Amazing stuff!
"Physicists have uncovered a link between magnetism and a mysterious phase of matter called the pseudogap, which appears in certain quantum materials just above the temperature at which they become superconducting. The findings could help researchers design new materials with sought-after properties such as high-temperature superconductivity, in which electric current flows without resistance.
Using a quantum simulator chilled to just above absolute zero, the researchers discovered a universal pattern in how electrons — which can have spin up or down — influence their neighbors’ spins as the system is cooled. The findings represent a significant step toward understanding unconventional superconductivity ...
In many high-temperature superconductors, the transition to the superconducting state does not emerge out of a conventional metallic state. Instead, the material first enters a curious intermediate regime known as the pseudogap, in which electrons start behaving in unusual ways, and fewer electronic states are available for electrons to flow through the material. ...
In materials containing an unaltered number of electrons, the electrons arrange themselves in an orderly, alternating magnetic pattern known as antiferromagnetism. In this pattern, neighboring electron spins point in opposite directions — like dancers following a precise left-right rhythm.
But when electrons are removed through a process known as doping, this magnetic order becomes strongly disrupted. For a long time, researchers assumed that doping destroyed long-range magnetic order entirely. The new study in PNAS, however, shows that at extremely low temperatures, a subtle form of organization remains, hidden beneath the apparent disorder. ..."
From the significance and abstract:
"Significance
Understanding strongly correlated fermions constitutes a major challenge of modern physics. Here, we take a significant step in this direction, by the finding of a universal scaling of spin and charge correlations upon entering the pseudogap phase in the paradigmatic Hubbard model, using our ultracold atom quantum simulator. This leads to a quantitative description of how doping suppresses the spin stiffness, concurrent with the emergence of dominant higher-order correlations that we observe in the system. Our characterization of the magnetic properties of the pseudogap in the paradigmatic Hubbard model paves the way for future studies of further collective phases of matter that the pseudogap is believed to give way to at even lower temperatures.
Abstract
In strongly correlated materials, interacting electrons are entangled and form collective quantum states, resulting in rich low-temperature phase diagrams. Notable examples include cuprate superconductors, in which superconductivity emerges at low doping out of an unusual “pseudogap” metallic state above the critical temperature.
The Fermi–Hubbard model, describing a wide range of phenomena associated with strong electron correlations, still offers major computational challenges despite its simple formulation. In this context, ultracold atoms quantum simulators have provided invaluable insights into the microscopic nature of correlated quantum states.
Here, we use a quantum gas microscope Fermi–Hubbard simulator to explore a wide range of dopings and temperatures in a regime where a pseudogap is known to develop. By measuring multipoint correlation functions up to fifth order, we uncover a universal scaling behavior in magnetic and higher-order spin–charge correlations characterized by a doping-dependent temperature scale. Accurate comparisons with determinant Quantum Monte Carlo and Minimally Entangled Typical Thermal States simulations confirm that this temperature scale is comparable to the pseudogap temperature.
Our quantitative findings reveal a qualitative behavior of magnetic properties and spin–charge correlations in an emergent pseudogap and pave the way toward the exploration of charge pairing and collective phenomena expected at lower temperatures."
Hidden Order in Quantum Confusion: The Pseudogap (original news release) "Quantum simulator using ultracold atoms reveals how subtle magnetic patterns shape one of the most puzzling states of matter."
Observation of emergent scaling of spin–charge correlations at the onset of the pseudogap (open access)
Fig. 4 Emergence of extended polarons in the pseudogap. (A) Example of polaron correlations
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