MATHEMATICAL SCIENCES

Chinese scholars proposed the supercritical magnetic pressure thermal effect


Recently, Professor Su Gang’s team and collaborators of the University of Chinese Academy of Sciences used their own accurate and efficient finite temperature tensor renormalization group method to give a complete pressure-temperature phase diagram of the Shastry-Sutherland lattice quantum magnetic model, and found that the phase diagram is very similar to the phase diagram of water, and found that there is a novel quantum association-induced cooling mechanism in the supercritical region above the critical point, named the supercritical magnetocalorimal effect. This effect gives a new principle of extremely low-temperature refrigeration without liquid helium. This work was recently published in Physical Review Letters.

Thwarting significant quantum fluctuations of quantum magnets at extremely low temperatures may lead to the emergence of novel states of matter and phase transitions that go beyond the Landau-Ginzburg-Wilson symmetry-breaking paradigm, such as quantum spin liquids with fractional excitation and quantum critical points of unconfinement. Due to the fact that the quantum magnet presents novel thermophysical properties at extremely low temperatures and the existence of a huge magnetic entropy density with a height adjustment, the system still has strong spin fluctuations at low temperatures far below the interaction energy standard, which is an important research direction that has attracted much attention internationally.

Recently, several experimental groups have made progress in the study of high-pressure thermodynamics of SrCu2(BO3)2 crystals that resist magnets. The specific heat evidence of the existence of the spin monomorphism of the block polymerization was found, and the similarity between the phase diagram of the magnetic material and the water phase diagram was discovered, that is, there was a first-order phase transition in both. terminates at an emerging isolated tipping point; Low-temperature NMR measurements of a magnetic field applied at high pressure provide experimental evidence that there is a quantum critical point near unconfinement, etc.

Using the accurate and efficient finite temperature tensor renormalization group method developed by the Su Gang research team, the Su Gang research team systematically gave the temperature-pressure phase diagram of the Shastry-Sutherland foiled lattice model related to the material, and found that at a low temperature two orders of magnitude below the system’s energy standard, the square polymerized spin monomorphic solid phase phase with symmetry breaking was theoretically obtained for the first time. The external magnetic field is continued to be applied on the square spin monomorph, and the quantum phase transition from the block monomorphism to the spin supersolid state is found, and experimental observable neutron scattering and magnetocaloric effects are given. These theoretical results confirm recent experimental advances on SrCu2(BO3)2 crystal materials.

They also found that in the supercritical region above the emerging critical point of the system, there is a significant magnetic entropy effect caused by quantum correlation changes, that is, from binary polymerization spin monomorphism to square polymerization spin monomorphic liquid. This is a new type of magnetic disorder-disordered transition effect, which is named the supercritical magnetocaloric thermal effect, which provides a new idea for the extremely low-temperature solid refrigeration of liquid-helium.

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(a) Pressure-temperature schematic of the Shastry-Sutherland model. There is a supercritical magnetocalorie effect above its emergence tipping point. (b) The isentropic lines of the supercritical region of the Shastry-Sutherland model are expected to be applied to quantum-associative cooling.   Photo courtesy of University of Chinese Academy of Sciences

(Source: Zhang Qingdan, China Science News)

Related paper information:https://doi.org/10.1103/PhysRevLett.131.116702



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