Topic : Examining symmetry of the superconducting order parameter in UTe2 via specific heat measurements in magnetic field

Speaker : Dr. Sangyun LEE (Dept of Physics, Univ. of Florida, USA)

Date & Time : 2025.04.18(Fri) 14:00~

Place :  Room No. 31317, Natural Science Building 1

Abstract : 

Spin-triplet superconductivity is one of the key platforms with the potential to host Majorana zero modes for topological qubits in quantum computation. I will focus on UTe2, a recently discovered unconventional superconductor where electron Cooper pairs take on a spin-triplet ground state. Here, I will discuss the specific heat C(H,T) of a high-quality single crystal of UTe2 with a single specific heat anomaly at the superconducting transition temperature Tc ≈ 2 K and a small zero-field residual Sommerfeld coefficient γ0 = C/T (T=0) ≈10 mJ/mol-K2. Magnetic field is applied up to 12 T along the three principal crystallographic axes of UTe2 to probe the nature of the superconducting state. The evolution of the residual Sommerfeld coefficient as a function of magnetic field, γ0 (H), is highly anisotropic and reveals distinct regions. In magnetic field up to 4 T applied along a, b, and c axes, I find γ0≈αi√H, with i=a,b,c, as expected for an unconventional superconductor with nodes (zeros) of the superconducting order parameter on the Fermi surface. A pronounced kink in γ0(H), however, is observed at roughly 4 T for field applied along both a and b axes, whereas a smooth change from square-root to linear behavior is observed at 4 T for H||c. These results strongly indicate that a zero-field ground state is stable up to 4 T and undergoes a field-induced evolution above 4 T. αc >αa>αb, indicating that the nodes in the low-field state are predominantly located in the vicinity of the a – b plane. The modification of the order parameter is strongest when field is applied in the a – b plane, which causes nodes to move away from the direction of the applied field. Both B2u+iB1u and B2u+iAu two-component order parameters can account for my observations.

Furthermore, I will introduce high magnetic field experiments concerning the measurement of physical properties under extreme conditions at National High Magnetic Field Laboratory (NHMFL).