Researchers from the Los Alamos National Laboratory report that the phenomenon of electronic symmetry breaking is common in superconducting materials in high magnetic fields. Using transport measurements near the field-tuned quantum critical point of CeRhIn5 at 50 Tesla, the researchers observed a fluctuating nematic-like state in which the material’s electrons aligned in a way to reduce the symmetry of the original crystal, something that now appears to be universal among unconventional superconductors. Unconventional superconductivity develops near a phase boundary separating magnetically ordered and magnetically disordered phases of a material.
A nematic state is most well known in liquid crystals, wherein the molecules of the liquid are parallel but not arranged in a periodic array. Researchers have observed nematic-like states in transition metal systems near magnetic and superconducting phase transitions. The occurrence of this property points to nematicity’s correlation with unconventional superconductivity. The difference, however, of the new nematic state found in CeRhIn5 relative to other systems is that it can be easily rotated by the magnetic field direction.The ability to find similarities and differences among classes of materials with phenomena such as this helps researchers establish the essential ingredients that cause novel functionalities such as superconductivity.
“The appearance of the electronic alignment, called nematic behavior, in a prototypical heavy-fermion superconductor highlights the interrelation of nematicity and unconventional superconductivity, suggesting nematicity to be common among correlated superconducting materials,” says Filip Ronning of Los Alamos National Laboratory, lead author of the paper published in Nature. Heavy fermions are intermetallic compounds, containing rare earth or actinide elements. “These heavy fermion materials have a different hierarchy of energy scales than is found in transition metal and organic materials, but they often have similar complex and intertwined physics coupling spin, charge and lattice degrees of freedom.”
Ronning says the remote use of the National High Magnetic Field Laboratory’s (CSA CSM) pulsed field magnet from a facility at Los Alamos was essential due to the large magnetic fields required to access this state. Another key contribution was the fabrication of micron-sized devices using focused ion-beam milling performed in Germany, which enabled the transport measurements in large magnetic fields.