Physicists at MIT have now cooled a gas of potassium atoms to several nanokelvins — just a hair above absolute zero — and trapped the atoms within a two-dimensional sheet of an optical lattice created by crisscrossing lasers. Using a high-resolution microscope, the researchers took images of the cooled atoms residing in the lattice.
The team believes that these spatial correlations may shed light on the origins of superconducting behavior. Superconductors are remarkable materials in which electrons pair up and travel without friction, meaning that no energy is lost in the journey. If superconductors can be designed to exist at room temperature, they could initiate an entirely new, incredibly efficient era for anything that relies on electrical power.
Martin Zwierlein, professor of physics and principal investigator at MIT’s NSF Center for Ultracold Atoms and at its Research Laboratory of Electronics, says his team’s results and experimental setup can help scientists identify ideal conditions for inducing superconductivity.
“Learning from this atomic model, we can understand what’s really going on in these superconductors, and what one should do to make higher-temperature superconductors, approaching hopefully room temperature,” Zwierlein says.
“Learning from this model, we can understand what’s really going on in these superconductors, and what one should do to make higher-temperature superconductors, approaching hopefully room temperature,” says Martin Zwierlein, professor of physics and principal investigator in MIT’s Research Laboratory of Electronics. Illustration: Sampson Wilcox
Ultimately, he says the team’s experiments in gases can help scientists identify ideal conditions for superconductivity to arise in solids.
Zwierlein explains: “For us, these effects occur at nanokelvin because we are working with dilute atomic gases. If you have a dense piece of matter, these same effects may well happen at room temperature.”
Currently, the team has been able to achieve ultracold temperatures in gases that are equivalent to hundreds of kelvins in solids. To induce superconductivity, Zwierlein says the group will have to cool their gases by another factor of five or so.
“We haven’t played all of our tricks yet, so we think we can get colder,” he says.
Strong electron correlations lie at the origin of high-temperature superconductivity. Its essence is believed to be captured by the Fermi-Hubbard model of repulsively interacting fermions on a lattice. Here we report on the site-resolved observation of charge and spin correlations in the two-dimensional (2D) Fermi-Hubbard model realized with ultracold atoms. Antiferromagnetic spin correlations are maximal at half-filling and weaken monotonically upon doping. At large doping, nearest-neighbor correlations between singly charged sites are negative, revealing the formation of a correlation hole, the suppressed probability of finding two fermions near each other. As the doping is reduced, the correlations become positive, signaling strong bunching of doublons and holes, in agreement with numerical calculations. The dynamics of the doublon-hole correlations should play an important role for transport in the Fermi-Hubbard model.
SOURCES – MIT News, Science