Nematic transitions in iron pnictide superconductors imaged with a quantum gas

Abstract

The SQCRAMscope is a recently realized Scanning Quantum CRyogenic Atom Microscope that utilizes an atomic Bose-Einstein condensate to measure magnetic fields emanating from solid-state samples. The quantum sensor does so with unprecedented DC sensitivity at micron resolution from room-to-cryogenic temperatures [1]. An additional advantage of the SQCRAMscope is the preservation of optical access to the sample: Magnetometry imaging of, e.g., electron transport may be performed in concert with other imaging techniques. This multimodal imaging capability can be brought to bear with great effect in the study of nematicity in iron-pnictide high-temperature superconductors, where the relationship between electronic and structural symmetry-breaking resulting in a nematic phase is under debate. Here, we combine the SQCRAMscope with an in situ microscope that measures optical birefringence near the surface. This enables simultaneous and spatially resolved detection of both bulk and surface manifestations of nematicity via transport and structural deformation channels, respectively. By performing the first local measurement of emergent resistivity anisotropy in iron pnictides, we observe a spatially inhomogeneous increase in the temperature at which optical birefringence appears near the surface over that at which anisotropic local transport appears within the bulk. This is consistent with the existence of a higher-temperature so-called 'extraordinary' surface nematic transition [2][3][4], albeit one that emerges inhomogeneously. More broadly, these measurements demonstrate the SQCRAMscope's ability to reveal important insights into the physics of complex quantum materials. arXiv:1907.12601v1 [cond-mat.str-el]

A scanning quantum cryogenic atom microscope at 6 K

“…We have also added high-resolution imaging along the vertical axis by installing an in-vacuum lens pair; see Ref. [4] for details regarding these lenses. This allows us to simultaneously image both the atoms and sample surface so as to spatially register the two.…”

“…We now describe these methods. Vibrations in the plane of the sample are measured using an imaging system at normal incidence to the sample, reported previously [4] to have a resolution of about 3 µm. Images of the the sample are recorded at a rate of 7.5 Hz, limited by the frame rate of the camera, over a period of roughly 10 s. Relative displacements between these images are determined using the registration of recognizable features on the sample surface with an accuracy of 0.04 µm, as described in Appendix B. Sub-resolution and sub-pixel accuracy in image registration is possible when only a rigid 2D translation between images is present [29].…”

“…We have recently demonstrated the SQCRAMscope's scientific utility by imaging electron nematic transport in an iron-based pnictide superconductor via magnetometry [4]. The SQCRAMscope is among the best micron-scale low-frequency magnetic field sensors available [2], can detect a quarter of an electric charge a few microns away [5], and is capable of sensing the Casimir-Polder force from a conductor within a micron of the atoms.…”

Direct visualization of electronic transport in a quantum anomalous Hall insulator

“…Macroscopic transport measurements can average over the sample volume in unexpected ways [36,37,38,9,39,40,41]. In quantum Hall systems, this problem is compounded by strong real-space variations in the conductivity tensor.…”

Critical dynamics and phase transition of a strongly interacting warm spin-gas

“…Investigation of new phases of matter has long captured much scientific interest [1][2][3][4][5][6][7][8][9][10][11][12][13]. The macroscopic phase of interacting particles is determined by an interplay between the energy and the entropy of the system.…”