Field-induced two-dimensionality in UTe₂

The heavy-fermion superconductor UTe2 hosts multiple superconducting phases. Probing the anisotropy of the reinforced superconductivity along b-axis (SC2) is challenging due to its field-dependent order parameter. Anisotropic voltages measured in the flux-flow regime evidence unexpectedly strong two-dimensionality in SC2 phase, contrasting with the low-anisotropy of its zero-field superconductivity. Experiments are based on electronic transport measurements with varying current density in a focused-ion-beam fabricated crystalline microstructure. While a-direction currents induce negligible voltage up to 35T in current densities below 0.18kA·cm^-2, substantial flux-flow voltage is observed for c-direction currents even at the lowest current density of 0.0135kA·cm^-2. This large vortex mobility vanishes with small field misalignment above 4° off H\\b. These results suggest a strong vortex lock-in effect, typically induced by strong order parameter modulation in layered superconductors like pnictides or cuprates. However, the normal-state resistivity anisotropy of ~50 is small compared to these famous examples and is therefore insufficient to induce the two dimensionality and vortex lock-in effect. A possible scenario may be field-driven emergent anisotropy from a density wave.