Absence of a bulk charge density wave signature in x-ray measurements of UTe$_2$

TL;DR

This study used x-ray diffraction to search for bulk charge density wave signatures in UTe$_2$, finding none, which challenges previous surface-based STM evidence and suggests the CDW may be surface-limited or purely electronic.

Contribution

The paper provides the first bulk x-ray diffraction search for CDW in UTe$_2$, setting upper bounds on lattice distortions and questioning the nature of surface STM observations.

Findings

No bulk CDW detected in UTe$_2$ via x-ray diffraction.

Estimated upper bound on lattice distortion is approximately 4×10^{-3} Å.

Results imply the STM-observed CDW may be surface-limited or purely electronic.

Abstract

The long-sought pair density wave (PDW) is an exotic phase of matter in which charge density wave (CDW) order is intertwined with the amplitude or phase of coexisting, superconducting order \cite{Berg2009,Berg2009b}. Originally predicted to exist in copper-oxides, circumstantial evidence for PDW order now exists in a variety of materials. Recently, scanning tunneling microscopy (STM) studies have reported evidence for a three-component charge density wave (CDW) at the surface of the heavy-fermion superconductor, UTe$_2$, persisting below its superconducting transition temperature. Here, we use hard x-ray diffraction measurements on crystals of UTe$_2$ at $T = 1.9$ K and $12$ K to search for a bulk signature of this CDW. Using STM measurements as a constraint, we calculate the expected locations of CDW superlattice peaks, and sweep a large volume of reciprocal space in search of a signature. We failed to find any evidence for a CDW near any of the expected superlattice positions in many Brillouin zones. We estimate an upper bound on the CDW lattice distortion of $u_{max} \lesssim 4 \times 10^{-3} \mathrm{\AA}$. Our results suggest that the CDW observed in STM is either purely electronic, somehow lacking a signature in the structural lattice, or is restricted to the material surface.