the world of quantum mechanics, electrical resistance is a by-product of electrons that collide with things. As electrons flow through one metal, they bounce off other electrons or impurities in the metal. The longer there are between these collisions, the lower the electrical resistance of the material.
For typical metals, the electrical resistance increases with temperature, following a complex equation. But in unusual cases, such as when a high-temperature superconductor heats up just above the point where superconduction stops, the equation becomes much simpler. In a foreign metal, electrical conductivity is directly linked to temperature and to two fundamental constants in the universe: Planck’s constant and Boltzmann’s constant. Consequently, foreign metals are also known as planckian metals.
Foreign metal models have been around for decades, but solving them accurately proved out of reach with existing methods. Quantum entanglements between electrons mean that physicists cannot treat electrons individually, and the sheer number of particles in a material makes calculations even more daunting.
Cha and her colleagues used two different methods to solve the problem. First, they used a quantum inclusion method based on ideas developed by Georges in the early 1990s. With this method, instead of performing detailed calculations on the entire quantum system, physicists perform detailed calculations on just a few atoms and deal with the rest. of the system in a simpler way. They then used a Monte Carlo quantum algorithm (named after the Mediterranean casino), which uses random sampling to calculate the answer to a problem. The researchers solved the foreign metal model to absolute zero (minus 273.15 degrees Celsius), the unreachable lower limit for temperatures in the universe.
The resulting theoretical model reveals the existence of foreign metals as a new state of matter that limits two previously known phases of matter: Mott rotating insulating crystals and Fermi liquids. “We discovered that there is an entire region in the phase space that exhibits Planckian behavior that does not belong to either of the two phases that we are transitioning between,” says Kim. “This liquid quantum spin state is not as blocked, but it is not completely free either. It is a slow, thick and muddy state. It is metallic but reluctantly metallic, and it is pushing the degree of chaos to the limit of quantum mechanics.” “
The new work could help physicists better understand the physics of higher-temperature superconductors. Perhaps surprisingly, the work has links to astrophysics. Like foreign metals, black holes exhibit properties that depend only on temperature and Planck and Boltzmann constants, such as the amount of time a black hole ‘sounds’ after it fuses with another black hole. “The fact that you find this same scale in all these different systems, from Planckian metals to black holes, is fascinating,” says Parcollet.
The electrons inside some ceramic crystals seem to dissipate in a familiar way
Peter Cha et al., Linear resistivity and Sachdev-Ye-Kitaev (SYK) spin liquid behavior in a critical quantum metal with spin-1/2 fermions, procedures of the National Academy of Sciences (2020). DOI: 10.1073 / pnas.2003179117
Provided by the Simons Foundation
Citation: Quantum physicists unravel the mystery of ‘foreign metals’, a new state of matter (2020, July 23) retrieved on July 23, 2020 from https://phys.org/news/2020-07-quantum -physicists-mystery-strange-metals .html
This document is subject to copyright. Other than fair dealing for private study or research purposes, no part may be reproduced without written permission. The content is provided for informational purposes only.
